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Methods and Tools for Defining Environmental Flows

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Methods and Tools for Defining Environmental Flows MethodsMethods andand toolstools forfor definingdefining EnvironmentalEnvironmental FlowsFlows Glauco Kimura de Freitas The Nature Conservancy GEF IW:LEARN Regional Workshop on Application of Environmental Flows in River Basin Management February, 11-15, 2008 TOPICSTOPICS 1. Overview of methods for flow assessment a. What is an environmental flow assessment? b. Categories of environmental flow assessment methodologies • Hydrologic • Hydraulic rating • Habitat simulation • Holistic 2. Examples of practical applications • Ecologically Sustainable Water Management (ESWM) 3. Choosing the right method a. Advantages and disadvantages b. Fitting tools and approaches to the situation ExpectedExpected OutcomesOutcomes • Understand what is an environmental flow assessment, when to use and why. • Know the differences between the four categories of environmental flow assessment methodologies, the advantages and disadvantages of each by a real example application • Being able to choose the right method based on the “pros and cons” and supported by your objectives. PremisesPremises • Reconnaissance that the discussion of environmental flow assessment methodologies is based on the fact that the ecosystems are a beneficiary of the flow regime, in other terms, they are an “user” of the river. • We need to quantify the ecosystems requirements, as well as other users requirements. • Based on such requirements we will need to incorporate them into a real scenario to accomplish multiple water uses. • We will have concrete elements to discuss priorities and trade offs. 1.1. OverviewOverview ofof methodsmethods forfor flowflow assessmentassessment What is an environmental flow assessment? “Is an assessment of how much of the original flow regime of a river should continue to flow down it and onto its floodplains in order to maintain specified, valued features of the ecosystem hydrological regimes for the rivers, the environmental flow requirements, each linked to a predetermined objective in terms of the ecosystem’s future condition...” Source: Tharme, 2003 DevelopingDeveloping environmentalenvironmental flowsflows • Evolution of environmental flows assessment methodologies • Tharme (2003) identified > 200 different methods • Review of different methods • Range from simple ‘rules of thumb’ to complex, multi-year processes integrating modeling and field data 1.1. OverviewOverview ofof methodsmethods forfor flowflow assessmentassessment Categories of environmental flows methodologies and examples • Tennant 1. Hydrologic •Q 90 2. Hydraulic rating • Wetted perimeter method •IFIM 3. Habitat simulation • PHABSIM 4. Holistic methods • Building Blocks Methodology (BBM) Source: Tharme, 2003 1.1. OverviewOverview ofof methodsmethods forfor flowflow assessmentassessment • Hydrological - Primarily use hydrological data (historical monthly or daily flow records) for making e-flow recommendations for maintaining river health at designated level • Hydraulic rating - use changes in simple hydraulic variables (e.g. wetted perimeter) across single river cross-section as surrogate for habitat factors limiting to target biota • Habitat simulation - Assess e-flows on basis of modeling of quantity and suitability of physical habitat available to target species under different flow regimes (integrated hydrological, hydraulic and biological response data) • Holistic – identify important flow events for all major components of river, model relationships between flow and ecological, geomorphological and social responses, and use in interdisciplinary team approach to establish recommended e-flow regime/implications of flow scenarios (bottom-up or top-down) Habitat simulation methodologies e.g. IFIM/PHABSIM (C) (B) Habitat suitability curves for target sp. 20 000 xsec 2 adult 1.0 1.0 juvenile 0.8 0.8 15 000 0.6 0.6 0.4 0.4 (A) 10 000 0.2 0.2 0.0 0.0 flow 0.0 0.1 0.2 0.3 0.4 0.5 0.0 0.1 0.2 0.3 0.4 0.5 -1 WUA + Velocity Depth = 5 000 1.0 xsec 1 0.8 0.6 0 0 5 10 15 20 25 0.4 0.2 0.0 Q 012345 V1 V2 V3 ........Velocity Channel Index DDD1 2 3 ........Depth CI1 CI2CI3 ........CI AAA1 2 3 ........Area 14000 existing 12000 proposed 10000 8000 6000 4000 Habitat area (WUA) 2000 0 1980 1981 1982 1983 19841985 1986 Time ShiftShift fromfrom minimumminimum flowflow toto flowflow regime:regime: • * magnitude, frequency, duration, timing, rate of change * flow components (low flows, freshes, floods) East Rapti R. (Nepal), Rajaya, 560 km2 120 100 Flow regime 80 Minimum flow 60 40 Discharge, m3/s 20 0 0 50 100 150 200 250 300 350 Days since 1 January, 1991 Source: Poff, et al. 1997 HolisticHolistic Methodologies:Methodologies: naturalnatural flowflow paradigmparadigm 1. Retain flood peak - scour channel & recharge banks & channel & recharge banks & Natural floodplain For ecological 2. Maintain low flow - aquatic maintenance ) habitat in dry season 6 1 3. Retain spring fresh - cue for x 10 3 fish life cycles (e.g. migration) 4. Vary low flow in wet season, but with removal of some floods Source: Postel & Richter, 2003 DISCHARGE (m DISCHARGE 3 4 2 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 2.2. ExampleExample ofof aa holisticholistic methodmethod applicationapplication Ecologically Sustainable Water Management (ESWM) – The Nature Conservancy Source: Richter, et al. 2003 1 4 Estimate 6 environmental Foster flow collaborative Design and requirements dialogue to implement search for search for an adaptive solutions management 3 Identify areas of plan potential incompatibility monitoring 5 funding 2 Conduct water governance Determine management influence experiments to of main resolve activities uncertainty I. Problem definition II. Search for solutions III. Adaptive management 2.2. ExampleExample ofof aa practicalpractical holisticholistic methodmethod applicationapplication 1 1. Estimate ecosystem flow requirements EstimateEstimate environmentalecosystem flowflow • Gathering historical hydrological flow requirementsrequirements data series (hydrological desk top analysis) 3 • Characterization of the natural flow Identify areas of regime (hydrological and hydraulic potential incompatibility analysis) • Identification of critical flow events 2 • Development of simulation models to Determine influence assess how biodiversity is related to of main the natural flow regime (habitat activities modeling ex. PHABSIM) Q (cms) J F M A M J J A S O N D Natural hydrograph Regulated hydrograph Channel-forming flows Cottonwood recruitment Juvenile salmon access to floodplain habitats Q (cms) Over-summer rearing Salmon spawning Adult salmon migration J F M A M J J A S O N D Determining flow needs for various ecosystem processes 2.2. ExampleExample ofof aa practicalpractical holisticholistic methodmethod applicationapplication 1 2. Determine influence of human Estimate environmental activities flow requirements • How much the human presence is influencing the natural flow 3 Identify areas of regime and the critical flow potential events? incompatibility 2 • Hydrological models (ex. water budget analysis) DetermineDetermine influenceinfluence ofof human main • Water withdrawals, activitiesactivities evaporation, transpiration x rainfall, etc. 2.2. ExampleExample ofof aa practicalpractical holisticholistic methodmethod applicationapplication 1 3. Identify areas of potential incompability Estimate environmental • Hydrological alteration analysis (ex. IHA flow software) requirements • Range of variability approach (RVA) 3 • Flow recommendation workshop / multi IdentifyIdentify areasareas ofof disciplinary teams potentialpotential incompatibilityincompatibility • Understand the natural and altered flow regimes 2 • How the biodiversity and socio economy is Determine influence impacted of main activities • Scenario analysis and hydrogram prescriptions (spatial and temporal analysis) 2.2. ExampleExample ofof aa practicalpractical holisticholistic methodmethod applicationapplication 4. Foster collaborative dialogue to search for 4 solutions Foster • Participatory meetings and workshops to assess collaborative the scenarios and flow recommendations dialogue to search for • Search for the accomplishment of distinct solutions objectives • Trade off analysis engaging decision makers, users, local communities, etc. 5 • Discuss “win win” solutions Conduct water management 5. Conduct water management experiments to resolve experiments to uncertainty resolve uncertainty • Experimental implementation of the best scenario(s) (“win – win” situations) 2.2. ExampleExample ofof aa practicalpractical holisticholistic methodmethod applicationapplication Design and implement an 6 adaptive management plan Design and implement using the knowledge gained in an adaptive steps 1-5, create an adaptive management plan management program to monitoring facilitate ecologically sustainable funding water management for the long governance term, including monitoring, funding and governance 3.3. ChoosingChoosing thethe rightright methodmethod 3.3. ChoosingChoosing thethe rightright methodmethod Hydrological methodologies: strengths and deficiencies • Simple, rapid, inexpensive desktop approaches • Low data needs, primarily flow data • Suitable for water resource planning purposes • Potential for regionalization for different river ecotypes • Simplistic, inflexible, low resolution output • Direct ecological links absent or limited (but recent advances made to improve ecological relevance of flow indices and to set flow targets) • Dynamic nature of flow regime seldom addressed • Suitable for low controversy situations QR90 3.3. ChoosingChoosing
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