Henrys Fork Basin Study Final Report 1 1.0 Introduction
Total Page:16
File Type:pdf, Size:1020Kb
Henrys Fork Basin Study Final Report Produced in partnership with the State of Idaho Water Resource Board U.S. Department of the Interior Idaho Water Resource Board Bureau of Reclamation State of Idaho Pacific Northwest Region Boise, Idaho Snake River Area Office Boise, Idaho January 2015 MISSION OF THE U.S. DEPARTMENT OF THE INTERIOR PROTECTING AMERICA'S GREAT OUTDOORS AND POWERING OUR FUTURE The U.S. Department of the Interior protects America's natural resources and heritage, honors our cultures and tribal communities, and supplies the energy to power our future. MISSION OF THE BUREAU OF RECLAMATION The mission of the Bureau of Reclamation is to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public. Photograph on front cover: Fly fishing, irrigated agriculture, and wildlife habitat are important activities in the Henrys Fork River basin Disclaimer The Henrys Fork Basin Study was funded jointly by the Bureau of Reclamation (Reclamation) and the Idaho Water Resource Board (IWRB), and is a collaborative product of the study participants as identified in Section 1.3, page 5 of this report. The purpose of the study is to assess current and future water supply and demand in the Henrys Fork Basin and adjacent areas that receive water from the basin, and to identify a range of potential strategies to address any projected imbalances. The study is a technical assessment and does not provide recommendations or represent a statement of policy or position of the Bureau of Reclamation, the Department of the Interior, or the funding partners. The study does not propose or address the feasibility of any specific project, program or plan. Nothing in the study is intended, nor shall the study be construed, to interpret, diminish, or modify the rights of any participant under applicable law. Nothing in the study represents a commitment for provision of Federal funds. All cost estimates included in this study are preliminary and intended only for comparative purposes. Henrys Fork Basin Study Final Report Produced in partnership with the State of Idaho Water Resource Board U.S. Department of the Interior Idaho Water Resource Board Bureau of Reclamation State of Idaho Pacific Northwest Region Boise, Idaho Snake River Area Office Boise, Idaho January 2015 This page intentionally left blank Abbreviations and Acronyms AWEP Agricultural Water Enhancement Program Basin Study Henrys Fork Basin Study CBWTP Columbia Basin Water Transaction Program cfs Cubic feet per second CIG Conservation Innovation Grant Program CRP Conservation Reserve Program ESA Endangered Species Act ESPA Eastern Snake Plain Aquifer ESPA CAMP Eastern Snake Plain Aquifer Comprehensive Aquifer Management Plan ESPAM Eastern Snake Plain Aquifer Model FERC Federal Energy Regulatory Commission FMID Fremont-Madison Irrigation District GCMs Global Circulation Models Henrys Fork River Henrys Fork of the Snake River Idaho CREP Idaho Conservation Reserve Enhancement Program IDFG Idaho Department of Fish and Game IDWR Idaho Department of Water Resources IWRB Idaho Water Resource Board IWTP Idaho Water Transactions Program LRP Local rental pools LW/D Less warming and drier climate scenario LW/W Less warming and wetter climate scenario MC Minor change climate scenario NEPA National Environmental Policy Act NFRC North Fork Reservoir Company NRCS U.S. Department of Agriculture, Natural Resources Conservation Service NWSRS National Wild and Scenic River System Plan Comprehensive State Water Plan Recharge Program Managed Aquifer Recharge Program Reclamation U.S. Department of the Interior, Bureau of Reclamation RMP Teton River Canyon Resource Management Plan State State of Idaho USGS U.S. Geological Survey Watershed Council Henry’s Fork Watershed Council Workgroup Henry’s Fork Watershed Council and other interested stakeholders Executive Summary EXECUTIVE SUMMARY Introduction The Bureau of Reclamation (Reclamation), in partnership with the Idaho Water Resource Board (IWRB), conducted a Henrys Fork Basin Study (Basin Study) and the results of this Basin Study are documented in this Final Report of the Henrys Fork Basin Study (Final Report). While the overall purpose of the Basin Study is to assess current and future water supply and demand in the Henrys Fork Basin and adjacent areas that receive water from the basin, and to identify a range of potential strategies to address any projected imbalances, it also assists the State and local planning efforts by exploring potential action alternatives for (1) meeting the complex water supply and management challenges in the basin, (2) meeting the goals of the Eastern Snake Plain Aquifer (ESPA) Comprehensive Aquifer Management Plan (CAMP) and Idaho State Water Plan, and (3) identifying risks posed to water supply by climate change and opportunities to mitigate that risk through developing water supplies, improving water management, and sustaining or improving environmental quality and ecological resiliency. This Basin Study complements the objectives of ESPA CAMP and policies of the State Water Plan by identifying specific alternatives to improve water supplies and water management in the upper Snake River basin. Reclamation and IWRB worked with the Henry’s Fork Watershed Council (Watershed Council) in developing alternatives to address the purposes of the Basin Study. The Watershed Council functioned as a stakeholder workgroup (Workgroup) throughout most of the process, providing review and input both collectively and as individuals. Throughout the Basin Study, the Watershed Council and many of its participating members elevated public awareness of the Basin Study process and clearly advertised opportunities for public review and involvement. The Henrys Fork of the Snake River (Henrys Fork River) is located in eastern Idaho, in the upper Snake River watershed. The river provides irrigation water for over 280,000 acres, sustains a world-class trout fishery, and is a strong hold for native Yellowstone cutthroat trout. Agricultural changes, population growth and its consequent urban development, drought conditions, and climate changes are impacting water resources. These factors are increasing the need to identify adaptation and mitigation strategies to resolve water supply imbalances and preserve ecological resiliency in the basin, especially with respect to climate change. Current water demands in the Henrys Fork River basin vary from year to year with varying annual precipitation amounts. Future water needs will vary with climate change impacts, population growth, changes in farming methods, water conservation, and other factors that January 2015 - Henrys Fork Study Final Report ES-1 Executive Summary may not be fully understood or predicted at this point in time. Declining aquifer levels and spring discharges, changing flows in the Snake River, and actions that have placed demands on already scarce water supplies (e.g., flow augmentation for anadromous fish survival) have resulted in insufficient supplies to satisfy existing beneficial uses across the upper Snake River basin. The ESPA CAMP identified an annual water budget deficit in the ESPA of 600,000 acre-feet, and established a long-term goal to adjust this deficit by implementing a mix of management strategies over a 20-year period (Reclamation 2012). The western portion of the Henrys Fork River basin overlies the ESPA so opportunities in the basin could support the objectives of the ESPA CAMP for stabilizing the ESPA. The Henrys Fork River basin contributes about 25 percent of the upper Snake River supply in eastern Idaho and also contributes to groundwater recharge in local aquifers and the ESPA. Climate change studies projected a shift in timing and increase in inflow volume to earlier in the year, which resulted in an increase in the end-of-month storage earlier in the year and a greater need to use reservoir storage to provide irrigation water later in the summer months (Reclamation 2011). A decrease of streamflows was shown to occur in the latter part of the summer in warmer months (Reclamation 2011). A decrease in instream flow in the late summer to early fall months would result in less water available for natural flow diversions and more pressure for deliveries from storage. For irrigation, reservoir management and ecological flow objectives, it was found that late season flow and reservoir objectives would be impacted the most by climate change, especially in the driest conditions (Reclamation 2011). The Workgroup, Reclamation, and IWRB initially identified 51 alternatives to address the Henrys Fork River basin water needs. From these 51 alternatives, a screened group of about 18 alternatives were evaluated, and the results were documented in the Final Henrys Fork Basin Special Study Interim Report dated July 2013 (Reclamation 2013a). Those alternatives were assessed so that only the most viable alternatives were passed on for more scrutiny and detail. The results of these assessments were presented to the Workgroup for input and the proposed alternatives were further filtered down to a group of 11 that were carried forward for additional analyses in this Basin Study. The IWRB and other water users requested the Teton Dam alternative be retained and evaluated for comparative purposes. The final analyses refined and revised the alternatives to a group of 12 alternatives, which were grouped into three major categories: surface storage, managed groundwater recharge, and water conservation.