Des Moines River Basin Master Reservoir Regulation Manual Feasibility Report with Integrated Environmental Assessment
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Des Moines River Basin Master Reservoir Regulation Manual Feasibility Report with Integrated Environmental Assessment Des Moines River, Saylorville Lake, & Lake Red Rock June 2018 This page was intentionally left blank. Des Moines River Basin Master Reservoir Regulation Manual Feasibility Report with Integrated Environmental Assessment Des Moines River, Saylorville Lake, & Lake Red Rock EXECUTIVE SUMMARY The U.S. Army Corps of Engineers (Corps), Rock Island District (District) impounded the Des Moines River by two congressionally authorized Civil Works projects, Red Rock Dam (authorized in 1938) and Saylorville Dam (authorized in 1958) (Figure ES-1), creating Lake Red Rock and Saylorville Lake. The projects’ authorized purposes included flood risk management (FRM) for the Des Moines and Mississippi Rivers, low flow augmentation for downstream water supply and water quality, fish and wildlife management, and recreation. The current Des Moines River Basin Master Reservoir Regulation Manual was approved in 1992. Reservoir Regulation manuals consist of operational parameters defining how, and when, water is stored and released. These include a schedule of releases, conservation pool levels to be maintained during non- flood or drought conditions, and downstream water level constraints. The following key issues inform the primary purpose and need of the Des Moines River Basin Master Reservoir Regulation Manual update and are individually discussed in subsequent paragraphs: 1. The Des Moines River has experienced a significant increase in the magnitude and frequency of flooding. 2. Sedimentation has negatively impacted water supply capacity. 3. Approved water control deviations have confirmed the need to update the water control plans for each of these reservoirs. The Des Moines River Basin has experienced significant land use changes. These changes influence runoff rates into tributaries of, and the main stem Des Moines River resulting in increased flood risk within the Des Moines River Basin. Following the 2008 Des Moines River flood, the District re- evaluated regulated flow frequencies on the Des Moines River. The Regulated Flow Frequency Study, completed in early 2010, concluded the frequency of flooding on the Des Moines River increased and indicated flood events like 1993 and 2008 are more likely to occur in the future. The water supply contract with the State of Iowa and the U.S. Government allots 18.86% of the usable storage between elevations 812 feet and 836 feet (NGVD29) for water supply storage. Potential changes to the water control plan at Saylorville Lake could improve the availability of water during drought conditions. ES-I During portions of 2016-2018, the District requested and obtained three temporary deviations from normal operating protocols. These deviations provided opportunities to determine the impact of potential changes to the water control plans for Saylorville Lake and Lake Red Rock. The purpose of the study is to update the Des Moines River Basin Master Reservoir Regulation Manual to better meet mission objectives based on changes in flood frequencies, land use, and reservoir sedimentation. The recommended plan would result in a revised Des Moines River Basin Master Reservoir Regulation Manual and updates to the Saylorville Lake and Lake Red Rock Water Control Plans. The District drafted this feasibility report with an integrated environmental assessment to present a detailed account of the planning, regulatory, and environmental considerations resulting in the Recommended Plan. Figure ES-1. Des Moines River Basin The final array of alternatives, 5A and 6, met all project goals and objectives with the exception of Goal 5 Objectives 5.a. Making improvements to the conditions for Red Rock and Ottumwa hydropower operations. Finally criteria used to select the recommended plan was based on which alternative reduced flood damages the most. Tables EA-20 and EA-21 in VI.B. Process for Selection of a Recommended Plan present the final comparison of alternative 5A and 6. Based on the environmental assessment and the resulting damage summary, Alternative 6 is the preferred alternative and is recommended for replacing the current Des Moines River Basin Master Reservoir Regulation Manual. The recommended plan is not anticipated to be controversial in nature as local emergency managers, Iowa Department of Natural Resources, city and county governments, and NGO’s ES-II have been active project partners through the National Environmental Policy Act (NEPA) process. Additionally, the recommended plan requires no construction and no additional implementation or operational costs. ES-III Page Intentionally Left Blank ES-IV Des Moines River Basin Master Reservoir Regulation Manual Feasibility Report with Integrated Environmental Assessment Des Moines River, Saylorville Lake, & Lake Red Rock EXECUTIVE SUMMARY .................................................................................................................. ES-I LIST OF ACRONYMS ....................................................................................................................... EA-v CHAPTER I: PURPOSE AND NEED FOR FEDERAL ACTION ................................................ EA-1 A. INTRODUCTION B. PURPOSE AND NEED C. DECISION D. AUTHORITY E. SCOPING AND SIGNIFICANT ISSUES F. PROBLEMS AND OPPORTUNITIES G. GOALS AND OBJECTIVES H. RELATED NEPA DOCUMENTATION AND OTHER STUDIES CHAPTER II: INVENTORY AND FORECASTED CONDITIONS .......................................... EA-13 A. INTRODUCTION B. GENERAL SETTING C. FLOODPLAIN RESOURCES D. LAND USE E. AQUATIC WILDLIFE RESOURCES F. ENDANGERED, THREATENED, & CANDIDATE SPECIES G. INVASIVE SPECIES H. VEGETATION I. RIVERS AND STREAMS, WATER QUALITY, WETLANDS J. HYDROLOGY AND HYDRAULICS K. STATE PARKS, CONSERVATION AREAS, AND OTHER AREAS OF RECREATIONAL, ECOLOGICAL, SCENIC, OR AESTHETIC IMPORTANCE L. HISTORICAL & CULTURAL RESOURCES M. SOCIOECONOMIC RESOURCES EA-i Des Moines River Basin Master Reservoir Regulation Manual Feasibility Report with Integrated Environmental Assessment N. HUMAN HEALTH & SAFETY O. SUSTAINABILITY, GREENING AND CLIMATE CHANGE P. CONSTRUCTED RESOURCES-PUBLIC STRUCTURES, UTILITIES, TRANSPORTATION, OTHER Q. RECREATION R. SEDIMENTATION/SOILS/PRIME AND UNIQUE FARMLAND S. HAZARDOUS, TOXIC, AND RADIOACTIVE WASTE (HTRW) CHAPTER III: FORMULATION OF ALTERNATIVES ........................................................... EA-58 A. ALTERNATIVE FORMULATION STRATEGIES FINAL ARRAY OF ALTERNATIVES B. ALTERNATIVES CONSIDERED BUT NOT CARRIED FORWARD FOR DETAILED ANALYSIS C. ALTERNATIVES CARRIED FORWARD FOR DETAILED ANALYSIS NO ACTION ALTERNATIVE 5a ALTERNATIVE 6 CHAPTER IV: EVALUATION OF ALTERNATIVE PLANS .................................................... EA-67 A. INTRODUCTION B. STEP 1: HYDRAULIC EVALUATION C. STEP 2: ECONOMIC EVALUATION CHAPTER V: THE ACTION ALTERNATIVES’ ENVIRONMENTAL CONSEQUENCES . EA-72 A. INTRODUCTION B. COMPARING FINAL ARRAY C. FLOODPLAIN RESOURCES D. LAND USE E. AQUATIC WILDLIFE RESOURCES F. ENDANGERED, THREATENED, & CANDIDATE SPECIES G. INVASIVE SPECIES H. VEGETATION I. RIVERS AND STREAMS, WATER QUALITY, WETLANDS J. HYDROLOGY AND HYDRAULICS K. STATE PARKS, CONSERVATION AREAS, AND OTHER AREAS OF RECREATIONAL, ECOLOGICAL, SCENIC, OR AESTHETIC IMPORTANCE L. HISTORICAL & CULTURAL RESOURCES M. SOCIOECONOMIC RESOURCES N. HUMAN HEALTH & SAFETY O. SUSTAINABILITY, GREENING AND CLIMATE CHANGE P. CONSTRUCTED RESOURCES-PUBLIC STRUCTURES, UTILITIES, TRANSPORTATION, OTHER Q. RECREATION R. SEDIMENTATION/SOILS/PRIME AND UNIQUE FARMLAND EA-ii Des Moines River Basin Master Reservoir Regulation Manual Feasibility Report with Integrated Environmental Assessment S. HAZARDOUS, TOXIC, AND RADIOACTIVE WASTE (HTRW) CHAPTER VI: SELECTED PLAN ................................................................................................. EA-80 A. ENVIRONMENTAL OPERATING PRINCIPLES AND CAMPAIGN PLAN GOALS B. PROCESS FOR SELECTION OF A RECOMMENDED PLAN C. DISCUSSION OF RECOMMENDED PLAN D. PARTNER COORDINATION E. ENVIRONMENTAL COMPLIANCE F. RELATIONSHIP BETWEEN SHORT-TERM USE AND LONG-TERM PRODUCTIVITY G. RELATIONSHIP TO LAND USE PLANS H. IRREVERSIBLE AND IRRETRIEVABLE COMMITMENT OF RESOURCES I. INDIRECT EFFECTS J. CUMULATIVE IMPACTS K. ADAPTIVE MANAGEMENT AND MONITORING PLAN L. RISK AND UNCERTAINTY M. CONCLUSIONS VII. LITERATURE CITED ............................................................................................................. EA-95 FIGURES Figure EA-1 Project Vicinity ...................................................................................................................... EA-2 Figure EA-2 Des Moines River Basin ................................................................................................. EA-15 Figure EA-3 Land Use Land Cover Class ........................................................................................... EA-17 Figure EA-4 Prairie Management at Lake Red Rock .......................................................................... EA-22 Figure EA-5 Major Rivers and Streams in the Des Moines River Watershed ..................................... EA-30 Figure EA-6 Des Moines River Basin Impaired Water Bodies ........................................................... EA-32 Figure EA-7 Des Moines River Wetland Area (ha) ............................................................................. EA-34 Figure EA-8 Statewide and Individual Gage Precipitation Records .................................................... EA-35 Figure