Texas Instream Flow Studies: Technical Overview

Texas Commission on Environmental Quality Report 369 Texas Parks and Wildlife Department May 2008 Texas Water Development Board

Texas Water Development Board Report 369

Texas Commission on Environmental Quality Texas Parks and Wildlife Department Texas Water Development Board

James E. Herring Chairman, Amarillo

Jack Hunt Vice Chairman, Houston

Joe M. Crutcher Member, Palestine

Thomas Weir Labatt, III Member, San Antonio

Lewis H. McMahan Member, Fort Worth

Edward G. Vaughan Member, Boerne

J. Kevin Ward Executive Administrator

Authorization for use or reproduction of any original material contained in this publication, i.e., not obtained from other sources, is freely granted. The Board would appreciate acknowledgment. The use of brand names in this publication does not indicate an endorsement by the Texas Water Development Board or the State of Texas.

Published and distributed by the Texas Water Development Board P.O. Box 13231, Capitol Station Austin, Texas 78711-3231

May 2008 (Printed on recycled paper) This page is intentionally blank. Table of Contents 1 Executive Summary...... 1 2 Introduction ...... 10 2.1 History of Texas Instream Flow Program...... 10 2.2 Texas Instream Flow Program Approach to Sub-basin Studies...... 11 2.2.1 Ecosystem Focus...... 11 2.2.2 Scientific Realities...... 13 2.2.3 Program Context...... 16 2.3 Layout of Technical Overview...... 16 3 Ecological Setting...... 22 3.1 Overview of Diversity of Texas...... 22 3.2 Overview of Riverine Components...... 23 3.2.1 Biology...... 23 3.2.2 Hydrology and Hydraulics...... 25 3.2.3 Water Quality...... 25 3.2.4 Geomorphology...... 26 3.3 Connectivity, Dimension, and Scale in Stream Systems...... 26 4 Peer Review and Stakeholder Input...... 31 4.1 Stakeholder Process...... 31 4.2 Peer Review...... 34 5 Study Design ...... 36 5.1 Reconnaissance and Information Evaluation...... 36 5.1.1 Compile, Review, and Georeference Available Studies and Data...... 38 5.1.2 Conduct Preliminary Field Surveys and Analyses...... 40 5.1.3 Develop Conceptual Models...... 41 5.2 Goal Development and Study Design...... 41 5.2.1 Develop Study Goals and Objectives...... 41 5.2.2 Indicators...... 44 5.2.3 Formulate Study Design...... 47 6 Hydrology and Hydraulics...... 50 6.1 Hydrologic Evaluation...... 50 6.1.1 Historical Flow Data...... 52 6.1.2 Naturalized Flow Data and Water Availability Modeling...... 53 6.1.3 Flow Frequency Analysis...... 54 6.2 Hydraulic Evaluation...... 54 6.2.1 Choosing a Representative Reach...... 55 6.2.2 Field Data Collection...... 56 6.2.3 Hydraulic Modeling...... 59 7 Biology...... 66 7.1 Hydrology and Riverine Ecosystems...... 66 7.2 Assessment of Current Conditions...... 68 7.2.1 Instream Habitat Surveys...... 69 7.2.2 Fish Surveys...... 69

Texas Water Development Board Report 369 7.2.3 Aquatic Invertebrate Surveys...... 70 7.2.4 Riparian Area Surveys...... 71 7.3 Instream Habitat...... 73 7.3.1 Quantity and Quality of Instream Microhabitat...... 74 7.3.2 Habitat Heterogeneity...... 77 8 Physical Processes...... 79 8.1 Physical Processes of Rivers...... 80 8.2 Human Impacts on Physical Processes of Rivers...... 82 8.3 Geomorphic Assessment...... 84 8.3.1 Geomorphic Thresholds...... 85 8.3.2 Assessment of Current Channel Conditions...... 85 8.4 Sediment Budgets...... 87 8.5 Classifying a River...... 88 8.5.1 River Styles Framework...... 89 9 Water Quality...... 94 9.1 Background...... 94 9.2 Water Quality Programs in Texas...... 95 9.2.1 Water Quality Standards and Assessment...... 95 9.2.2 Surface Water Quality Standards...... 95 9.2.3 Surface Water Quality Monitoring...... 97 9.2.4 Texas Water Quality Inventory...... 97 9.2.5 Texas Pollutant Discharge Elimination System...... 97 9.2.6 Total Maximum Daily Loads...... 98 9.3 Water Quality for Instream Flow Studies...... 99 10 Integration...... 101 10.1 Subsistence Flows...... 101 10.2 Base Flows...... 103 10.2.1 Physical Habitat Model...... 103 10.3 High Flow Pulses...... 105 10.4 Overbank Flows...... 105 10.5 Other Considerations...... 107 10.6 Study Report...... 107 11 Next Steps: Implementation, Monitoring, and Adaptive Management...... 110 11.1 Implementation Issues...... 110 11.2 Monitoring...... 112 11.3 Adaptive Management...... 112 12 Conclusion...... 114 13 Acknowledgments...... 115 14 References...... 116 15 Appendix...... 130 15.1 Acronyms/Symbols...... 130 15.2 Glossary of Selected Terms...... 130

vi Texas Water Development Board Report 369 List of Figures Figure 1-1 Steps in sub-basin studies of the Texas Instream Flow Program...... 1 Figure 1-2 Development of subsistence flow recommendationx from results of multidisciplinary activities...... 6 Figure 1-3 Development of base flow recommendations from results of multidisciplinary activities...... 7 Figure 1-4 Development of high flow pulse recommendations from results of multidisciplinary activities...... 8 Figure 1-5 Development of overbank flow recommendations from results of multidisciplinary activities...... 9 Figure 2-1 Steps in sub-basin studies of the Texas Instream Flow Program...... 17 Figure 3-1 Nomenclatures describing the spatial scale of riverine ecosystems...... 29 Figure 4-1 Stages of stakeholder participation in sub-basin specific studies of the Texas Instream Flow Program...... 33 Figure 5-1 Conceptual model developed for a portion of the Murray-Darling Basin, Australia .... 42 Figure 6-1 Flow duration curve calculated from daily data for pre-development and post- development conditions...... 55 Figure 6-2 Cumulative probability curve with flow rates suitable for habitat modeling...... 55 Figure 6-3 Stage-discharge curve developed for hydraulic model input...... 58 Figure 7-1 Hydrological representation of the riparian zone as a sum of transitional gradients.... 74 Figure 8-1 Hierarchical relationship of River Styles mapping categories...... 90 Figure 8-2 Example of longitudinal segmentation of a river system based on River Styles methodology...... 92 Figure 10-1 Development of subsistence flow recommendations from results of multidisciplinary activities...... 102 Figure 10-2 Development of base flows from results of multidisciplinary activities...... 104 Figure 10-3 Development of high flow pulse recommendations from results of multidisciplinary activities...... 106 Figure 10-4 Development of overbank flowrecommendations from results of multidisciplinary activities...... 108

List of Text Boxes Text Box 5.1 Example of goals, objectives, indicators, and conceptual models for the Murray Darling Basin, Australia...... 43 Text Box 5.2 Use of ecological indicators in Texas Instream Flow Program sub-basin studies...... 46

List of Tables Table 1-1 Summary of sub-basin study activities during Step 1...... 2 Table 1-2 Summary of sub-basin study activities during Step 2...... 3 Table 1-3 Summary of sub-basin study activities during Step 3...... 4 Table 1-4 Summary of sub-basin study activities during Step 4...... 5 Table 2-1 Environmental considerations related to streams/rivers as directed by state statutes.... 12 Table 2-2 Example components of an instream flow regime and supported processes...... 14 Table 2-3 Human activities that may affect riverine ecosystems...... 15

Texas Water Development Board Report 369 vii Table 2-4 Summary of sub-basin study activities during Step 1...... 18 Table 2-5 Summary of sub-basin study activities during Step 2...... 19 Table 2-6 Summary of sub-basin study activities during Step 3...... 20 Table 2-7 Summary of sub-basin study activities during Step 4...... 21 Table 5-1 Summary of development of sub-basin study design from statewide goals and objectives...... 37 Table 5-2 Example indicators for Murray-Darling Basin, Australia...... 45 Table 5-3 Example ecosystem endpoints for aquatic ecosystems...... 46 Table 5-4 Texas Commission on Environmental Quality site-specific uses and criteria for the Lower Sabine River ...... 48 Table 5-5 Texas Commission on Environmental Quality site-specific criteria for tributaries of the Lower Sabine River...... 48 Table 5-6 Attributes of aquatic life use categories...... 49 Table 8-1 Classification of riverbed types ...... 81 Table 8-2 Geomorphic “naturalness” classification of river segments...... 83 Table 8-3 Potential alterations in channel characteristics due to changes in transport variables... 83 Table 9-1 Attributes of aquatic life use categories ...... 96 Table 10-1 Definitions and objectives for instream flow components...... 101

viii Texas Water Development Board Report 369 1 Executive Summary

enate Bill 2, enacted in 2001 by the Reconnaissance and 77th Texas Legislature, established Information Evaluation theS Texas Instream Flow Program, which is jointly administered by the Goal Development Consistent with Texas Commission on Environmen- Sound Ecological Environment tal Quality, Texas Parks and Wildlife Department, and Texas Water Devel- opment Board (hereafter referred to Study Design as “the Agencies”). The purpose of the program is to perform scientific and Multidisciplinary Data engineering studies to determine flow Collection and Evaluation conditions necessary for supporting a sound ecological environment in the Data Integration to Generate river basins of Texas. This document Flow Recommendations identifies a process for developing and conducting those studies. To accomplish the program’s goals, Draft Study Report flow regimes that promote ecological integrity and maintain biodiversity will Final Study Report be determined, with the understanding SB 2 Ends that maintaining the physical habitats, Post-SB 2 water quality, and hydrologic character Next Steps: of specific river sub-basins will contrib- Implementation, Monitoring, ute to a sound ecological environment. and Adaptive Management In consultation with stakeholders, study- Figure 1-1. Steps in sub-basin studies of the specific goals and objectives consistent Texas Instream Flow Program. with the definition of a sound ecological environment will be determined. These tions will need to be tailored for each definitions will be compatible with all individual system. The study approach applicable state and federal laws, as well adopted for the instream flow program as statewide goals of the Texas Instream focuses on the flow requirements of the Flow Program. entire riverine ecosystem. Studies will be Studies for specific river sub-basins multidisciplinary in nature, including the will be conducted as shown in Figure disciplines of hydrology and hydraulics, 1-1. Activities listed above the horizon- biology, geomorphology, and water qual- tal line in Figure 1-1 are components of ity. Studies will also address connectivity the Senate Bill 2 authorization for the and linkages between each discipline. Texas Instream Flow Program. Those Multidisciplinary studies will be inte- activities are described in more detail in grated to develop a flow regime com- Tables 1-1 through 1-4 and throughout posed of several flow components such this document. as subsistence and base flows, high flow The geographic vastness of Texas pulses, and overbank flow components results in a wide diversity of aquatic eco- as shown in Figures 1-2 through 1-5. Flow systems. Within the context of overall components will be identified for wet, program goals and objectives, methods average, and dry hydrologic conditions, and procedures for technical studies in as appropriate. support of instream flow recommenda- The Texas Instream Flow Program

Texas Water Development Board Report 369 Table 1-1. Summary of sub-basin study activities during Step 1.

Step 1: Reconnaissance and Information Evaluation Purpose • Compile, review, and georeference available studies/data. • Identify historic and current conditions, significant issues, and concerns. • Conduct preliminary field surveys and analysis. Data Sources • U.S. Geological Survey and other gage data. • Federal/state/local studies and reports. • Historic air photos/Digital Orthographic Quarter Quadrangle/maps/soil surveys. • Current water quality models and standards. Activities Stakeholder Participation • Provide historic and current perspective of resource. • Identify important concerns and opportunities for study participation. • Select sub-basin workgroup. Hydrology and Hydraulics • Calculate flow statistics for historic and existing conditions. • Identify existing features (such as tributaries) and existing and proposed alterations (for example, diversions, impoundments, and land uses) affecting hydrologic character. Biology • Identify historic and current species assemblages, representative macro- and mesohabitat types, and other biological issues and considerations. • Assess historic and current condition of stream biota and riparian resources. • Identify potential study reaches and sites. Geomorphology • Analyze aerial photography and other historic data as available. • Assess channel bed form and banks, active channel and floodplain processes, and changes in sediment regime and causes. • Make preliminary geomorphic classification of river segment. Water Quality • Assess historic and current water quality and aquatic life uses. • Identify water quality issues and constituents of concern. Output • Synthesized summary of available studies/data, including GIS layers. • Conceptual models describing the relationships between ecological health and flow regime. • Prioritized list of research needs to address identified knowledge gaps. Scale: All Scales

Texas Water Development Board Report 369 Table 1-2. Summary of sub-basin study activities during Step 2.

Step 2: Goal Development and Study Design Purpose • Develop sub-basin goals and objectives consistent with a sound ecological environment. • Create study design, including descriptions of intensive study sites, specific technical tools and sampling criteria, and target flow ranges and seasons for field data collection. Data Sources • Goals and objectives of agencies, cooperators, and stakeholders. • Results of reconnaissance activities from Step 1. Activities Stakeholder Participation • Sub-basin workgroup assists Agencies in developing study design. Hydrology and Hydraulics • Determine data collection requirements for hydraulic modeling to support biological, geomorphic, and water quality studies. • Assess hydraulic conditions within study sites. Biology • Confirm location of key/representative habitats within study sites. • Choose appropriate sampling methods and estimate resource requirements. Geomorphology • Determine appropriate methods subject to constraints (including available historical data). • Confirm presence of suitable geomorphic features within study sites. Water Quality • Confirm location of key water quality areas of concern within study sites. • Assess need for additional water quality modeling and determine data collection requirements. Output • Study design consistent with Technical Overview. Scale: All Scales

has been designed so that instream flow all the varied conditions that may be studies may be conducted by qualified encountered in Texas. Those conducting third parties with the Agencies’ oversight. studies will need to be in communication In that event, this document will serve as with the Agencies to review and approve a general overview of the requirements necessary adaptations of the methods of such a study. This document does described in this document. not provide sufficient guidance to meet

Texas Water Development Board Report 369 Table 1-3. Summary of sub-basin study activities during Step 3.

Step 3: Multidisciplinary Data Collection and Evaluation Purpose • Collect input data required for models and analyses. • Continuously monitor water quality and flow conditions at study sites. • Determine relationships between flow, water quality, biology, habitat, channel, and floodplain conditions. Data Sources • Hydrologic measurements and bathymetric mapping. • Biological data collection and habitat mapping. • Geomorphic data collection and mapping. • Water quality data collection. Activities Stakeholder Participation • Sub-basin study and data collection workshops/field demonstrations. Hydrology and Hydraulics • Monitor stage/discharge continuously during study period. • Map substrate, woody debris, and variations in hydraulic roughness. • Model hydraulic characteristics in relation to flow, including extent of inundation associated with flood events. Biology • Collect appropriate biological and habitat use data. • Describe habitat criteria and significant conditions for key species/guilds/life stages. • Conduct habitat modeling to assess habitat-flow relationships, including diversity. • Conduct riparian studies and estimate riparian requirements. Geomorphology • Develop sediment budgets. • Identify factors controlling geomorphic behavior of river segment. • Assess channel adjusting and overbank flow behavior, including flow conditions that initiate sediment and large woody debris movement and deposition. Water Quality • Monitor water quality at site during study period. • Validate previous models and conduct water quality modeling studies as needed. • Assess flow/water quality relationships. Output • Documentation of methods and data (hardcopy and electronic formats). • Habitat versus flow relationships. • Flows required to maintain water quality and channel/riparian areas. • Refined conceptual models that describe ecological health and flow regime. Scale: Study Sites

Texas Water Development Board Report 369 Table 1-4. Summary of sub-basin study activities during Step 4.

Step 4: Data Integration to Generate Flow Recommendations Purpose • Construct instream flow regime (including subsistence, base, and overbank flows and high flow pulses) that best meets sub-basin goals and objectives. Data Sources • Results of previous studies from Step 1. • Sub-basin study goals and objectives from Step 2. • Results of multidisciplinary studies from Step 3. Activities Stakeholder Participation • Sub-basin workgroup provides input on data synthesis and interpretation. • Review and comment on study report. Hydrology and Hydraulics • Calculate occurrence of various flow rates during historical and current conditions. • Determine annual variability of hydrologic characteristics, including description of wet, average, and dry hydrologic conditions. • Develop hydrologic time series to evaluate habitat suitability of proposed flow regime. • Calculate variability of proposed flow regime and compare with historic/current conditions. • Evaluate how proposed flow regimes would impact current operating conditions. Biology • Develop flow ranges at appropriate temporal scales for key species/guilds/life stages. • Construct habitat time series for historic, current, and proposed flow regimes. Geomorphology • Estimate, if possible, historic channel conditions. • Evaluate consequences of various flow regimes for channel/riparian areas. • Estimate feasibility of alternative intervention actions. Water Quality • Identify flow conditions that satisfy key water quality/biology relationships. • Consider water quality issues related to proposed flow regime components. Output • Instream flow study report, including description of flow recommendations, ecological significance of flow components, and study methods and analysis. Scale: River Segment

Texas Water Development Board Report 369 Subsistence Flows

Spatial scale: River Reach

Temporal scale: Hourly Flow, Varies from Month to Month

Primary discipline: Hydrology/Hydraulics Biology Geomorphology Water Quality

Identify Biological Considerations

Identify Water Quality Constituents of Concern

Calculate Low Flow Conduct Water Quality Statistics Modeling Studies

Assess Low Flow-Water Quality Relationship

Other Biological Considerations

Subsistence Flows

Figure 1-2. Development of subsistence flow recommendations from results of multidisciplinary activities.

Texas Water Development Board Report 369 Base Flows

Spatial scale: River Reach

Temporal scale: Daily Flow Range, Varies from Month to Month

Primary discipline: Hydrology/Hydraulics Biology Geomorphology Water Quality

Assess Bed Form Identify Biological Issues and Banks and Key Species

Calculate Base Flow Collect Biological Statistics Data

Model Hydraulic Characteristics in Determine Habitat Relation to Flow Criteria

Assess Habitat-Flow Relationships, including Diversity

Describe Wet, Normal, and Dry Years

Consider Biological and Riparian Issues

Consider Water Quality Issues

Base Flows

Figure 1-3. Development of base flow recommendations from results of multidisciplinary activities.

Texas Water Development Board Report 369 High Flow Pulses

Spatial scale: River Segment

Temporal scale: Multiple High Flow, Pulses Throughout the Year

Primary discipline: Hydrology/Hydraulics Biology Geomorphology Water Quality

Assess Active Channel Processes

Develop Sediment Budgets

Assess Channel Adjusting Flow Behavior

Describe Signiﬁcant Consider Biological Habitat Conditions Issues

Calculate High Flow Consider Water Quality Statistics Issues

High Flow Pulses

Figure 1-4. Development of high flow pulse recommendations from results of multidisciplinary activities.

Texas Water Development Board Report 369 Overbank Flows

Spatial scale: River Segment

Temporal scale: Extreme Flow Events, Occur Less Than Once per Year

Primary discipline: Hydrology/Hydraulics Biology Geomorphology Water Quality

Calculate Flood Assess Active Floodplain Frequency Statistics and Channel Processes

Model Extent of Flood Events

Assess Overbank Flow Behavior

Consider Biological Conduct Riparian Issues Studies

Consider Water Quality Estimate Riparian Issues Requirements

Overbank Flows

Figure 1-5. Development of overbank flow recommendations from results of multidisciplinary activities.

Texas Water Development Board Report 369 2 Introduction

n 2001, the 77th session of the Tex- life enthusiasts spent almost $4 as Legislature enacted Senate Bill 2 billion. establishingI the Texas Instream Flow Program. The program is being coop- Further, the health and maintenance eratively developed and jointly admin- of various riparian areas, hardwood bot- istered by the Texas Commission on tomlands, and associated wetland eco- Environmental Quality, Texas Parks and systems are intimately linked to instream Wildlife Department, and Texas Water flows. For example, instream flows affect Development Board (hereafter referred the volume of nutrients and organic to as “the Agencies”). Its purpose is materials from both natural and human to perform scientific and engineering sources that can be assimilated by riv- studies to determine flow conditions ers and riparian areas. They also affect necessary to support a sound ecological the tremendous diversity of plants and environment in the river basins of Tex- animals, several of which are known to as. This document identifies a process occur exclusively in Texas, that depend for developing and conducting those on rivers, streams, and riparian areas. instream flow studies. The urgency and seriousness with 2.1 which the state embarks upon this pro- History of Texas Instream gram to determine instream flow require- Flow Program ments is not to be underestimated. At Senate Bill 2 directs the Texas Commis- stake are much of the state’s irreplaceable sion on Environmental Quality, Texas natural resources and water supplies for Parks and Wildlife Department, and its citizens, economy, and environment. Texas Water Development Board (the The population of Texas is expected to Agencies) to “jointly establish and con- nearly double in the next 50 years, from tinuously maintain an instream flow data almost 21 million people in the year collection and evaluation program…” In 2000 to about 46 million in 2060 with addition, the legislation directed the attendant shortages of water (TWDB, Agencies to “conduct studies and analy- 2007). If the state does not ensure suf- ses to determine appropriate method- ficient water to meet projected needs, ologies for determining flow conditions socioeconomic models predict reduced in the state rivers and streams necessary economic growth and vitality (TWDB, to support a sound ecological environ- 2007). Additionally, the impact on hunt- ment.” In response to this directive, the ing and fishing could be tremendous. Agencies developed the Texas Instream Sansom (1995) states that Flow Program. In October 2002, the Agencies signed Texas ranks first among the states a Memorandum of Agreement, which in hunting opportunities and sec- provided an operating agreement among ond in fishing. It is today the num- the Agencies and established an Instream ber one destination in the world Flow Studies Coordinating Committee for birdwatchers. The impact of comprising the Agencies’ executive lead- these activities on the economy ership and an Interagency Science Team of the state is substantial: In 1993 of staff scientists and engineers. We com- alone, visitors to Texas state parks pleted a Programmatic Work Plan for the spent nearly $200 million, while instream flows program in December hunters, anglers, and other wild- 2002 (TIFP, 2002). The Work Plan iden-

10 Texas Water Development Board Report 369 tified priority studies and interim dead- results will acknowledge and document lines for publications, outlined the roles uncertainty. As scientific understanding of the state agencies, and presented the of the issues surrounding instream flow scope of the studies and general methods requirements deepens, procedures and for conducting the studies. In August methods employed in the program will 2003, the Agencies completed a precur- need to adapt and change over time. In sor to this document, a draft Technical order to fit within its program context, Overview of Texas instream flow studies, the Texas Instream Flow Program will which provided an in-depth discussion be transparent to the public, involve of the methods proposed for use by the stakeholders and scientific peers, and Texas Instream Flow Program. strive for compatibility with existing In June 2003, we submitted the Work programs related to environmental Plan and draft Technical Overview to monitoring and protection of Texas the National Research Council of the streams and rivers. National Academy of Sciences as part of a scientific peer review. They completed 2.2.1 the review in February 2005 and docu- Ecosystem Focus mented their results in a report (NRC, Senate Bill 2 gives the Texas Instream 2005). After revising the Technical Over- Flow Program a mandate to identify view in response to the recommenda- instream flow conditions that support a tions of the National Research Council, “sound ecological environment” without the Agencies submitted it for stakeholder precisely defining this term. However, evaluation in May 2006. The Agencies Senate Bill 2 was adopted in the con- have incorporated recommendations text of the existing state statutes shown and comments from that evaluation in in Table 2-1. These statutes make clear this document. that the activities of the Agencies must Additional information about the provide adequate water quality and fish Texas Instream Flow Program is avail- and wildlife habitat, link terrestrial and able at this Web site: www.twdb.state. riparian habitats to the aquatic envi- tx.us/instreamflows/index.html ronment, and consider both short- and long-term consequences. In response 2.2 to Senate Bill 2 and these statutes, the Texas Instream Flow Agencies have adopted an approach Program Approach to for the program that focuses on entire Sub-basin Studies riverine ecosystems and have proposed The Texas Instream Flow Program will the following definition for a sound eco- conduct sub-basin studies that focus logical environment: on the entire ecosystem, are subject to scientific realities, and reflect a larger A resilient, functioning ecosystem program context. The program will characterized by intact, natural maintain a focus on the overall river- processes and a balanced, inte- ine ecosystem by conducting multidis- grated, and adaptive community ciplinary studies, considering a range of organisms comparable to that of spatial and temporal scales, focus- of the natural habitat of a region. ing on essential ecosystem processes, and recommending a flow regime to Ensuring a sound ecological environ- meet study goals and objectives. The ment requires maintaining the ecological program will consider scientific reali- integrity and conserving the biological ties by recognizing that instream flows diversity of a riverine ecosystem. To meet are only part of the requirements for a these goals, the Agencies recognize that sound ecological environment. Study it is important to maintain the natural

Texas Water Development Board Report 369 11 Table 2-1. Environmental considerations related to streams/rivers as directed by state statutes.

Consideration Statute

will not cause…adverse impact on…the environment of the stream 30 TAC 297.45(b)

no adverse impact to…the environment 30 TAC 297.45(d)

assess the effects…on fish and wildlife habitats...consider whether the proposed 30 TAC 297.53(a) project would affect river or stream segments of unique ecological value

mitigate adverse impacts, if any, on fish and wildlife habitat 30 TAC 297.53(b)

assessment…shall include the project site as well as potentially impacted habitat 30 TAC 297.53(c) upstream, adjoining, and downstream

…”no net loss” of wetland functions and values 30 TAC 297.53(e)

In addition to aquatic and wildlife habitat, wetland functions also include, but are not limited to, water quality protection through sediment catchment and filtration, storage plans for flood control, erosion control, groundwater recharge, and other uses.

shall examine both direct and indirect impacts to terrestrial and riparian habitats, 30 TAC 297.53(f)6 as well as long- and short-term effects to the watershed or ecoregion

assess the effects…on water quality of the stream or river…consider the 30 TAC 297.54(a) maintenance of State of Texas Surface Water Quality Standards…and the need for all existing instream flows to be passed up to that amount necessary to maintain the water quality standards for the affected stream

to protect fish and wildlife resources, including permit conditions, mitigation, and TPWC 12.024(b) schedules of flow or releases

conditions considered…necessary to maintain existing instream uses and water TWC 11.147(d) quality of the stream or river

conditions considered…necessary to maintain fish and wildlife habitats TWC 11.147(e)

shall assess the effects…on water quality in this state TWC 11.150

assess the effects…on fish and wildlife habitats and may require…reasonable TWC 11.152 actions to mitigate adverse impacts

determine the potential impact…on…instream uses TWC 16.012(k)

TAC=Texas Administrative Code TPWC=Texas Parks and Wildlife Code TWC=Texas Water Code

12 Texas Water Development Board Report 369 habitat diversity, hydrologic character, number of technical studies covering dif- and water quality of river systems. ferent disciplines. Because of their complexity, it is Instream flow recommendations will widely accepted that riverine ecosystems be in the form of flow regimes contain- require multidisciplinary studies (see, for ing several components. Because they example, Palmer and others, 2003; Wohl occur over a range of flows, essential and others, 2005). Components related riverine ecosystem processes cannot be to hydrology, geomorphology, biology, preserved by a single “minimum” flow water quality, and connectivity must be rate. Although the outcome of many considered in order to adequately address instream flow methods are single-flow flow requirements of aquatic ecosystems recommendations, Annear and others (Annear and others, 2004). As a result, (2004) concluded that such recommen- the Texas Instream Flow Program will dations have not succeeded in adequately follow this multidisciplinary conceptual maintaining riverine ecosystems. model. River scientists now recognize that In addition, instream flow studies a range of flows are required to main- require a multiscale approach because tain healthy riverine ecosystems (Brown riverine ecosystems have many com- and King, 2003; Schofield and others, ponents that interact across a range of 2003). Based on the results of techni- scales. Spatial scales of riverine ecosys- cal studies, the instream flow program tems range from molecular interactions will identify a set of flow components of water quality constituents to basinwide that support important processes (Table processes affecting sediment supply to the 2-2). In general, there should be some channel. Temporal scales may range from correspondence between instream flow less than a few hours for some chemical recommendations and historical hydro- processes to thousands of years or longer logic patterns for a sub-basin. for geologic changes in the watershed. In response, the Agencies have developed 2.2.2 an approach that considers a range of Scientific Realities spatial and temporal scales. While conducting sub-basin studies, An ecosystem approach also requires the Agencies will be aware of scientific the Texas Instream Flow Program to realities. We recognize the important, focus on essential ecological processes. but not exclusive, role that flows play in Riverine ecosystems are complex sys- supporting a sound ecological environ- tems of interacting abiotic and biotic ment. We also recognize that knowl- components. To manage these systems edge and understanding of riverine eco- effectively, at least a basic understand- systems are imperfect, and as a result, ing of these interactions (such as food study findings will incorporate uncer- web dynamics, reproductive cues, spe- tainty. As understanding of these eco- cies recruitment, and colonization) systems increases, the procedures and is required. Attempting to manage a methods used to develop flow recom- riverine ecosystem without adequate mendations for Texas rivers will need to understanding of such processes can be adapt and change. problematic. For example, many river Because almost every process in restoration projects in California have riverine ecosystems is flow related, been unnecessary, unsuccessful, or even instream flows play an important part detrimental because essential riverine in creating a sound ecological environ- processes were not understood (Kon- ment. In most cases, implementing dolf, 1998). Understanding the essential adequate instream flows should result processes of a specific river ecosystem in the riverine environment meeting its will undoubtedly require conducting a ecological goals. But adequate timing

Texas Water Development Board Report 369 13 Table 2-2. Example components of an instream flow regime and supported processes.

Component Hydrology Geomorphology Biology Water quality Subsistence Infrequent, Increase deposition Provide restricted Elevate temperature flows low flows of fine and organic aquatic habitat and constituent particles concentrations Limit connectivity Maintain adequate levels of dissolved oxygen

Base flows Average flow Maintain soil Provide suitable aquatic Provide suitable in- conditions, moisture and habitat channel water quality including groundwater table Provide connectivity variability Maintain a diversity of along channel corridor habitats

High flow In-channel, Maintain channel Serve as recruitment Restore in-channel pulses short and substrate events for organisms water quality after duration, characteristics prolonged low flow Provide connectivity high flows periods Prevent encroachment to near-channel water of riparian vegetation bodies

Overbank Infrequent, Provide lateral Provide new life phase Restore water quality flows high flows channel movement cues for organisms in floodplain water that exceed and floodplain bodies Maintain diversity of the channel maintenance riparian vegetation Recharge floodplain Provide conditions for water table seedling development Form new habitats Provide connectivity to Flush organic material floodplain into channel Deposit nutrients in floodplain

Sources: Adapted from MEA (2005); NRC (2005).

and quantity of instream flows may not additional factors and their ecological be enough to ensure ecosystem goals are effects as is practical within time and met because instream flow regimes in budget constraints. and of themselves are not sufficient to Scientific studies of river ecosystems maintain the ecological condition of a are conducted in the field on complex river (Schofield and others, 2003). The systems that are imperfectly understood. instream flow program will identify fac- As such, they are subject to the vagaries tors in addition to flow alteration that of field conditions (changing climatic affect whether ecosystem goals for river conditions, natural variability in species segments in the study are attained. Such abundances, and fluctuations in distur- factors may include both human activi- bance regimes) and limitations in scien- ties (Table 2-3) and the recent occurrence tific understanding. Results are inherent- of natural disturbances, such as extreme ly uncertain. To the extent possible, the floods and droughts or hurricanes. The Agencies will quantify the uncertainty in Agencies will report and quantify these study results and make this information

14 Texas Water Development Board Report 369 Table 2-3. Human activities that may affect riverine ecosystems.

Category Activities Watershed Vegetative clearing Overgrazing Soil exposure or Land use change Land grading compaction Hard surfacing Urbanization Irrigation and drainage Roads and railroads Channel Streambank armoring Channelization Streambed disturbance Utility crossings Dredging Woody debris removal Structural Dams and levees Storm water Reduction of floodplain Bridges discharge outlets

Flow Withdrawal of water Increased return Changed magnitude alteration flows and timing of peak flows Species Biotic harvesting Exotic species Pollution Point source Diffuse

Sources: Adapted from FISRWG (1998); Giller (2005). available to decision makers, stakehold- • agreed-upon flow is being ers, and the public. released Because of scientific uncertainty, the • overall objective (desired Agencies strongly endorse the concept river condition) is being of adaptive management. Within the achieved context of adaptive management, imple- • objectives for different com- mentation of instream flow results will ponents of the regime are be monitored to see whether the estab- being met lished goals are being reached. If goals • environmental flow alloca- are not met, an adaptive process would tion needs to be modified be invoked to adjust implementation in light of the observed measures. Procedures for implement- responses. ing instream flow recommendations in Texas should be capable of evaluating Through time, the Agencies will the effectiveness of instream flows and adapt and change study procedures refining and adapting the flow regime as and methods as necessary to improve necessary. As stated by King and Brown the program. At first glance, it would (2003), seem advantageous to examine all of the primary study areas in Texas with one a monitoring program is particu- identical set of methods and procedures larly important given the gener- suitable for all conditions because this ally poor understanding of the would facilitate comparing results from links between flow and ecologi- one study to the next. However, given the cal response. The implementation diversity of Texas river systems, one set of an agreed flow regime should of tools may not be sufficient. Because allow for adaptive management each basin represents a unique set of fea- based on the monitoring. The tures or issues, established methods and monitoring program should be procedures may need to be refined and designed to provide essential varied in order to study all of the major feedback on whether the: rivers of Texas. The Agencies expect to

Texas Water Development Board Report 369 15 gain significant understanding of large 2.3 riverine ecosystems during initial stud- Layout of Technical ies of these systems. This understand- Overview ing will be used to refine methods and Identifying a process to develop procedures for future studies. instream flow studies for major Texas river sub-basins is not a trivial task, and 2.2.3 there are few models available for guid- Program Context ance. Few programs have attempted to The Agencies recognize that the Texas apply procedures to a range of condi- Instream Flow Program will function tions as diverse as those found in Texas. within a broader context that includes (Chapter 3 of this document describes political and socioeconomic concerns the general complexity of riverine eco- and other government programs relat- systems and the diversity of ecological ed to managing river ecosystems. The conditions across the state.) program will be conducted in the pub- The process of identifying instream lic view, and the Agencies will develop flows for Texas’ rivers must be robust, sub-basin goals, objectives, and study that is, suitable in any river basin yet designs with stakeholder input. In addi- adaptable to the specific conditions of tion, peers from the scientific communi- every river basin. Study procedures may ty will provide reviews of study designs need to vary significantly from one river and reports. We expect the peer review basin to another. Any description of such process to increase public confidence in a process represents a trade-off between study results and, therefore, the likeli- providing detailed guidance required to hood that flow recommendations will conduct a specific study and general guid- be implemented. ance applicable to a range of conditions. The Agencies also recognize that the This document is intended to describe instream flow program will be conducted the general framework of the process. It within the broader context of federal, does not provide an exhaustive list of the state, and local activities that affect, conditions that might be encountered regulate, or monitor rivers within Texas. during instream flow studies in Texas. The program will use data from these It does, however, describe the organiza- programs for evaluating and monitoring tional process the Agencies will follow to river ecosystems. We will evaluate and assess available data, set goals, conduct incorporate the results of any pertinent studies, integrate results, develop and research efforts completed by other par- implement recommendations, monitor ties. To the extent possible, study objec- river conditions, and adapt recommen- tives will be structured to take advantage dations as necessary. It also describes of ongoing programs. For example, water the general technical capabilities that quality investigations will be structured the Agencies can provide in support of to complement or rely on existing Texas instream flow studies. Commission on Environmental Qual- The overall process the Agencies ity water quality programs conducted in will follow in a sub-basin instream flow partnership with local river authorities. study is shown in Figure 2-1. Individual The goal will be to build the instream flow steps in the process are also described in program in conjunction with existing Tables 2-4 through 2-7. The first step in activities rather than to create an entirely the process involves reconnaissance of new process or duplicate existing efforts. the specific sub-basin and evaluation of This should reduce expense, redundancy, previously collected data (Table 2-4). The and conflicting regulation while improv- Agencies, with the assistance of coopera- ing ecosystem understanding. tors and/or contractors, will assemble and evaluate available data for the river

16 Texas Water Development Board Report 369 system. These data may include results of Reconnaissance and Information Evaluation monitoring, research, and study efforts conducted by the Agencies, other state and federal agencies, universities, and/or Goal Development Consistent with other organizations. This first step will Sound Ecological Environment be completed with the help of stakeholders, including local river authorities, who Study Design are likely to possess or have knowledge of data related to a specific river segment. We will supplement previously collected Multidisciplinary Data Collection and Evaluation data and the current understanding of the river ecosystem with reconnaissance activities and preliminary analysis. Data Integration to Generate The main objective of this step is to Flow Recommendations develop a conceptual model based on available information of the relation- Draft Study Report ship between ecological health and flow regime. Research efforts needed to address identified knowledge gaps will also be pri- Final Study Report oritized. Activities related to this step are SB 2 Ends discussed in Chapters 4 and 5. Post-SB 2 Next Steps: The second step of a sub-basin Implementation, Monitoring, instream flow study is to develop goals and Adaptive Management consistent with a sound ecological environment and other statewide goals and Figure 2-1. Steps in sub-basin studies of the objectives. Activities will be a coopera- Texas Instream Flow Program. tive effort of the Agencies and stakeholders for the specific sub-basin (Table 2-5). for scientific peer review and modified The Agencies will present the current as necessary. Activities in this step are understanding of the condition and discussed in Chapters 4 and 5. behavior of the river ecosystem, as well The third step is multidisciplinary as the potential for improving that condi- data collection and evaluation accom- tion. Stakeholders and the Agencies will plished by technical studies of the river develop objectives for the desired con- ecosystem (Table 2-6). The Agencies dition of the river and goals and objec- and/or their contractors will conduct tives for reaching and/or maintaining these studies, with input/assistance that desired condition. To measure prog- from stakeholders and in accordance ress toward the desired river condition, with the study design agreed upon with a set of ecological indicators will also be stakeholders and finalized after scien- selected. The Agencies will develop plans tific peer review. The Agencies will coor- for technical studies to determine the dinate efforts to make efficient use of relationship of the instream flow regime staff, expertise, and resources. Studies to the ecological condition of the river will not only be multidisciplinary, but within the sub-basin. With stakehold- also interdisciplinary in nature. To col- ers, we will select potential study sites lect data across the desired range of flow and evaluate their suitability. The final and seasonal conditions, it will be neces- result of this step will be a study design sary to conduct studies over more than describing sub-basin goals and objec- one year. Several river segment studies tives, ecological indicators, and methods will be conducted simultaneously to and procedures for the technical stud- maximize efficiency. For example, when ies. The study design will be submitted hydrologic and/or seasonal conditions

Texas Water Development Board Report 369 17 Table 2-4. Summary of sub-basin study activities during Step 1.

Step 1: Reconnaissance and Information Evaluation Purpose • Compile, review, and georeference available studies/data. • Identify historic and current conditions, significant issues, and concerns. • Conduct preliminary field surveys and analysis. Data Sources • U.S. Geological Survey and other gage data. • Federal/state/local studies and reports. • Historic air photos/Digital Orthographic Quarter Quadrangles/maps/soil surveys. • Current water quality models and standards. Activities Stakeholder Participation • Provide historic and current perspective of resource. • Identify important concerns and opportunities for study participation. • Select sub-basin workgroup. Hydrology and Hydraulics • Calculate flow statistics for historic and existing conditions. • Identify existing features (such as tributaries) and existing and proposed alterations (diversions, impoundments, and land uses) affecting hydrologic character. Biology • Identify historic and current species assemblages, representative macro- and mesohabitat types, and other biological issues and considerations. • Assess historic and current condition of stream biota and riparian resources. • Identify potential study reaches and sites. Geomorphology • Analyze aerial photography and other historic data as available. • Assess channel bed form and banks, active channel and floodplain processes, and changes in sediment regime and causes. • Make preliminary geomorphic classification of river segment. Water Quality • Assess historic and current water quality and aquatic life uses. • Identify water quality issues and constituents of concern. Output • Synthesized summary of available studies/data, including GIS layers. • Conceptual models describing the relationships between ecological health and flow regime. • Prioritized list of research needs to address identified knowledge gaps. Scale: All Scales are unfavorable on one river segment, The fourth step of a sub-basin data collection efforts will be focused on instream flow study is data integration a different river segment where condi- to generate flow recommendations. tions are more favorable. Coordination Activities in this step are outlined in of multidisciplinary studies is described Table 2-7. Using the results of technical in Chapter 5. The activities of individual studies, the Agencies, with stakeholder disciplines are described in Chapters 6 input, will develop recommendations for through 9. an instream flow regime to meet study

18 Texas Water Development Board Report 369 Table 2-5. Summary of sub-basin study activities during Step 2.

objectives. This will require synthesizing report will be submitted for scientific study results across several spatial and peer review and modified as needed. temporal scales as well as between disci- The peer review process is described in plines. The Agencies will present results Chapter 4. Procedures to integrate study as a range of flows over seasons and results and generate flow recommenda- years, quantifying to the greatest extent tions are discussed in Chapter 10. possible the ecological consequences of The purpose of the Texas Instream deviations from these targets. A study Flow Program authorized by Senate Bill report will include documentation of 2 is to perform scientific and engineer- raw data, collection procedures, meth- ing studies to determine instream flow ods of analysis, and conclusions. It will conditions necessary to support a sound also describe the uncertainties related ecological environment in a specific sub- to study results and the ecological risk basin. Activities that occur after instream associated with that uncertainty. The flow recommendations are developed,

Texas Water Development Board Report 369 19 Table 2-6. Summary of sub-basin study activities during Step 3.

Step 3: Multidisciplinary Data Collection and Evaluation Purpose • Collect input data required for models and analyses. • Monitor water quality and flow conditions continuously at study sites. • Determine relationships between flow, water quality, biology, habitat, channel, and floodplain conditions. Data Sources • Hydrologic measurements and bathymetric mapping. • Biological data collection and habitat mapping. • Geomorphic data collection and mapping. • Water quality data collection. Activities Stakeholder Participation • Sub-basin study and data collection workshops/field demonstrations. Hydrology and Hydraulics • Monitor stage/discharge continuously during study period. • Map substrate, woody debris, and variations in hydraulic roughness. • Model hydraulic characteristics in relation to flow, including extent of inundation associated with flood events. Biology • Collect appropriate biological and habitat utilization data. • Describe habitat criteria and significant conditions for key species/guilds/life stages. • Conduct habitat modeling to assess habitat-flow relationships, including diversity. • Conduct riparian studies and estimate riparian requirements. Geomorphology • Develop sediment budgets. • Identify factors controlling geomorphic behavior of river segment. • Assess channel adjusting and overbank flow behavior, including flow conditions that initiate sediment and large woody debris movement and deposition. Water Quality • Monitor water quality at site during study period. • Validate previous models and conduct water quality modeling studies as needed. • Assess flow/water quality relationships. Output • Documentation of methods and data (hardcopy and electronic formats). • Habitat versus flow relationships. • Flows required to maintain water quality and channel/riparian areas. • Refined conceptual models that describe ecological health and flow regime. Scale: All Scales including implementation, monitor- flow effort. Without it, previous steps are ing, and adaptive management, are not rendered ineffectual and a sound ecologi- addressed by Senate Bill 2 and are not cal environment is not protected. Adap- described in detail in this document. tive management is widely recognized Implementation is, however, arguably as a necessary approach for managing the most important step in an instream complex ecosystems and is considered

20 Texas Water Development Board Report 369 Table 2-7. Summary of sub-basin study activities during Step 4.

to be a foundational component of a up a process for the critically important state-of-the-art instream flow program activities of implementing, monitoring, (NRC, 2005). An effective monitoring and adaptively managing environmental program is required in order to validate flow recommendations based on the best implementation and is integral to adap- available science. This includes, when tive management. Senate Bill 3, passed in available, results of studies completed by 2007 by the 80th Texas Legislature, sets the Texas Instream Flow Program.

Texas Water Development Board Report 369 21 3 Ecological Setting

iven the wide diversity of aquatic 1999). These maps may be found at this ecosystems in Texas (Edwards and Web site: www.lib.utexas.edu/maps/ others,G 1989), the geographical vastness texas.html of the state, and the different character- Texas has approximately 307,385 istics among and within river basins, the kilometers (191,000 miles) of low- to tools used to sample, model, and other- medium-gradient, warm water streams wise identify instream flows necessary and rivers. Most Texas rivers originate to maintain a sound ecological environ- within the boundaries of the state and ment will be tailored to each sub-basin, flow into the bays and estuaries border- consistent with the overall goals of the ing the Gulf of Mexico after traversing Texas Instream Flow Program. several different physiographic regions and biotic provinces. Rainfall varies from 3.1 more than 127 centimeters (50 inches) Overview of per year in the east to less than 25 centi- Diversity of Texas meters (10 inches) per year in the west. A series of maps illustrate the relevant Although the base flows of some Texas characteristics of Texas. The Physio- rivers and streams are groundwater graphic Map of Texas shows the phys- dependent (spring-fed), most stream- iographic provinces and provides infor- flows are directly related to episodic mation on topography, geologic struc- rainfall-runoff events. Other stream ture, and bedrock types (BEG, 1996a). segments are dominated by wastewater The River Basin Map of Texas depicts return flows from municipal areas. the watershed boundaries of the major Collectively, Texas’ rivers and streams river basins and the patterns of annual are biologically diverse, to some degree rainfall, in addition to information on resulting from the wide range of topog- watershed area, reservoirs, and factors raphy, plant communities, and geology influencing river basin character (BEG, found within the state’s borders. A recent 1996b). The Major Texas Aquifers and publication on biodiversity in the United Minor Texas Aquifers maps delineate States indicates that overall, Texas ranks major and minor aquifers (TWDB, second in diversity, third in endemism, 1990a and 1990b). The Geology of Texas and fourth in extinctions of flora and map depicts the geology of Texas and fauna (Stein, 2002). Streams and rivers provides a synopsis of geologic histo- provide habitat for more than 255 species ry (BEG, 1992). The Vegetation/Cover of fish, of which more than 150 are native Types of Texas map delineates the cat- freshwater species (Hubbs and others, egories of vegetation and cover types. 1991). Native fish communities consist It also provides information on natural entirely of warm water species, and their and human factors affecting plant asso- diversity reflects transitions from a Mis- ciations, species richness, and the eco- sissippi Valley fauna in the north and east logical regions of the state (BEG, 2000). to a Rio Grande fauna in the south and The Land-Resource Map of Texas delin- west (Conner and Suttkus, 1986). Con- eates land resources based on ground- sequently, East Texas rivers have much water recharge, mineral, physical prop- more diverse communities than rivers in erty, land form, dynamic process, and West Texas (Edwards and others, 1989; biological resource (wetland) units. It Linam and others, 2002). The native also summarizes information on the stream fish fauna in Texas is composed importance and use of each unit (BEG, mainly of cyprinids (minnows), percids

22 Texas Water Development Board Report 369 (darters and perches), catostomids (suck- also provide flood control and generate ers), centrarchids (sunfishes and basses), hydroelectric power. Nonnative species ictalurids (catfishes), and members of introductions have altered the composi- nearly 20 other families. More than 50 tion of lotic assemblages and in some species of unionid mussels inhabit Texas instances have negatively influenced rivers, streams, canals, reservoirs, lakes, native species within a drainage or subd- and ponds (Howells and others, 1996). rainage. Two recent assessments docu- Mussel populations in Texas are comment changes in Texas fish assemblages mercially valuable (shell harvesting) yet (Anderson and others, 1995; Hubbs and little studied. Aquatic invertebrates in others, 1997). Texas streams are diverse, but this fauna remains lightly documented, and it is 3.2 possible that the number of species of Overview of Riverine aquatic invertebrates occurring through- Components out the state numbers in the thousands. The Senate Bill 2 mandate to develop In addition, the biogeographic origins instream flow recommendations that of the faunal elements found in Texas maintain a sound ecological environ- streams are equally diverse, with known ment in rivers and streams clearly dic- representatives from the Gulf Coastal tates that the function and structure of Plain, Chihuahuan Desert, Great Plains, aquatic ecosystems must be preserved. and the Neotropics. Similar to the fishes, To this end, the scope of studies will invertebrate diversity and densities are address the riverine components of higher in eastern Texas when compared biology, hydrology and hydraulics, water to those of the western portion of the quality, and geomorphology. Connec- state. Texas also has its share of nonna- tivity, scale, and dimension (see Section tive species that inhabit aquatic environ- 3.3) are also important because these ments. The most problematic of these riverine components interact within include riparian, submerged, and floating complex spatiotemporal dimensions plants, aquatic snails, mussels and clams, and across scales to create and maintain fish, and mammals. the structure and function of lotic sys- The physical, chemical, and biological tems. Thus, a successful instream flow characteristics of the river basins reflect program will require an interdisciplin- many geologic, hydrologic, and human ary approach to address these complex influences, especially those associated systems in a scientifically sound and with municipal, industrial, and agricul- comprehensive manner. tural development over the last century. No major river in Texas remains com- 3.2.1 pletely free flowing or free from non- Biology point or point source pollution. Instream The biological component of instream and riparian habitats have been altered flow studies includes developing an by land use practices, channel modifica- understanding of relationships between tions, and changes to hydrologic regimes aquatic communities, life histories, from dam construction and operation, and habitats (instream or riparian). It surface water diversion, and groundwa- must also include an understanding of ter pumping. All of the major rivers in the physical processes that create and Texas are regulated to some extent by maintain system habitat, water qual- the water supply operations of the 196 ity, and hydrology (Bovee and others, major reservoirs (defined as those with 1998; Annear and others, 2004). Riv- a conservation storage capacity greater erine communities include freshwater than 5,000 acre-feet or about 6.2 million and estuarine fishes; other vertebrates, cubic meters). Some of these reservoirs such as turtles; invertebrates, such as

Texas Water Development Board Report 369 23 caddisflies, stoneflies, mayflies, and regime may change water quality and dragonflies; mollusks, such as mussels create a system that favors a noncharac- and snails; crustaceans, such as cray- teristic assemblage. Elevated water tem- fish and river shrimp; aquatic macro- peratures or depressed dissolved oxygen phytes and algae; and riparian flora and concentrations can lead to fish kills or fauna. Some are obligate riverine spe- uninhabitable zones or may favor toler- cies requiring flowing water habitat for ant species. all or part of their life cycle. Others are The life history and ecology of lotic habitat specialists that require specific organisms must be considered in evalu- substrates, current velocities, or depths. ating instream flows. Using fish as an Riverine obligates and habitat special- example, the fundamental aspects of ists are generally well suited as target interest are growth, survival, and repro- species for instream flow evaluations. ductive success (spawning and recruit- Hydrology plays a key role in deter- ment). Information on foraging behavior, mining the composition, distribution, habitat use, the timing of those activities and diversity of aquatic communities (nocturnal versus daytime), and temper- since many riverine biota have evolved ature regime is essential to understand- life history strategies that correspond ing growth. Data on habitat use of prey to the natural flow regime, that is, the species may also provide valuable infor- magnitude, duration, frequency, timing, mation. Ensuring reproductive success and rate of change of flow conditions involves many habitat considerations (Poff and Ward, 1989; Richter and oth- (current velocity, depth, substrate com- ers, 1996). Flow regimes largely deter- position and embeddedness, cover, and mine the quality and quantity of physical area) for spawning adults, eggs, fry, and habitat available to aquatic organisms in juveniles. Spawning behavior or repro- rivers and streams (Bunn and Arthing- ductive mode (Johnston, 1999) and water ton, 2002). Habitat conditions are gen- quality issues, such as temperature cues, erally characterized in terms of current are also important in ensuring repro- velocity, depth, substrate composition, ductive success. Other issues (such as and instream cover, such as large woody migration patterns) associated with life debris, undercut banks, boulders, macro- history strategies may be important in phytes, and other cover types (Bovee and some systems. others, 1998). Habitat complexity (het- Temporal considerations (spawning erogeneity) is a primary factor affecting season, timing of peak flows, and photo- diversity of fish assemblages (Gorman period) also relate to life history strate- and Karr, 1978; Angermeier, 1987; Bunn gies (Stalnaker and others, 1996). With and Arthington, 2002), and heteroge- respect to interannual (between years) neous habitats offer more possibilities variation in flows, short-lived fishes may for resource (niche) partitioning (Woot- require certain flows every year while ton, 1990). Flow regimes also influence populations of long-lived fishes may be physical (geomorphology) and chemical sustained by meeting flow conditions (water quality) conditions in rivers and less frequently. Intra-annual (within a streams, which, in turn, influence bio- year) variation in flows is important to logical processes. organisms that respond to the seasonal Water quality is interrelated with peaks and lows of natural flow regimes flow, has a major influence on aquatic for spawning or migratory behaviors. biota, and varies widely across the state. Scientists making instream flow recom- For example, conductivity may range mendations must be aware of temporal from 100 microsiemens per centimeter in considerations and incorporate interan- East Texas to more than 100,000 in some nual flow variability on an appropriate West Texas streams. Altering the flow scale. For example, the life history of a

24 Texas Water Development Board Report 369 long-lived (decades) species such as pad- address biological processes such as dlefish is different from that of certain habitat use and spawning. For example, minnows, which may live, reproduce, flows downstream from hydropower and die in two or less years. These con- facilities may vary profoundly on an siderations dictate that temporal aspects hourly basis, which may be important of instream flow management differ in assessing habitat availability and use. between groups of organisms. Further- When considering dissolved oxygen, more, habitat requirements of species whose concentrations vary diurnally, may shift seasonally and diurnally, and an hourly or other sub-daily step may they may also differ by sex or life stage. be required. Larger time steps (months, years) are more suitable for addressing 3.2.2 physical processes such as creating and Hydrology and Hydraulics maintaining habitats. Hydrologic time Hydrology refers to the flow of water series can be developed to reflect natural, and has four dimensions: lateral (chan- historical, and proposed flow conditions. nel-floodplain interactions), longitu- Developing these time series will allow dinal (headwater to mouth), vertical comprehensive assessment of potential (channel-groundwater interactions), impacts to fish and wildlife resources. and temporal aspects including inter- In a basin-level assessment, the and intra-annual variation. Character- hydrologic network (geography of flows) istics of hydrology that define the flow is important to understand. Watershed regime include the magnitude, duration, contributions, water right diversions, timing, frequency, and rate of change. reservoir operations, return flows, and Following the recommendation of lateral and vertical exchanges are some the National Research Council (2005), of the factors that should be described in the Texas Instream Flow Program will multiple spatial and temporal scales. identify a set of four components of Hydraulics refers to the distribution a flow regime intended to support a of water velocities and depths result- sound ecological environment. These ing from the channel morphology and components are subsistence flows, base discharge through the channel. Since flows, high flow pulses, and overbank many aquatic organisms prefer particular flows. Subsistence flows are low flows combinations of velocities and depths, maintained during times of drought. hydraulic conditions are important for Base flows represent the range of “aver- describing instream habitat. A hydraulic age” or “normal” flow conditions in model can be used to describe how veloc- the absence of significant precipitation ities and depths change with changing or runoff events. High flow pulses are flow. In fact, a major effect of hydrologic short duration, high magnitude (but still alteration is a change in the hydraulics within channel) flow events that occur that directly influence habitat. during or immediately following storm events. Overbank flows are infrequent, 3.2.3 high magnitude flow events that exceed Water Quality channel banks and enter the floodplain. Water quality parameters, including (Further descriptions of these flows are temperature, dissolved oxygen, pH, provided in Section 6.1.) Additional flow conductivity, turbidity (fine sediment), components may be necessary for some and other parameters, are important sub-basins. to growth, survival, and reproduction Hydrologic time series are an impor- of aquatic organisms. Water quality tant tool for assessing potential impacts characteristics reflect watershed geol- to riverine ecosystems. Daily time steps ogy, land use, climate, and sources of or shorter intervals may be needed to organic matter and nutrients. Because

Texas Water Development Board Report 369 25 stream fishes and macroinvertebrates years. Over a period of several years, the are cold-blooded, water temperature has overall effect of large-magnitude events a significant influence on their growth may be less than the combined effect of (metabolic rate), survival (lethal tem- moderate flow events that occur many peratures), and reproduction (spawning times during that same time period. cues and egg incubation) (Armour, 1991). The relative geomorphic importance of Temperature ranges tolerated by organ- large-, moderate-, and small-magnitude isms vary by taxa and life-stage. Factors flow events will vary between basins that influence temperature include flow, and sub-basins. channel width in combination with Individual flow components play riparian shading, thermal inputs, tur- different roles in maintaining the physi- bulence, and current velocity. In addi- cal features of a river system. High flow tion to the importance of temperature, pulses play an important role in devel- dissolved oxygen also influences sur- oping and maintaining in-channel habi- vival and distribution of lotic biota as tats. Although smaller in magnitude mentioned previously in Section 3.2.1. than overbank flows, high flow pulses Streamflow, water temperature, turbu- occur more frequently and, therefore, lence, organic matter decomposition, play a more active role in sculpting in- algal and macrophyte photosynthesis channel habitats. In contrast, overbank and respiration, and animal respira- flows play a critical role in developing tion all influence dissolved oxygen con- and maintaining riparian areas and centrations in lotic systems. Turbidity, floodplain habitats. The duration, rate conductivity, pH, and other factors may of increase and decrease, and sequence constrain or limit the distribution and of flow events also influence physical abundance of aquatic biota. processes and may have important biological consequences. For example, as 3.2.4 flow recedes after a large flow event, Geomorphology fine sediments may accumulate within Geomorphology considers the physi- in-channel habitats. This may reduce cal processes that form and maintain the suitability of the habitat for spawn- stream channels and habitats, flush ing, foraging, or refuge for some species fine sediments, and transport sediment (Milhouse, 1998). loads. In combination with the char- Changes in the hydrologic regime acteristics of the available sediment influence geomorphic processes by supply, the balance of flow magnitude altering the magnitude, duration, and and frequency acts to form the physi- frequency of flow events that transport cal characteristics of a river or stream. sediment. Geomorphic processes are also As a result, geomorphic processes vary altered by disturbances to the sediment between and within basins and sub- regime, such as trapping coarse sedi- basins. For example, geomorphic pro- ments in reservoirs or land use changes. cesses occur over a range of flows, but When either the hydrologic or sediment stream power, the energy available for regime is altered, an understanding of sediment transport processes, increases geomorphic processes is required to with discharge. As a result, individual, evaluate potential consequences to the large-magnitude flow events have a physical features of a river. greater immediate effect on the physical features of a river system than individu- 3.3 al, small-magnitude events. However, in Connectivity, Dimension, many basins or sub-basins, large-mag- and Scale in Stream Systems nitude flow events occur infrequently, Connectivity, dimension, and scale are such as once a year or once every few important considerations in developing

26 Texas Water Development Board Report 369 and executing many aspects of sub-basin and aquifers; some lotic systems recharge studies, including the development of aquifers, and base flows in others may conceptual models, design of technical be supported by spring flows and seeps. evaluations to ensure spatial scales are Temporal aspects are related to the tim- commensurate among the disciplines, ing of events that mediate connectivity and integration of study results (NRC, (such as overbank flows that connect 2005). instream processes with floodplains) The physical, chemical, and biological and the life history of aquatic and ripar- processes that facilitate ecosystem func- ian species. tion define the boundaries of a stream or In addition to connectivity, dimen- river ecosystem. Those boundaries may sion of stream segments is an important not be readily apparent if one considers consideration in developing sub-basin the broad possibilities for connectivity studies. The longitudinal dimension of beyond the apparent channel or study streams refers to processes that operate reach to areas that include upstream from headwaters to mouth. The river and downstream river reaches, tribu- continuum concept describes natural taries, the surrounding floodplain, and changes in physical gradients and biolog- groundwater, among others. Adding to ical attributes facilitated by the unidirec- the complexity is that processes influ- tional flow of water and matter (Vannote enced by connectivity may operate at and others, 1980). Many studies have different spatial and temporal scales. been conducted to test or complement The riverine ecosystem includes not the river continuum predictions. For only the water and habitat in the chan- example, the nutrient spiraling concept nel, but also encompasses these broader states that nutrients have open cycles, or connections. spirals, because of the dynamics of flow Connectivity refers to the movement (Newbold and others, 1981; Elwood and and exchange of water, nutrients, sedi- others, 1983). The length of a given spiral ments, organic matter, and organisms is a function of transport rate, physical within the riverine ecosystem. Connec- retention, and biological uptake. Stazner tivity is complex, encompassing physical, and Higler (1986) developed the stream hydrological, chemical, and biological hydraulics concept to explain biological processes. It occurs laterally, longitudi- zonation in the longitudinal dimension nally, vertically, and temporally. Lateral as related to clear changes in hydraulic connectivity between the floodplain and conditions. the river channel is important to main- Studies have also expanded the con- tenance and function of riparian areas cept into lateral and vertical dimensions. and unique floodplain features, such as The flood pulse concept describes the oxbow lakes. Longitudinal connectivity process by which matter (nutrients, sedi- is important for transporting and pro- ments, and biota) is regularly exchanged cessing nutrients and organic matter, between the river and the floodplain migratory species, and physical process- (Junk and others, 1989). The ecological es (such as sediment transport). Water characteristics and productivity of both quality characteristics also show a strong the river and the floodplain are linked longitudinal dynamic. Vertical connec- and influenced by the frequency and tivity is important biologically since the duration of overbanking events. The hyporheic zone—the zone under a river hyporheic corridor concept recognizes or stream comprising substrate whose the importance of subsurface-surface interstices are filled with water—may interactions, thus, addressing the verti- support tremendous populations of mac- cal and lateral dimensions (Stanford and roinvertebrates. Vertical connections Ward, 1993). also exist between the stream channel Physical, hydrological, chemical, and

Texas Water Development Board Report 369 27 biological processes reflect temporal riparian habitat operate at multiple scales, aspects of ecosystem function. Water making the recognition of those scaling quality may change both diurnally and issues particularly important in assessing seasonally. For example, dissolved oxy- instream flow requirements (Poff, 1997; gen in streams may decrease at night Fausch and others, 2002). Relevant scales because of plant and algae respiration for lotic species of fish and invertebrates and during summer months when stream can include microhabitat, channel unit waters are warmer. Streamflows also vary or mesohabitat, stream reach, and basin seasonally, reflecting the seasonal pat- or watershed (Poff, 1997). For example, at terns in precipitation and evaporation, the microhabitat scale many flow-depen- as well as human influences from diver- dent species demonstrate preferences sion and pumping. Flows can also vary for faster current. At the mesohabitat over longer time periods (several years to scale, riffle-dwelling species use riffles decades) reflecting the cyclic patterns of almost exclusively although others may drought and flood experienced in Texas. use them only at night. At the reach scale, As a result of the hydrologic dynamics, riparian conditions may influence tro- changes in hydraulics and geomorphol- phic structure (the presence of sufficient ogy influence habitat dynamics and, thus, particulate organic matter input, such biological processes. as leaf matter, to facilitate a shredder- Human influences have the poten- dominated macroinvertebrate commu- tial to affect instream resources through nity). At the basin or watershed scale, these connections and linkages. For barriers to migration may render some instance, alterations to landscapes habitats unavailable at all times. Conse- through urbanization and floodplain quently, the scale of resource issues must development may have substantial effects be incorporated into the study design, on instream processes even when miles selection of models and tools, and inte- away from the area of interest. Similarly, gration of study results. water development projects and their Researchers have published many associated changes in flow regimes influ- nomenclatures describing the spatial ence connectivity. Impoundments trap scale of riverine ecosystems (Frissell sediment and disrupt habitat-forming and others, 1986; Imhof and others, 1996; physical processes, alter thermal and Harby and others, 2004; Brierley and nutrient regimes, modify dissolved oxy- Fryirs, 2005). Unfortunately, there has gen regimes and turbidity, and block been little standardization of terminol- migratory passages for aquatic organisms ogy, which may contribute to confusion (Collier and others, 2000). Reduced high during multidisciplinary studies (Benda, flow pulses and overbank flows alter the 2002). In order to ensure the consider- connectivity between floodplains, ripar- ation of appropriate spatial scales and ian areas, and the river channel, affecting improve communication among dis- the lateral exchange of nutrients, organic ciplines, the Agencies have agreed on matter, sediment, and biota (Nilsson and a common nomenclature for riverine Svedmark, 2002). Groundwater pump- spatial scale during sub-basin instream ing can also have an effect by reducing flow studies (Figure 3-1). The nomen- levels in aquifers that may provide base clature of Frissell and others (1986) is flow to streams. At a smaller scale, water from the perspective of fisheries biology diversions can reduce flow, making shal- and is adapted for small streams in the low, erosional habitats unsuitable, and Pacific Northwest. This accounts for the also affect longitudinal connectivity by relatively small overall spatial extent of inhibiting upstream migration by some units. In contrast, the units of Imhoff and aquatic organisms. others (1996) are adapted for larger river Processes that influence instream and systems and include explicit recognition

28 Texas Water Development Board Report 369 of the effect of the watershed on river a. Sub-basin—the full geographic processes at larger scales. Harby and scope of priority studies within others (2004) reflect a habitat model- major river basins in Texas, ing perspective. Their nomenclature also including the main channel, flood- includes a unit called “picohabitat” (not plain, tributaries, and contributing shown in Figure 3-1) whose dimension watershed area of all study is on the order of centimeters. Brierley segments. and Fryirs (2005) reflect the perspective b. Segment—subset of sub-basin study of fluvial geomorphology. area. For priority studies, segments Individual disciplines may continue are equated to the corresponding to use discipline-specific nomenclature river segments described in 30 during sub-basin studies, but terms will Texas Administrative Code §307.1 be related to the common nomencla- through 307.10. The Agencies ture. For example, geomorphic studies recognize that significant processes may still be conducted with a focus on at this scale extend beyond the “landscape units” and their effect on geo- channel and include tributaries and morphic processes. If used in commu- contributing watershed area. nication with other program staff, this c. Reach—subdivision of a segment unit designation will be defined by its that exhibits relatively homoge- common nomenclature (Figure 3-1). neous channel and floodplain Definitions of spatial scale units conditions (hydrology/hydraulics, adopted by the Texas Instream Flow biology, geomorphology, and water Program are as follows: quality) bounded by breaks such as

1,000,000 Sub-Basin

100,000 Watershed Ecoregion Watershed Segment

Sub- Landscape 10,000 watershed Unit

Macro- Reach 1,000 Reach Stream habitat Geo- Reach morphic Unit 100 Segment Spatial Scale [meters]

Meso- Hydraulic Meso- 10 Reach habitat Unit habitat Site

1 Pool/Rifﬂe Habitat Micro- Micro- Micro- Micro- Element habitat habitat habitat habitat 0.1 Frissell and Imhof and Harby and Brierly and TIFP others (1986) others (1996) others (2004) Fryirs (2005)

Authors

Figure 3-1. Nomenclatures describing the spatial scale of riverine ecosystems. TIFP=Texas Instream Flow Program

Texas Water Development Board Report 369 29 the confluence of major tributaries bars (Trush and others, 2000). For and significant geomorphic features. smaller streams, mesohabitats are The number of reaches within a known by such names as pool, riffle, segment depends on the degree of run, and chute. heterogeneity. e. Microhabitat—zones of similar d. Mesohabitat—basic structural ele physical characteristics within a ments of a river or stream from an mesohabitat unit. Differentiated ecological perspective. For alluvial by aspects such as substrate type, rivers, these elements include scour water velocity, and water depth. pools and submerged transverse

30 Texas Water Development Board Report 369 4 Peer Review and Stakeholder Input

lthough the Agencies have statu- proceedings. They may also be involved tory responsibility to carry out in developing future monitoring and theA Texas Instream Flow Program, they adaptive management strategies. seek collaboration with the public on the execution of instream flow studies. 4.1 This collaboration is crucial to build- Stakeholder Process ing support for the goals and objectives Stakeholder participation is critically of the program and ensuring that local important to maintaining the trans- knowledge and values are incorporated parency and credibility of instream in the studies. Meaningful participation flow studies. The Agencies have cho- in the process increases public confi- sen to commit substantial time and dence in both the science employed by resources to developing a public- and and recommendations resulting from peer-reviewed study methodology and instream flow studies. In order to cul- a process to integrate stakeholders into tivate public confidence, the Agencies the instream flow program. are committed to program transparen- The Texas Legislature has charged cy, stakeholder participation, and sci- the Agencies with the ultimate responsi- entific peer review. Public documents bility for instream flow studies and data will describe the approach and methods collection. Texas Water Code §16.059(a) of the program. For all sub-basin stud- provides that ies, the Agencies will make available to the public final study designs, reports, the Parks and Wildlife Depart- and supporting documents. These will ment, the commission, and the be posted on the Texas Instream Flow board, in cooperation with oth- Program Web site: www.twdb.state. er appropriate governmental tx.us/instreamflows/index.html agencies, shall jointly establish The Agencies are dedicated to imple- and continuously maintain an menting a process in which stakeholders instream flow data collection and may provide input and have the oppor- evaluation program and shall con- tunity to participate in the instream duct studies and analyses to deter- flow studies. The Agencies also seek mine appropriate methodologies stakeholder technical and/or financial for determining flow conditions participation in performing the stud- in the state’s rivers and streams ies, which can maximize resources and necessary to support a sound eco- assist in meeting statutory deadlines. logical environment. Additionally, the program was designed so that instream flow studies could be The legislature also imposed a dead- conducted by qualified third parties with line of December 31, 2016, for the Agen- the Agencies’ oversight. cies to complete priority studies. Finally, although implementation is The stakeholder process will offer the beyond the scope of the Texas Instream opportunity to work with the Agencies Flow Program, the Agencies envision throughout the course of individual stud- that participating stakeholders may be ies through a sub-basin specific work- involved in implementing instream flow recommendations through the Senate Bill 3 process established by the 80th The original deadline in Senate Bill 2 called for completion of priority studies by December 31, Texas Legislature or other regulatory 2010. Senate Bill 3 extended the deadline to 2016.

Texas Water Development Board Report 369 31 group with broad representation. Likely to the table. Six stages in the stakeholder parties include, but are not limited to, process are described below. public agencies, regional water planning groups, river authorities, groundwater Stage 1: conservation districts, municipalities, Identify and Engage Stakeholders industries, agricultural interests, com- Because the success of the stakeholder mercial and sport fishing interests, process depends on garnering local par- recreational interests, environmental ticipation and support, the Agencies will groups, public interest organizations, rely on local resources to publicize and and academic institutions. The Agen- communicate information about the sub- cies will seek input and participation on basin study. We will notify stakehold- both technical and nontechnical issues. ers of sub-basin orientation meetings During this process, the Agencies will through existing, locally oriented means ensure consistency with statewide goals of communication, such as civic groups, as well as with state and federal legislation local entities, newsletters, press releases and policies. We will seek stakeholder to newspapers, or other local outlets that involvement in each step of the instream could disseminate information about ini- flow study process (Figure 4-1). tial meetings. Examples of entities that The Texas Instream Flow Program may reach people likely to be interested stakeholder process includes these pri- in participating include chambers of mary goals: commerce, libraries, schools, volunteer organizations, trade groups, Clean Rivers • Obtain information from stakeholders Program steering committees, and envi- that will allow the Agencies and others ronmental groups. Media outlets such as to understand local concerns and local newspapers, radio, television, and perspectives. the Internet may also be used. • Engage stakeholders in study design Because they are local organizations development. that already have working stakeholder • Encourage stakeholders to commit groups established for the Clean Rivers meaningful time and resources to and other basin-specific programs, river developing and performing the sub- authorities may be effective at dissemi- basin studies. nating information to stakeholders. They • Obtain comments from stakeholders can send meeting announcements and on study results. information to groups or individuals who • Build trust in the underlying science have shown interest in their work. The and performance of the sub-basin Agencies may contract with local river studies so that study results are authorities or other local resources to considered valid, credible, and usable assist in identifying stakeholders, dis- by the Agencies and other interested tributing information, and arranging parties. meetings at local sites. Although a river authority may also serve as a stakeholder, To meet these goals, stakeholders will its input will be considered at the same be engaged in the process of develop- level and manner as input received from ing goals and study designs for specific other stakeholders. sub-basin instream flow studies. The Finally, the Agencies will offer alter- National Research Council (2005) noted nate opportunities for participation, such that stakeholder involvement in goal set- as submitting online and email com- ting is particularly important given the ments, to ensure that all stakeholders, potential for conflict among water users. regardless of meeting attendance, have We also recognize that stakeholders will the opportunity to provide input. bring valuable knowledge of Texas rivers

32 Texas Water Development Board Report 369 Stage 1: Identify and Engage Stakeholders Reconnaissance and Information Evaluation Stage 2: Conduct Sub-basin Orientation Meetings

Goal Development Consistent with Sound Ecological Environment Stage 3: Establish Sub-basin Workgroups and Conduct Study Design Workshops Study Design Peer Review

Stage 4: Conduct Data Multidisciplinary Collection Workshops/Field Data Collection Demonstrations (by request) and Evaluation

Data Integration Stage 5: Conduct Data to Generate Flow Integration Workshops Recommendations

Peer Draft Study Report Review

Stage 6: Final Study Report Review Study Report SB 2 Ends Post-SB 2 Next Steps: Implementation, Monitoring, and Adaptive Management

Figure 4-1. Stages of stakeholder participation in sub-basin specific studies of the Texas Instream Flow Program.

Stage 2: lar business hours to allow for broader Conduct Sub-basin attendance and participation. Orientation Meetings At the orientation meeting, the Agen- After notifying potential stakeholders cies will specifically through local sources, we will hold an initial stakeholder orientation meeting(s) • educate stakeholders about the to query local residents about their his- purpose of the studies and how the toric and current perspectives of the sub- data will be used; basins as well as to identify important • describe the role of stakeholders in concerns. Stakeholders will be asked to the process; give ideas about what they would like to • seek involvement from stakeholders see as a result of the studies. Orientation to participate in the study process; meetings may be held outside of regu- • obtain stakeholder input that can be

Texas Water Development Board Report 369 33 used in instream flow studies; and Stage 4: • discuss the relationship between Conduct Data Collection Workshops/ science and policy and explain to Field Demonstrations (by request) stakeholders that at some point At the request of sub-basin workgroups, different parties will make choices members will be invited to attend sub- regarding what to do with the basin study and data collection work- study results according to current shops/field demonstrations so that they legislation, mandates, and policies. can better understand field techniques and constraints. An important component of the orientation meeting will be for the Agencies Stage 5: to invite stakeholders to serve, along with Conduct Data Integration Workshops Agency staff, on sub-basin workgroups Sub-basin workshops will be held at the whose purpose will be to develop the conclusion of the field studies. At these study design. Workgroups will be estab- workshops, the Agencies will outline and lished with the intent of bringing to the explain the data and garner workgroup table key stakeholders who will provide input on the methods used to integrate a diverse representation of the issues so data and generate instream flow recom- that all perspectives can be considered. mendations. As the Agencies draft the We will establish an email list to actively study report, we will consider comments notify stakeholders, regardless of wheth- from the sub-basin workgroup. er or not they continue on as sub-basin workgroup members, about the progress Stage 6: of the process and give them the oppor- Review Study Report tunity to provide additional input as the In the interest of efficiency and consisten- studies progress. cy with statewide goals, sound scientific principles, and state and federal legisla- Stage 3: tion and policies, the Agencies will take Establish Sub-basin Workgroups and the lead in developing the study report. Conduct Study Design Workshops However, the report will be provided to Stakeholders who express an interest stakeholders for review and comment in participating in the sub-basin work- before it is finalized. The Agencies will groups will be notified of a series of consider all comments before finalizing workshops in which they will be asked the report. All feedback received from to participate in the process of designing stakeholders will be published, along the study. At these workshops, sub-basin with responses from the Agencies. workgroup participants will assist in 4.2 • applying the definition of “sound Peer Review ecological environment” (as de- Scientific peer review is recognized as scribed in Section 5.2) to the sub- an important part of an instream flow basin or segment; assessment program (Arthington and • identifying specific study areas within others, 1998; NRC, 2005). In order to the sub-basin; ensure public trust in the science behind • determining study goals and ob- instream flow recommendations, the jectives; and activities of the Texas Instream Flow • developing a draft time frame for Program will be peer reviewed. The the design and performance of the National Research Council (2005) rec- study, recognizing all statutory and ommended “scientists not working practical resource limitations. directly on the studies” review the sam-

34 Texas Water Development Board Report 369 pling methodologies, results of the indi- will require varied approaches in con- vidual technical studies, and the prog- ducting the instream flow studies, and ress of the overall instream flow pro- the Agencies must ensure that models gram. Results of these reviews should and methods are applied appropriately. then be communicated to the “involved Peer review will provide critical input scientists, instream flow scientific com- for improving the technical soundness munity at large, and stakeholders” and of products and recommendations and be assessed through “an independent, will also increase public trust by ensuring interdisciplinary, periodic peer review that sound science is at the foundation process” (NRC, 2005). of these studies. The Agencies intend to establish a In addition, research findings related peer review team consisting of inde- to instream flow assessments will be sub- pendent experts in the fields of biology, mitted for publication in peer-reviewed hydrology and hydraulics, water quality, journals. The Agencies submitted the and geomorphology (physical process- original version of this document for peer es). This peer review team will review review by national experts (NRC, 2005). all sub-basin study designs and reports. Incorporating scientific peer review of In addition to the peer review team, the the instream flow program is intended Agencies may bring in experts from oth- to increase public trust and improve the er disciplines to assist in particular situa- technical soundness of products and tions. The diversity of sub-basin studies recommendations.

Texas Water Development Board Report 369 35 5 Study Design

ub-basin study designs will neces- design will be submitted for both scien- sarily flow from the statewide goals tific peer review and stakeholder com- andS objectives of the Texas Instream ment, with subsequent revisions to be Flow Program as outlined by Senate made as necessary. Bill 2 and tackle the specific issues associated with a defined study area. 5.1 The evolution of this approach begins Reconnaissance and with the overall legislative directive and Information Evaluation narrows down to a specific sub-basin in Prior to initiating program efforts, the question (Table 5-1). Key to developing Agencies will identify the geographic a consistent approach for the studies scope of the study. Study areas will con- across basins is ensuring that the goal sist of sub-basins (portions of a major statements for a specific geographical river basin) composed of multiple Texas area are consistent with the statewide Commission on Environmental Quality goal of supporting a sound ecologi- designated stream segments (30 Texas cal environment. Goals, as opposed Administrative Code, §307.10[1] Appen- to objectives, should be general state- dix A). Study areas will extend from the ments about desired outcomes (for river channel to the riparian and flood- example, conservation of paddlefish plain area of the segments and consider populations). Once the study goals are tributaries, floodplain areas, groundwa- identified, objectives should be estab- ter interactions, and watershed areas. lished that represent the specific means The Agencies will assemble and of achieving those study goals. evaluate previously collected data for the A variety of tasks critical to estab- study area to determine what historic lishing sub-basin study goals and objec- conditions may have been like, assess the tives will form the foundation of a suit- current understanding of the system, and able study design. The study design will identify knowledge gaps and areas where include a summary of available data additional data should be collected. This and reconnaissance surveys; concep- step provides a preliminary understand- tual models of the river system; goals, ing of the river ecosystem and any issues objectives, and indicators for the study; of acute and/or historical concern. and descriptions of the proposed study Once knowledge gaps are identified, sites, methods, and tools. In the recon- the Agencies will undertake prelimi- naissance and information evaluation nary data collection and reconnaissance phase, the Agencies will identify coop- efforts focused on familiarizing agency erators and stakeholders and assemble personnel with the study area and cur- available data with their assistance. After rent condition of the river ecosystem. preliminary analysis of that data, field Access points and potential study sites surveys will be conducted to address will be located. Data collection will focus data needs. Following that process and on filling in gaps in the available data in cooperation with stakeholders and and establishing the current condition cooperators, primary issues related to of the system. the study will be defined along with After completing a preliminary analy- statements of goals and objectives. The sis of historical and reconnaissance data, Agencies will also guide the selection the Agencies will summarize findings, of appropriate indicators and complete including geographic information system a draft study design. The draft study (GIS) data layers and conceptual models

36 Texas Water Development Board Report 369 Table 5-1. Summary of development of sub-basin study design from statewide goals and objectives.

Legislative Directive: “…conduct studies and analyses to determine appropriate methodologies for determining flow conditions in the state’s rivers and streams necessary to support a sound ecological environment.”

Statewide Goal: Sound Ecological Environment A resilient, functioning ecosystem characterized by intact, natural processes and a balanced, integrated, and adaptive community of organisms comparable to that of the natural habitat of a region.

Statewide Objectives: To Meet the Criterion of “Sound” • Evaluate intact natural processes: n Characterize system hydrology and hydraulics n Examine status of geomorphic processes within the system n Characterize system water quality n Define connectivity issues within the system • Evaluate biological communities: n Examine the integrity of the biological community n Examine biodiversity within the system n Define the influence and relationship of other riverine components relative to biology of system

Study Goals: Develop goal statements for the specific sub-basin and relate them to the statewide goal. Pri- mary focus would be to apply the definition of sound ecological environment relative to the specific sub-basin. These goals should be general statements about desired outcomes, allowing cooperators and stakeholders to grasp the intent of the study (for example, to ensure conservation of riparian areas in the Sulphur Basin).

Study Objectives: Objectives should be established that are the specific means of accomplishing the stated sub- basin goals. (For the example goal above: provide sufficient timing and frequency of overbank flows to conserve hardwood bottomlands.)

Tasks Necessary to Develop Sub-basin Goals and Objectives: • Identify cooperators and stakeholders • Define distinct geographical scope of study area • Assemble existing information and determine reconnaissance needs • Use field surveys to develop additional baseline data and address data gaps • Develop a conceptual model of the system in question using existing and reconnaissance information • Define primary issues affecting instream flows • Establish goals and specific objectives

Indicators and Study Design: Well-defined objectives will lead naturally to the selection of indicators, which are measurable factors representing the disciplines of hydrology, geomorphology, water quality, or biology and are responsive to variations in flow. Addressing some objectives will require using multiple indicators from each of the disciplines. (For the example goal above: conserving hardwood bottomlands may require indicators related to soil moisture, frequency of overbank flows, and influx of sediment and nutrients.) Once important indicators have been selected, a specific study design with procedures and means for implementation can be developed.

Texas Water Development Board Report 369 37 describing the relationship between flow tains a network of surface water flow regimes and ecological health. The sum- gages within Texas. This network pro- mary will provide the best description vides invaluable flow data for hydrologic available of the current condition of the studies. In order to develop rating curves river system. If data are available, we will for gage locations, the Survey collects estimate historical conditions for the riv- channel cross-sectional data that may er, as well as compile a comprehensive also prove useful for geomorphic inves- list of stressors. tigations (Juracek, 2000). In addition, they periodically collect water quality 5.1.1 and sediment data at some gage sites and Compile, Review, and Georeference have completed studies on water quality Available Studies and Data and quantity issues. The Survey is also a All available data and study reports source of aerial photography and digital related to the hydrologic, biologic, geo- elevation and topographic maps. morphic, water quality, and connectiv- The U.S. Army Corps of Engineers pro- ity of the study area will be assembled. vides engineering services to the nation, Given the interdisciplinary nature of including water resources and other civil instream flow studies, relevant data works projects. They serve as the national span several academic disciplines. Vari- regulatory authority for wetland issues ous public agencies, private consul- (Section 404 of the U.S. Clean Water Act) tants, academic researchers, and others and cooperate with local entities on flood have collected a substantial amount of control and aquatic restoration projects. data on various aspects of stream ecol- The Corps of Engineers conducts hydro- ogy for most Texas rivers. The primary logic and hydraulic modeling in support objective of this task is to compile and of the National Flood Insurance Program organize previously collected informa- administered by the Federal Emergen- tion on the hydrology, biology, physical cy Management Agency. They provide habitat, and water quality of the pro- information that includes studies and data posed study area. This approach was related to dams, operation of reservoirs, employed for the Guadalupe (Longley restoration projects, and flood studies on and others, 1997) and Trinity rivers specific river segments. (Kiesling and Flowers, 2002). The Trin- The U.S. Fish and Wildlife Service ity River report also included a GIS tool is the national agency charged with with spatial coverages and attribute conserving, protecting, and enhancing tables for the various data sets. fish, wildlife, plants, and habitats. They Many federal programs related to nat- have conducted studies related to spe- ural resources will be valuable sources of cific species and locations in Texas, and information for sub-basin studies. Agen- they also compile information on best cies with such programs include the U.S. management practices related to invasive Geological Survey, U.S. Army Corps of species, habitat restoration, and wetland Engineers, U.S. Fish and Wildlife Service, preservation. U.S. Environmental Protection Agency, The Natural Resources Conservation Natural Resources Conservation Service, Service provides technical assistance to and National Oceanic and Atmospheric landowners, communities, state and Administration. local governments, and other federal The U.S. Geological Survey is the pri- agencies to help them conserve soil, mary federal agency responsible for col- water, and other natural resources. The lecting, monitoring, and analyzing natu- Conservation Service is a source of aerial ral resources data. In cooperation with photography, including soils maps and the Texas Water Development Board and surveys, and information related to sedi- other local partners, the Survey main- ment processes.

38 Texas Water Development Board Report 369 Responsibilities of the National Oce- All major river basins in Texas have anic and Atmospheric Administration one or more regional water resource include maintaining and improving management agencies, usually a river marine and coastal ecosystems, deliver- authority. These authorities, most of ing weather, climate, and water infor- which were created by the state as con- mation, and understanding the science servation and reclamation districts in the and consequences of climate change. 1930s, have unique statutory responsibil- The organization is a source of weather, ities outlined in their respective enabling Landsat, and other data. legislations. Local river authorities are The Agencies have also gathered the Texas Commission on Environmental considerable data relative to riverine Quality’s primary partners in the Clean ecosystems in Texas. For example, the Rivers Program and engage in monitor- Texas Water Development Board has ing that may include flow gaging, water conducted planning studies related to quality monitoring, biological sampling, instream flow requirements downstream and weather data collection. They also of proposed water supply reservoirs. have local knowledge of river conditions Through research and planning funds, and behavior, both current and histori- the agency has also contracted with uni- cal, have frequent contacts with stake- versities and other entities to conduct holders in their basins, and are aware of research and collect data of direct inter- activities and issues related to the river est to instream flow studies. The Texas systems they manage. Natural Resources Information System, Many academic institutions in Texas a division of the Texas Water Develop- maintain active research programs relat- ment Board, is the state’s clearinghouse ed to various aspects of stream ecology, for maps, aerial photos, and digital natu- engineering, and water resource man- ral resources data. The Texas Parks and agement. These include the University Wildlife Department has completed of Texas, Texas A&M University, Texas studies related to riparian and aquatic State University, Texas Christian Uni- species, as well as completing or coop- versity, Baylor University, and others. erating on instream flow studies. The Information available from these sources Texas Commission on Environmental includes research reports, publications, Quality administers the water right per- monitoring data, theses and disserta- mitting process that includes hydrologic tions, museum records, and other data and ecological analyses associated with related to specific rivers and streams. requests to impound and divert water. Engineering and consulting compa- The Commission also administers the nies and private organizations may be Texas Clean Rivers Program and state an additional source of information. For and federal water quality permit pro- example, The Nature Conservancy of grams, both of which provide water qual- Texas collects and maintains information ity monitoring data and modeling studies related to rare, endemic, and invasive for all major rivers in Texas. species statewide. Private organizations Other state agencies also have data like the Caddo Lake Institute provide of interest to instream flow studies. data, technical reports, and documents For example, the Texas Department of related to specific river segments or loca- Transportation has data related to chan- tions in Texas. nel cross sections and test bores at bridge During the reconnaissance and infor- construction sites. When available, such mation evaluation step of an instream data can be used to evaluate long-term flow study, to the extent possible, all river channel adjustments (Phillips and available data related to a study area will others, 2005). The Texas General Land be incorporated into GIS, showing the Office is a source of historical maps. type of data collected, location and tim-

Texas Water Development Board Report 369 39 ing of collection, and entity collecting instream cover, such as woody debris and the data. Available data for a study area boulders, will be delineated throughout will be reviewed and evaluated. Data the stream segment. Cross-sectional collection methods will be assessed to measurements will be taken at regular determine each data set’s quality and intervals along the channel. The longi- comparability to other data sets. Avail- tudinal extent of mesohabitat types can able studies and data will be summarized be measured by logging the longitudinal for each study area. position along the channel with Global Positioning System (GPS) instruments 5.1.2 and coding the upper and lower bound- Conduct Preliminary Field Surveys aries of mesohabitats. These mesohabitat and Analyses surveys will be performed when flows After reviewing the available data, pre- are at or less than the median value and liminary field surveys and analyses will habitat features are relatively easy to be conducted to fill in data necessary identify. for describing the current condition of Preliminary field surveys and analy- the river ecosystem, confirming issues sis will focus on establishing the cur- and concerns suggested by initial anal- rent condition of the riverine ecosys- yses, and identifying sites suitable for tem, investigating trends in condition intensive technical studies. Initial field obvious from field surveys or previously efforts will involve air, land, and water collected data, and selecting study sites level reconnaissance, as appropriate, to for intensive technical studies. A more identify potential representative reach- detailed description of technical activi- es, study sites, human impacts, and ties is provided in Chapters 6 through extant fish and wildlife resources. 9. Activities in the four disciplines will Aerial Surveys: During the aerial include the following: survey, notes and photographs will be Hydrology: Analyze historic gage taken related to potential access points, data to determine flow statistics repre- instream habitat features, and floodplain sentative of the hydrologic character of characteristics (such as the presence of the study area. Identify historical and oxbow lakes, width of riparian corridor, current features affecting hydrologic nature of human activity). This will pro- character, as well as potential future vide a general overview of the study area changes. in a time-efficient manner. Aerial sur- Biology: Identify species, habitats, veys should be performed when flows and important issues and considerations are at or less than the median value and within the study area. Species of interest habitat features are relatively easy to will include those historically and cur- identify. rently present. Particular attention will Land Surveys: Access points for be paid to key species (defined as those launching boats, locations for remote related to study objectives or that are par- sensors, and survey points will be visited ticularly flow sensitive). Biota of interest before making final determinations on may include plants, amphibians, birds, study site and boundaries. Preliminary and mammals associated with floodplain assessment of riparian and floodplain and riparian areas, as well as in-channel areas will also be made. resources, such as aquatic vegetation, Boat Surveys: Longitudinal surface invertebrates, mussels, and fish. Current surveys will be performed for each study and prior condition of stream and ripar- area for either the entire study area or ian biota will be assessed. representative reaches. During the sur- Geomorphology: Analyze previ- vey, areas with different mesohabitat ously collected data. Field surveys will features, overhead cover, substrate, and focus on preliminary channel, bed form,

40 Texas Water Development Board Report 369 and bank assessment and identification objectives and prioritizing of active channel and floodplain pro- management actions; cesses. Evidence of changes in sediment • indication of additional research regime and their causes will be docu- necessary to improve understanding; mented. Geomorphic classification of • estimates of natural conditions for the river segment will begin. Results may highly regulated systems; be constrained by limited data collected • assistance in selecting appropriate prior to these efforts and the short time indicators and assessment tools; and frame available to observe large spatial • identification of key habitats and and temporal scale processes. suitable sampling locations and Water Quality: Assess the water qual- study sites. ity condition of the study area. Available data will be analyzed to identify trends, An example of a conceptual model for issues, and constituents of concern. Field a portion of the Murray-Darling Basin surveys will supplement available data. (Australia) is provided in Figure 5-1.

5.1.3 5.2 Develop Conceptual Models Goal Development and Using the previously collected data and Study Design the results of reconnaissance surveys During the second step of a sub-basin and preliminary analysis, a basic con- instream flow study, stakeholders and ceptual model of the study area will be the Agencies will collaborate to devel- developed. Such models provide a con- op study goals that are consistent with cise visualization of the current under- statewide goals and objectives. standing of the riverine ecosystem. A conceptual model will also relate the 5.2.1 components of the hydrologic regime Develop Study Goals and Objectives with the technical components of the Together with stakeholders, the Agen- instream flow study (such as biology cies will review the statewide goals for and water quality), thereby aiding in instream flow projects and develop identifying relationships between flow goals for the sub-basin instream flow regimes and the ecological health. study based on the desired condition Since several disciplines are involved in of the river ecosystem. In essence, they describing these relationships, the con- will define what a sound ecological envi- ceptual model will provide basic guid- ronment means for the specific study ance on how disciplines must cooperate area. An example goal is the “vision of in order to complete technical studies a healthy and productive River Murray” and how components of the flow regime adopted in Australia (Text Box 5.1). will be integrated. Conceptual models Once sub-basin goals are defined, of riverine ecosystems are beneficial objectives will be developed that describe for developing study designs (CRCFE, what ecological outcomes would result 2001) because they provide from achieving study goals. For example, in Australia, the goal of “a healthy and • clear articulation of how rivers productive River Murray” led to several function objectives. One of these objectives was to • improved communication with the reinstate ecologically significant elements nonscientific community; of the flow regime. This objective was fur- • visual description of current ther defined to include reproducing some conditions, trends, and impacts of of the natural high, low, and zero flow management actions; behavior of the river, as well as flow vari- • assistance in setting goals and ability, seasonality, and annual volume.

Texas Water Development Board Report 369 41 Figure 5-1. Conceptual model developed for a portion of the Murray-Darling Basin, Australia (from CRCFE, 2001).

42 Texas Water Development Board Report 369 Text Box 5.1. Example of goals, objectives, indicators, and conceptual models for the Murray-Darling Basin, Australia.

The Murray-Darling Basin is one of Australia’s largest drainage divisions, with just over 1 million square kilometers (386,000 square miles). The basin includes the three largest rivers in Australia—the Darling River at 2,740 kilometers (1,700 miles), the Murray at 2,530 kilometers (1,575 miles), and the Murrumbidgee at 1,690 kilometers (1,050 miles). In addition, the basin contains some 30,000 wetland areas. According to the Australian Department of Environment, Water, Heritage and the Arts (2008), at the time of Euro- pean settlement, about 28 percent of Australia’s mammal species, 48 percent of its birds, and 19 percent of its reptiles were found within the basin. Many of these species are now extinct or endangered. Over-allocation of water, increasing instream and dry land salinity, and impacts of global climatic change are recognized as threats to the long-term productivity and sustainability of the Murray-Darling Basin. Conceptual models of the Murray-Darling Basin were developed for eight different geomorphic process zones (CRCFE, 2001). Zones included headwater pool, confined, armored, mobile, meandering, anabranching, distributary, and lowland confined zones. Geomorphic processes and the attendant biological and ecological processes vary from zone to zone. The conceptual model for the mobile zone is shown in Figure 5-1. Note that some of the terminology shown in this figure may be defined differently in Australia or be unique to Australia. Collective efforts at all levels of government to restore the Murray to a healthy working river began in November 2003 (MDBC, 2005b). The national, state, and local governments involved in allocating the resources of the Murray-Darling Basin adopted the vision of a healthy and productive River Murray as their goal. In order to meet this goal, they agreed on the objectives summarized below:

1. Reinstate ecologically significant elements of the flow regime 2. Overcome barriers to migration of native fish species 3. Maintain current levels of channel stability 4. Protect and restore key habitat features in the river and riparian zone 5. Prevent the extinction of native species from the riverine system 6. Improve connectivity between the river and riparian zone 7. Manage flow-related water quality to sustain ecological processes and productive capacity (MDBC, 2005b)

Indicators related to these objectives are currently being developed. A number of indicators have been approved for basinwide application, including 13 indicators related to fish (MDBC, 2003a), 3 related to macroivertebrates (MDBC, 2003c), and 12 related to hydrology (MDBC, 2003b). Some indicators related to riparian and channel areas have been designated for specific regions. Water quality indicators are under development. Example indicators for each category are provided in Table 5.2.

Texas Water Development Board Report 369 43 5.2.2 Indicators cies that cannot be removed. Rather than Sub-basin objectives lead quite naturally attempt to recreate unachievable or even to the choice of indicators. See Text Box unknown historical conditions, we argue 5.2 and Table 5-3 for a description of for a more pragmatic approach in which how ecological indicators may be used the restoration goal should be to move for the Texas Instream Flow Program. the river towards the least degraded and Potential indicators include the entire most ecologically dynamic state possible, realm of hydrological, biological, physi- given the regional context. cal, and chemical indicators. For a sub- Using available data and conceptual basin, a list of all practical indicators will models, the Agencies and stakeholders be developed consistent with study goals will collaborate to evaluate the range of and objectives identified by stakehold- conditions achievable and determine ers for the study area. This list will then appropriate desired conditions for each be pared down to ecologically signifi- specific river segment. cant indicators that are directly related The Agencies will also provide input to components of the flow regime. For to stakeholders as objectives and indica- example, in the Murray-Darling Basin tors are developed and will assist stake- of Australia, 12 hydrologic indicators holders in choosing objectives that rep- were identified based on the objective resent measurable progress toward goals. of reinstating ecologically significant Selection of indicators will also consider elements of the flow regime (Text Box current standards, methods, capabilities, 5.1). These included the number of high and limitations of data collection equip- and low flow events, the magnitude of ment and techniques. Goals, objectives, difference between annual flow maxima and indicators will also conform to appli- and minima, the timing of flow maxima cable federal and state law, including the and minima within the year, and annual federal Clean Water Act, Endangered flow volumes. Species Act, the Texas Administrative In developing program goals, the Code, Texas Water Code, and Texas Agencies will consider the feasibility of Parks and Wildlife Code. goals given the current state of the river Goals, objectives, and indicators will and constraints on system management. consider existing programs, such as the For example, large rivers in developed Texas Commission on Environmental countries are highly impacted by devel- Quality’s Water Quality Standards for opment, and, thus, most riverine scien- designated and undesignated stream tists agree that it is not feasible to attempt segments in Texas (30 Texas Admin- to return a river to pristine, natural con- istrative Code §307.10[1] Appendix A ditions (Rutherford and others, 2000; and Appendix D). For example, for the Schofield and others, 2003). Instead, the Lower Sabine River, the Commission has goal for such rivers should be to improve already established site-specific uses and their ecological condition. Palmer and criteria for designated segments (Table 5- others (2005) put it this way: 4) and several smaller tributaries (Table The first step in river restoration 5-5). In addition, the aquatic life uses are should be articulation of a guiding image based upon additional criteria related that describes the dynamic, ecologically to the condition of the river ecosystem healthy river that could exist at a given (Table 5-6). Although developed within site. This image may be influenced by the context of a water quality regulatory irrevocable changes to catchment hydrol- program, these criteria may be incor- ogy and geomorphology, by permanent porated into goals, objectives, and indi- infrastructure on the floodplain and cators if they are relevant to identified banks, or by introduced nonnative spe- instream flow issues.

44 Texas Water Development Board Report 369 Table 5-2. Example indicators for Murray-Darling Basin, Australia.

Category Sub-category Indicator Comments/Description Hydrologya High flow Number of 1 in 10 1 in 10 year annual return interval flood year floods calculated for natural conditions. Low and Number of low flow Low flow event defined as below the 90th zero flow events exceedence percentile for natural conditions. Variability Seasonal amplitude Difference in flow magnitude between yearly high and low flows. Seasonality Seasonal period Change in timing of annual high and low flow index events from natural to current conditions. Flow volume Median annual flow Median of annual flow volumes. Mean annual flow Mean of annual flow volumes. Biology Macro- Richness Biodiversity indicated by the number of taxa. invertebrateb Pollution sensitivity Observed families graded for sensitivity to score pollution. The average of the grades is the score for the site. Fishc Total species richness Total species richness (native and alien) at each site compared to a predicted maximum species richness. Proportion native Proportion of fish species at each site that are species native species. Proportion Proportion of individual fish (native and megacarnivores alien) at each site that are megacarnivores (eat prey >15mm length). Ripariand Waterbird breeding Successful breeding in at least 3 years out of 10. Healthy vegetation 55% of the Barmah-Millewa Forest in healthy area condition. Geomorphologye Channel stability Maintain current level of channel erosion. Water Qualityf Total phosphorus • Upland rivers: < 20 µg/L • Lowland rivers flowing to the coast: < 25 µg/L • Lowland rivers in the Murray-Darling Basin: < 50 µg/L • Lakes and reservoirs: < 10 µg/L • Estuaries: < 30 µg/L Sources: aMDBC (2003b); bMDBC (2003c); cMDBC (2003a); dfor the Barmah-Millewa Forest only, MDBC (2005a); efor the main channel of the River Murray only, MDBC (2005b); fNSWDEC (2008) mm=millimeters µg/L=micrograms per liter

Texas Water Development Board Report 369 45 Text Box 5.2. Use of ecological indicators in Texas Instream Flow Program sub-basin studies.

Ecological Indicators

Ecological indicators can be used to assess the condition of the environment. Ecological indicators selected to encompass the hydrologic, biologic, geomorphic, and water quality objectives set in consultation with stakeholders for a particular sub-basin will be monitored at spatial and temporal scales that reflect the processes relevant to establishing and maintaining a diverse and sustainable aquatic environment. Following the implementation of instream flow recommendations, long-term monitoring and assessing of the aquatic ecosystem using ecological indicators will ensue. These indicators will be used to measure progress toward achieving a sound ecological environment in a particular sub-basin. They will also be used to document the conditions, trends, processes, and phenomena associated with the aquatic ecosystem. Assessment of monitoring data will inform adaptive management decisions in the sub-basin. Sub-basin indicators should be derived from a statewide suite of indicators modified for regional differences. The consistent use of a suite of indicators across Texas will aid in comparing ecological conditions. At the sub-basin level, these indicators will form a bridge between study goals and objectives and the goals of the instream flow program. Examples of ecological indicators relevant to aquatic ecosystems are presented in the table below.

Table 5-3. Example ecosystem endpoints for aquatic ecosystems.

Endpoint type Example of measures to assess endpoint Species-level Species productivity; status of endangered, threatened, or endpoints economic species; species diversity; key species Community/ Water quality; flow patterns; hydrodynamics; fish productivity ecosystem-level and diversity; invertebrate productivity and diversity; plant endpoints productivity and diversity; detrital dynamics; habitat quality; habitat structural diversity; trophic structure; biogeochemical cycling; spatial dynamics (dispersal, migration) Landscape-level Spatial mosaic of habitat types (channel complexity); flood endpoints frequency and intensity; drought frequency and intensity; anthropogenic disturbance; climate change; sediment/ materials transport Source: Modified from Harwell and others (1999)

Ecological indicators should be selected on the basis of their intrinsic importance (measure a species or process directly), the ability to serve as an early warning indicator (rapid identification of potential effects), the ability to serve as a sensitive indicator (reliability in predicting response), or the ability to stand in for a process (Harwell and others, 1999; Dale and Beyeler, 2001). Additional considerations include the ease and cost of monitoring and the availability of historical data. A challenge in selecting the appropriate suite of indicators is determining which of the numerous measures adequately characterize the aquatic ecosystem, yet are simple enough to be effectively and efficiently monitored and modeled. This challenge includes identifying indicators thought to be flow sensitive so that they will reliably link changes taking place in the ecosystem to changes in hydrologic regime. The use of too many indicators may be cumbersome, but if too few indicators are adopted, they may not adequately capture the multiple levels of complexity within the aquatic ecosystem.

46 Texas Water Development Board Report 369 5.2.3 Formulate Study Design Before completing a study design, the holders. The Agencies will add descrip- Agencies and stakeholders participat- tions of proposed technical studies and ing in sub-basin workgroups will reach how they address specific objectives consensus on the technical studies that and indicators. These descriptions will need to be conducted to address iden- include study site locations, data collec- tified objectives and indicators. The tion methods and protocols, and mul- study design will include the summary tidisciplinary coordination. The draft of available data, results of preliminary study design will be submitted for peer analyses and reconnaissance surveys, review and comment. Necessary revi- assessment of current conditions, and a sions will be incorporated before a final conceptual model of the river system. It study design is approved by stakehold- will also include study goals, objectives, ers and the Agencies. and indicators developed with stake-

Texas Water Development Board Report 369 47 F 91 91 Temp. Bacteria 126/200 126/200 #/100ml Bacteria 126/200 126/200 #/100ml SU 6.0-8.5 6.0-8.5 pH range Criteria 5.0 5.0 DO Criteria mg/l 5.0 4.0 mg/l 200 200 mg/l TDS Dissolved oxygen -2 4 50 50 mg/l SO -1 Water supply Water 50 50 Cl mg/l Uses Water Water supply supply supply Public Public Aquatic life Aquatic Intermediate High High High Uses Aquatic life Aquatic Recreation recreation recreation Contact Contact Recreation recreation recreation Contact Contact 307.10(1) Appendix A 307.10(4) Appendix D § §

name Segment Dempsey Creek Unnamed tributaryUnnamed of Caney Creek above tidal above Caney Sabine RiverSabine RiverSabine Creek Texas Commission on Environmental Quality site-specific uses and criteria for the Lower Sabine River. Sabine QualityRiver. Lower site-specificfor the on Environmental uses and criteria Commission Texas Sabine site-specificRiver. Lower for tributaries of the uses and criteria TCEQ TCEQ segments Tributaries to TCEQ SegmentsTributaries 30 Texas Administrative Code Administrative 30 Texas Code Administrative 30 Texas =sulfate ion 0503 0503 0503 0502 =Chloride ion -2 4 -1 Segment Segment number name number Tributary SO SU=standard units pH=potenz hydrogen, hydrogen ion concentration pH=potenz hydrogen hydrogen, DO=dissolved oxygen mg/l=milligrams per liter mg/l=milligrams per liter Cl Source: Source: /100ml=per 100 milliliters /100ml=per 100 milliliters TDS=total dissolved solids Table 5-4. Table 5-5. Table

48 Texas Water Development Board Report 369 Trophic structure imbalanced Severely imbalanced Moderate Balanced Balanced slightly to Species richness high Exceptionally Exceptionally Low High Moderate Diversity ally high Exception- Low High Moderate species Sensitive abundance Present Very low in Very Abundant Absent Species assemblage expected species absent Exceptional or unusual Exceptional Some expected species Most regionally expected species Usual associationUsual of regionally

307.7(b)(3)(A)(i) § Habitat characteristics variability Highly diverse Moderately diverse Moderately Uniform Outstanding natural Attributes of aquatic life use categories. use categories. life of aquatic Attributes use Texas Administrative Code Administrative Texas Aquatic lifeAquatic Exceptional Limited Intermediate High Source: Table 5-6. Table

Texas Water Development Board Report 369 49 6 Hydrology and Hydraulics

s noted by Richter and others ed to develop flow component recom- (2003), a river’s hydrologic flow mendations. Two-dimensional hydrau- regimeA is recognized as a ‘‘master vari- lic modeling will be used to determine able’’ that drives variation in other com- in-channel hydraulic conditions over a ponents of the river ecosystem. As a range of flows. These modeling efforts result, evaluations of a river’s hydrology will assist in studying the relationship and hydraulics play a key role in devel- of flows to habitat conditions, which, in oping instream flow components. In turn, will help determine suitable base addition to providing an analysis of the flows. A one-dimensional hydraulic hydrologic regime, these evaluations model will be used to estimate inun- assist with biological, geomorphic, and dation of riparian areas and assist in water quality studies. Hydrologic data developing overbank flows. Additional will also assist in developing all four hydraulic modeling may be conducted in instream flow regime components: response to concerns related to sub-basin subsistence flows, base flows, high flow studies. Hydraulic modeling techniques pulses, and overbank flows. In addition, are discussed in Section 6.2. hydraulic modeling will provide an estimate of the extent of various habitats 6.1 during base flows and of inundation Hydrologic Evaluation during overbank flows. A hydrologic evaluation of a river’s flow Because water diversions affect the regime is required in order to deter- flow regime in frequency, timing, dura- mine instream flow requirements that tion, rate of change, and magnitude of support the river ecosystem. This eval- streamflow, hydrologic data will help uation should consider both the condi- assess the changes that have occurred in tion of the river prior and subsequent hydrologic regimes. For example, hydro- to human-induced flow modifications. logic time series data can be analyzed to Most major rivers in Texas have been assess current conditions, calculate alter- significantly modified over the last 30 or ations in quantity and timing of flows, more years. During this extended peri- and characterize the physical behavior od of modification, significant changes of water in the system at an ecologically may have occurred, which should be relevant scale. Low flow statistics, such considered when making instream flow as the seven-day, two-year low flow recommendations. known as 7Q2, will provide information Across Texas, natural flow regimes that will ultimately assist in developing exhibit tremendous variability and subsistence flow recommendations. include seasonal periods of low flow, Median and percent exceedence flow short duration floods, and stable base statistics will likewise assist in develop- flows. These large variations can be ing base flow recommendations. High attributed to the geographical variation flow and flood frequency statistics will and size of the state, which experiences aid in developing high flow pulse and disparate regional precipitation patterns overbank flow recommendations. Flow (average annual rainfall is 58 inches or statistics will also be used to describe 147 centimeters per year in coastal East hydrologic conditions as wet, average, Texas but only 8 inches or 20 centimeters or dry. Hydrologic evaluation methods in arid West Texas) and seasonal pat- are discussed in Section 6.1. terns of rainfall. Texas has 3,700 named Hydraulic modeling will be conduct- streams and rivers, very few of which can

50 Texas Water Development Board Report 369 be considered free-flowing. Every major es can be far reaching because rivers, river basin in Texas has been impounded, streams, and riparian areas cumulatively and nearly 6,000 dams have been con- assimilate large volumes of nutrients and structed statewide (Graf, 1999). Nearly organic materials from both natural and 200 reservoirs constructed for flood human sources, such as wastewater and control and/or municipal supply have nonpoint source runoff. a storage capacity greater than 5,000 In order to protect river ecosystems, acre-feet (6.2 million cubic meters). For the National Research Council recom- most sub-basins in Texas, the available mended that the Texas Instream Flow reservoir storage volume is large enough Program specify four hydrologic flow to capture more than twice the average components (NRC, 2005). These com- annual rainfall-runoff volume. This large ponents are overbank flows, high flow reservoir storage-to-runoff ratio makes pulses, base flows, and subsistence flows. Texas rivers and streams vulnerable to Each plays an important part in main- flow regime changes and associated eco- taining the health of a river ecosystem. logical effects. After a complete evaluation of the hydro- Many aquatic species have specific logic regime and other technical studies, habitat and life history requirements the instream flow program will identify that are intimately linked to seasonal a flow regime that includes these four trends and natural flow regimes (Rich- components. For a specific sub-basin, ter and others, 1996). Although aquatic additional flow components may also ecosystems can respond to alterations be required. in the natural flow regime, there is usu- Maintaining riparian areas depends ally some cost to biological integrity on the timing, duration, and magnitude and diversity. Fishes in prairie stream of overbank flows. These flows inundate communities, for example, are adapt- active floodplain areas and can connect ed to harsh environmental conditions, the main channel to sloughs, adjacent such as low flow events, but may also bayous, and other types of riparian wet- have spawning activities keyed to high lands. A lack of overbank flows may flow events. When flow conditions are result in changes in the vegetative com- altered, generalist species may dominate munity of riparian areas, for example, aquatic communities at the expense of shifts from hardwood bottomland to specialists adapted to flowing water habi- upland vegetation. tats. Shifts in community structure can High flow pulses are important for be significant downstream of reservoirs, channel maintenance. Accumulation of and negative impacts on upstream fish sediments or vegetative encroachment communities have also been documented may occur if high flow pulses with appro- (Winston and others, 1991). priate magnitude, frequency, and dura- The health and maintenance of various tion are not provided. These and other riparian areas, hardwood bottomlands, processes can result in reduced channel and associated wetland ecosystems is also capacity to handle flood flows. intimately linked to natural flow regimes. In addition, overbank flows and high Attenuation of high flows by flood con- flow pulses create and maintain physi- trol projects and water supply reservoirs cal habitat features within the channel. influences the long-standing relationship These two components recruit large between streams and riparian areas. This woody debris to the channel, maintain attenuation disrupts exchanges of nutri- the depth of pools, and sculpt other fea- ents, organic materials, sediments, and tures of the channel that maintain habitat water between stream resources and suitability and diversity. floodplains causing detrimental effects Diminished base flows, largely on riparian ecosystems. Consequenc- because of direct diversions, inadequate

Texas Water Development Board Report 369 51 reservoir releases, and pumping that allow exotic species to survive and domi- reduces groundwater flow to streams, nate in areas previously hospitable only cause reductions in habitat diversity and to highly adapted native species. availability, loss of stream productivity, A detailed hydrologic evaluation is and alterations to trophic and commu- required to accurately analyze the effects nity structure. Reduced base flows can of a modified flow regime on a river also cause biologically important changes system. The evaluation must address in water quality characteristics, such as runoff inputs, water diversions, water reduced assimilative capacity, reaeration, impoundments, flood control structures, and thermal buffering capacity, as well and proposed water development proj- as alterations to nutrient dynamics and ects on the river system. The analysis organic matter processing. must evaluate both intra- and interan- Subsistence flows are naturally occur- nual flow variations (Richter and others, ring low flow events. Humans, however, 1996). Hydrologic evaluation in support may have increased the duration and fre- of the instream flow studies will include quency of these events. This can seriously analysis of both historical and natural- affect fish and wildlife resources. Des- ized flow data. Historical flow data, iccated streams obviously provide little described in Section 6.1.1, are available aquatic habitat, and extended periods of from streamflow gaging sites within the low flow generally result in pool habitats state. Naturalized flow data are devel- separated by dry reaches of streambed. If oped by removing the estimated effects pools become severely reduced, tempera- of human diversions from the historical tures can rise to lethal levels and dissolved data. This process is described in Sec- oxygen levels may be insufficient for the tion 6.1.2. survival of many species. Consequently, populations of aquatic organisms need- 6.1.1 ed for recruitment may not exist once Historical Flow Data streamflows return to base flow levels. Historical streamflow information will The threat of significant, adverse effects be compiled from U.S. Geological Sur- on river and stream communities is vey and other gaging stations located especially serious in over-appropriated within the project area. Statistical anal- river basins such as the Rio Grande. In ysis will be performed on the report- addition, the integrity of spring-fed eco- ed daily averaged flows to determine systems is compromised by excessive median, average, and percentile flows groundwater pumping rates. Of the 281 for each month, season, and year. These springs in Texas identified by Brune (1981) data can be used to determine periods as historically significant, more than one of wet, average, and dry hydrologic quarter (80) no longer flow, and those conditions. that remain experience periods of signifi- The entire period of record at each cantly diminished discharges. gage will be analyzed unless a water Alternatively, some river systems may development project directly affects the experience negative ecological impacts gage data. In that case, pre- and post- due to increased subsistence flows. This development flows will be separated for can occur when water is stored in reser- individual analysis. voirs during the normally wet portion In some cases, a gage site may not of the year and returned to the river as be present in the immediate vicinity of return flows or irrigation releases dur- a study site; however, the existing net- ing the normally dry portion of the year. work of U.S. Geological Survey gaging Interbasin transfers may also result in sites is designed so that each significant increased subsistence flows in some watershed contains its own unique gag- basins. Increased subsistence flows may ing station. The network also ensures

52 Texas Water Development Board Report 369 that there are sufficient “representative” no longer be observed on most rivers watersheds gaged throughout the state in Texas, they must be estimated from so that flow on an ungaged watershed available data. This can be accomplished can be estimated with reasonable accu- by accounting for reservoir attenuation racy. Within the same river, watershed and evaporation and removing known area multipliers may be used to com- return flows from and adding diver- pare projected flow at a study site to the sions to a historical flow record. How- flow measured at the nearest upstream ever, in cases where an on-channel res- or downstream gage. If area multipliers ervoir or flood control structure exists are inappropriate for a particular site, upstream of a study site, pre-impound- hydrologic models like HEC-HMS (HEC, ment flows downstream of the site or 2005) or TxRR (Matsumoto, 1995) that flows upstream of the reservoir usually account for land use and soil type may provide a better means of determining be used to predict runoff from rainfall naturalized flows than estimating and data. accounting for reservoir attenuation To use a hydrologic model for a rain- and losses. fall-runoff evaluation, the watershed of Water availability models used for the study site must be delineated. Water- water rights permitting in Texas include shed delineation will be performed using naturalized flow sequences on a monthly the best quality topographic information time step as part of their input data sets. available. Hydrologic Unit Code water- Input data for specific river basins can be shed boundaries will be used in conjunc- obtained from the Texas Commission on tion with Digital Elevation Models or Environmental Quality Web site: www. National Elevation Datasets at 10- or 30- tceq.state.tx.us/permitting/water_supply/ meter resolution, published by the U.S. water_rights/wam.html Geological Survey to delineate water- Because flow variations on shorter shed boundaries. A data layer of 12-digit time steps are important to riverine eco- Hydrologic Unit Code watershed bound- systems, monthly summary volumes are aries is currently being developed for inadequate to evaluate instream flows. most of Texas by the Natural Resources Naturalized flow data with a daily time Conservation Service and U.S. Geologi- step will be required for most studies cal Survey. If these models or data sets in the instream flow program. In addi- are unavailable, digital raster graphic or tion, areas immediately downstream of U.S. Geological Survey 7.5 minute topo- hydropower operations may occasionally graphic quadrangle maps will be used to require hourly flow data to evaluate cur- assist in delineating watersheds. Spatial rent conditions. However, even in these representation of rivers and lakes (based cases, characterization of natural condi- on U.S. Geological Survey topographic tions (without hydropower operation) quad sheets corrected using aerial pho- would rarely require data with shorter tography) can be obtained from the Texas than a daily time step. Natural Resources Information System. Daily average naturalized flows may Much of this work can be handled easily be calculated by disaggregating monthly in a GIS environment. Information from naturalized flows to a daily time step and the Texas Natural Resources Information routing daily flows through the river net- System can be obtained at this Web site: work. Options to complete this process www.tnris.state.tx.us have been included in the most recent version of the Water Rights Analysis 6.1.2 Package, which forms the basis for water Naturalized Flow Data and availability modeling in Texas (Wurbs, Water Availability Modeling and others 2005). The most appropri- Since natural river flow regimes can ate method for flow disaggregation and

Texas Water Development Board Report 369 53 calibration of routing parameters will ing the time series data from smallest to be determined for each sub-basin study. largest. The percent of time that flow is Once daily naturalized flows are calcu- below a certain value (cumulative prob- lated, they will provide a baseline for ability) is calculated by dividing the num- estimating the effect of allocated water ber of days with flow equal to or less than rights by applying each project’s operat- the value by the total number of days in ing rules to the same daily time series. the time series. A cumulative probability Because many factors can modify curve is obtained by plotting flow versus the natural flow regime, caution will be cumulative probability (Figure 6-2.) By exercised when interpreting results. For inspecting cumulative probability curves, example, water right diversions, in-chan- suitable flow rates at which to develop nel impoundments, and changes in the hydraulic models for habitat modeling watershed that affect timing and quantity can be determined. Flow quantity is con- of runoff (such as an increase in impervi- sidered to be a limiting factor for habitat ous cover associated with urban develop- at low flow rates. At the median (50th ment) can all affect results. In addition, percentile) flow rate and above, flow the daily distribution of naturalized flows quantity is not believed to be a limiting is generated from flow gage data mea- factor for habitat. Therefore, a flow range sured in a system that may have already from the median flow down to the 10th been impacted by diversions. percentile is considered appropriate for habitat modeling. As a general rule, at 6.1.3 least six flow rates across this range are Flow Frequency Analysis chosen for modeling. In order to allow Frequency analysis on the time series additional validation of the hydraulic of flows can provide a good idea of model, flow rates when biological sam- both the “flashiness” of the river (its pling or other fieldwork took place may tendency to carry a large percentage also be modeled. of its flow in large, infrequent events) and the degree of human impact. Flow 6.2 data for naturalized, pre-development, Hydraulic Evaluation current and/or other conditions may Hydraulic evaluation based on numeri- be analyzed and compared. Flow dura- cal modeling provides input for devel- tion curves are particularly useful for oping both overbank and base flow assessing daily flow data. These curves components. For overbank flow devel- are developed by first ordering the time opment, one-dimensional hydraulic series data from largest to smallest. The modeling will provide water surface percent of time that flow exceeds a cer- elevations to estimate the extent of tain value (percent exceedence) is then inundation in riparian areas associat- calculated by dividing the number of ed with various flow rates. Nislow and days with flow equal to or greater than others (2003) used such an approach the value by the total number of days in to make a “spatially explicit assess- the time series. A flow duration curve is ment of hydrologic alteration.” For base obtained by plotting flow versus percent flow development, a two-dimensional exceedence. Changes in the hydrologic hydraulic model will be used to provide regime can be visualized by plotting input for a habitat model. Additional flow duration curves for pre- and post- hydraulic modeling may be conducted development conditions on the same in response to concerns related to a spe- graph (Figure 6-1). cific river sub-basin. Cumulative probability curves are Three components of an instream also useful in assessing daily flow data. flow study, as they pertain specifically Developing these curves requires order- to hydraulic evaluation, are discussed

54 Texas Water Development Board Report 369 in the following sections: the choice of a 6.2.1 representative river reach, field data col- Choosing a Representative Reach lection, and the application of a hydraulic In most cases, it is impractical to moni- model. tor, analyze, and hydraulically model an

10,000

1,000 ) Flow (cfs

100

10 0 10 20 30 40 50 60 70 80 90 100 Percent Time Pre-development Post-development

Figure 6-1. Flow duration curve calculated from daily data for pre-development and post-development conditions.

1,750

1,500

Q 6=1240 1,250

1,000 Q 5=935

Flow (cfs) 750

Q 4=555 500

Q 3=306

250 Q 2=194

Q1 =113 P1=10 PPP2=18 3=26 4=34 P5=42 P6=50 0 0 10 20 30 40 50 60 Percent Time Figure 6-2. Cumulative probability curve with flow rates suitable for habitat modeling. cfs=cubic feet per second, 35.3 cubic feet per second is equal to 1 cubic meter per second

Texas Water Development Board Report 369 55 entire river. Instead, one or more repre- structures and bed forms common to the sentative reaches are selected in order study sub-basin are present. A represen- to estimate conditions for the river as a tative reach whose frequency of pools, whole. Representative study reaches are riffles, and runs corresponds to the fre- selected using a combination of criteria. quency of occurrence of those forms in Within a river sub-basin, one or more the sub-basin gives a good representation reach-length study sites may be select- of the response of the entire sub-basin to ed, each reflecting the unique charac- some disturbance. teristics of a particular region of the Upstream and downstream bound- sub-basin. A study reach may be select- aries of the hydraulic model are chosen ed to address a particular concern in a with the behavior of the numerical model specific sub-basin; for example, a reach in mind. Complicated banks and bathym- may be located directly downstream of etry near the upstream and downstream a proposed diversion. boundaries can cause numerical insta- The possible length of a study reach is bility problems for hydraulic models. limited by the hydraulic model that will Selecting upstream and downstream be used. The lower computing power boundaries that minimize such condi- required by a one-dimensional model tions is, therefore, standard practice. makes it feasible to model a relatively More complicated banks and bathymetry large study area, for example, an area are limited to the interior of the mod- extending across the active floodplain eled section. In order to obtain suitable and along the river for many miles. The boundaries, the modeled reach may be greater computational power required extended outside of the area of interest. by two-dimensional models limits their In this case, extraneous hydraulic model feasibility to smaller study areas, such information will be removed from the as an area extending across the channel study reach analysis. and along the river for no more than a few miles. In practice, this is not a severe 6.2.2 limitation because the purpose of the Field Data Collection study also limits the required length of To use a physically based hydraulic mod- the study reach. For example, habitat el, at least three boundary conditions studies, which employ two-dimensional must be specified: upstream boundary hydraulic models, do not require study flow rate, downstream boundary water reaches of more than a mile or two in surface elevation, and bathymetry. Flow length (1.6 to 3.2 kilometers). rate at the upstream boundary and water The choice of study site length and surface elevation at the downstream boundary locations is influenced by many boundary describe the flow of water factors, including the requirements for mass into and out of the system, respec- accurate hydraulic modeling. For one- tively. Spatial variations in flow within dimensional hydraulic modeling, a com- the study reach are most influenced by mon rule-of-thumb has been to choose representative structures and bed forms a site whose length is 20 to 30 channel located within the study reach, so the widths or of sufficient length to encom- accuracy of model output of depth and pass one complete meander wavelength velocity depends on the accuracy of the (Leopold and Wolman, 1957; Waddle, data that describe the bottom bathymet- 2001). These same minimum criteria are ric boundary (Carter and Shankar, 1997; applicable to multidimensional model- Lane and others, 1999). Furthermore, ing; however, rather than establish reach the scale at which information about length based upon rules-of-thumb, reach the spatial variability in flow is desired length is established to ensure that a dictates the scale at which both bathy- representative distribution of channel metric data and model verification data

56 Texas Water Development Board Report 369 (velocity and depth at specific locations in water surface slope. Elevation can be at specific flows) are collected. determined using either traditional dif- Flow rates at the study site will be ferential leveling or vertically accurate determined by field measurements. A GPS techniques. Semipermanent vertical sufficient number of measurements will benchmarks and pressure transducers be collected to develop a rating curve installed at upstream and downstream describing the river stage versus dis- boundaries of a reach will remain in place charge relationship. Many instrument for the duration of the study. Upstream options exist for measuring river flow and downstream water surface elevation rate, including acoustic doppler cur- measurements will be used as bound- rent profilers, portable acoustic doppler ary conditions for modeling. Additional velocity meters, electromagnetic velocity water surface elevation measurements measurement devices, and mechanical will be used for verifying both one- and velocity measurement devices. For chan- two-dimensional model output. nels with maximum depth greater than Bathymetric data for one-dimen- 1.5 meters (about 5 feet), a boat-mounted sional hydraulic models will be collected acoustic doppler current profiler is used on channel cross sections that extend to measure flow. It calculates flow by beyond riparian areas of interest. Data integrating sonically measured vertical in out-of-channel areas will be collected velocity profiles across a lateral transect with traditional or GPS surveying equip- perpendicular to flow direction (Gordon, ment. For streams too large to wade, data 1989). Alternatively, a velocity meter is will be collected in the channel by way of used to measure point velocities that a boat-mounted differential GPS linked are, in turn, used to integrate cross-sec- to a depth sounder, and the number of tional flow by traditional U.S. Geologi- channel cross sections required will be a cal Survey flow measurement methods function of channel complexity. In gen- (Prasuhn, 1987). In shallow conditions eral, the greater the number of changes (depths less than 0.66 meters or 2.2 feet) in discharge, slope, shape, and roughness where it is possible to wade across the along the channel, the greater the num- river, hand-held devices are more practi- ber of cross sections required to charac- cal than an acoustic doppler current pro- terize hydraulic behavior. Data related to filer for flow measurement. In order to relative hydraulic roughness of channel verify two-dimensional hydraulic model and overbank areas will be collected at output, velocity measurements will also the same time. For a complete descrip- be taken at a number of points within a tion of data collection requirements for study reach. one-dimensional hydraulic modeling, see Flow rates measured at the site may Brunner (2002). be compared with flow rates reported Bathymetric data for two-dimension- at nearby U.S. Geological Survey gag- al models will be collected at very high ing stations. Flow statistics calculated spatial resolution using a boat-mounted using historical gaging station data will differential GPS linked to a depth sound- be used, along with an appropriate mul- er. Depending on conditions (including tiplier, to estimate flow regime statistics tree canopy, overhead banks, availabil- at the study reach site. For sites with little ity of correctional signals), it may be hydrologic correlation to a gaging station, impossible to obtain positional data with additional analysis will be performed as sufficient vertical accuracy with avail- described in Section 6.1.1. able GPS equipment. In such cases, a Water surface elevation data will be network of pressure transducers will be collected at upstream and downstream used to record water surface elevations boundaries, as well as at any intermedi- at locations along the study reach where ate areas that exhibit significant changes significant changes in water surface slope

Texas Water Development Board Report 369 57 occur (such as the head and foot of riffles to describe the cross section above the and pools). The water surface elevation at median flow water line. any location in the study reach can then Combining flow rate data with water be interpolated. The vertical component surface elevation data, a stage-discharge of bathymetric data may be obtained by curve for the study reach will be devel- subtracting the fixed distance from the oped (Figure 6-3). Such a curve is used to water’s surface to the boat-mounted develop input data (water surface eleva- depth sounder’s transducer face. tions) for hydraulic modeling across a Because quantifying the spatial vari- range of flows of interest. The curve is ability of habitat use is the objective of developed by measuring several water habitat flow studies, sufficient bathymet- surface elevations (stages) and dis- ric data must be collected to describe the charges and fitting a curve to the data. causes of spatial variation in flow. Domi- The shape of the stage-discharge curve nant bed forms, banks, outcrops, and is determined by the hydraulic control other channel structures that influence downstream of the measurement point. flow patterns within the reach must be For natural stream channels, hydraulic resolved at a scale sufficient to model the control may be dominated by a single flow patterns caused by those structures. feature, such as a bedrock outcrop, If necessary, additional bed and bank gravel riffle, or sand bar or may be the elevation data may be collected using result of a number of features along the traditional surveying or other techniques downstream channel. Because hydraulic

h 6 =85.8 85.8

85.6 h 5 =85.56

85.4

Q =1240 ) h =85.22 6 et 4 85.2 (fe e Q =935

ag 5 St 85 h 3 =84.96

Q 4 =555 h 2 =84.83 84.8

h1 = 84.72 Q 3 =306 84.6

Q 2 = 194 84.4

0 Q 1 = 200 400 600 800 1,000 1,200 1,400 1,600 113 Discharge (cfs)

Measurements Estimate Curve: Q=868(h–84.5)1.35

Figure 6-3. Stage-discharge curve developed for hydraulic model input. cfs=cubic feet per second, 35.3 cubic feet per second is equal to 1 cubic meter per second

58 Texas Water Development Board Report 369 control may vary with discharge (larger One-dimensional hydraulic modeling flows submerge different features in the channel or floodplain), stage-discharge One-dimensional hydraulic models curves should not be used to estimate require relatively little computational water surface elevations well beyond the power and their numerical basis is range of measured data. When conduct- less difficult to understand than mul- ing two-dimensional hydraulic modeling tidimensional models. They require in support of habitat studies, flows of cross-sectional bathymetry data, and interest range from about the 10 to 50 the modeled channel length must far percent cumulative probability flows. exceed the channel width. These mod- Hydraulic control can also change over els are suitable for studies investigat- time as downstream features, such as ing parameters, such as water surface sand bars, change. Therefore, stage-dis- elevation or chemical concentrations charge curves developed for hydraulic that vary along the length of the chan- modeling input are not suitable (in most nel and are relatively constant across cases) for estimating water surface eleva- the channel width. They are often used tions over extended time periods. to study water quality and overbanking flood flows. Regulatory water quality 6.2.3 models in Texas traditionally rely upon Hydraulic Modeling one-dimensional hydraulic advection A numerical hydraulic model will be models to determine constituent trans- used to model the distributions of water port. Modeling of flood-flow water sur- surface elevation, depth, and veloc- face profiles and overbanking can also ity within the study site for a particu- be performed with a one-dimensional lar flow of interest. The results will be model, such as HEC-RAS, WSP2, or used to evaluate overbank flows based MIKE11. Until the mid-1990s, habitat on the expected inundation of riparian studies related to base flows also relied areas or to evaluate base flow conditions on one-dimensional hydraulic models. based on habitat availability. There are However, since most rivers have spatial- many options for modeling the water ly complex hydraulic habitats, includ- surface elevation, depth, and veloc- ing across-channel velocity variations, ity nonuniformities within a study site, many investigators have found two- the most basic option being choice of dimensional models more suitable for model dimensionality. One-dimension- habitat flow studies (Leclerc and others, al hydraulic models calculate the aver- 1995; Moyle and others, 1998; Railsback, age water surface elevation, depth, and 1999; Crowder and Diplas, 2000). One- velocity for a cross section or portion dimensional models remain useful for of a cross section. Multidimensional many studies related to water quality hydraulic models (both two- and three- and water surface elevation. dimensional) are capable of resolving There are a number of one-dimen- depth and velocity at many points in a sional hydraulic models that may be cross section. One-dimensional mod- appropriate for modeling inundation els are generally capable of providing of riparian areas (for example, HEC- water surface elevation data suitable for RAS, WSP2, and MIKE11). Although evaluating inundation of riparian areas other models may be acceptable, the during overbank flows. Two-dimen- Agencies prefer HEC-RAS for over- sional hydraulic models have been used bank flow studies for several reasons. most recently for habitat flow studies The HEC-RAS code is well known, and in Texas. Hydraulic models suitable for extensive training and documentation is study objectives will be chosen for spe- available for this software (Annear and cific sub-basin instream flow studies. others, 2004). Additionally, it has been

Texas Water Development Board Report 369 59 used with success for similar studies in this manner. Three-dimensional models other states (Nislow and others, 2003; may be applied if strong vertical velocity Philip Williams and Associates, 2003) gradients exist within a study reach or and within Texas (Freese and Nichols, if knowledge of three-dimensional flow 2005). The HEC-RAS model uses energy variation would improve the analysis of and momentum equations to calculate habitat availability. However, in most water surface elevations for both steady cases, a two-dimensional model will and unsteady flow and is specifically suffice. designed for floodplain management There are myriad formulations and applications. (Additional information assumptions incorporated into a typical on HEC-RAS can be found in Brunner multidimensional hydraulic model. Mod- (2002) and Annear and others (2004)). el formulations applicable to hydraulic evaluations in Texas instream flow stud- Multidimensional hydraulic modeling ies are discussed below.

Multidimensional hydraulic models Governing equations offer a number of features that make Multidimensional fluid mechanics them especially useful in habitat stud- models applicable to river studies are ies. They quantify lateral (across the built upon the Navier-Stokes equations channel) circulation patterns, velocity for fluid flow. Since computational lim- variation, and water surface elevation itations preclude direct solution of the variation that cannot be quantified exact equations, most available hydrau- with one-dimensional models. Addi- lic models are based upon the shallow tionally, complicated river structures water form of the Reynolds-averaged such as islands, cutoffs, backwaters, and Navier-Stokes (RANS) equations that debris can be incorporated into multi- include the Boussinesq approxima- dimensional models (Bates and others, tion and assume hydrostatic pressure. 1997). Multidimensional models pro- A detailed explanation of the general duce a spatially explicit representation modeling formulations is not presented of hydraulic habitat offering expanded here because it is presented in many options for instream habitat analysis manuscripts, texts, and referenced lit- (Bovee, 1996; Hardy, 1998). erature (see King and others, 1975; King, Both two- and three-dimensional 1982; USACE, 1993; Leclerc and others, hydraulic models are available for use in 1995; Walters, 1995; Finnie and others, studies of habitat during base flow con- 1999). Additionally, each specific model ditions. Two-dimensional models tradi- employs slightly different formulations, tionally used in river studies are depth- and an exhaustive discussion of all avail- averaged so only horizontal variations able models is beyond the scope of this in flow are simulated. Electrofishing and text. other biological data collection tech- The assumptions, simplifications, niques allow development of hydraulic and solution methods all place limita- habitat descriptions in terms of mean tions on the types of hydraulic problems column velocity, a good match for two- that can be solved by a particular model. dimensional models. Three-dimensional For example, a depth-averaged, shallow models capture both horizontal and ver- water RANS model is not strictly appli- tical velocity variations, which are mod- cable to situations in which large vertical eled in vertical layers above each node. velocities are present. With such limita- Velocities at specific points in the water tions in mind, a model can be chosen to column would be resolvable with three- describe adequately the hydraulic condi- dimensional models, but hydraulic habi- tions at each study site. tat requirements are seldom described in For modeling a typical river reach in

60 Texas Water Development Board Report 369 Texas, the shallow water RANS equations hydraulic models, although finite vol- are generally applicable because hydrau- ume methods are gaining popularity. lic conditions are primarily subcritical, Finite element models have been used low gradient, and without significant extensively for instream flow studies density effects (no surface freezing and because of their ability to incorporate no saline tidal water). When considering irregular elements that describe irregular overall channel hydraulics, the horizon- boundary geometries and to adequately tal velocity gradients are more important resolve flow patterns diagonally across than vertical velocity gradients, allow- each element (Leclerc and others, 1995; ing a depth-averaged (two-dimensional) Mathews and Tallent, 1996; Austin and model implementing the RANS equa- Wentzel, 2001; Osting and others, 2004a; tions to be used (Leclerc and others, 1995; 2004b). This aspect allows use of finite Vadas and Orth, 1998; Lane and others, element models with nodes oriented in 1999; Crowder and Diplas, 2000). How- geographically correct locations, that is, ever, two-dimensional depth-averaged with irregular elements that follow the models are less applicable where three- patterns of a sinuous river. dimensional flow effects dominate, such Finite difference models give best as in the immediate vicinity (within cen- results with regular elements and when timeters or inches) of large woody debris. flow patterns trend generally in the same Unfortunately, the extremely small grid plane as the element edges. In instances scale required to address these types of where flow can potentially be trending problems limits the usefulness of apply- at any angle with respect to the regular ing three-dimensional models. elements (in the instance of a sinuous An additional limitation to applying river), a finite difference model may most two- and some three-dimensional not perform as well as a finite element hydraulic models is presented by the model and may require a correction to presence of steep bed gradients (slopes the coordinate system. Curvilinear coor- greater than 20 percent) oriented in the dinate system transformations have been direction of flow. Such conditions cause used with success (Hodges and Imberger, vertical pressure gradients that lead to 2001), but the transposition of geograph- possible flow separations. Modeling the ically correct node locations to a curvi- effect of vertical pressure gradients is linear reference frame introduces a level not strictly possible with a depth-aver- of complexity that is easily bypassed by aged, hydrostatic model using the shal- using a finite element model. A finite low water equations with the hydrostatic difference model should, however, be assumption (this applies to most two- considered for use if some crucial aspect and some three-dimensional models). is available in the finite difference model Smoothing the bathymetry to remove (for example, non-hydrostatic solution). steep slopes may reduce slope-induced Finite difference models are also faster model convergence problems. However, for a given cell resolution than finite ele- this introduces another level of separa- ment models. For models with very fine tion of the model from the observed sys- cells and very large domains, the compu- tem. Quantifying the error introduced by tational speed of finite difference models slope smoothing is difficult. Fortunately, may prove beneficial. these conditions do not occur frequently in Texas rivers. Numerical mesh A high-resolution mesh will be gener- Solution methods ated on which the numerical hydraulic Models relying on the finite element model will calculate depth and velocity. or the finite difference solution meth- Within guidelines that are discussed od make up the majority of available below, appropriate mesh resolution

Texas Water Development Board Report 369 61 will be ultimately determined by engi- utilization analysis is generally between neering judgment and experience. 2 and 5 square meters (about 20 to 55 Areas with complex hydraulics (steep square feet). Therefore, a hydraulic mesh longitudinal bathymetry, bridge areas, of comparable resolution will provide island areas, flow restrictions, and flow adequate resolution of macroscopic obstructions) will be afforded more ele- velocity fields to meet study objectives. ments than simple areas with relatively uniform bathymetry. Bathymetry The mesh boundary will be estab- The results of any hydraulic model lished using a bathymetry data point file depend on an accurate depiction of the that consists of water’s edge horizontal bathymetric boundary condition (Cart- position data. These data points can be er and Shankar, 1997; Lane and others, collected at high flows using a laser range 1999; Crowder and Diplas, 2000). The finder coupled with a differential GPS. bathymetric boundary is defined by the Alternatively, recent Digital Orthograph- elevation of each mesh node. At the ic Quarter Quadrangle aerial photos may relatively fine scale at which a mesh will be used in conjunction with the extent be generated, accurately describing bed of the bathymetry point file to establish form will be important for modeling the mesh boundary. velocity variations. To determine the The horizontal distribution of mesh elevation of the nodes, it will be neces- elements should be carefully controlled sary to interpolate from the bed eleva- since their shape and orientation affect tion data since the resolution of bathym- the accuracy of model results (Freeman, etry scatter point data may be coarser 1992). For one model, RMA2, a discus- than the hydraulic mesh. Interpolation, sion of element shape requirements is however, is a source of error because the included in the users’ manual, with the traditional interpolation techniques, guidance that elements should not have such as inverse distance weighting, interior angles less than 10 degrees, Thiessen polygon, cubic spline, and should be planar (no concave or convex two-dimensional kriging, do not take elements), and the area of adjacent ele- into account the known shape of a river ments should not differ by more than channel (such as the high gradient near 50 percent (Donnell and others, 2001). the banks and the relatively low gradient Mesh generation and visualization soft- along the length of the channel). Some ware, such as the Surface Water Model- of these methods include provisions to ing System (EMSI, 2005), make it easy weight the interpolation anisotropically. to evaluate meshes and implement such However, the sinuous nature of most requirements. rivers prevents use of these techniques The mesh should not be generated because the proportion of anisotropy at a spatial scale significantly finer than changes with changing flow direction. the available bathymetry data. Bathym- To address this problem, the Texas etry significantly affects model output Water Development Board developed the (Carter and Shankar, 1997; Lane and oth- Mesh Elevating and Bathymetry Adjust- ers, 1999; Crowder and Diplas, 2000). If ing Algorithm and uses it for assigning accurate bathymetric data are not avail- elevations to nodes in the mesh. For able, the mesh should remain coarse applying the anisotropic interpolation, to avoid resolving velocity fields over a the changing direction of river flow is bed form that may not truly be present. taken into account by transforming the Similarly, minimum mesh size will be Cartesian coordinate system into a coor- limited by the assumptions of the specific dinate system that follows river planform model that is being used. The horizontal by defining distance along the flow path resolution of cells used in fish habitat and from the centerline. Rectangular

62 Texas Water Development Board Report 369 search areas are defined for each node bridge abutments, and discarded debris) that weights the node (interpolates) aver- that cause local velocity variations may age elevation more heavily with bathy- be difficult to include in the model. Their metric scatter data located along the flow physical size is usually much smaller path than with data perpendicular to the than the numerical model’s grid resolu- flow path. A modified inverse distance tion, and subgrid scale effects cannot be weighting algorithm is used to calculate resolved by the model. In general, the the weighted average of the subset of approach taken for submerged objects scatter points (Franke, 1982). is to artificially increase the roughness in the area to compensate for overall Substrate, roughness, and moving beds hydraulic effect. For large objects that are Multidimensional models apply the not submerged over the range of flows shear stress caused by bed roughness as and provide complete impedance to flow a body force acting upon the column of (such as bridge abutments), the simplest water located above the point of calcu- method is to modify the mesh, removing lation. The bed roughness parameters the elements in question. typically applied were not originally In areas with sandy substrate, bed derived for this manner of application forms may change as the energy of flow but rather for application in one-dimen- changes. In the region closest to the bed, sional calculations of flow for an entire river velocity fields have a symbiotic cross section (Prasuhn, 1987; Arcement relationship with a mobile bed. Effects and Schneider, 1989). The body force of that relationship may propagate up calculation is, however, still applicable the water column, affecting the overall in multidimensional models because 1) hydraulics differently at varying flows. it models the friction force at the bot- Typically, these effects are incorporated tom boundary and the turbulence in into a model by using different roughness the water column (just like it does in parameters for different flows. However, the one-dimensional equations); 2) the if river hydraulics cannot be adequately specified roughness applies over the described by altering roughness, then a entire domain of influence (the entire three-dimensional model that couples volume for which the calculation is hydraulics with sediment transport will being made); and 3) no hard and fast be required. rules exist for roughness coefficients in Objects, such as large woody debris either one or multiple dimensions. A and bed forms that are clearly mobile numerical estimate of roughness for a at higher flows, pose a problem for one-dimensional model may be slightly modeling. Past experience suggests that different from the estimate of rough- the best approach is to model the river ness for a two-dimensional model for as a snapshot in time, that time being the same system (say, 10 percent differ- the day or days when bathymetry and ence), but the actual value is no more channel geometry were measured. The than an estimate or an educated guess. object may not be observed within the At higher flows, resistance caused by study site during the next trip to the field large-scale bed forms is stronger than the and another may have appeared. Unless resistance caused by material roughness the objects clearly impede flow on a (grain size). Conversely, material rough- large scale and affect either or both the ness is dominant at lower flows. When upstream and downstream water surface modeling a range from very low flows elevations, their presence is not really with shallow depths to median flows important for the study. On average, with moderate depths, the roughness similar objects or bed forms are pres- parameter will change. ent at some location in the river at any Obstructions (such as boulders, given time.

Texas Water Development Board Report 369 63 Substrate mapping will be carried one channel width apart. Alternatively, out during the collection of bathymet- acoustic doppler current profiler cross ric data. Information on substrate can be sections can be measured at the same used to initially estimate the Manning’s spacing. For three-dimensional models, roughness coefficient used in calibration vertical velocity profiles should also be of the hydraulic model. measured at the same spacing.

Validation of model output Discussion of RMA-2 Validation of model output will be per- There are a number of multidimension- formed using field-collected data. Water al hydraulic models that may be appro- surface elevation data collected at many priate for modeling habitat (RMA-2, points throughout the study reach for FESWMS, CCHE2D, RMA-10, CH3D- each flow of interest will be used to vali- WES, and EFDC). Some hydraulic date model water surface elevation out- models have been designed specifically put. Point velocity readings, measured for fish habitat studies (such as River2D, during biological sampling, will be used HYDROSIM, and SSIIM2D). The Texas to validate model velocity output. Addi- Water Development Board has selected tional point velocity measurements will RMA-2 for several recent habitat flow be taken for a range of modeled flows studies for several reasons (Mathews in areas where significant hydraulic gra- and Tallent, 1996; Osting and others, dients are present. Horizontal and ver- 2004a; 2004b). The RMA-2 code is well tical velocity profiles across an entire known and has been used with success cross section will be measured using by others (Deering, 1990; King, 1992; the acoustic doppler current profiler at Finnie and others, 1999; Crowder and the downstream boundary and in areas Diplas, 2000). The model can handle where point velocity measurements are wetting and drying of elements which not available, not practical, or insuffi- is a necessary feature for low flow stud- cient to define the flow. ies. The code can be modified to accept Validation should be performed for a large array of nodes and elements each calibrated model and include a com- (typical instream flow models have parison of depth and velocity data mea- used roughly 50,000 nodes and 20,000 sured in the field to depth and velocity elements). Most important, RMA-2 output from the model. Such validation resolves flow features to a scale that should be performed in many locations is relevant to habitat studies. If other throughout the model’s spatial domain. models are better suited to specific At a minimum, the depth and velocity conditions at a specific site, they may measurements that are used for the flow be used. A brief discussion of the RMA- rate calculation should be used again to 2 model is included below, but many of compare model output across that same the concepts and modeling approaches cross section. Additionally, depth and described are applicable to other two- velocity measured at each biological dimensional models as well. sampling location should be compared RMA-2 is a two-dimensional, depth- to model output. averaged, finite-element hydraulic model Ideally, additional depth and veloc- that can solve steady-state and transient ity measurements should be collected problems. Water surface elevation and to increase confidence in each calibrated depth-averaged velocity flow fields are model’s output. For a depth-averaged, calculated from the Reynolds-averaged two-dimensional model, at least three form of the shallow water Navier-Stokes depth and velocity measurements (left equations for turbulent flows. Bottom margin, mid-channel, and right margin) friction is applied using Manning’s or should be taken at cross sections located Chezy’s equation. Eddy viscosity coef-

64 Texas Water Development Board Report 369 ficients are used to model turbulence and 5000 Pascal-seconds and also characteristics. The code was originally that the cell Peclet number should be developed in 1973 for the U.S. Army between 15 and 40 (Donnell and oth- Corps of Engineers, with subsequent ers, 2001). Richards (1990) presents a enhancements made by Resource Man- model in which the best replication of agement Associates and the Corps’ flow separation is achieved when the Waterways Experiment Station (Free- Peclet number is four. Since the appro- man, 1992; Donnell and others, 2001). priate eddy viscosity value depends on Input requirements of the model cell depth, velocity, and length scales, the include the finite element mesh (bathym- Peclet number criterion is used to deter- etry), downstream boundary condition mine the absolute eddy viscosity values. (the water surface elevation), upstream For habitat flow studies, the cell Peclet boundary condition (the flow rate or ini- number is specified between 15 and 20, tial velocity profile), bottom roughness resulting in eddy viscosity settings as low coefficients, and eddy viscosities. With as 50 Pascal-seconds when using small all other model settings held constant, cells (< 5 meters or 16.5 feet in length) bottom roughness and eddy viscosity are as is typical for habitat flow studies. An used as calibration parameters. At the absolute eddy viscosity value for each discretion of the modeler, both of these element can be individually assigned, but parameters can be varied spatially across RMA-2 can also assign eddy viscosity the domain of the model. automatically at each time step or itera- Bottom roughness is incorporated tion based upon cell Peclet number and into RMA-2 using either Chezy’s or Man- modeled velocity. ning’s roughness coefficients. Roughness To improve model convergence, values are user-specified based upon bed RMA-2 offers two wetting and drying materials (substrate grain size or vegeta- features that remove dry cells of the tion) and bed form. Reference materials mesh from the computations when are consulted for appropriate Manning’s they become completely dry between roughness values based upon the mate- iterations. For habitat flow studies where rials and flow conditions at the site (see the same mesh is used for a range of Chow, 1964; Prasuhn, 1987; Arcement flow rates (from roughly median flow and Schneider, 1989; USACE, 1993). down to a roughly 15 percentile flow), Eddy viscosity can be described as the ability of the model to automatically an amalgamation of terms that include eliminate dry cells from the calculation absolute fluid viscosity, Reynolds stress- without diverging saves time and effort. es, and some simplifying assumptions The Marsh Porosity feature is used in constructed to allow for solving the mod- combination with the wetting and dry- el. In RMA-2, eddy viscosity is specified ing feature as specified in Donnell and for each element, and appropriate values others (2001). vary with velocity, depth, and cell-length Although RMA-2 has been recently scales (Richards, 1990; Freeman, 1992). used for habitat flow studies in Texas, The cell Peclet number (defined in Don- some limitations exist that may preclude nell and others [2001] as fluid density its use on some study reaches. The RMA- times average elemental velocity, times 2 model is limited to subcritical flow cell length in flow direction, divided by problems in reaches without steep local eddy viscosity) incorporates those scales bed slopes. If situations violating these and is used to determine appropriate conditions are encountered, another eddy viscosity values. more suitable hydraulic model will be The RMA-2 manual suggests that used (such as FESWMS or River2D). eddy viscosity should be between 500

Texas Water Development Board Report 369 65 7 Biology

iological evaluations, surveys, ripar- largely determine magnitudes of flows, ian assessments and models, and but the timing and duration of these instreamB microhabitat and mesohabi- types of events may be influenced by life tat models will play a substantial role histories of aquatic and terrestrial (ripar- in identifying flow conditions needed ian) communities. Conceptual models, to maintain a sound ecological envi- targeted assessments, and/or available ronment. Specific elements will vary information, rather than instream habi- according to the portion of the flow tat modeling, will be most effective for regime under consideration. developing these flows. For subsistence flow recommendations, biological considerations may 7.1 dictate which water quality constituents Hydrology and (such as dissolved oxygen, temperature, Riverine Ecosystems and turbidity) will be of primary con- Because hydrology plays a substantial cern in a particular reach of river. Habitat role in determining the composition, considerations will include maintaining distribution, and diversity of aquatic adequate flows so that key habitats are communities, a central focus of instream not dewatered or reduced to unsuitable flow studies is to relate the biology of a conditions for lotic-adapted species lotic system to its flow regime. (Bovee (such as mussels, riffle-dwelling fishes, and others, 1998; Annear and others, and invertebrates) or other key or imper- 2004). Riverine biota have evolved life iled species. history strategies that correspond to Base flow recommendations will natural flow regimes. Information to rely primarily on habitat models that address flow requirements in key habi- use habitat criteria derived from bio- tats, such as shallow water habitats, logical data to assess instream habitat during critical time periods (spawning (quantity, quality, and diversity) relative and rearing) is an essential element of to streamflow. These models provide a instream flow studies. means to identify a range of flows that Biological evaluations will focus on provide suitable habitat conditions and fish assemblages but may also address allow for quantitative comparisons of other vertebrates, invertebrates, or plants different flow scenarios, such as differ- as study objectives dictate. Habitat and ent release schedules from reservoirs or water quality requirements, life history, hydropower operations. and other ecological factors, such as Biological considerations, such as connectivity, will be assessed to pro- migration, spawning cues, and mainte- vide input to habitat models and insight nance of key habitats through geomor- into the integration element. Fish are phic processes, will play an important advantageous target organisms because role in developing the high flow pulse they are relatively easy to identify; use a component of the flow regime. To devel- wide array of habitats, including flow- op overbank flow recommendations, the sensitive habitats; offer a wide range of Agencies will evaluate and model ripar- life histories, many of which are tied to ian systems and linkages between aquatic flow dynamics; are generally well stud- biota (such as floodplain spawning fishes) ied relative to other aquatic taxa; are a and active floodplain and channel pro- good integrator of overall health of the cesses. The historical flow data related to system; and have a high public profile high flow pulses and overbank flows will and commercial importance. Nonethe-

66 Texas Water Development Board Report 369 less, in some systems and as objectives in riverine systems (Ward and others, dictate, it is likely that other focal taxa 2002) and is essential to survival, growth, such as mussels will need to be included and reproduction of many riverine spe- to ensure that the goals of the instream cies and the maintenance and function flow program are met. Likewise, specific of riparian areas (NRC, 2002). information or models may need to be Riparian areas are important compo- developed to identify flow conditions nents of river ecosystems, and riparian necessary to maintain riparian areas, structure and function depend on flow such as hardwood bottomlands, riparian regimes (NRC, 2002). Riparian areas are wetlands, oxbows, and other habitats. defined as ecotones or corridors between Flow regimes largely determine the terrestrial and aquatic realms (Melanson, quality and quantity of physical habitat 1993) and are often the only portion of available to aquatic organisms in rivers the landscape moist enough to support and streams (see Bunn and Arthington, tree growth and survival in drier western 2002). Habitat complexity or heterogene- climates (Busch and Scott, 1995). Accord- ity is a primary factor affecting diversity ing to the National Research Council among fish assemblages (Gorman and (2002), riparian areas Karr, 1978; Bunn and Arthington, 2002) because heterogeneous habitats offer are transitional between terres- more possibilities for resource partition- trial and aquatic ecosystems and ing (Wootton, 1990). Channel morphol- are distinguished by gradients in ogy, the sequence of riffles, pools, and biophysical conditions, ecologi- other habitats, and substrate composi- cal processes, and biota. They are tion result from interactions of flows and areas through which surface and watershed geology. Lotic biota respond subsurface hydrology connect (in terms of abundance, distribution, and waterbodies with their adjacent diversity) to changes in physical habitat. uplands. They include those por- Flow-dependent organisms, such as riv- tions of terrestrial ecosystems that erine fish, tend to show preferences for significantly influence exchanges specific habitat conditions as character- of energy and matter with aquatic ized by current velocity, depth, substrate ecosystems (i.e., a zone of influ- composition and distribution, and cover ence). Riparian areas are adjacent (Schlosser, 1982). This habitat-prefer- to perennial, intermittent, and ence behavior is a primary assumption ephemeral streams, lakes, and of habitat-based instream flow models estuarine-marine shorelines. (Annear and others, 2004). In addition to their usual flow requirements, many Riparian areas perform key eco- riverine fishes time migration, spawning, logical functions that contribute to the and other activities to seasonal changes health of the entire ecosystem (Wagner, in flow regimes (see Stalnaker and oth- 2004). They support physical, chemical, ers, 1996). Flow regimes also influence and biological processes in rivers and physical and chemical conditions in riv- streams, including biogeochemical and ers and streams, which, in turn, influ- nutrient cycling, organic matter and sed- ence biological processes. For example, iment exchange, temperature dynamics changes in a flow regime may result in (through shading), and stabilization of the accumulation of fine sediments in streambanks. Riparian areas often have otherwise suitable habitats, impairing the high biodiversity and biological produc- reproductive success of biota. Connec- tivity (NRC, 2002). Additionally, riparian tivity, the movement of energy, organic habitats are essential for many vertebrate and inorganic matter, water, and biota species and provide critical physical and within an ecosystem, plays a major role biological linkages between terrestrial

Texas Water Development Board Report 369 67 and aquatic environments (Busch and 7.2 Scott, 1995; Gregory and others, 1991). Assessment of It is estimated that 80 percent of all ver- Current Conditions tebrate species in the desert southwest Assessing the current biological con- depend on riparian areas for at least some dition of each system in relationship part of their life cycle (Wagner, 2004). to instream flows and identifying key Changes in hydrology can lead to loss physical, hydrologic, and chemical pro- of connectivity between riparian areas cesses and critical time periods is an and stream channels, resulting in reduced important starting point for further diversity and altered ecological integrity biological studies. Data requirements (Nilsson and Svedmark, 2002). For exam- include information on life history traits ple, reproduction and growth of riparian (such as spawning season requirements plant species are closely associated with and foraging traits), environmental peak flows and related channel processes requirements (habitat, temperature, such as meandering (Busch and Scott, and dissolved oxygen), species distri- 1995). Studies by Busch and others (1992) butions, community composition, and of plant water uptake in floodplain eco- connectivity considerations. systems indicate that maintaining cotton- Previously collected information will wood and willow populations depends on be assembled from several sources: 1) groundwater moisture sources, which, reports by state agencies in Texas (the in turn, are closely linked to instream Texas Parks and Wildlife Department, flows. Busch and Scott (1995) conclude Texas Commission on Environmental that establishing and maintaining ripar- Quality, and Texas Water Development ian plant communities are a function Board or predecessor agencies) and state of the interplay among surface water agency reports from Louisiana, Okla- dynamics, groundwater, and river chan- homa, and New Mexico; 2) federal agen- nel processes. They maintain that the cies (such as the U.S. Geological Survey, health of natural riparian ecosystems is U.S. Fish and Wildlife Service, U.S. Army linked to the periodic occurrence of flood Corps of Engineers, and U.S. Bureau flows, associated channel dynamics, and of Reclamation); 3) journal articles; 4) the preservation of base flows capable of reports from river authorities and water sustaining high floodplain water tables. districts (including Texas Clean Rivers Additionally, dam construction, diver- Program assessments and reports); 5) sions, and groundwater pumping have university studies and museum records; directly or indirectly caused changes in and 6) other sources. To the extent pos- the hydrologic and fluvial processes nec- sible, data compatible with spatial anal- essary for riparian vegetation establish- ysis will be organized into an ArcGIS- ment and persistence (Lytle and Merritt, based tool for use in study planning and 2004). Hydrologic changes contributing design. These previously collected data to the decline of riparian ecosystems as will be reviewed and analyzed as appro- a result of dams typically include com- priate and summarized to describe cur- plete inundation and subsequent elimi- rent knowledge, facilitate development nation of riparian habitat upstream of of conceptual models, and identify data dams and changes in the frequency and gaps. Field surveys (see Section 7.2.2 for magnitude of peak flows, shifts in the example) will be conducted to address timing of peak flow, and changes in the data gaps and identify trends in assem- rate of river stage decline downstream blage dynamics. Further, these initial (Lytle and Merritt, 2004). surveys will facilitate the development of study goals, objectives, and indicators (see Section 5.2.2); sampling strategies; identification of taxa of interest;

68 Texas Water Development Board Report 369 and delineation of study boundaries and 7.2.2 intensive study areas. Fish Surveys For each study reach, identifiable meso- 7.2.1 habitats will be sampled for fish using Instream Habitat Surveys the most appropriate gear, such as For each study reach, GPS units will be seines or electrofishers. Sample reach used to delineate mesohabitats accord- lengths will be based upon a multiplier ing to the following characteristics: (40 times the mean wetted width) with a maximum of 1,000 meters (about 0.6 • Pool—flat surface, slow current, miles) or one full meander wavelength usually relatively deep (whichever is longer). Physical measure- • Backwater—flat surface, very slow ments will be made in association with or no current, usually out of main each sampling event (such as each seine current haul) and will include current veloc- • Run/Glide—low slope, smooth, un- ity, depth, substrate composition and broken surface embeddedness, instream cover (large • Riffle—moderate slope, broken surface woody debris, boulders, undercut banks, • Rapid—moderate to high slope, very macrophytes, and velocity shelters), and turbulent (for example, a boulder other measurements as deemed neces- field) sary. Notes on climatic conditions and • Chute—very high velocities in con- mesohabitat typing will be recorded. In fined channel addition to providing data on relationships between mesohabitats and fish If the mesohabitat can be further dis- presence and abundance, this informa- criminated, it will be assigned a quali- tion will facilitate the design of appro- fier for relative current speed and depth, priate sampling strategies for collect- using “fast” or “slow” for current velocity ing quantitative microhabitat utiliza- and “shallow’ or “deep” for depth. Notes tion data (see Section 7.3.1). It will also on location and density of woody debris provide data on current conditions for and other instream cover, unique habi- monitoring and verification and allow tat features (such as a unique outcrop), appropriate biological indices to be and substrate composition will be taken. calculated. Released fish will be iden- Measurements of current velocity and tified, measured, photodocumented, depth will be take to facilitate develop- and examined for disease and other ing objective criteria for defining mesho- anomalies. Voucher specimens will be habitat types in each sub-basin study. preserved in 10 percent formalin for This preliminary evaluation of the spatial identification quality control checks. mosaic of habitat types within each reach In all cases, fish collecting will proceed will offer guidance on development of as long as additional species are being study boundaries, stratification strategies collected. for sampling, and other study design fac- Boat electrofishing (900 seconds tors. These mesohabitat surveys should minimum) will focus on habitats too be performed when flows are at or below deep or swift for effective backpack or the median flow and habitat features are seine sampling (such as pools and fast relatively easy to evaluate. Standardized runs). An attempt will be made to collect field guides and sampling protocols will all shocked fish and special effort will be provided to field crews in order to be exerted to collect fishes that may be maximize the accuracy and repeatability rolling on the bottom. When a particular of habitat data collection. habitat has been thoroughly sampled, electrofishing will pause to enumer- ate the collected fish. Site information,

Texas Water Development Board Report 369 69 personnel, and output settings will be an area approximately 1 meter by 0.5 recorded. Electrofishing time and species meter (3.3 feet by 1.65 feet) directly in enumeration will be recorded for each front of the collecting net. Three sam- habitat type sampled. ples each will be collected from each Backpack electrofishing (900 seconds major habitat present (riffle, run, and minimum) will focus on areas shallow pool) in the study reach, with sampling enough for effective sampling (such as to occur from downstream to upstream. riffles and shallow runs). If necessary, One of each sample type will be taken seines placed downstream of the back- alternatively from the right, left, and pack crew can be used to assist in fish middle portion of the stream channel collection. Fishes collected from each of each habitat. For riffles and runs, the habitat sampled will be processed inde- streamflow will carry dislodged inverte- pendently. Site information, personnel, brates into the collection net. For pool and output settings will be recorded. samples, where water velocity is mini- Electrofishing time and species abun- mal, the collector will swirl the net in a dance will be recorded for each habitat circular fashion through the area being type sampled. Fifteen minutes is the min- kicked to maximize the collection effort. imum trigger time for all electrofishing Bulk benthic samples will be washed methods combined. in a standard wash bucket (600 micro Seining (at least 10 effective seine meters or less) to eliminate fine silt and hauls) will be conducted in various habi- sand. Remainders of the bulk benthic tats using a variety of seines and sein- samples will be individually preserved ing techniques (riffles kicks) in order to in at least 70 percent isopropyl alcohol. complement shocking efforts. Examples The preservative will be replaced with of commonly used seines include a 9.1 fresh isopropyl alcohol after 12 hours to meter x 1.8 meter x 7.6 centimeter (30 ensure proper preservation. feet x 6 feet x 1/4 inch) mesh seine for Woody debris will be collected in sampling pools and open runs and a 4.6 amounts sufficient to fill a 1-gallon (3.8 meter x 1.8 meter x 5.7 centimeter (15 liters) collection jar and then preserved feet x 6 feet x 3/16 inch) mesh seine for with at least 70 percent isopropyl alco- sampling riffles, runs, and small pools. hol. The debris will be collected from All seines will be constructed of delta throughout the study reach and include weave mesh with double lead weights well-seasoned and highly-reticulated on the bottom line. Site information wood with irregular or rough surfaces. and personnel will be recorded. Fishes Green wood or very small diameter (less collected from each seine haul will be than 2 centimeters or ¾ inch) pieces will processed independently. be avoided. Hand-collected sampling consists of 7.2.3 collecting miscellaneous aquatic inver- Aquatic Invertebrate Surveys tebrates from stones, woody debris, and For each study reach, three types of sam- other substrates as appropriate. Special ples will be collected: kick net, woody effort will be made to collect a wide vari- debris (snag), and hand picked. Physical ety of immature mayflies to aid in iden- habitat data (see previous section) may tifying specimens collected in benthic also be collected in association with samples. Specimens collected will be aquatic invertebrate surveys. For ben- preserved in at least 70 percent isopro- thic samples, nine kick-net samples will pyl alcohol. Miscellaneous invertebrates be taken for 20 seconds each using a will be collected from throughout the large, tapered kick net (600 micrometer study reach. Mussels (including shells) mesh, 330 x 508 millimeter frame size, and macrocrustaceans will also be col- or similar net). Sampling will occur over lected if observed.

70 Texas Water Development Board Report 369 Benthic samples will be rinsed mens per square meter through a sieve (600 micrometers or • Snag samples: number of specimens less), using tap water to remove fine sedi- per cubic centimeter ments. Sample contents will be sorted completely (in portions as necessary) A benthic Index of Biotic Integrity in white enamel or plastic pans with all may also be calculated. invertebrates stored in individual vials and preserved with at least 70 percent 7.2.4 isopropyl alcohol. Specimen vials will Riparian Area Surveys be labeled to show collection location, Because hardwood bottomlands and type of habitat, date collected, and col- other wetland systems (such as oxbows) lector. Snag samples will be rinsed into are important riparian habitat types, a white enamel or plastic pan and the they warrant detailed assessment. Pre- contents collected by rinsing through a viously collected data related to the sieve (600 micrometers or less) using tap location of important riparian fea- water. Individual pieces of woody debris tures will be compiled from maps, GIS will be carefully examined to ensure that sources, aerial photography and satel- all attached invertebrates have been lite imagery, and other sources. Recon- removed. Invertebrates removed from naissance-level data will be gathered to the snag samples in the laboratory will be assess areas that need additional inves- collectively preserved in at least 70 per- tigation (such as modeling or extensive cent isopropyl alcohol. Snag material will data collection). Riparian areas will be be measured volumetrically (cubic cen- evaluated in terms of connectivity to timeters) in order to obtain an estimate the river channel within a biological and of the amount of surface area sampled. hydrological context. This can be accomplished by adding the The following methodology will be woody debris to a large container par- used to determine the extent, hydro- tially filled with a known volume of water logic requirements, and connectivity of and then measuring the volume of water riparian areas associated with sub-basin displaced. instream flow studies. Specimens will be identified to the lowest possible taxonomic level using Extent and identification appropriate references (Pennak, 1989; of riparian area distribution Merritt and Cummins, 1996). For sample analysis, the following metrics (TNRCC, There are several integral factors that 1999) will be calculated, as appropriate: must be assessed in order to determine the status and condition of ripar- • Taxa richness ian ecosystems. As a critical first step, • Ephemeroptera-Plecoptera- identifying and distributing riparian Trichoptera ratio area extent will be accomplished by • Ratio of Ephemeroptera-Plecoptera- combining information from several Trichoptera and Chironomidae different approaches: remote sensing, abundances topography, soils, hydrology, and veg- • Percentage Cheumatopsyche of total etative sampling/ground-truthing. This Trichoptera information must be correlated in order • Percentage contribution of dominant to determine overall riparian ecosystem taxon status and management requirements. • Percentage exotic species The methodology to address these fac- • Ratio of scraper and filtering collector tors in determining riparian area distri- functional feeding groups bution follows. • Benthic densities: number of speci-

Texas Water Development Board Report 369 71 Remote sensing assembled and correlated to the soils, Although there is not a consistent topography, and riparian vegetation methodology for monitoring riparian classification layer on the base map. area trends, remote sensing is increas- ingly being used as an important land- Vegetative sampling/ground-truthing scape assessment of riparian communi- Vegetation community types delineated ty composition and distribution (NRC, from the above remote sensing methods 2002). To form a base map for the dis- will be ground-truthed (field verified) tribution of riparian habitat along the and sampled for specific data on species river reaches in question, Landsat the- structure and composition, age class, matic mapper imagery (ETM+) from percent canopy cover, and other related 1999 and 2001 will be compiled. For a factors. These results will be correlated more detailed interpretation of ripar- to important riparian functions, such as ian habitat, Digital Orthographic Quar- streambank stabilization, temperature ter Quadrangles from 1995 and 2004 dynamics, and nutrient cycling. will then be assembled. Vegetation and landscape features will be digitized and Determining hydrologic flow converted into shape file layers using requirements necessary for ArcGIS. These shape files will be over- maintaining riparian areas laid on the ETM+ base map. When determining flow requirements Topography for maintaining healthy riparian eco- U.S. Geological Survey topography data systems, understanding the characteris- (Digital Elevation Models, Triangulated tics of natural flow patterns (frequency, Irregular Networks) will be compiled magnitude, duration, timing, and rate of and combined with the ETM+ base map change) is crucial (NRC, 2002). How- to produce a vertical representation of ever, a standard methodology for deter- the river reach being studied. These mining overbank flow requirements of data will also be used when determining riparian ecosystems has yet to be devel- the hydrologic requirements for main- oped. Therefore, a model will be devel- taining a healthy riparian ecosystem. oped using three components: U.S. Geological Survey topography data and Soils hydrologic boundary files for delineat- Riparian areas have been disturbed by ing watersheds and NEXRAD rainfall agricultural practices, logging, land data (over a 50-year period) to deter- clearing, and other factors, which can mine peak discharges. Once the model make classifying riparian areas by vege- has been constructed, the results will be tative indicators difficult because native correlated to the seed dispersal and ger- indicators may no longer be present. mination time frame of the dominant Therefore, soil characteristics derived native vegetation type found within the from data in the 1:24,000 Soil Survey riparian plant communities (or linked to Geographic Database will also be used life histories of other taxa, such as fish- in assessing riparian area extent. Ripar- es that use riparian areas) to determine ian soils types will be identified and the duration, magnitude, and timing of digitized as an additional layer on the overbank flow recommendations. ETM+ base map to further delineate riparian area extent. Connectivity of riparian ecosystems

Hydrology To further elaborate on the importance Hydrology layers from the U.S. Geo- of hydrology to the ecological integrity logical Survey 1:24,000 data will be of riparian systems, Tabacchi (2005)

72 Texas Water Development Board Report 369 maintains that the gradient of inun- produce the probability of inundation dation may be the most objective and curve. This curve will be compared to strongest indicator of riparian influ- the ETM+ base map produced through ence, with the gradient of inundation by the above procedures. surface waters as an obvious parameter of influence. He cites Gold and Kellogg 7.3 (1997) who point out that water table Instream Habitat dynamics should be recognized as a Most instream flow studies model habi- full component of a riparian model. By tat availability in response to discharge considering groundwater and surface with the assumption that physical and water dynamics as main controls of the hydraulic variables determine the spa- riparian ecosystem, Tabacchi (2005) tial distribution of aquatic organisms developed a model that delineates an (Bovee and others, 1998; Annear and indicator variable from hydrological others, 2004). Habitat availability is data series. This model is illustrated used as a surrogate for empirical infor- in Figure 7-1 in which the lower, gray mation relating antecedent flow pat- line depicts the long-period probabil- terns to specific life-history events or ity of inundation by groundwater as a flow-dependent biological responses function of elevation. The upper, black at the individual, population, or com- line represents the long-period prob- munity level. These relationships are ability of inundation by groundwater difficult to develop because they are as a function of river water level. The resource and time intensive. Resource Unsaturated Zone of the water table limitations and time constraints (stud- and the Flooded Zone are also shown. ies are expected to be completed in The Transitional Water Table Distance three to five years) mean that data can- is the physical difference in elevation not be collected at all flows; additionally, between the inflexion points of the two high flows present practical difficulties curves. The riparian zone is defined as and safety hazards. Thus, representa- the common domain of the 95 percent tive flow windows will be selected for confidence intervals for the two cumu- sampling. Habitat modeling provides a lative distribution functions. Transition useful tool to simulate conditions that curves can be asymmetric. This model time or resources preclude measuring. defines the space of interaction between However, modeling that involves mak- nonatmospheric water and substrate ing extrapolations beyond the condi- as a gradient of probability of inunda- tions sampled is fraught with uncer- tion of both superficial area (Flooded tainty, and care will be taken to ensure Zone) and unsaturated groundwater assumptions are documented. Models zone (Unsaturated Zone). Swamp zones also tend to simplify complex ecological occur when the Unsaturated Zone over- processes. Adaptive management has laps the Flooded Zone. The Transitional been suggested to address such uncer- Water Table Distance defines the cou- tainty in instream flow management pling between surface and groundwater. and restoration (Castleberry and oth- An important attribute of this model is ers, 1996; see Richter and others, 1997). that it can be coupled to a Digital Ele- Two complementary approaches to vation Model to produce a map of the assessing instream habitat are discussed. riparian zone. The first is an assessment of the rela- One way to test this model is to sample tionships between instream microhabi- groundwater depth in the sites selected tat and streamflow and the second is an for vegetative sampling/ground-truthing assessment of habitat heterogeneity and and couple it with surface water data to streamflow.

Texas Water Development Board Report 369 73 7.3.1 unbiased data, several questions must Quantity and Quality of Instream be considered: Microhabitat One focus of the biological study ele- 1. At what flows should data be col ment is to assess the quantity and qual- lected? Data should be collected ity of instream microhabitats used by over a range of streamflows so that lotic organisms and relate that utiliza- the full complement of potential tion to streamflow. Several steps are habitats are available and thereby involved in this assessment: provide choice of biota. Sampling over a range of flows may also • Sample assemblages and measure minimize the influence of food habitat conditions availability, competition, and pre • Calculate habitat suitability criteria dation on habitat selection (Power, • Integrate criteria with simulations 1984; Orth, 1987). of instream habitat over a range of 2. When should data be collected? flows Habitat use can vary with life stage, • Develop habitat time series season, and life-history events, such as spawning or migration, and diurnally (nighttime versus daytime; Sample assemblages and Johnson and Covich, 2000). Shift in measure habitat conditions habitat use can be accounted for by incorporating temporal aspects Sampling should be conducted in a into study design, such as seasonal quantitative manner to relate species and diurnal sampling protocols. presence and density to microhabitat 3. Which taxa will be sampled in each conditions. To develop accurate and study? Taxa will be determined

Unsaturated Zone Flooded Zone

Transitional Water Table Distance Probability of inundation of Probability

0 Aquatic Riparian Terrestrial

Elevation Figure 7-1. Hydrological representation of the riparian zone as a sum of transitional gradients (modified from Tabacchi, 2005).

74 Texas Water Development Board Report 369 during the study design phase and exception of boat electrofishing, these will be based on literature review techniques are limited to relatively shal- and empirical information collected low habitats (about 1 meter or 3.3 feet during initial sampling. deep); high current velocities may also 4. What variables will be measured preclude sampling in some locations. to describe habitat conditions? Collecting habitat use data of macro- Most habitat-based instream flow invertebrates attempts to be more quan- studies focus on current velocity, titative than initial invertebrate surveys depth, substrate, and instream and may, therefore, require equal-area cover (Bovee and others, 1998). benthic samplers. These quantitative Other variables may need to be samplers can only be effectively deployed addressed depending on taxa. in wadable areas of rivers and streams. For example, near-bed hydraulics Gore and others (2001) recommends (shear stress) has been used to collecting between 25 and 50 random relate macroinvertebrate and samples along transects located in riffles mussel distributions and, in some since these are key habitats likely to be cases, densities to microhabitat most affected by reduced flows. Direct conditions (Gore and others, 2001; visual observations may work well for Hardison and Layzer, 2001). some taxa (such as mussels) in some rivers. In addition, standard hemispheres Many approaches for collecting (Statzner and Müller, 1989; Hardison and quantitative data on microhabitat uti- Layzer, 2001) can be used to estimate lization have been developed and used shear stress on stream bottoms and can in instream flow assessments. However, be used as surrogates for invertebrates, given the diversity in characteristics thus avoiding long sample processing among rivers, one approach will not times and identification issues associated be suitable for all systems studied, and with macroinvertebrate habitat utiliza- appropriate collecting techniques will tion studies. vary with habitat conditions and specific A primary assumption of habitat- taxa. In Texas, “bio-grids,” composed of based instream flow models is that flow- equal area (10 square meters or 33 square dependent species such as riverine fish feet) sampling cells formed with ropes tend to demonstrate preferences for and taut lines, have been used to develop specific habitat conditions (Annear and suitability criteria for fishes in the Colo- others, 2004). For example, many darter rado River (Mosier and Ray, 1992) and species prefer high velocity, shallow hab- for aquatic macrophytes in the San Mar- itats over clean cobble and gravel sub- cos River (Saunders and others, 2001). strates. In addition, instream cover may Within each cell, biota are sampled and provide shelter from current or preda- habitat characterized. Bio-grids are used tors and exists in many forms, including for sampling in shallow habitats (such undercut banks, macrophytes, boulders, as riffles, runs); however, they can be and large and small woody debris. Some modified to facilitate boat electrofishing species may directly associate with par- by converting cells into sampling lanes. ticular instream structures during dif- Stratified random sampling designs have ferent life stages or life-history events. been used across the country from trout Large woody debris provides sites for streams in the west to species-rich riv- macroinvertebrate colonization and may ers in the southeast. Many fish sampling be relatively abundant in some streams. tools are at the disposal of biologists, To locate and characterize microhabitat including backpack and boat-mounted conditions within each biological sample electrofishers, prepositioned area elec- unit, the following measurements will trofishers, and various seines. With the be made:

Texas Water Development Board Report 369 75 • Mean column velocity, using a wading Calculate habitat suitability criteria rod and current velocity meter • Water depth, using a wading rod Many approaches have been used to • Substrate composition, using a calculate habitat suitability criteria of modified Wentworth scale (Bunte fish (Bovee, 1986; Vadas and Orth, 2001) and Abt, 2001) and macroinvertebrates (see Gore and • Embeddedness, a measure of the others, 2001). Utilization criteria are degree that interstitial spaces sur- calculated based on relative propor- rounding substrate (large gravel tions of habitat used by target species or and cobble) are occupied by smaller guilds, and preference criteria account substrates like silt and sand for the availability of habitat conditions. • Instream cover, such as woody The concept of nonparametric toler- debris, macrophytes, velocity shelters ance limits has been applied to develop- formed by objects and substrates, and ing suitability criteria for instream flow undercut banks studies (Bovee, 1986; Mosier and Ray, • Mesohabitat type (see Section 7.2.1), 1992). These tolerance limits delineate • Other hydraulic variables (such as a range of habitat conditions used by a shear stress) as required by study proportion of the sampled population. design Binary criteria indicate an on-off switch • Location information, using position and dictate that habitat conditions are averaging GPS units. either completely suitable or not, and univariate criteria (weighted) represent An attempt will be made to sample a range of suitabilities given different homogeneous patches of microhabitat, habitat conditions in one environmen- but in some sample units it may be nec- tal variable. Hydraulic criteria, such as essary to average multiple measurements the Froude number and shear stress, to characterize microhabitat conditions may be useful (Jowett, 1993). accurately. Recent instream flow evaluations of In some cases, it may be necessary complex and species-rich communi- to identify target species that have key ties have used habitat guilds or species habitat requirements (such as a shallow with similar habitat utilization patterns habitat for spawning) and critical time to simplify assessments (Leonard and periods (for example, limited spawning Orth, 1988; Aadland, 1993; Mosier and season). Species that use key habitats may Ray, 1992). Balancing instream flow be most important because these habi- requirements for a large number of target tats are substantially affected by reduced species simultaneously is problematic. streamflows. For example, many darter Guilding provides a means to reduce the species in Texas solely use riffle habitats, number of response curves involved in which, as flows decline, become exposed integration but also reflects an assem- or unsuitable (insufficient depth or cur- blage-based approach to addressing rent velocity) for occupation. Further, instream flow requirements, thereby darter species have specific critical time avoiding stochastic factors (biotic and periods for spawning, which generally abiotic) that influence individual spe- occur during the spring months when cies (Vadas and Orth, 2000). Perhaps streamflow conditions are higher. Thus, most important, mesohabitats can be obtaining information on microhabitat- defined using biological criteria derived utilization data on riffle-dwelling species from habitat guilds (Leonard and Orth, may be most important in some river 1988; Aadland, 1993; Bain and Knight, segments. 1996; Vadas and Orth, 2000). Statistical

76 Texas Water Development Board Report 369 approaches to define guilds include clus- Develop habitat time series tering (Aadland, 1993) and multivariate (Vadas and Orth, 2000) methods, many Habitat time series will be produced of which are readily available in statistical using habitat-discharge relationships software packages (such as SAS). How- and hydrologic time series (Bovee and ever, the approach used to derive criteria others, 1998). A necessary compo- for habitat guilds may vary by basin or nent of this analysis is hydrologic time sub-basin study area; it is also possible series at temporal scales (such as daily that habitat guilds can be transferred and monthly) appropriate for the taxa from one study area (or basin) to anoth- of interest. Hydrologic time series (see er (NRC, 2005), but statistical methods Chapter 6) can be derived for natu- would need to be found or developed ral conditions, historical conditions, to test transferability (see Freeman and and proposed conditions after project others 1999 for a discussion of transfer- implementation. Habitat time series ability of suitability criteria). Peterson are useful for evaluating potential and Rabeni (1995) advocate use of fish impacts to habitat conditions through guilds for stream fish community studies time, resulting from hydrologic altera- and also indicate the use of guilds would tion. Time series provide a method to increase the cost efficiency of a study. link temporal aspects of life history and It would reduce sampling efforts while ecology with alterations to flow regimes obtaining a reasonable level of precision. (Stalnaker and others, 1996). The tim- Further, it may also be necessary to gen- ing, duration, and amount of habitat can erate habitat suitability criteria for indi- provide insight into potential habitat vidual target species, particularly those bottlenecks (Bovee and others, 1994). with specialized habitat requirements (such as fluvial habitat specialists) or 7.3.2 specific environmental requirements at Habitat Heterogeneity critical times. Imperiled species may also A complementary assessment will relate receive separate attention. For example, habitat heterogeneity with streamflow. Mosier and Ray (1992) recommended Riverine habitat heterogeneity (or diver- flow regimes in the Colorado River but sity or complexity) plays a strong role in also included provisions for increased supporting diversity in aquatic assem- flows to facilitate spawning conditions blages (Gorman and Karr, 1978; Schloss- for the Cycleptus elongates, blue sucker. er, 1982; Poff and Ward, 1990; Reeves and others, 1993; Bunn and Arthington, Integrate habitat suitability criteria 2002; Robinson and others, 2002). The with simulations of instream habitat relationship of diverse assemblages to over a range of flows diverse habitat is generally accepted (see Ward and Tockner, 2001), but other Habitat-discharge relationships will be factors such as predation, competition, developed by integrating habitat suit- and disturbance regimes may confound ability criteria for target species and assemblage-habitat relationships (Poff guilds with models of instream habitat and Ward, 1990; Robinson and others, simulated over a range of flows. These 2002). Lotic ecologists are integrating relationships will provide information the themes of landscape ecology into to identify subsistence and base flows riverine ecology (Fausch and others, needed to support assemblages and key 2002; Ward and others, 2002; Wiens, species. This study component is dis- 2002), and this may have important cussed in detail in Section 10.2.1. implications in assessing instream flow requirements.

Texas Water Development Board Report 369 77 Spatially explicit habitat models others, 1998; Freeman and others, 2001) derived from GIS systems and two- or benthic communities (Pardo and dimensional hydrodynamic models will Armitage, 1997). The National Research yield the types of information regularly Council (2005) recommended exploring used in landscape ecology to evaluate the use of habitat guilds to develop objec- spatial heterogeneity. Techniques of tive criteria for designating mesohabi- landscape ecology have been applied tats. Using biological criteria to classify successfully to the study of riverine habi- mesohabitats is intuitively a biologically tat (Bovee, 1996; Hardy, 1998; Gergel and sound approach since it is tied to the others, 2002). Software such as Frag- use of mesohabitats by lotic organisms. stats enables analysis of spatial patterns However, the specific approach used in and characteristics, such as patch size each basin study will depend on the habi- (of habitat types), number and density, tat characteristics of the river basin and diversity and dominance of patch types, biological communities. The second step and shape of patches and their edges is to model how mesohabitat changes (McGarigal and Marks, 1995; Johnson with streamflow, using a spatially explicit and Gage, 1997). habitat model (see Chapter 10). The third An assessment of how habitat het- step is to characterize the resultant habi- erogeneity changes with respect to tat mosaic at each flow level, using land- streamflow will be conducted. The first scape metrics (patch size and diversity). step is to classify instream habitat at an Bowen and others (2003) conducted intermediate scale. Jowett (1993) used a spatial analysis of area, number, and Froude numbers to distinguish pools and density of shallow water patches in the riffles. Vadas and Orth (1998) developed Yellowstone and Missouri rivers to assess hydraulic criteria to classify mesohabitat the effects of flow regulation. Combin- types (riffles, runs, and pools) in warm- ing these relationships with hydrologic water streams (less than 50 meters or 165 time series can then produce time series feet wide). These criteria may be trans- of various metrics that describe habitat ferred to other streams but could require heterogeneity. The result of the assess- modification if used in larger rivers and ment is specific relationships between streams in Texas. A second approach flow and habitat heterogeneity through classifies mesohabitats (shallow, margin time, which can be used in a comple- habitat) based on biological criteria using mentary assessment of instream habitat- fish (Bain and Knight, 1996; Bowen and discharge functions.

78 Texas Water Development Board Report 369 8 Physical Processes

treams and rivers transport not only formed into a smaller, confined water but also sediment. Water car- rectangular channel now unable riesS silt, sand, gravel and other material to meander. Floodplains were from where it is eroded in the water- abandoned. Cumulatively, this shed to where it is deposited in the flume-like morphology and flood- river channel, floodplain, or terminal plain isolation greatly reduced delta. Sediment transport and deposi- habitat quantity and complexity tion processes directly link a river to its important to numerous aquatic watershed and riparian areas and sculpt and riparian species. Salmon the physical features of the channel and populations were immediately floodplain. In combination with the and significantly affected. hydrologic flow regime, these physical features form the habitats to which all In the Texas Instream Flow Program, biological elements in the river ecosys- the importance placed on physical pro- tem have adapted and become depen- cesses will vary for each instream flow dent. As a result, physical processes, component. Subsistence flows generally which vary over a wide range of spatial have little effect on the physical features and temporal scales, play an important of a river system. The effects of base flows role in developing and maintaining a are limited to working on the condition sound ecological environment for river of the bed forms. However, during stud- systems. ies to develop base flow requirements, If physical processes are ignored or an assessment of channel bed forms and poorly understood when setting instream banks will assist biologists in identifying flows, the long-term health of the river important physical habitats. Investigat- system cannot be maintained. In order ing these habitats will highlight desired for instream flow recommendations to conditions, such as sediment composi- be effective, the desired physical features tion of transverse channel bars and depth of a river must be maintained. For most of scour pools. Appropriate high flow river systems, base flows are not suf- pulses and overbank flows required to ficient to maintain these features. An maintain these conditions can then be appropriate sediment regime and higher developed. flow components are also required. Man- High flow pulses play an important agement of the Trinity River in north- part in developing and maintaining in- ern California illustrates this point. As channel habitats. The ability of modest, described by Trush and others (2000), but more frequent, high flow events to managers selected instream flows down- move more sediment over time than larg- stream of Lewiston Dam to provide “ideal er, infrequent events is well documented hydraulic conditions” for salmon habitat. (Wolman and Miller, 1960) for humid Unfortunately, providing “ideal” base climates. In arid or semihumid climates, flows without considering sediment and channel maintenance depends more other flow regime components required on larger, infrequent events (Wolman to maintain physical habitats had unin- and Gerson, 1978; Huckleberry, 1994). tended consequences. Trush and others Although smaller in magnitude than (2000) describe the effects: overbank flows, high flow pulses occur more frequently and, therefore, play a The river’s complex alternate bar more active role in sculpting in-channel morphology was quickly trans- habitats. Geomorphic studies will assess

Texas Water Development Board Report 369 79 the active channel processes responsible phic data for Texas’ rivers is problematic. for developing physical habitats. These Studies can describe current conditions processes may include pool scouring and by collecting data related to processes on sediment sorting, in addition to creating each river. However, without previously specific bed forms or specialized chan- collected data, past conditions cannot be nel habitats such as undercut banks. The understood and predictions of the future Agencies will develop sediment budgets response of a river are less accurate. To describing the sources and deposition correct this situation, a monitoring pro- of sediment in the river system. These gram that collects geomorphic data for budgets are used to identify sediment major rivers will be required. limitations or excesses that may affect the ability to achieve desired outcomes. The 8.1 ability of current and alternative sedi- Physical Processes of Rivers ment and hydrologic regimes to adjust Sediment transport processes begin channel features can then be assessed. with the erosion of soil, rock, and Recommendations for high flow pulses organic material in the watershed. This will take into consideration seasonality, material is then transported by surface magnitude, frequency, duration, and rate runoff to a stream channel. Total sedi- of increase and decrease. ment load in the channel consists of Overbank flows provide critical func- mineral and organic matter that is sus- tions in support of river ecosystems. pended, float load that is fine sediment These include developing and maintain- and buoyant organic material, and bed ing floodplain habitats, providing nutri- load composed of coarse material mov- ents and sediments to riparian areas, ing along the channel bottom. The rate transporting organic debris to the chan- of sediment transport through the sys- nel, and preventing channel constriction tem depends on the sediment supply due to encroaching vegetation. Geomor- and the river’s ability to transport that phic field studies will determine active supply. The quantity and type of sedi- floodplain areas and assess active flood- ment material determines river channel plain and channel processes. Hydraulic stability, slope, and geomorphic fea- modeling of the extent of inundation tures, such as the presence of sand or (described in Section 6.2) and results gravel beds. of riparian area surveys (described in Because sediment movement is Section 7.2.4) may assist in develop- the process that creates and maintains ing appropriate overbank flow recom- important physical habitats, it is crucial mendations. Geomorphic assessment to the ecological health of a river. For of overbank flow and high flow pulse example, riffles in alluvial rivers may pro- behavior will also analyze bank stability. vide necessary spawning areas for fish. If The duration and magnitude of flows will proper timing, pattern, and velocity of be adjusted in order to reduce adverse flow are not maintained, algal growth impacts to channel banks. and accumulation of fine mineral mate- Two factors make incorporating an rial may occur in riffle areas. This result, understanding of physical processes into in turn, may impair the reproductive suc- the instream flow studies difficult. First, cess of biota by impeding the movement Texas’ rivers experience a large range of of oxygen through the substrate. climatic and geologic conditions and, The physical laws that govern sedi- therefore, the function and behavior of ment transport in streams and rivers can their physical processes vary greatly. As be expressed by the following formula a result, geomorphic studies need to be (Lane, 1955): tailored to the specific sub-basin being investigated. Second, the lack of geomor- QS×D50 = a×Q×S

80 Texas Water Development Board Report 369 This equation relates bed load dis- The energy/sediment signature of a charge (QS) to stream discharge (Q) in river can be seen on the landscape of terms of the median particle size of bed its fluvial valley. The active floodplain material (D50), channel slope (S), and is a river system’s major landscape fea- a proportionality constant (a). Stream ture and is maintained by the present- power, a term often used to discuss the day discharge and sediment transport transport capacity of a stream or river, mechanisms, which are driven by the is defined as the discharge times the present-day climate. After a large distur- channel slope times the specific weight bance such as a major flood, it may take of water and is proportional to the right several years for a floodplain to regain hand side of Lane’s equation. If the dis- a shape and form similar to its original charge in a river is changed, the stream landscape. Lateral migration of the chan- power is also changed. Lane’s equation nel can account for much of the depos- demonstrates that such a change would ited sediments in a floodplain. Vertical be accompanied by a change in the sedi- accretion and the attachment of river ment discharge or the particle size pat- islands to one bank or the other may also tern or some combination of these two help to build the floodplain. variables. River characteristics and behavior As predicted by Lane’s equation, riv- vary across Texas based on several fac- ers do adjust to the relative inputs of sed- tors. These include bed material, flashi- iment and water. The river’s planform, ness, flood dominance, climate/geologic bed slope, flow depth, flow velocity, and region, and groundwater/surface water shear stress respond to changes in input interactions. Difference in bed material rates of water and sediment and the grain is responsible for much of the variation size of sediment supplies. For example, in characteristics and behavior observed if there is an increase in sediment load from one river basin to another. Knighton while the flow rate remains constant, the (1984) provides a simple classification of channel bed aggrades in a location near rivers based on bed types (Table 8-1). the sediment input point. Conversely, if Brussock, Brown, and Dixon (1985) discharge (and thereby transport capac- found that in Texas, riverbed type varied ity) increases without an increase in sedi- along the length of rivers, from upstream ment load, channel widening or scour- to downstream location. They classified ing may occur in order to decrease the regions in Texas as midcontinental, east- channel slope. ern Coastal, or ephemeral and character-

Table 8-1. Classification of riverbed types. Class Type Character Sand Composed largely of sand-sized material (this size is Non- transported over a large range of discharges and called cohesive “mobile” or “live” bed) Gravel Composed of gravel or small cobble material transported at high discharges Boulder Composed of large cobbles and boulders that are moved by infrequent large flows Silt/Clay Composed mainly of silt and clay with degree of cohesiveness Cohesive related to the amount of clay Bedrock Composed of no unconsolidated material Source: Adapted from Knighton (1984)

Texas Water Development Board Report 369 81 ized the beds of rivers for each region. from channels, channelization, stream- The midcontinental region has rivers bank armoring, water withdrawals, and that are gravel bedded in their extreme construction of trails, roads, dams, and upstream areas, slowly change to sand levees. Table 8-3 lists possible changes in bedded in their middle reaches, and start channel characteristics due to changes in out with sand beds and change to gravel flow and sediment discharge associated beds in the lower reaches. Eastern coastal with some of these activities. region rivers have a sand bed throughout Damming rivers can have significant their lengths. The ephemeral region is effects on natural geomorphic processes. generally the areas of West Texas, the Petts (1979) found there were generally High Plains, Rolling Red plains, Edwards two major changes that occur down- plateau, and part of the Rio Grande plain. stream of dams. One was a reduction of Rivers and streams in this region are peak flows by amounts ranging from 25 similar to those in the midcontinental to 75 percent. The other was a marked region, but small- and mid-sized streams decrease in sediment discharge, especial- are dry most of the year. ly for those reaches immediately down- The beds of rivers are typically per- stream of a dam. Both of these changes meable to water, which can flow into or affect the pattern of erosion and deposi- out of the streambed and banks depend- tion and consequently cause alterations ing on local conditions. Water accumu- in stream channel characteristics. These lation or depletion can be determined changes and their associated alterations by measuring the river discharge and in stream channel characteristics are groundwater level from wells near the shown in the two, far-right-hand col- channel. These interactions are impor- umns of Table 8-3. tant to the channel and indirectly influ- The impact of a dam on a river’s sedi- ence the active processes of the channel. ment discharge regime is directly related Because of the increasing use of ground- to the reservoir’s sediment-trapping effi- water in some regions, there is a need for ciency. As shown in the following for- better understanding of river/groundwa- mula, sediment-trapping efficiency can ter exchanges in parts of the state. be estimated from the reservoir capacity to inflow ratio (Brune, 1953; Verstraeten 8.2 and Poesen, 2000). Human Impacts on Physical log C/I Processes of Rivers E = 100(0.970.19 ) All human activities that affect sediment loading or discharge have the potential In the equation, E is the sediment- to impact the physical process of a river trapping efficiency in percent; C is the segment in variable and complex ways total reservoir capacity in units of vol- (Williams and Wolman, 1984; Collier ume, and I is the mean annual inflow in and others, 1996; Friedman and others, the same units of volume as the reservoir 1998; Graf, 1999; Brandt, 2000; Graf, capacity. The sediment-trapping effi- 2001; Wohl, 2004). River segments can ciency of reservoirs can be as high as 99 be classified according to the impact of percent (Williams and Wolman, 1984). human activities on their geomorphic As a result, the physical processes of riv- processes (Table 8-2). ers downstream of dams can be greatly The Federal Interagency Stream Res- impacted by the loss of trapped sedi- toration Working Group (1998) provides ment. Effects will extend downstream a list of human activities that may affect of the dam until the missing sediment is watershed processes, including land use resupplied by the tributaries, banks, or changes, overgrazing, clearing of ripar- channel of the river. ian vegetation, removal of woody debris The only fail-safe way to determine

82 Texas Water Development Board Report 369 100 artificial Completely Completely by design engineered completely in sediment determined North & South Sulphur rivers Sulphur Completely Completely Channel Altered or changes 90 to100 artificial Essentially sediment channel in sediment Largely artificial Houston Bray’s Bayou, Bray’s Altered patterns or Altered patterns Altered or changes S - - Mostly + 50 to 90 50 to -,+ modified + or - + or - + or - Q, Q Q, sediment sediment modification of flow and in sediment Major Major Guadalupe River (IH-35 to IH-10)(IH-35 to Altered patterns or Altered patterns Altered or changes S - + + +,- + or - + or - + or - Q, Q Q, S - - - + 10 to 50 10 to -,- modified + or - + or - Q, Q Q, Substantially sediment sediment modification of flow and in sediment Major Major Upper Upper Guadalupe River Altered patterns or Altered patterns Altered or changes S - + + + +,+ + or - + or - Q, Q Q, <10 S ------+ Q sediment sediment modification of flow and Partially modified in sediment Obvious Altered patterns or Altered patterns Altered or changes S Change in transport variable - - + + + + + Q Potential alteration in channel characteristicsPotential <10 natural - - - - - + Q Essentially sediment modification of flow and human activitieshuman in sediment No evidence of Minor Altered or changes - + + + + + Q 0 natural Completely Completely human activitieshuman humans undisturbed No evidence of Same as before Completely Completely Geomorphic “naturalness” classification of river segments. of classification river “naturalness” Geomorphic in channel characteristicschanges transport due to alterations variables. Potential type Adapted from Graf (1999) Adapted from (1979) Petts Channel % Change + and - indicate an increase+ and - indicate or decrease, in a variable respectively, or characteristic. or 0 indicatesvariable no change in the or characteristic. cell An empty Sinuosity Depth Meander wavelength Bank full area Change gradient Channel Transport variable Transport Width ratio Width-to-depth materials landform cross section, Example Pattern, Description Minor Notes: Q isstream the discharge and QSbed-load the discharge for a river. Source: Source:

Table 8-2. Table 8-3. Table

Texas Water Development Board Report 369 83 the effects of a dam or other human dis- • Preliminary estimates of sediment turbance is to observe the river channel yields and the impact of man’s over time and evaluate changes in chan- activities on those yields nel characteristics. Examples of these • Influence of large floods and types of studies in Texas include studies climatic change of the Trinity River’s Livingston Dam • Appraisal and design of project (Phillips and Mussleman, 2003; Phillips, impacts and enhancement measures Slattery, and Mussleman, 2004) and the Sabine River’s Toledo Bend Dam (Phil- 8.3 lips, 2003). Geomorphic Assessment The potential effects of human- A geomorphic assessment of a river induced disturbances on the geomorphic channel provides knowledge about the processes of rivers can be estimated by causes and effects of hydrologic or sedi- observing control and response variables. ment regime changes over time (Rosgen, Control variables are large-scale envi- 2001). The assessment should include ronmental factors that control patterns historic records, maps, aerial photo- found in local features. These variables graphs, Digital Orthographic Quarter can be measured from maps or other Quadrangles, streamgage records, and data and include geology, soils, land use, other data sources that illustrate chang- hydrology, planform channel features, es the river has undergone. For example, and valley characteristics. Response vari- an inspection of historical aerial photo- ables are environmental features of the graphs can indicate changes in meander river channel on a more local or site- wavelengths and transverse migration of specific scale. Measurements of these the channel. To provide a picture of cur- variables are collected in the field at a rent conditions on the river, the assess- specific location. Examples of response ment should also include collection of variables include channel shape, cross- on-site data. By investigating signs left sectional dimensions, substrate, bank on the landscape, on-site data collection shape, floodplain characteristics, veg- may also provide a picture of past river etation, and channel patterns. conditions and human activities near A complete geomorphic assessment the site. Finally, the assessment should is required to adequately understand the estimate if the channel area is stable or effects of human impacts on the physical unstable and how long it will remain in processes of a river. This assessment can, this state. In combination with other in turn, be used to better manage the studies, a geomorphic assessment will river system. The following aspects of lead to a better understanding of human geomorphic analysis are of direct interest impacts on the river system. to managing river systems: An important outcome of a geomorphic assessment is an understand- • Qualitative field methods to ing of the river system’s stability. Rivers identify the stability of the system are highly dynamic and responsive to • Quantitative studies to trace and changes in their controlling variables. survey sediment sources Their sediment transport rates are relat- • Analysis of river channel and plan ed to their sediment supplies. Continued form plus prediction of future removal of sediment from the system will changes cause the river to find a replacement sup- • Studies of channel processes (bank ply. Geomorphic stability occurs when a erosion, sediment transport, and river segment adjusts to a change in the morphological form processes) sediment or water load without under- going net erosion or deposition. Con- versely, when the response of the river to

84 Texas Water Development Board Report 369 a change includes significant erosion or channel width increased by 5.5 meters deposition, the segment is considered to or 18 feet (Bradley and Smith, 1984). be unstable. Note that stability is based A channel avulsion (a major change in on net erosion or deposition within a channel direction, location, or form) is a river segment, and the natural process common response when a geomorphic of transverse channel migration does not threshold has been passed and the river indicate an unstable river. system has become unstable. Because geomorphic definitions of stability depend on bed material and 8.3.2 sediment loading rate, not all changes in Assessment of Current river characteristics are signs of system Channel Conditions instability or disturbance. For example, A geomorphic assessment can be used a decrease in the sediment transport to identify current or potential probability of anabranching rivers (which lems within a river system. The analysis have multiple, active channels and low is based on measurements of physical migration rates) is considered natural features of the river system, including and not a sign of instability (Nanson and planform characteristics, cross-section- Knighton, 1996). In addition, a portion of al and longitudinal features, and bank a river system may be unstable as part of and bed materials. its natural behavior. For example, sand- bedded rivers have a bed that is moving Planform measurements most of the time. In parts of Texas dominated by flash floods, various portions of Planform characteristics of the river a river system can be naturally unstable should be measured using aerial photo- (Baker, 1977; Beard, 1975). graphs. A comparison of measurements taken from historical and current aerial 8.3.1 photos can be used to analyze changes Geomorphic Thresholds in the river. These are examples of char- A geomorphic threshold is an ener- acteristics that can be measured and gy or mass-transfer level that, when compared: surpassed, causes the river system to seek out a new state of equilibrium. If • Meander belt width—the distance a geomorphic threshold is not exceed- between lines drawn tangential to ed, minor disturbances in discharge the extreme limits of fully developed or sediment regime will cause only meanders minor, short-term disturbances to a • Sinuosity—the stream length divided river’s geomorphic behavior. But when by the valley length a geomorphic threshold is surpassed, • Meander wavelength—the down even minor disturbances to hydrologic valley distance between two cor- or sediment regimes can cause signifi- responding points of successive cant changes in river characteristics. meanders of the same phase After crossing a threshold, the system will remain unstable until adjustments Cross-sectional measurements are made and a new and different stable state is established. During an unstable Cross-sectional data are collected in the period, river behavior can change dra- field. This data should include at least matically from predisturbance condi- the following points from both sides of tions. For example, water diversion to the channel: floodplain elevation, top the Milk River of Montana caused the and toe of bank, bankfull width and meander migration rate to increase to depth, lower limit of vegetation, and 0.85 meters (2.8 feet) per year, and the water surface. These and other cross-

Texas Water Development Board Report 369 85 section parameters are recorded from ered a good estimate of channel slope. the viewpoint of looking downstream, If a straight line is not obtained, addi- with the right and left bank defined by tional riffle locations in the upstream or this orientation. These are examples of downstream direction are measured. measurements made from cross-sec- A longitudinal thalweg profile of a tional data: river is an important measurement and is helpful for both hydraulic studies and • Base flow width—the average flow the identification of bed forms (Madej, width during base flow conditions. 1999). Topographic maps do not produce Base flow is the normal level of the good quality profiles since they show the flow when the river is not responding water surface and not the bed character- to a storm istics. Therefore, channel profiles must • Base flow depth—the mean depth be developed from survey points col- during base flow conditions lected from the thalweg at various loca- • Base flow wetted perimeter—the tions along the length of the river. wetted perimeter as measured during There are different methods for base flow conditions evaluating channel bed form depending • Bank height—the distance from the on the riverbed material. Bed form con- top of the bank to the bottom of the figurations for sand-bedded streams are bank defined by the forms created in the bed. • Bank slope angle—the angle of the These include ripples, dunes, antidunes, bank made between the lines drawn and flat beds. These features are formed from the top of the bank to the bottom by different shear stresses acting on the and one across the channel bed cohesionless bed. Ripples form where • Rooting depth—the depth from the shear stress is low and the bed mate- top of the bank to subsurface level rial is fine. Dunes form at intermediate where roots stop their domination. stresses and have a geometry related to There can be two measurements for the depth of water flow. Antidunes are this depth, one for grass or under- low amplitude waves that are in phase story vegetation and one for tree root with the surface water waves. Although masses these bed forms are common in sand- bedded rivers, the mechanisms that cause their formation in streams are Longitudinal feature measurements poorly understood. Bed form configurations in gravel- Since the elevation of the channel bed bedded rivers are defined by across- varies both laterally and longitudinal- channel features, such as pools and rif- ly, channel slope measurements must fles. At base flow levels, pools generally be taken carefully. Because the depth have a slower velocity with deeper water of pools varies along the channel, the depth, and riffles have shallower depth most accurate way to measure slope and faster velocity. Scour pools are found is to locate survey points at the top of around logs and other woody debris or riffles or ripples and obtain the distance large boulders. When one of these objects between them. Locations on adjacent is moved or repositioned, the configura- riffles are not suitable. Instead, riffles tion of the associated scour pool will also that are separated by at least one addi- change. Examples of bed form measure- tional riffle should be measured. Gen- ments that can be taken for a gravel bed erally, the crests of at least three riffles stream include the following: are measured. If a relatively straight line is found when the three points are • Riffle length—the distance between plotted, the slope of the line is consid- the top and bottom of the riffle

86 Texas Water Development Board Report 369 • Riffle gradient—the change in and occur in valleys or on broad plains, elevation of the channel bed from the and gravel- and cobble-bedded streams top to the bottom of the riffle divided have steeper gradients and are found in by the riffle length environments with more relief. In Texas, • Inter-pool length—the longitudinal sand-bedded streams occur in the marine distance between the deepest points deposited sediments of the Coastal Plains of successive pools, measured along or in areas with granite uplifts. Gravel- the centerline of the channel and cobble-bedded streams occur in and • Inter-pool gradient—the change in around the Edwards Plateau and similar elevation of the channel bed between locations where larger sediment material deepest points of successive pools is produced. divided by the length of the inter- pool distance 8.4 Sediment Budgets When rocks are weathered, they pro- Bed and bank material analysis duce sediment particles that are moved to the stream channel by runoff. Once The materials making up the bed and in the channel, this sediment is trans- banks of a stream are an important part ported to the ocean through a long- of the channel system. They influence term cycle of local erosional and deposi- the morphological form of the channel, tional actions that reduce the size of the erosion and deposition rates, hydrau- original hill slope-produced particles as lics, and other stream functions. Due they move downstream. Sediment par- to the complex interactions of erosion, ticles can be deposited along the way deposition, and transport, there will be in alluvial channel-margin deposits, on a heterogeneous mix of materials in any the floodplain, or in the channel itself. river. However, the mean particle size These deposited materials can be re- is generally thought to be the control- entrained by the river from the channel, ling influence on physical processes. banks, or floodplain. Boulder-bedded streams contain bed A sediment budget is an evaluation material with diameters greater than of sediment particle movement and can 256 millimeters (10.1 inches). Cobble- be conducted from two viewpoints: what bedded streams contain bed material is moving (transport process) or where with mean diameters between 64 to 256 the sediment is located in the watershed millimeters (2.5 to 10.1 inches). Gravel- (sediment deposition). Both viewpoints bedded streams have material between are valuable when analyzing the health of 2 to 64 millimeters (0.08 to 2.5 inches) an aquatic system. The transport-process in mean diameter, and sand-bedded viewpoint focuses on how particles are streams contain bed material composed moved between locations. The method of sediment with diameters less than 2 of transport can be as suspended load millimeters (0.08 inch). A sieve analysis, (fine-grained particles that travel in the as described by Bunte and Abt (2001), water column) or as bed load (coarse- is completed in order to determine the grained material that travels along the size of bed material. channel bed). The sediment-deposition Gravel- and cobble-bedded streams viewpoint is not only interested in what differ from sand- and boulder-bedded is moving, but also what is temporarily streams by more than just bed material being stored and where. size. They also have different stream A sediment budget explains the input, morphology and occur in different transport, storage, and export of sedi- topographic and geological locations. ment for a particular system. The sys- Sand-bedded streams have low gradients tem could be as large as the Mississippi

Texas Water Development Board Report 369 87 River system or as small as an individual habitat composition, riparian vegeta- landform, such as a hill slope. The sedi- tion, and other characteristics of a river ment budget characterizes the landform as it flows from its headwaters to the being studied by describing the expected ocean. As a result, geomorphic clas- changes or evaluating measured impacts sification of river segments, reaches, on the site (such as rates of erosion or and small portions of the channel is an deposition). System activity is explained important component of a river study. and the effects of different events (such Results can be used for documenting as flow events) on the landform are and analyzing physical river processes described. The final outcome is a pre- and selecting reaches for instream habi- diction of future system responses or a tat and water quality studies. comparison of the responses of similar There are many types of river clas- landforms under different conditions. sification schemes. Simple schemes can There are several methods for conduct- vary from a simple description of the ing sediment budget studies related to planform to classification based on data river systems. Examples include mod- from a cross section. More complex clas- els, analogy, inference, and data from sification systems evaluate geomorphic historical records or monitoring. Sedi- processes at many different scales, such ment budget studies also vary based on as physiographic province, watershed, the processes being investigated, sizes of valley, channel reach, or morphological material of interest, temporal and spa- unit (see Rosgen, 1996). The National tial scales, and available resources and Research Council (2005) suggested that data. For a more complete description a geomorphic classification scheme for of sediment budget studies, see Reid and water allocation studies should Dunne (1996). Sediment budget studies for the Texas Instream Flow Program will • be hierarchical in its structure; be tailored to the issues of interest in a • be physically based; particular sub-basin. • include the floodplain; An incipient motion study of bed • relate channel to physiographic and sediment mobility may be included with hydrologic setting; and a sediment budget analysis. Results of • contain channel morphology, such as such studies could be used to determine planform, slope, and bed morphology. flows required to provide preferred sediment characteristics in the channel or River system classification is evolving minimize bank erosion. Incipient motion from simple reach analysis to large geo- studies require an understanding of sedi- morphic database analysis with the use ment sizes present plus the transport of GIS. Geomorphic river classification energy available to move the material. schemes have been reviewed by Thorne Calculating incipient motion can be a (1997) and Montgomery and Buffing- very complex problem and there are sev- ton (1998). Kondolf and others (2003) eral methods from which to choose. For reviewed 21 classification schemes and studies in the Texas Instream Flow Pro- mentioned several newer schemes that gram, the choice to conduct an incipi- they did not evaluate, including Raven ent-motion study and the selection of and others (1998) and Brierley and Fryirs methodology will be decided on a reach- (2000). As comprehensive as their review by-reach basis. was, there are even more schemes available, including Rowntree and Wadeson 8.5 (1998) and Parrott and others (1989). Classifying a River Although there are many river classi- Physical processes explain most of the fication schemes to choose from, very few changes in channel structure, aquatic include all of the features recommended

88 Texas Water Development Board Report 369 by the National Research Council (2005). watershed, landscape unit, river style, For example, the first recommended fea- geomorphic unit, and hydraulic unit. ture for a scheme is a hierarchical nature. These categories have different spatial To set up that structure, large map units scales and are related hierarchically (Fig- of the classification scheme must inter- ure 8-1). The geomorphic variables relat- lock with constraints of the small-scale ed to a mapping unit are related to the map units. Of the schemes reviewed by evolutionary time during which changes Kondolf and others (2003), only two, in geomorphic conditions within that Bethemont and others (1996) and Fris- unit occurred. sell and others (1986), have a completely hierarchical nature. Lotspeich (1980) is Landscape characteristics nearly hierarchical, but does not work on the scale at which fishery data would be In an evaluation of landscape charac- collected. Bethemont and others (1996) teristics, River Styles divides these char- fail to evaluate physical features of the acteristics into control and response substrate, sediment load, and morpho- variables. The control variables include dynamic adjustments. Frissell and others geology, soils, land use, hydrology, and (1986) meet the first and second criteria valley characteristics. Response vari- of the National Research Council, but ables are environmental features of the their classification system was developed river channel generally collected from for small, mountain streams. field sites. Brierley and Fryirs (2005) have devel- Geology and climate are high-lev- oped a framework for conducting geo- el controls on the character of a river morphic analysis of river systems that has system. With the aid of a GIS system, the potential to incorporate all five of the these features can be overlaid at a state- features recommended by the National wide coverage scale. When the two are Research Council. An assessment algo- merged, a new map is created showing rithm, called River StylesTM, based on the different geologic and climatic areas. this framework is currently being used By overlaying a map of river systems, the for environmental studies in Australia. map units that the river touches or cross- es can be observed. Each of these areas 8.5.1 can be delineated as a different zone of River Styles Framework the river. The River Styles framework is a scaled The United States Soil Conserva- hierarchy in both time and space that tion Service (1982) provides a map of 20 organizes map units and information land resource areas within Texas, which about a river system into a structured may be further subdivided into smaller database. The framework was created Common Resource Areas (NRCS, 2006). in Australia and is used in that nation’s These areas are characterized by group- river health program. The scheme clas- ing soils, climate, water resources, and sifies the parts of a river system by land- land uses. Though these areas are gen- scape characteristics, river behavior, and erally characterized as one continuous potential changes. The latter includes unit usually comprising several thousand predicting expected future changes, acres, they can be segmented further. such as those due to human influence This map can be used to create zones or climate-driven effects. in the river system as the river flows The River Styles methodology works through or along the boundary of each with the natural diversity of river forms land resource area. and creates classes by an organized, Variability in hydrology and water- open-ended, and generic procedure. shed characteristics can also be used The main spatial map categories are the to differentiate river segments. As an

Texas Water Development Board Report 369 89 example, a plot can be made of river mile Brackettville. The physical features of versus watershed area. When a nonlinear rivers with a low index value are pre- jump occurs on this plot, the river-mile dominantly influenced by relatively location should be viewed as the bound- low-magnitude, frequently occurring ary of two different units. floods. The influence of less frequent, Flashiness (a river’s tendency to carry large-magnitude floods dominates when a high percentage of its flows in short the index values are high (Baker, 1977). duration, large-magnitude events that The Flash Flood Magnitude Index and occur infrequently) is an important fea- other statistics related to flow patterns ture of Texas rivers. The Flash Flood should be calculated to provide a way of Magnitude Index developed by Beard comparing Texas rivers. (1975) varies across the state from 0.14 Changes in valley characteristics, for the North Sulphur River near Cooper such as valley shape and width and chan- to 0.9 for the West Nueces River near nel location in the valley, can be used to

Watershed Watershed area determined by drainage divide. Determines the boundary conditions within which rivers operate.

Landscape Unit Topographic unit determined on Geomorphic Unit the basis of local relief, valley Instream and floodplain landforms slope, and morphology. Defines (pools, bars, levees, and the valley setting. backwaters) that reflect distinct form-process associations. Assemblages are used to interpret river character and behavior.

River Style Length of channel, which has a characteristic assemblage of geomorphic units. Identiﬁed on the basis of planform, channel Hydraulic Unit geometry, and textural controls. Uniform patches of ﬂow and substrate material within a geomorphic unit. Determines the availability of habitat. Various biophysical parameters are measured to ascertain the structure of each hydraulic unit.

Figure 8-1. Hierarchical relationship of River Styles mapping categories (from Brierley and Fryirs, 2005).

90 Texas Water Development Board Report 369 create classification units to further sub- have occurred since the late Quaternary divide a river channel system. Channel Period (last 2 million years), including features, such as channel slope, sinuosity, present and possible future changes. A and channel bed form, are used to further river’s response to changes in climate, classify channel reaches into large-scale vegetation, and river base levels over units. The major feature used in this clas- this extended period is related to the sification is sinuosity as measured from system’s thresholds. If the changes push aerial photographs or digital imagery. At a river beyond a threshold value, the a finer resolution, field measurements river will be actively seeking a new pat- such as bank and bed composition, veg- tern of behavior. If the changes do not etation associations, and cross-section exceed a threshold, the river may change characteristics, can also be used to iden- for a time but will gradually return to its tify geomorphic and hydraulic units. historical characteristics. Just as the channel is connected to the For a major portion of the time peri- floodplain, the river channel is connect- od of interest, changes have occurred ed longitudinally to itself. Control condi- exclusively due to the forces of nature. tions for physical processes change along These changes in river behavior can be the length of the river, which, in turn, traced to past geologic and climatic his- change the characteristics of the channel, tory. The earliest civilizations used water floodplain, and valley. A classification courses to fulfill their needs for trans- based on the River Styles approach seeks portation and water supply. As technol- to identify the location of these changes ogy and civilizations have developed, in controls and characteristics. humans have learned to further modify An example of the classification of river systems for their own use. Since a river into various river types along its European settlement of Texas, humans length is shown in Figure 8-2. Although have exerted a strong influence on river this river system is very simplified, the behavior. The following direct, human- figure does show how the River Styles induced changes have the greatest impact method classifies river segments based to Texas’ rivers: on significant geomorphic factors. • Dams have been used by humans to River behavior capture water for future use and power generation. They change river flow An important part of the River Styles and sediment supply downstream, framework is an analysis of the various impacting river processes and creating flow levels that maintain a river’s mor- changes to the river’s morphology. phometric characteristics and ability • Channelization is a way that humans to do work. Flow levels are primarily have engineered rivers to improve determined by climate (through rain- flood routing and facilitate shipping fall), geology (through erosive nature of and recreational boating. Such rocks and soil characteristics), vegeta- “improvements” have been known to tion, and human activities. Flows with a completely change the processes of significant impact on river geomorphic a river and eliminate natural process behavior are divided into three basic diversity. groupings: base flows, high flow pulses, • Sand and gravel removal from and overbank flows. the riverbed and banks can affect processes by depleting the supply Change analysis of sediment needed to dissipate the energy of the river. Generally, fluvial geomorphology is • Woody debris removal from the interested in changes in a river that channel, wetlands, and river corridor

Texas Water Development Board Report 369 91 affects flood processes and habitat for the river had a high meander migration wildlife along rivers. rate while the land use in the watershed was grazing, a change to a more urban Indirect, human-induced changes to area would increase bank erosion. The Texas’ rivers include these activities: river may have a constant rate of lateral movement across its floodplain, but this • Forest removal impacts the behavior rate may be invisible with short time of small watersheds, causing them to scale observations. By reviewing aerial produce more sediment and, in some photographs and tracing the river’s path instances, more runoff. The increased over long periods of time (50 years), the sediment may alter the composition process and rate of movement becomes of various parts of the river system, clear. The following changes can be iden- such as gravel bars. tified from historical data: • Urbanization affects the soil’s ability to absorb water, alters runoff timing, • Land use pattern and increases flood magnitude. • Channel planform values (sinuosity, • Mining in a watershed changes the width) pattern and timing of water running • Gradient and channel length off the land, exposes chemicals to • Bank erosion or protection this runoff, and changes the sediment supplied to the river. The river Unfortunately, geomorphic data are processes must adjust to these limited for most river segments in Texas. changes. Without these data, predicting a river’s response to water diversions or dams is What the river did in the past helps difficult although some inferences can explain what it will do in the future. If be made from historical aerial photo-

Imposed Boundary Conditions

Landscape Tablelands Escarpment Foothills Alluvial Plain Unit

Channel/Valley Relationship

Valley Setting Laterally Confined Partly Laterally Unconfined Confined Unconfined

Flux Boundary Conditions Accumu- Process Zone Source Transfer Accumulation lation Sediment Mixed Suspen - Bedload Mixed Suspen- Transport Load ded Load Load ded Load Regime

River Type Intact Gorge Partly-conﬁned, Low Mean- Valley Fill with bedrock Sinuosity, dering control sand bed

Figure 8-2. Example of longitudinal segmentation of a river system based on River Styles methodology (from Brierley and Fryirs, 2005).

92 Texas Water Development Board Report 369 graphs or other sources. The Agencies information, the Texas Instream Flow are exploring the potential of using his- Program can use the following principles torical measurement data at U.S. Geo- to guide interpretation of the system’s logical Survey gage locations to make response: some generalizations about channel aggradation/degradation rates. These • Evaluate the river’s variability and types of evaluations could improve the capacity for change in its valley understanding of historic river processes setting at specific locations. • Identify the balance between ero- When historical geomorphic data sional and depositional processes are not available, change analysis will be • Interpret the balance between input limited to observation of trends in the variables and resisting forces as time geomorphic processes measured under proceeds current conditions. This can be accom- • Identify threshold conditions that plished by sediment budget analysis and lead to change initiating a monitoring program that col- • Estimate how the river system may lects geomorphic process data. With this change with proposed flow regimes

Texas Water Development Board Report 369 93 9 Water Quality

ater quality issues are linked to 9.1 other disciplines discussed in Background thisW document. From the standpoint of Water quality is an integral compo- achieving a sound ecological environ- nent of aquatic ecosystems and must ment, water quality and quantity can- be addressed when evaluating the envi- not be separated. Water quality is rec- ronmental consequences of modifying ognized as an important component flow regimes. Sufficient instream flows of the Texas Instream Flow Program are needed to maintain the appropri- because water chemistry may influ- ate physical, chemical, and biological ence species composition, nutrient integrity of rivers and streams. The cycles, and sediment loadings, among native aquatic community of a stream other factors. At the same time, chan- has adapted to a range of flows and the nel morphology, flow, and the physi- resulting variations in water quality cal structure of the riparian zone can over time. However, significant chang- directly influence water chemistry. For es in both flow and water quality have example, channel-forming processes occurred in Texas rivers during the last affect instream habitat that can influ- 100 years in direct response to human ence stream reaeration, an important activities. Agricultural, municipal, and determinant of instream dissolved industrial water use has reduced flow oxygen and the assimilative capacity from some springs. In addition, riv- for oxygen-demanding constituents. ers have been impounded and diverted Temperature is similarly affected by for the same purposes and for flood channel morphology and the physical control. Each of these activities has structure of the riparian zone through noticeable impacts on water quality. the depth-to-width ratio (or surface For example, impoundments can cause area-to-volume ratio) of the channel changes in temperature regimes, sedi- and by the amount of shading provided ment transport, and nutrient cycling. by riparian canopy. Dissolved oxygen Wastewater discharge plants are asso- and temperature are significant water ciated with increases in flow, tempera- quality components supporting the ture, organic loading, and nutrients biological integrity of waters. Hence, in receiving waters. Some of these water quality both shapes and is shaped impacts are unavoidable consequences by the other forces and agents acting in of human activities (such as loss of sedi- riverine systems. ment transport through reservoirs), and This chapter describes the state’s water quality impacts resulting from existing water quality programs, based point source discharges and nonpoint on the federal Clean Water Act and the source runoff are addressed through Texas Water Code §26, and demon- water quality management programs. strates linkages between water quality The Texas Commission on Environ- and variable flow regimes. The goals and mental Quality has jurisdiction over the objectives of the state’s program include state’s water quality programs, including assessing and protecting the physical, adoption of surface water quality stan- chemical, and biological integrity of dards, enforcement of water quality rules, the state’s water bodies. This chapter is and issuance of permits, in addition to focused on water chemistry. its water quality planning responsibilities (Texas Water Code §5.013a). The Com- mission monitors water quality through-

94 Texas Water Development Board Report 369 out the state, identifies beneficial uses and streams, relevant parameters must for surface water bodies, adopts water be defined and measured, the types and quality standards designed to support sources of pollution must be identified, the identified uses, and manages water and plans to protect or restore water quality through regulating point source quality must be implemented. Texas discharges and funding remedies for non- uses a varying cycle of activities to man- point source pollution. The Commission age water quality based on statutorily prepares the State of Texas Water Quality determined time frames. These steps Inventory and submits the report to the are included in the cycle: U.S. Environmental Protection Agency biennially in even-numbered years as • Establishing or revising water quality required by section 305(b) of the Clean standards Water Act. The most recent submission • Determining appropriate aquatic life was prepared in 2004 (TCEQ, 2004a). use designations Additionally, the Commission develops • Collecting data at routine, fixed a list of impaired stream segments (seg- stations or at special project sites ments where one or more of the identi- • Assessing water quality and iden- fied uses is not supported) as required tifying those waters that do not meet under section 303(d) of the Clean Water established criteria or where one or Act. more uses (such as recreational and Summaries of applicable programs public water supply) are not met are presented below; detailed descrip- • Implementing pollution control tions are located at the Web sites listed measures and monitoring the results with each program. 9.2.2 9.2 Surface Water Quality Standards Water Quality Programs The Texas Surface Water Quality Stan- in Texas dards (30 Texas Administrative Code The Clean Water Act framework, imple- §307.7) fulfill these state and federal mented by the Texas Commission on requirements: Environmental Quality, has five major components, laid out in the following • Establish uses sequence: • Set criteria to maintain the established uses • Establish the uses of the water that • Establish an anti-degradation policy will be protected • Determine the criteria necessary to The rules establish numerical and protect those uses narrative goals for water quality through- • Base decisions on meeting those out the state and provide a basis on which criteria Texas Commission on Environmental • Conduct ambient monitoring to Quality programs can establish reason- ensure criteria are met and uses are able methods to implement and attain maintained the state’s water quality goals. • Require corrective action when it is Water quality standards have been determined that uses are impaired developed for all surface waters in the state. The Commission has developed 9.2.1 segment-specific uses and water qual- Water Quality Standards ity criteria for 225 classified water qual- and Assessment ity segments representing 14,238 miles In order to protect the physical, chemi- (22,909 kilometers) of perennial streams cal, and biological integrity of rivers (TCEQ, 2004b). Aquatic life use desig-

Texas Water Development Board Report 369 95 nations have been determined for an to be a multistressor indicator of aquatic additional 319 unclassified stream seg- ecosystem health and not necessarily ments totaling over 6,000 stream miles designed to be strictly flow sensitive. It or 9,654 kilometers (Table 9-1). Water is not clear if values from the Index of quality standards have been adopted for Biotic Integrity would change under a all streams that have been identified as different set of flow conditions. Finally, priority segments in the Programmatic some elements of a sound ecological Work Plan (TIFP, 2002). environment are not represented by Although established aquatic life use aquatic life use designations. For exam- designations seem to be a logical place ple, the health of riparian zones may not from which to start assessing aspects of be fully captured by these designations. a sound ecological environment in Tex- The state is committed to protecting des- as rivers and streams, there are limita- ignated aquatic life uses and developing tions to their applicability to the Texas instream flow recommendations that will Instream Flow Program. First, the origi- reflect consistency with these designated nal designations for classified segments uses. The Texas Commission on Envi- were based on dissolved oxygen crite- ronmental Quality continues to evaluate ria. Aquatic life use designations were the effectiveness of all assessment tools, added later under the general assumption including the sensitivity of the Index to that 5.0 milligrams per liter of dissolved flow variation and is considering how all oxygen equaled a “high aquatic life use” stressors, including flow, affect biological (6.0=exceptional, 4.0=intermediate). integrity. For the purpose of simplicity, Consequently, designations in classified it may benefit the Texas Instream Flow segments may not be biologically based Program to heed the recommendation in some instances. Second, the Index of the National Research Council (2005) of Biotic Integrity now relied upon for and adopt ecological indicators that are assessing aquatic life uses was developed linked directly to flow variability. for small-to-moderately sized streams The Texas Surface Water Quality and has not been tested extensively in Standards are available on the Texas larger rivers, such as those selected as Commission on Environmental Quality priority instream flow segments. The Web site: www.tceq.state.tx.us/nav/eq/ Index (separately determined for both eq_swqs.html invertebrates and fish) was also designed

Table 9-1. Attributes of aquatic life use categories.

Aquatic Habitat Species Sensitive Species Trophic life use characteristics assemblage species Diversity richness structure Exceptional Outstanding Exceptional or Abundant Exception- Exception- Balanced natural unusual ally high ally high variability High Highly diverse Usual association Present High High Balanced of regionally to slightly expected species imbalanced Intermediate Moderately Some expected Very low Moderate Moderate Moderately diverse species abundance imbalanced

Limited Uniform Most regionally Absent Low Low Severely expected species imbalanced absent

Source: 30 Texas Administrative Code §307.7(b)(3)(A)(i)

96 Texas Water Development Board Report 369 9.2.3 9.2.4 Surface Water Quality Monitoring Texas Water Quality Inventory The Surface Water Quality Monitoring The state carries out a regular program Program has been evaluating biological, of monitoring and assessing Texas sur- chemical, and physical characteristics face waters to compare conditions to of Texas’ surface waters since 1967. This established standards and to determine program establishes the water quality which water bodies are meeting the sampling procedures of the Texas Com- standards for their identified uses, and mission on Environmental Quality and which are not. The Texas Commission maintains the ambient water quality on Environmental Quality works in col- database collected by the Commission’s laboration with state, federal, regional, various partners. A large number of fixed and local stakeholders to collect and sampling sites are maintained statewide, assess this data. The Clean Rivers Pro- and special studies and intensive sur- gram is the primary agent of this moni- veys are performed to identify causes toring program. Assessment results and sources of pollutants and quantify are published periodically in the Texas point and nonpoint source loads. This Water Quality Inventory and 303(d) program also performs assessments of List, as required by Sections 305(b) and aquatic life use in unclassified streams 303(d) of the federal Clean Water Act. and of receiving water in response to The Texas Water Quality Inventory discharge permitting action. It also and 303(d) List include detailed descrip- performs use attainability analyses to tions of the status of surface waters of the ensure that water quality standards and state. These reports document public criteria are appropriate for a water body. health concerns, fitness for use by aquat- Available guidance allows any qualified ic species and other wildlife, and specific practitioner to also perform aquatic life pollutants and their possible sources. use assessments, receiving water assess- The Texas Water Quality Water Inven- ments, and use attainability analyses. tory and 303(d) List are available on the The Texas Clean Rivers Program is Texas Commission for Environmental a collaboration of the Texas Commis- Quality Web site: www.tceq.state.tx.us/ sion on Environmental Quality, 15 water compliance/monitoring/water/quality/ resource agencies (corresponding to data/wqm/305_303.html the 15 major river basins), and a myriad of other cooperators. The cooperat- 9.2.5 ing agencies collect water quality data Texas Pollutant Discharge throughout their respective basins under Elimination System this program, which allows watershed The State of Texas assumed the author- issues to be addressed at a local level, ity to administer the National Pollutant with coordination at the state level to Discharge Elimination System program assure consistency and quality of water in Texas on September 14, 1998. The quality data. program is a federal regulatory pro- For details on the Surface Water gram to control discharges of pollutants Quality Monitoring program see: www. to surface waters of the United States. tceq.state.tx.us/compliance/monitoring/ The Texas Pollutant Discharge Elimina- water/quality/data/wqm/mtr/swqm.html tion System program now has federal Details of the Texas Clean Rivers Pro- regulatory authority over discharges of gram are available at this Web site: www. pollutants to Texas surface water, with tceq.state.tx.us/compliance/monitoring/ the exception of discharges associated crp/index.html with oil, gas, and geothermal explora- tion and development activities, which

Texas Water Development Board Report 369 97 are regulated by the Texas Railroad Discharge Elimination System procedures Commission. see: www.tceq.state.tx.us/permitting/ Under the program, the Texas Com- water_quality/wq_assessment/standards/ mission on Environmental Quality WQ_standards_implementing.html implements the Texas Surface Water Quality Standards when issuing per- 9.2.6 mits for wastewater or other autho- Total Maximum Daily Loads rized discharges into the surface waters The Total Maximum Daily Load pro- of the state. Water quality models are gram works to improve and restore commonly applied to determine permit water quality in impaired or threatened limits for dissolved oxygen needed to water bodies in Texas. To restore qual- protect existing aquatic life uses. Since ity, it is first necessary to determine the municipal wastewater is the predomi- sources and causes of the pollution. The nant type of wastewater discharge into goal of a Total Maximum Daily Load rivers and streams, much effort has been project is to expended on modeling dissolved oxygen. The type of model used depends on the • determine the maximum amount of 1) type of water body, 2) availability of pollutant that a water body can receive site-specific information, 3) location of and still both attain and maintain its the discharge point, and 4) availability of water quality standards; and previously developed models. Calibrated • allocate this allowable amount (load) models are used when available. to point and nonpoint sources in the For wastewater discharge permits, watershed. one critical dilution flow is defined as the instream flow necessary to meet Total maximum daily loads must be established human health and aquatic submitted to the Environmental Protec- life criteria. Acute and chronic aquat- tion Agency for review and approval. A ic life criteria have been adopted that total maximum daily load is normally account for both frequency and dura- prepared for each pollutant in every tion of exposure to stressors. The critical impaired water body. Based on the envi- dilutions are the 7Q2 flows for chronic ronmental target, the state develops an aquatic life criteria, and one quarter of implementation plan to mitigate human- the 7Q2 flows for acute aquatic life cri- caused sources of pollution within the teria. A functional aquatic environment watershed and restore full use to the with its requisite flows provides assimi- water body. An implementation plan lative capacity, and the Commission’s outlines the steps necessary to reduce water right permitting program recog- pollutant loads through regulatory and nizes the important linkage between voluntary activities. The program is water quality and quantity. As a result, authorized by and created to fulfill the the Commission coordinates its recom- requirements of Section 303(d) of the mendations for special conditions for Clean Water Act and its implementing water right permits with the appropri- regulations. Detailed information on the ate water quality programs. Although program is available on the Texas Com- the critical dilution flow is functionally mission on Environmental Quality Web used for modeling parameters such as site: www.tceq.state.tx.us/implementation/ dissolved oxygen during low flow, high water/tmdl/index.html temperature periods (worst-case sce- nario), those flows are not necessarily suitable for supporting a sound ecological environment on a long-term basis. For details on the Texas Pollutant

98 Texas Water Development Board Report 369 9.3 sons. Several of the species are endemic Water Quality for and are listed as federally endangered. Instream Flow Studies In response to these factors, Saunders Texas has invested considerable resourc- and others (2001) selected SNTEMP, a es in developing water quality models, steady-state model that predicts mean especially in the Total Maximum Daily and maximum daily water temperature Load and Texas Pollutant Discharge in relation to stream distance (Bartholow, Elimination System programs. The 1989), to evaluate the effects of flow on application of water quality modeling temperature regimes in the San Marcos approaches used for total maximum River. In a similar manner, the choice daily load development and permitting of water quality modeling approach for decisions to instream flow studies will the Texas Instream Flow studies will be provide consistency among programs; made based on the circumstances of each this is particularly important for regu- study. latory programs like the Pollutant Dis- The spatial resolution needed for charge Elimination System and water a model depends largely on the type rights permitting and for developing of water body to be evaluated and its and protecting water quality standards. hydraulic characteristics. Water quality To ensure that results and recommen- attributes of rivers and streams change dations related to water quality are longitudinally as various constitu- integrated with the state’s water quality ents are input, assimilated, deposited standards and regulatory framework, into the sediments, and re-suspended. water quality studies identified in the Streams usually exhibit vertical and lat- Texas Instream Flow Program’s study eral homogeneity because of turbulent design process will be closely coordi- transport of chemical constituents. Con- nated with the Commission’s existing sequently, a longitudinally segmented, water quality programs. one-dimensional water quality model The selection of a specific water such as QUAL-TX (described by Ward quality modeling approach depends on and Benaman, 1999a), a modification a number of factors, including but not of the U.S. Environmental Protection limited to 1) the temporal and spatial Agency’s QUAL-2E, is considered suffi- scale needed, 2) the geomorphic and cient for modeling dissolved oxygen and hydraulic characteristics of the water temperature in most stream segments. body, and 3) the constituents of con- In the absence of site-specific informa- cern. Since the instream flow program tion, QUAL-TX is the model most com- will emphasize rivers and streams, the monly applied by the state’s water quality modeling approaches that have been program. It includes regionally specific applied to lotic segments are particularly hydraulic relations and a “Texas” equa- appropriate. tion for stream reaeration developed For example, temperature regimes from site-specific field measurements play an important role in many Texas (Ward and Benaman, 1999b). QUAL-TX rivers and streams. Spring-fed streams also excludes a number of subroutines with stable hydrographs and tempera- found in QUAL2E that are of limited util- ture regimes (such as the San Marcos and ity in Texas, such as ice cover. QUAL-TX Devils rivers) support unique ecosystems is suitable for the purpose of modeling with relatively stenothermal faunal and the effects of pollutant loadings on dis- floral components. Water temperature at solved oxygen. the spring source is usually constant (or Rivers and streams exhibit seasonally nearly so) year round, and the volume of predictable variations in water quality flow influences the downstream extent of throughout most of Texas. The warm- thermally suitable habitat during all sea- est temperatures (late summer) typically

Texas Water Development Board Report 369 99 coincide with the lowest flows of the and capture local-scale variation in flow year, causing water quality conditions and water quality conditions based on that may be stressful to aquatic organ- instream habitats (NRC, 2005). Unfortu- isms. Since this appears to be a well- nately, no single model is currently avail- defined period critical to maintaining able to accomplish all these feats. Part of the health of aquatic communities, the the strategy for integrating instream flow Texas Commission on Environmental study elements will require new ways of Quality has focused water quality mod- thinking about how to model water qual- eling, especially for dissolved oxygen, ity parameters in conjunction with the on these critical conditions, using the four flow components. The Texas Com- QUAL-TX model. Because QUAL-TX mission on Environmental Quality will is a steady-state model, it is not as use- address alternate water quality models ful for predicting water quality under a or emerging technologies such as hydro- variety of other flow conditions (such as logic information systems (NRC, 2005) high flow pulses and overbank flows). as budget and time permits. An ideal model would simulate water All of these program components chemistry and temperature under a full must be re-evaluated on a cycle vary- range of flow conditions to assess the ing from two to five years. Water quality effects of alternative management strat- studies identified as instream flow study egies; account for sediment and non- tasks will be closely coordinated with the point source loadings from watershed Commission’s existing water quality pro- activities; incorporate point-source dis- grams. This will minimize redundancy charges, instream chemical transforma- of efforts and ensure consistency among tion processes and sediment transport; programs.

100 Texas Water Development Board Report 369 10 Integration

s described in Chapter 4, stake- integrated to make recommendations for holder involvement will be sought these flow components. Important con- inA each step of the instream flow study nectivity linkages within the river eco- process, including integration of data to system will also be considered, as well as generate flow recommendations. When interannual and intra-annual hydrologic field studies are completed, the Agen- variation. cies will conduct workshops to present and explain the results to the sub-basin 10.1 workgroups. During those workshops, Subsistence Flows the Agencies will garner stakeholder The primary objective of subsistence input on the methods used to integrate flow recommendations will be to main- data and generate the instream flow tain water quality criteria. Secondary recommendations. objectives for a specific sub-basin may As discussed in Chapter 6, descrip- include providing life cycle cues based tions of flow recommendations will on naturally occurring periods of low include four components of the hydro- flow or providing habitat that ensures a logic regime: subsistence flows, base population is able to recolonize the riv- flows, high flow pulses, and overbank er system once normal, base flow rates flows (Table 10-1). As the studies for the return. Texas Instream Flow Program evolve, Developing recommendations for definitions and objectives for these flow subsistence flows requires integrating components may need to be modified, technical studies from various disciplines and additional flow components may be (Figure 10-1). Biological studies will iden- required to support a sound ecological tify key considerations related to these environment for a specific river sub- reduced flow rates. Examples include basin. Results of technical studies in identifying location and characteristics hydrology and hydraulics, biology, geo- of refuge habitats for species during low morphology, and water quality will be flow events and describing the effect of

Table 10-1. Definitions and objectives for instream flow components.

Subsistence flows Definition: Infrequent, seasonal periods of low flow Objectives: Maintain water quality criteria Base flows Definition: Normal flow conditions between storm events Objectives: Ensure adequate habitat conditions, including variability, to support the natural biological community High flow pulses Definition: Short-duration, in-channel, high flow events following storm events Objectives: Maintain important physical habitat features Provide longitudinal connectivity along the river channel Overbank flows Definition: Infrequent, high flow events that exceed the normal channel Objectives: Maintain riparian areas Provide lateral connectivity between the river channel and active floodplain

Texas Water Development Board Report 369 101 Subsistence Flows

Spatial scale: River Reach

Temporal scale: Hourly Flow, Varies from Month to Month

Primary discipline: Hydrology/Hydraulics Biology Geomorphology Water Quality

Identify Biological Considerations

Identify Water Quality Constituents of Concern

Calculate Low Flow Conduct Water Quality Statistics Modeling Studies

Assess Low Flow-Water Quality Relationship

Other Biological Considerations

Subsistence Flows

Figure 10-1. Development of subsistence flow recommendations from results of multidisciplinary activities.

102 Texas Water Development Board Report 369 such events on important species or com- of these studies will assist biologists in munities. Based on these considerations, determining sites and flow conditions water quality constituents of concern will for biological data collection. Based on be identified. Examples include stream these data collection efforts, biologists temperatures and dissolved oxygen will determine habitat criteria for target concentrations determined to be detri- species or guilds. For each intensive habi- mental for certain species or chemical tat study site, a hydraulic model will be constituents whose elevated concentra- used to evaluate hydraulic characteristics tions are identified as concerns by the over the range of flows of interest. A GIS- Agencies and stakeholders. Appropri- based physical habitat model will be used ate water quality modeling studies will to assess habitat versus flow relationships, be conducted to assist in determining including diversity (described in Section the relationship between low flows and 10.2.1). Base flow recommendations will constituents of concern (see Chapter 9). include ranges of flow appropriate for Example studies include application of wet, average, and dry hydrologic condi- QUAL-TX or other computer models. tions as defined by studies of the specific Hydrologic studies will assist by calculat- river sub-basin. Recommendations will ing low flow statistics characterizing the be finalized after assessing biological natural occurrence and severity of low considerations related to water quality flow events. Statistics of interest include for these flow ranges. 7Q2 flow, which is used in regulating water quality standards. Subsistence 10.2.1 flow recommendations will be drafted Physical Habitat Model in order to reduce unnatural variation in A GIS-based physical habitat model constituents of concern. After checking is used to predict habitat conditions the impact on other biological consider- within a habitat study site for a range ations, subsistence flow recommenda- of simulated flow conditions. Hydraulic tions will be finalized. models provide the simulated flow conditions; geographic coverages provide 10.2 information about substrate and cover. Base Flows From these data, GIS forms a spatially The primary objective of base flow explicit habitat model that can be used recommendations will be to ensure to query spatial information. For each adequate habitat conditions, including simulated flow, the spatial availability variability, to support the natural bio- of suitable habitat can then be queried logical community of the specific river using habitat suitability criteria for sub-basin. These habitat conditions are habitat guilds and target species. For expected to vary from day to day, season each guild and target species, a micro- to season, and year to year. This vari- habitat-discharge relationship is devel- ability is essential in order to balance the oped to provide information on how distinct habitat requirements of various microhabitat suitability changes with species, guilds, and assemblages. respect to streamflow. Similarly, using Developing recommendations for mesohabitat criteria, the habitat model base flows requires integrating technical can be queried to develop spatial maps studies from various disciplines (Figure of mesohabitat and mesohabitat-dis- 10-2). Biological studies will identify key charge relationships at each simulated species and habitat issues related to a flow. Spatial maps of mesohabitat can specific sub-basin. Geomorphic studies be further analyzed using landscape will assess channel bed forms and banks, analysis software (such as Fragstats) to and hydrologic studies will calculate base describe habitat heterogeneity in terms flow statistics for the sub-basin. Results of diversity, patch size, location of edg-

Texas Water Development Board Report 369 103 Base Flows

Spatial scale: River Reach

Temporal scale: Daily Flow Range, Varies from Month to Month

Primary discipline: Hydrology/Hydraulics Biology Geomorphology Water Quality

Assess Bed Form Identify Biological Issues and Banks and Key Species

Calculate Base Flow Collect Biological Statistics Data

Model Hydraulic Characteristics in Determine Habitat Relation to Flow Criteria

Assess Habitat-Flow Relationships, including Diversity

Describe Wet, Normal, and Dry Years

Consider Biological and Riparian Issues

Consider Water Quality Issues

Base Flows

Figure 10-2. Development of base flow recommendations from results of multidisciplinary activities.

104 Texas Water Development Board Report 369 es and transition zones (ecotones), and high flow pulses. High flow pulses also other landscape metrics. provide longitudinal connectivity along Habitat time series will be produced the river corridor for many species. Sec- using hydrologic time series and micro- ondary objectives for high flow pulses habitat-discharge relationships and, may include improving recruitment for separately, relationships between habitat specific species or other basin-specific heterogeneity and discharge. By compar- objectives. ing hydrologic time series derived from Developing recommendations for naturalized and alternative flow regimes, high flow pulses requires integrating implications of changes in flow regimes technical studies from several disci- can be assessed. For example, the per- plines (Figure 10-3). Geomorphic stud- cent reduction in habitat area between ies will assess active channel processes flow regimes can be calculated to help that shape the physical features of the identify time periods of greater or lesser riverine system. Those studies will also impact. Coupled with data on critical develop sediment budgets to describe time periods of life history events (such the transport and storage of various siz- as spring spawning of fishes), habitat es of sediment within the river system. time series can help identify when par- Finally, geomorphic studies will assess ticular inter- or intra-annual flow levels the channel-adjusting flow behavior of are necessary. the river within the sub-basin. Biological Habitat duration curves can be studies will identify biological consider- derived from time series as well. From ations related to high flow pulses, includ- these curves, mean values and exceed- ing water quality. If necessary, additional ance probabilities of different habitat studies to consider water quality issues conditions (such as 85th percentile habi- will be completed. Hydrologic stud- tat values and minimum and maximum ies will calculate high flow statistics to diversity) can be calculated. Coupled describe the historical and current mag- with habitat thresholds (Capra and oth- nitude, frequency, timing, and shape of ers, 1995; Bovee and others, 1998; Saun- high flow pulses. Final recommendations ders and others, 2001), duration curves for high flow pulses will balance current can be used to assess how often and sediment supplies and flow regimes to for how long periods of flow result in achieve desired results. habitat conditions below, above, or at a threshold. Overall, many combinations 10.4 of spatial and temporal analyses are pos- Overbank Flows sible and can be used to identify base The primary objectives of overbank flow conditions that minimize impacts flow recommendations will be to main- on or maximize value of microhabitat tain riparian areas and provide lateral conditions, key habitats, and habitat connectivity between the river channel heterogeneity. and active floodplain. Requirements for maintaining riparian areas will be spe- 10.3 cific to each river sub-basin but may High Flow Pulses include transporting sediments and The primary objectives of high flow nutrients to riparian areas, recharging pulse recommendations will be to main- floodplain aquifers, and providing suit- tain important physical habitat features able conditions for seedlings. Require- and longitudinal connectivity along the ments for lateral connectivity will also river channel. Many physical features of vary according to basin-specific fac- a river or stream that provide impor- tors, such as the presence of fish or tant habitat during base flow conditions other biota using floodplain habitat cannot be maintained without suitable during and after flood events. Second-

Texas Water Development Board Report 369 105 High Flow Pulses

Spatial scale: River Segment

Temporal scale: Multiple High Flow, Pulses Throughout the Year

Primary discipline: Hydrology/Hydraulics Biology Geomorphology Water Quality

Assess Active Channel Processes

Develop Sediment Budgets

Assess Channel Adjusting Flow Behavior

Describe Signiﬁcant Consider Biological Habitat Conditions Issues

Calculate High Flow Consider Water Quality Statistics Issues

High Flow Pulses

Figure 10-3. Development of high flow pulse recommendations from results of multidisciplinary activities.

106 Texas Water Development Board Report 369 ary objectives for overbank flows may estuaries). The Agencies will ensure include moving organic debris to the compatibility with the statutory respon- main channel, providing life cycle cues sibilities of river authorities and other for various species, and maintaining regional water resource management the balance of species in aquatic and agencies by including these entities as riparian communities. stakeholders during the completion of Developing recommendations for sub-basin studies. overbank flows requires integrating Because the Agencies are directly technical studies from various disciplines involved in many of these programs, (Figure 10-4). Geomorphic studies will they are in a unique position to ensure assess the active floodplain and chan- that the Texas Instream Flow Program is nel processes. Hydrologic studies will compatible with other state and federal calculate flood frequency statistics, and water resource programs. State fresh- hydraulic studies will model the extent water inflow requirements for bays and of inundation associated with flood estuaries are developed based on data events. This information will assist in collection and analytical studies jointly assessing overbank flow behavior, which completed by the Texas Water Develop- will be used to develop recommenda- ment Board and Texas Parks and Wild- tions for overbank flows. Initial recom- life Department. The Texas Commission mendations will be based on providing on Environmental Quality administers flows that inundate the active floodplain the state Total Maximum Daily Load and provide sufficient flow and stream Program required by the federal Clean power for active floodplain processes. Water Act. In the Texas Clean Rivers After conducting riparian studies, biolo- Program, the Commission collaborates gists will determine riparian require- with 14 partner agencies to conduct ments, such as timing and duration of water quality monitoring, assessment, events, which will be used to modify and public outreach activities. The Tex- initial recommendations. Studies will as Water Development Board facilitates identify biological considerations relat- water supply planning efforts mandated ed to overbank flows, as well as water by Texas state law. The Texas Parks and quality considerations. Examples of Wildlife Department regulates fish and biological considerations include flood wildlife resources. Through these and recession rates to minimize stranding of other programs and activities, the Agen- fish in floodplain areas or the amount of cies have working relationships with habitat available for biota using flood- many state and federal agencies, allowing plains. Final recommendations for communication and cooperation regard- overbank flows will address all of these ing program compatibility. considerations. 10.6 10.5 Study Report Other Considerations The Agencies will prepare a final study Before final instream flow recommen- report for each specific river sub-basin. dations are made, the Texas Instream The report will include instream flow Flow Program will consider other fac- recommendations for flow components tors for a specific river sub-basin that such as subsistence flows, base flows, may not have been addressed by tech- high flow pulses, and overbank flows. nical studies. For example, these fac- It will also describe the significance of tors include compatibility with other each flow component for the specific state and federal programs related to river sub-basin and fully document study surface water resources (such as fresh- methods and analysis techniques. water inflow requirements to bays and Each study report will include

Texas Water Development Board Report 369 107 Overbank Flows

Spatial scale: River Segment

Temporal scale: Extreme Flow Events, Occur Less Than Once per Year

Primary discipline: Hydrology/Hydraulics Biology Geomorphology Water Quality

Calculate Flood Assess Active Floodplain Frequency Statistics and Channel Processes

Model Extent of Flood Events

Assess Overbank Flow Behavior

Consider Biological Conduct Riparian Issues Studies

Consider Water Quality Estimate Riparian Issues Requirements

Overbank Flows

Figure 10-4. Development of overbank flow recommendations from results of multidisciplinary activities.

108 Texas Water Development Board Report 369 descriptions of the scientific realities The draft study report will be writ- related to instream flow recommenda- ten after meeting with the sub-basin tions for the specific river sub-basin (see workgroups and obtaining their input Section 2.2.2). In addition, the report related to integrating data and generating will identify factors, including flow alter- instream flow recommendations. The ation, that are inhibiting the achieve- draft study report will then be submitted ment of a sound ecological environment to scientific peer review, as described in within the specific river sub-basin. The Chapter 4. After completing any neces- report will also document uncertainty sary changes identified by peer review, in study results and conclusions, as well the report will be presented to stakehold- as opportunities to adapt, refine, and ers for further comment before being improve flow recommendations through finalized. The final report will include additional data collection, monitoring, feedback received from stakeholders or analysis. Alternative flow regimes and and peers, along with responses from their consequences will be described. the Agencies.

Texas Water Development Board Report 369 109 11 Next Steps: Implementation, Monitoring, and Adaptive Management

he product of the Texas Instream process has made initial flow recom- Flow Program, as envisioned by mendations for an area, the results of SenateT Bill 2 of the 77th Texas Legisla- the detailed study may be considered ture, is a series of instream flow recom- as part of the process of reviewing and mendations that will achieve a sound refining flow recommendations. Senate ecological environment in rivers and Bill 3 mandates that this review occur at streams. After study reports are com- least once every 10 years. pleted, an additional process will be necessary to translate recommenda- 11.1 tions into action. Implementation Issues Senate Bill 3, passed by the 80th Tex- The implementation of flow recom- as Legislature in 2007, creates a process mendations developed by the instream to generate regulatory environmental flow program is addressed by Senate flow standards based on “the best avail- Bill 3. The legislation initiates a process able science.” That legislation ensures for developing management strategies that the development of management to meet flow recommendations gen- strategies to meet instream flow rec- erated from the best available science, ommendations will be ongoing and including Texas Instream Flow Program adaptive and will consider and address studies. The Senate Bill 3 process will local issues. Management strategies will also address environmental flows for outline steps or policies requiring adop- specific bay and basin systems. These tion by state agencies, stakeholders, and flows include both freshwater inflow possibly the legislature to implement requirements to bays and estuaries and new flow regimes. The strategies will instream flow requirements within the also include recommendations related basin. Results of the instream flow pro- to monitoring and adaptively manag- gram and other studies will provide a ing the aquatic environment through scientific basis for selecting environ- periodic review and refinement of flow mental flows in portions of basin and recommendations. Senate Bill 3 creates bay systems. opportunities to use the Texas Instream For each river sub-basin studied by Flow Program studies in developing the the Texas Instream Flow Program, a full regulatory framework necessary to sup- complement of modeling and analyses port a sound ecological environment. will be used to derive instream flow The Senate Bill 3 process has already recommendations for a complete range begun, with instream flow recommen- of flow patterns that would collectively dations for certain basins due prior to achieve a sound ecological environment. the completion of the detailed Texas The program seeks to identify a range of Instream Flow Program studies for flow components, from subsistence to those areas. Technical experts partici- overbank flows, (a flow regime) to ensure pating in the Senate Bill 3 process will that the variability in physical, biologi- make recommendations based on the cal, and chemical processes is main- best science available. In the event the tained through time. Additionally, flow Texas Instream Flow Program completes regimes will be tailored to specific hydro- a detailed study after the Senate Bill 3 logic conditions. For example, annual

110 Texas Water Development Board Report 369 flow regimes (with monthly or seasonal Instream Flow Program or other scien- targets) can be developed for dry, aver- tific studies are completed. As part of age, and wet hydrologic conditions. As their duties under Senate Bill 3, basin and a result, specific flow or management bay area stakeholder committees will be objectives and corresponding recom- required to develop strategies to meet mendations can be derived for each of instream flow recommendations. these conditions. For example, during Results of the Texas Instream Flow dry conditions objectives might include, Program will be in a form that can be but would not be limited to, water quality readily integrated into the Senate Bill conditions needed for key or indicator 3 process. Study results will be docu- species to survive. During wet condi- mented in a report (see Chapter 10) that tions, objectives may include, but will will provide a basis for implementation. not be limited to, riparian and channel Information in the report will include a maintenance. Desired habitat conditions revised conceptual model of the aquatic or indicators could be developed for each ecosystem in a specific sub-basin. The hydrologic condition. report will detail the ecological signifi- Implementing flow recommendations cance of flow recommendations, dis- will be a pivotal step in the instream flow cuss the uncertainties associated with program, and a necessary component of analyses, anticipate needs for adap- implementation will be striking a balance tive management, and describe some between human needs and ecosystem of the non-flow-related factors affect- requirements for fresh water. This bal- ing ecosystem health. The report may ance may be more easily struck in regions also describe options for adjusting river of the state where freshwater resources operations to meet study goals or top- are plentiful due to climatic or other con- ics for additional study should resources ditions. Implementation challenges will become available in the future. To form arise from the disparate legal treatment management strategies for implement- of surface and groundwaters that are ing instream flow recommendations as hydrologically connected and from ever- part of environmental flows for basin changing land uses that directly affect and bay systems, stakeholder committees watershed dynamics. Different sets of established by Senate Bill 3 may adapt issues will be confronted in systems with study results from the Instream Flow rivers impounded by large storage reser- Program. voirs, river basins with unallocated water, The Texas Instream Flow Program and fully appropriated river basins. has identified six priority river basins in A legitimate concern is that by the which to initiate studies and implement time the instream flow recommenda- recommendations (TIFP, 2002). These tions are available for a particular sub- priority basins represent a small subset basin, human water demands may out- of the total number of rivers and streams pace supplies. Senate Bill 3 addresses this in the state. Ultimately, the program concern by mandating that basin and will need to be expanded to encompass bay expert science teams recommend these other rivers and streams. Expan- environmental flow regimes based on the sion should be based on a priority-set- best science available. This will provide ting system and may involve additional a measure of protection to areas where studies. studies have not yet been completed. In addition, the Agencies anticipate Once flow recommendations have been that classification tools will be devel- made, other provisions of Senate Bill 3 oped to aid in applying instream flow ensure they will be reviewed, monitored, standards to the state’s myriad rivers and and refined in the future when the Texas streams. It would be a nearly impossible

Texas Water Development Board Report 369 111 task to individually study all of the state’s geomorphology, and water quality) con- 191,000 river miles (307,385 kilometers). sistent with implementation goals. By determining hydrologically, ecologi- A comprehensive monitoring pro- cally, and geomorphologically similar gram should be based on a suite of eco- aquatic ecosystem units, the Agencies logical indicators adapted to could establish and apply streamlined methods for developing instream flow • describe the biological, chemical, recommendations. This type of approach physical, and hydrologic char- is being successfully used in New Jersey acteristics of the reach prior to the and is under development in other states initiation of field studies (establish (Henriksen and others, 2006). current conditions); • address the goals and objectives of 11.2 the study recommendations; Monitoring • address changing water management A monitoring program is required in strategies with sufficient flexibility; order to evaluate the effectiveness of • evaluate the long-term effectiveness implemented flow regimes in meeting of permit conditions or operational resource management objectives. Sen- plans in meeting the stated objectives; ate Bill 3 tasks basin and bay stakeholder and committees with developing work plans • provide a sound technical basis for that include monitoring. Results of the recommending adjustments to oper- Texas Instream Flow Program will assist ational plans in the event that objec in developing these monitoring plans tives are not being achieved. for the instream portion of specific sub- basins. Monitoring will be considered 11.3 during the design phase of the pro- Adaptive Management gram’s studies when goals, objectives, The final step of the instream flow and indicators are developed for a sub- program is targeted at addressing the basin. A successful monitoring program uncertainty of management outcomes will need clear goals and objectives that that arise from the complexity of the provide the basis for scientific investiga- natural environment. Adaptive manage- tion, appropriate allocation of resources ment, that is an experimental or “scien- for data collection and interpretation, tific” approach to managing resources, quality assurance procedures and peer is a concept that is gaining acceptance review, flexibility that allows modifi- by the resource conservation and man- cations when warranted by changes agement community (Salafsky and oth- in conditions or new information, and ers, 2001). The basic premise of adap- access to “user-friendly” monitoring tive management is the realization information by interested parties. that even the best-informed decisions Networks for monitoring aspects sometimes fail to achieve a desired end of the state’s rivers and streams already result because of faulty assumptions exist (such as the U.S. Geological Sur- or changing circumstances, including vey streamflow gages, Texas Clean Riv- new concerns, altered watershed land ers Program, and university studies), and use or cover, or new policy initiatives. these data sources should be integrated Through systematic testing of manage- into an instream flow monitoring pro- ment assumptions, recommended strat- gram. Additional monitoring should be egies can be modified to ensure that designed to complement existing sources goals are achieved. The Texas Instream and ensure adequate coverage of the four Flow Program will not be successful if study components (hydrology, biology, instream flow recommendations are

112 Texas Water Development Board Report 369 implemented but there is no further flow study design to integration of mul- analysis of whether goals were attained. tidisciplinary information to the estab- It is highly likely that much will be lishment of monitoring programs, will learned in the early years of implemen- be modified as new techniques and tation of instream flow recommenda- ideas are formulated and experience tions. It should be expected that various and knowledge are gained. aspects of the program, from instream

Texas Water Development Board Report 369 113 12 Conclusion

he goal of the Texas Instream Flow is being developed and will be refined Program is to determine flow during initial studies. This process is conditionsT necessary for supporting a described in general terms in Chapters 4 sound ecological environment within and 5. As greater understanding is devel- the rivers and streams of Texas. This oped in this area, the description of this document describes the general pro- process will be further clarified in future cess and scientific studies the Agen- revisions of this or other documents. cies will use to make those determina- This document is intended to describe tions. Studies will be multidisciplinary the general framework of the process. It in nature, including the disciplines of does not provide an exhaustive list of the hydrology and hydraulics, biology, geo- conditions that might be encountered morphology, and water quality, and will during instream flow studies in Texas. address linkages between and within It does, however, describe the organiza- disciplines. Results will be integrated tional process the Agencies will follow to to develop a flow regime composed assess available data, set goals, conduct of several flow components (such as studies, integrate results, develop and subsistence and base flows, high flow implement recommendations, monitor pulses, and overbank flow components) river conditions, and adapt recommen- for a variety of hydrologic conditions dations as necessary. It also describes (wet, average, and dry). The Agencies the general technical capabilities that expect to gain significant understand- the Agencies can provide in support of ing of large riverine ecosystems during instream flow studies. these studies. This understanding will The Texas Instream Flow Program be used to refine methods and pro- has been designed so that instream flow cedures for future studies and will be studies may be conducted by qualified documented in future revisions of this third parties with the Agencies’ over- or other documents. sight. In that event, this document In collaboration with local stake- will serve as a general overview of the holders, study-specific goals, objectives, requirements of such a study. This docu- and indicators consistent with a sound ment does not provide sufficient guid- ecological environment will be deter- ance to meet all the varied conditions mined for each sub-basin and will play that may be encountered in Texas. Those an important role in selecting technical conducting studies should communicate methods to determine instream flow with the Agencies before modifying or requirements. The manner in which adopting the methods described in this the Agencies solicit and incorporate document. stakeholder input and local knowledge

114 Texas Water Development Board Report 369 13 Acknowledgments

his document represents the col- The National Research Council’s lective effort of many former and review of the Texas Instream Flow Pro- currentT staff members of the Texas gram, including a draft version of this Commission on Environmental Qual- document, was insightful and very ben- ity, Texas Parks and Wildlife Depart- eficial for further development. In a ment, and Texas Water Development similar manner, comments and feedback Board. The list of those who contrib- from many others outside the Agencies uted by writing, reviewing, editing, or improved this document. Staff of other illustrating the text is too lengthy to state and federal agencies, river authori- present here. But the Agencies are truly ties, and universities, members of the appreciative of their efforts. Overseeing public, and other stakeholders all took boards and commissions and executive the time to review earlier drafts of this directors/administrators of the Agen- document and provide feedback in writ- cies contributed to the quality of this ing or in person. The Agencies appreciate document by supporting the efforts their interest and assistance in improving of the Texas Instream Flow Program the Texas Instream Flow Program. and authorizing the National Research Council review of the program.

Texas Water Development Board Report 369 115 14 References

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Texas Water Development Board Report 369 129 15 Appendix

15.1 incrementally as managers learn from Acronyms/Symbols experience and as new scientific findings and social changes demand. 7Q2 Seven-Day Two-Year Low Flow a progressive build up of D Median particle diameter aggradation: 50 the channel bed with sediment over sev- ETM+ Enhanced Thematic Mapper eral years, distinguished from the rise Plus and fall of the channel bed during a single GIS Geographic Information flood, which is due to a normal sequence System of scour and deposition. GPS Global Positioning System anabranch: a secondary channel of a Q Discharge stream which leaves and then rejoins the main channel. The two channels are QS Sediment discharge (bed load separated by stable, vegetated islands. portion) aquatic life use: a beneficial use designa- 15.2 tion in which the water body provides Glossary of Selected Terms suitable habitat for survival and repro- 303(d) list: statewide list of water bod- duction of desirable fish, shellfish, and ies that are not meeting water quality other aquatic organisms. standards set for their use. The list is armoring: the formation of an erosion- produced by the Texas Commission on resistant layer of relatively large particles Environmental Quality every two years on a streambed or bank resulting from and submitted to the U.S. Environmental removal of finer particles by erosion. Protection Agency. assemblage: an organism group of inter- 7Q2: see seven-day two-year low flow acting species in a given ecosystem, for abiotic: any non-biological feature or example, a fish assemblage or a benthic process, such as geological or meteoro- macroinvertebrate assemblage. logical characteristics. assimilative capacity: the ability of a acre-foot: the volume of water needed to natural body of water to degrade and/or cover 1 acre to a depth of 1 foot. It equals disperse chemical substances without 325,851 gallons or 43,560 cubic feet. adverse effects. If the rate of introduction of pollutants into the environment active floodplain: area of a floodplain exceeds its assimilative capacity, habitat periodically covered by floods during and wildlife may be adversely affected. current hydrologic and geomorphic conditions, as opposed to terraces, which attenuation: the process whereby the are areas of the historic floodplain that magnitude of a flood event is reduced are seldom or never covered by floods by slowing, modifying, or diverting the during current conditions. flow of water. adaptive management: a process for bank: the sloping land bordering a chan- implementing policy decisions as an nel that forms the usual (not the flood) ongoing activity that requires monitoring boundaries of a channel. The bank has and adjustment. Adaptive management a steeper slope than the bottom of the applies scientific principles and meth- channel and is usually steeper than the ods to improve resource management land surrounding the channel. Right and

130 Texas Water Development Board Report 369 left banks are named facing downstream specified at the boundaries of the area (in the direction of flow). being modeled. bank stability: occurs when the chan- calibration: to check, adjust, or deter- nel bank configuration does not change mine by comparison that a computer significantly over time. Examples of bank model will produce results that meet or instability include channel widening exceed some defined criteria within a or narrowing and large changes in the specified degree of confidence. meander migration rate. canopy: the overhanging cover formed base flows: the component of an instream by branches and foliage. flow regime that represents normal flow channel: a natural or artificial water- conditions (including variability) between course that continuously or intermit- precipitation events. Base flows provide a tently contains water, with definite bed range of suitable habitat conditions that and banks that confine all but overbank- support the natural biological commu- ing streamflows. nity of a specific river sub-basin. Chezy’s equation: an empirical equa- related to the measurement bathymetric: tion used to estimate the average hydrau- of water depth within a water body. lic conditions of flow within a channel bed forms: three-dimensional configura- cross section. Alternative to Manning’s tions of bed material, which are formed equation. in streambeds by the action of flowing Chezy’s roughness: a coefficient in Che- water. zy’s equation that accounts for energy bed load: sediment that is transported by loss due to the friction between the chan- a stream on or very close to the bed. nel and the water. bed stability: occurs when the aver- Clean Rivers Program: see Texas Clean age elevation of the streambed does not Rivers Program change significantly over time. Aggrada- Clean Water Act: see federal Clean tion and degradation are the two forms Water Act of bed instability. connectivity: refers to the movement and pertaining to the bottom of a benthic: exchange of water, nutrients, sediments, body of water, on or within the bottom organic matter, and organisms within the substrate material. riverine ecosystem. Connectivity occurs biodiversity: the variety of plant, animal, laterally (between the stream and its and microorganism species present in floodplain), longitudinally (along the the ecosystem and the community struc- stream), vertically (between the stream tures they form. and groundwater), and temporally. biogeochemical cycling: the flow of control variables: large-scale environ- chemical substances to and from the mental factors that control patterns major environmental reservoirs: Atmo- found in local geomorphic features. sphere, Hydrosphere, Lithosphere, and Examples include geology, soils, land use, Biosphere. hydrology, planform channel features, and valley characteristics. biota: the plant (flora) and animal life (fauna) of a region or ecosystem. cover (instream cover): overhanging or instream structure, such as tree roots, boundary conditions: definition or undercut streambanks, boulders, or statement of conditions or phenomena aquatic vegetation that offer protection at the boundaries of a model; water lev- for aquatic organisms. els, flows, and concentrations that are

Texas Water Development Board Report 369 131 current velocity: the velocity of water endemism: the characteristic of being flow in a stream, measured in units of confined to or indigenous in, a certain length per time such as feet per sec- area or region. ond (ft/s or fps) or meters per second federal Clean Water Act: more formally (m/s). referred to as the Federal Water Pollution cutoff: where the stream cuts through Control Act, the Clean Water Act con- the neck of a meander bend. stitutes the basic federal water pollution control statute for the United States. detritus: decaying organic matter (pre- dominantly leaves and other matter from finite difference: a method of solving the vegetation). governing equations of a numerical model by dividing the spatial domain into a Digital Elevation Model: a representa- mesh of nodes. Solution of the governing tion of a topographic surface arranged equations is approximated from values in a data file as a set of regularly spaced at the node locations. x, y, z coordinates where z represents elevation. finite element: a method of solving the governing equations of a numerical mod- Digital Orthographic Quarter Quad- el by dividing the spatial domain into rangle: a digital aerial photography data elements in each of which the solution of set that has been processed to correspond the governing equations is approximated to U.S. Geological Survey 1:12,000-scale by a continuous function. quarter-quadrangle topographic maps. finite volume: a method of solving the Discharge (Q): the volume of water pass- governing equations of a numerical mod- ing a point per unit time. el by dividing the spatial domain into a ecoregion: a geographic area over which mesh of nodes and corresponding vol- the macroclimate is sufficiently uniform umes around each node. Solution of the to permit development of similar ecosys- governing equations is obtained from tems on sites with similar geophysical approximations of the fluxes across the properties. Ecoregions contain multiple boundaries of adjacent volumes. landscapes with different spatial patterns a measure of a river or stream’s of ecosystems. flashiness: tendency to carry a high percentage of its ecosystem: an assemblage of living flow volume in large, infrequent events organisms interacting with physical and rather than more moderate flows that chemical features as an environmental occur frequently. unit. flood: a flow that exceeds the normal ecotone: a transition zone between channel capacity and goes over the banks two distinctly different ecosystems or of a stream or river. communities. flood frequency: how often, on average, eddy viscosity: a model parameter that a discharge of a given magnitude occurs reproduces the effects of turbulent mix- at a particular location on a stream. Usu- ing in fluid flow. ally expressed as the probability that the discharge will exceed some size in a sin- electrofishing: a biological collection method that uses electric current to gle year (the 1-in-100 year flood has a 1 facilitate capturing fishes. percent probability of being equaled or exceeded in any one year). embeddedness: a measure of the degree that gravel and larger substrates are floodplain: a relatively flat area adja- surrounded by fine particles (silt and cent to a stream that is periodically sand). inundated.

132 Texas Water Development Board Report 369 flow duration curve: a measure of the especially valuable for wildlife breeding, range and variability of a stream’s flow. nesting, and habitat. The flow duration curve represents the high flow pulses: the component of an percent of time during which specified instream flow regime that represents flow rates are exceeded at a given loca- short-duration, in-channel, high flow tion. This is usually presented as a graph events following storm events. They of flow rate (discharge) versus percent of maintain important physical habitat time that flows are greater than, or equal features and longitudinal connectivity to, that flow. along the river channel. flow-sensitive habitats: habitats that hydraulic control: a feature in a stream show hydraulic response to relatively (such as a constriction or weir) that small changes in streamflow; responses controls the upstream water surface may be reflected in changes in depth, elevation. velocity patterns, wetted width and/ or habitat area; may be substantially hydraulic model: a computer model of a affected by reductions in stream flows. segment of river used to evaluate hydrau- Examples include shallow-water, edge, lic conditions. and riffle habitat. hydraulic roughness: an estimate of food web: a model structure used to the resistance to flow due to energy loss represent the links between organisms caused by friction between the channel within an environment, based upon the and the water. Chezy’s and Manning’s order in which various organisms con- roughness are two different ways to sume one another. express this parameter. freshwater inflow requirements: fresh- hydrograph: graph showing the variation water flows required to maintain the of water elevation, velocity, streamflow, natural salinity, nutrient, and sediment or other property of water at a particular delivery in a bay or estuary that supports location with respect to time. their unique biological communities and hydrologic model: a computer model of ensures a healthy ecosystem. a watershed used to evaluate how pre- Froude number: ratio of the inertial to cipitation contributes to flow in streams gravitational forces within a fluid. Froude (rainfall/runoff analysis). numbers greater than 1 correspond to hyporheic zone: the zone under a river super-critical flow, less than 1 to sub- or stream comprising substrate whose critical flow. interstices are filled with water. a group of species or organ- guild: impaired water body: a water body that isms that use the same environmental cannot reasonably be expected to attain resources (habitat, food source, etc.) or or maintain applicable water quality life history strategy (e.g., reproduction) standards, and at least one beneficial use in the same way. shows some degree of degradation. the native environment or habitat: imperiled species: declining, rare, or specific surroundings where a plant or uncommon species; species federally animal naturally grows or lives. Habitat listed as threatened or endangered, or includes physical factors such as temper- candidates for such; and species with ature, moisture, and light together with limited distributions. biological factors such as the presence of food or predator organisms. Index of Biotic Integrity: a multi-metric measure of biological condition devel- hardwood bottomland: hardwood for- oped from collection data for fish or ested lowlands adjacent to some rivers,

Texas Water Development Board Report 369 133 other organisms. It consists of metrics in Manning’s equation: an empirical equa- three broad categories: species composition used to estimate the average hydrau- tion, trophic composition, and organism lic conditions of flow within a channel abundance and condition. cross section. instream flow recommendation: the Manning’s roughness: a coefficient in instream flow conditions (i.e., the mag- Manning’s equation that accounts for nitude and timing of flow events) neces- energy loss due to the friction between sary to maintain an ecologically sound the channel and the water. Many hydrau- environment in rivers and streams as lic models use this coefficient to estimate developed by applying the best avail- resistance to flow. able methods. Recommendations are in mean column velocity: the average the form of an instream flow regime that velocity of fluid flow measured in a col- includes subsistence flows, base flows, umn extending from the surface of the high flow pulses, and overbank flows. water to the bed of the channel. Often interstitial spaces: gaps between the referred to simply as “velocity” or “cur- particles that make up the streambed. rent velocity.” In contrast, point velocity is measured at a single point in the water key habitats: flow-sensitive habitats column. as well as habitats that support key species. median particle size (D50): value for which half the particles in a sample key species: species that are targeted have a greater diameter and half a lesser for instream flow assessment or more diameter. generally taxa of interest; may include lotic-adapted species, imperiled species, mesohabitat: basic structural elements sport fishes, or other species related to of a river or stream such as pools, back- study objectives. waters, runs/glides, and riffles. lotic: relating to moving water such as microhabitat: zones of similar physi- streams and rivers. cal characteristics within a mesohabitat unit, differentiated by aspects such as lotic-adapted species: species for substrate type, water velocity, and water which all or part of their life history is depth. dependent on flowing water. Examples of lotic-adapted species are riffle-dwell- modified Wentworth scale: a specific ing fishes such as darters, blue sucker, scale used to classify substrate particles riverine mussels, aquatic invertebrates, by their diameter. Categories in this scale and others. include boulder, cobble, pebble, gravel, sand, silt, and clay. macroinvertebrate: an animal without a backbone, large enough to be seen with- National Elevation Dataset: a Digital out magnification and unable to pass Elevation Map developed and main- through 0.595 mm mesh. tained by the U.S. Geological Survey that provides the best available elevation data macrophyte: macroscopic plants in the for the conterminous area of the United aquatic environment. The most common States. macrophytes are the rooted vascular plants that are usually arranged in zones naturalized conditions: an estimate of in aquatic ecosystems and restricted in natural conditions obtained by attempt- their area by the extent of illumination ing to remove effects of human activities through the water and sediment deposi- from a set of measured conditions. tion along the shoreline. Navier-Stokes equations: a set of equations that describe the physics govern-

134 Texas Water Development Board Report 369 ing the motion of a fluid. In addition to recruitment: survival of young plants applications in hydraulic studies of rivers and animals from birth to a life stage less and streams, these equations are used vulnerable to environmental change. to model weather, ocean currents, and resilience (ecosystem): the ability of an aerodynamics. ecosystem to maintain or restore bio- nutrient cycle: the cyclic conversions diversity, biotic integrity, and ecologi- of nutrients from one form to another cal structure and processes following within biological communities. A simple disturbance. example is the production and release response variables: environmental fea- of molecular oxygen from water during tures of the river channel on a local or photosynthesis by plants and the subse- site-specific scale. Examples include quent reduction of atmospheric oxygen channel shape, cross-sectional dimen- to water by the respiratory metabolism sions, substrate, bank shape, floodplain of other biota. characteristics, vegetation, and channel overbank flows: the component of an patterns. instream flow regime that represents return flow: the portion of a diverted infrequent, high flow events that exceed flow that is not consumptively used and the normal channel. These flows main- returns to its original source or another tain riparian areas and provide lateral body of water. connectivity between the river channel and active floodplain. They may also pro- riparian area: a zone of transition vide life-cycle cues for various species. between aquatic and terrestrial ecosystems that exhibits, through the zone’s the relationship between Peclet number: existing or potential soil-vegetation com- properties of the mesh, fluid velocity, and plex, the influence of surface or subsur- eddy viscosity for a hydraulic computer face water. model. River Styles (RS): a framework for con- an area with physiographic province: ducting geomorphic analysis of river similar characteristics based on geology, systems. soil type, and topography. river (or riverine) ecosystem: the biotic the velocity of fluid flow point velocity: and abiotic components within the main measured at a single point within a vol- channel and adjoining floodplain and ume of flowing water. riparian area of a river segment, their rating curve: a graph showing the rela- structural relationships, and the pro- tionship between water surface elevation cesses that maintain them. and discharge of a stream or river at a routing parameters: coefficients that, given location. Also called a stage-dis- along with mathematical routing equa- charge curve. tions, can be used to estimate the attenu- reach: in general, a length of stream with ation and lag (time delay) associated with relatively homogenous characteristics. In the movement of flow through a length terms of the Texas Instream Flow Pro- of stream channel. gram, a subdivision of a segment that runoff: rainwater or snowmelt that is exhibits relatively homogeneous channel transported to streams by overland flow, and floodplain conditions (hydrologic/ drains, or ground water. hydraulic, biological, geomorphic, and water quality). scour: the erosive action of running water in streams, which excavates and carries away material from the bed and banks.

Texas Water Development Board Report 369 135 Or, pertaining to a place on a streambed ticle in a stream channel. It is affected by swept (scoured) by running water. discharge and slope. Section 404: the section of the federal sub-basin: in general, a portion of a river Clean Water Act delineating restrictions basin. In relation to the Texas Instream on the dredging and filling of wetlands Flow Program, the full geographic and disruption of beds and banks of scope of priority studies within major streams. river basins, including the main channel, floodplain, tributaries, and contributing sediment trapping efficiency (E): the watershed area of all study segments. ratio of sediment retained within the reservoir to the sediment inflow to the sub-critical flow: flow characterized by reservoir. low velocity and a Froude number less than 1. segment: a water body or portion of a water body that is individually defined subsistence flows: the component of and classified in the Texas Surface an instream flow regime that represents Water Quality Standards. A segment is infrequent, naturally occurring low flow intended to have relatively homogeneous events that occur for a seasonal period chemical, physical, and hydrological of time. They maintain water quality characteristics. criteria and provide sufficient habitat to ensure organism populations capable of seven-day two-year low flow (7Q2): the recolonizing the river system once nor- lowest average streamflow for seven con- mal, base flows return. secutive days with a recurrence interval of two years, as statistically determined super-critical flow: flow characterized from historical data. Some water quality by high velocity and a Froude number standards do not apply at streamflows greater than 1. that are less than the 7Q2 flow. sustainability: the long-term capacity of shear stress: the frictional force per unit an ecosystem to maintain ecological pro- area exerted on the streambed by flowing cesses and functions, biological diversity, water. An important factor in the move- and productivity. ment of bed material and description of taxa: groups of organisms or eco- habitat for some organisms. systems categorized by common sinuosity: a measure of meander “inten- characteristics. sity.” The ratio of the length of a stream Texas Clean Rivers Program: a program measured along its thalweg to the length administered by the Texas Commission of the valley through which the stream on Environmental Quality which con- flows. ducts water quality monitoring, assess- sound ecological environment: a func- ment, and public outreach activities in tioning ecosystem characterized by the state. Local river authorities are pri- intact, natural processes, resilience, and a mary partners in this program. balanced, integrated, and adaptive com- thalweg: a line following the deepest part munity of organisms comparable to that of the bed of a channel. of the natural habitat of a region. time series: a set of data collected the number of species species richness: sequentially, usually at fixed intervals in an assemblage or sample. of time. For example, a hydrologic time stage: see water surface elevation. series may provide average daily flow values at a particular location for a number stream power: a measure of energy avail- of years of observation. A habitat time able to move sediment, or any other par- series could provide an estimate of cor-

136 Texas Water Development Board Report 369 responding average daily habitat condi- its designated use. Criteria are set for tions for the same time period. individual pollutants based on different water uses, such as public water supply, Total Dissolved Solids: a water quality aquatic habitat, industrial supply, or parameter that measures the solids (usu- recreation. ally mineral salts) dissolved in water. water quality standards: state-adopt- Total Maximum Daily Load: the maxi- ed and U.S. Environmental Protection mum quantity of a particular water pol- Agency-approved ambient standards for lutant that can be discharged into a body water bodies. Standards include the use of water without violating a water quality of the water body and the water quality standard. criteria that must be met to protect the transport capacity: the capacity of a riv- designated use or uses. er to carry sediment in suspension or to the surface below which soil move sediment along the riverbed. water table: is saturated with water. Its depth below trophic structure: the feeding relation- the ground surface is influenced by ships among species within a food web/ rainfall and human development (wells, chain or a single ecosystem. drainage ditches, loss of wetlands, etc.). Typically, the depth below the surface to validation: comparison of computer model results with a set of data that were the upper layer of groundwater. not used for calibration. wetland: An area (including a swamp, marsh, bog, prairie pothole, or similar water availability model: a numerical surface water flow model used to deter- area) having a predominance of hydric mine the availability of surface water for soils that are inundated or saturated by water right permitting in the state. surface or groundwater at a frequency and duration sufficient to support and watershed: the area enclosed by a topo- that under normal circumstances sup- graphic divide, which drains to a specific ports the growth and regeneration of location on a stream or river. hydrophytic vegetation. The term “hydric water surface elevation (or stage): the soil” means soil that, in its undrained elevation of a water surface above or condition, is saturated, flooded, or pond- below an established reference level, ed long enough during a growing season such as sea level. to develop an anaerobic condition that supports the growth and regeneration of water quality: the chemical, physical, hydrophytic vegetation. (“Hydrophytic biological, radiological, and thermal con- vegetation” is a plant growing in water dition of water. or a substrate, which is at least periodi- water quality criteria: a specific level or cally deficient in oxygen during a grow- range of levels of water quality expected ing season as a result of excessive water to render a body of water suitable for content.)

Texas Water Development Board Report 369 137 Texas Commission on Environmental Quality P.O. Box 13087 Austin, Texas 78711-3087

Texas Parks and Wildlife 4200 Smith School Road Austin, Texas 78744

Texas Water Development Board P.O. Box 13231, Capitol Station Austin, Texas 78711-3231