APPENDIX H-2 Hydrology and Hydrologic Models 2006 Table of Contents Items Page Appendix H-2 Hydrology and Hydrologic Models...................................................................H2-1 Description of Study Area.......................................................................................................H2-1 Background.................................................................................................................H2-1 Salton Sea Watershed................................................................................................H2-2 Summary of Goals and Approaches.......................................................................................H2-9 Historical Hydrology and Salt Loads.......................................................................................H2-9 Period of Historical Analysis........................................................................................H2-9 Inflows from Mexico..................................................................................................H2-10 New River......................................................................................................H2-10 Alamo River...................................................................................................H2-10 Salt Loads.....................................................................................................H2-10 Inflows from Imperial Valley......................................................................................H2-11 New River......................................................................................................H2-11 Alamo River...................................................................................................H2-11 IID Direct Drains............................................................................................H2-11 Groundwater Inflows.....................................................................................H2-12 Salt Loads.....................................................................................................H2-12 Inflows from Coachella Valley...................................................................................H2-12 Whitewater River/Coachella Valley Storm Channel and Direct Drains..........H2-12 Groundwater Inflows.....................................................................................H2-13 Salt Loads.....................................................................................................H2-13 Inflow from Portions of the Watershed Not Tributary to Irrigated Areas of Imperial and Coachella Valleys.................................................................................H2-13 San Felipe Creek...........................................................................................H2-13 Salt Creek......................................................................................................H2-14 Other Surface Inflows....................................................................................H2-14 Groundwater Inflows.....................................................................................H2-14 Salt Loads.....................................................................................................H2-19 Precipitation..............................................................................................................H2-19 Evaporation...............................................................................................................H2-19 Estimated Historical Water Balance for the Salton Sea............................................H2-20 Estimated Historical Salt Balance for the Salton Sea................................................H2-20 Description of No Action Alternative-CEQA Conditions........................................................H2-24 Development of the Hydrologic Model......................................................................H2-32 Study Period..............................................................................................................H2-32 Summary of Projects Considered in No Action Alternative-CEQA Conditions..........H2-32 Inflows from Mexico..................................................................................................H2-33 Mexicali Wastewater Improvements..............................................................H2-34 Mexicali Power Plants...................................................................................H2-34 All-American Canal Lining Project.................................................................H2-34 Inflows from Imperial Valley......................................................................................H2-34 IID Water Conservation and Transfer Project................................................H2-39 Sedimentation/Silt Total Maximum Daily Loads for New and Alamo Rivers.H2-41 Inflows from Coachella Valley...................................................................................H2-41 QSA Related Projects...................................................................................H2-42 Coachella Valley Water Management Plan...................................................H2-42 Salton Sea Ecosystem H2-iii 2006 Restoration Draft PEIR 062890002SAC Table of Contents Inflows from Portions of the Watershed Not Tributary to Irrigated Areas of the Imperial and Coachella Valleys.................................................................................H2-42 Evaporation and Precipitation...................................................................................H2-43 Summary of Projected Salton Sea Inflows and Salt Loads under No Action Alternative-CEQA Conditions....................................................................................H2-43 Description of No Action Alternative-Variability Conditions...................................................H2-44 Basis for No Action Alternative-Variability Conditions...............................................H2-44 Analytical Approach..................................................................................................H2-54 Inflows from Mexico..................................................................................................H2-54 Enlargement of the Colorado River-Tijuana Aqueduct..................................H2-54 All-American Canal Lining Project.................................................................H2-54 Increased Water Use and Reuse Within Mexico...........................................H2-54 Reduced Availability of Colorado River Surplus Flows..................................H2-54 Probability Distribution...................................................................................H2-55 Range of Future Inflows................................................................................H2-55 Inflows from Imperial Valley......................................................................................H2-55 Implementation of Total Maximum Daily Loads.............................................H2-55 Possible Future Water Use Determinations by Reclamation or State Water Resources Control Board ...................................................................H2-55 Colorado River Basin Salinity Control Forum................................................H2-56 Improved On-farm Water Use Efficiency.......................................................H2-56 Change in Cropping Patterns........................................................................H2-56 Agriculture to Urban Land Use Conversions.................................................H2-63 Colorado River Supply Reliability and Shortage Criteria...............................H2-63 Probability Distributions and Range of Future Inflows...................................H2-63 Inflows from Coachella Valley...................................................................................H2-64 Change in Assumptions for the Coachella Valley Water District Water Management Plan.........................................................................................H2-64 Probability Distributions and Range of Future Inflows...................................H2-71 Inflows from Portions of the Watershed Not Tributary to Irrigated Areas of Imperial and Coachella Valleys.................................................................................H2-71 Climate Change........................................................................................................H2-71 Evaporation...................................................................................................H2-72 Range of Future Evaporation....................................................................................H2-83 Projected Range of Inflows.......................................................................................H2-83 Considering Uncertainty in Sizing/Placement of Major Infrastructure.......................H2-83 Considering Uncertainty in Comparing Alternatives..................................................H2-84 Spatial and Temporal Disaggregation of Flows.........................................................H2-84 Spatial Disaggregation of Flows....................................................................H2-84 Monthly Downscaling....................................................................................H2-84 General Conclusions...................................................................................H2-109 References..........................................................................................................................H2-110 2006 H2-iv Salton Sea Ecosystem Restoration Draft PEIR Table of Contents List of Tables Items Page H2-1 Estimated Historic Inflows to the Salton Sea...............................................................H2-23 H2-2 Relative Contribution of Inflow Sources to the Salton Sea (1950 to 2002)..................H2-24 H2-3 Relative Contribution of Inflow Sources to the Salton Sea Salt Loads (1950 to 2002)...........................................................................................................H2-24 H2-4 Estimated Historical Salt Loads to the Salton Sea.......................................................H2-31 H2-5 Projected Salton Sea Inflows for No Action Alternative-CEQA Conditions..................H2-37 H2-6 Quantification Settlement Agreement Delivery Schedule by Conservation Method................................................................................................H2-40 H2-7 Projected Salt Loads to the Salton Sea Under No Action Alternative-CEQA Conditions....................................................................................H2-53 H2-8 Spatial and Temporal Disaggregation Methods for Data Sources...............................H2-91 List of Figures Items Page H2-1 Salton Sea Watershed and Major Contributing Streams ............................................H2-3 H2-2 Long term Average Monthly Temperature, Precipitation, and Evapotranspiration at Brawley (1927-2005)...............................................................................................H2-5 H2-3 Annual Precipitation and Percent Cumulative Departure from the Mean Values at Brawley (1927-2005)...................................................................................................H2-7 H2-4 Relationship Between San Felipe Creek Discharge and Precipitation at Brawley.................................................................................................................H2-15 H2-5 Historical Salt Creek Discharge and Estimated Baseflow from Seepage/Groundwater..............................................................................................H2-17 H2-6 Estimated Annual Evaporation Rates Determined from Water Budget and Plan Evaporation Measurements......................................................................................H2-21 H2-7 Estimated Historical Inflows to the Salton Sea..........................................................H2-25 H2-8 Measured and Simulated Salton Sea Salinity...........................................................H2-27 H2-9 Estimated Historic Salt Leads to the Salton Sea.......................................................H2-29 H2-10 Relationship Between Colorado River Flow at the Northerly United States-Mexico Border and Flows into Imperial Valley from Mexico..........................H2-35 H2-11 Projected Salton Sea Inflows for No Action Alternative-CEQA Conditions...............H2-45 H2-12 Comparison of Average Annual Inflows to the Salton Sea Under Historic, QSA No Action Alternative, and No Action Alternative-CEQA Conditions.........................H2-47 H2-13 Projected No Action Alternative-CEQA Conditions Inflows.......................................H2-49 H2-14 Projected Salt Loads to the Salton Sea Under No Action Alternative-CEQA Conditions....................................................................................H2-51 H2-15 Distribution of Possible Reductions in Mexico Inflows..............................................H2-57 H2-16 Possible Inflows from Mexico for No Action Alternative-Variability Conditions.........H2-59 H2-17 Salt Concentrations at Numeric Criteria Stations......................................................H2-61 H2-18 Distribution of Possible Future Reductions in Imperial Irrigation District Tailwater Flows to the Salton Sea.............................................................................H2-65 H2-19 Distribution of Uncertainty in Imperial Irrigation District Tailwater Volumes..............H2-67 H2-20 Possible Inflows from Imperial Valley for No Action Alternative-Variability Conditions..............................................................................H2-69 Salton Sea Ecosystem H2-v 2006 Restoration Draft PEIR Table of Contents H2-21 Estimated Future Salton Sea Inflows from the Coachella Valley with and without Coachella Valley Water Management Plan Implementation.........................H2-73 H2-22 Distribution of Possible Future Reductions in Coachella Valley Flows.....................H2-75 H2-23 Possible Inflows from the Coachella Valley for No Action Alternative-Variability Conditions..............................................................................H2-77 H2-24 Projected Change in California Annual Average Daily Mean Temperature 1961 to 2100 Relative to 1961 to 1990.....................................................................H2-79 H2-25 Projected Seasonal Daily Precipitation Changes for California for 1961 to 2100 Relative to 1961 to 1990 Average....................................................................H2-81 H2-26 Distribution of Uncertainty Increase in Evaporation Rates due to Future Climate Change........................................................................................................H2-85 H2-27 Possible Total Salton Sea Inflows for No Action Alternative-Variability Conditions..............................................................................H2-87 H2-28 Components of Inflows to Salton Sea.......................................................................H2-89 H2-29 Monthly Flow Pattern for New River near Calexico...................................................H2-93 H2-30 Monthly Flow Pattern for New River Contribution from Imperial Valley.....................H2-95 H2-31 Monthly Flow Pattern for Alamo River near Niland...................................................H2-97 H2-32 Monthly Flow Pattern for San Felipe Creek near Westmorland................................H2-99 H2-33 Monthly Flow Pattern for Salt Creek near Mecca....................................................H2-101 H2-34 Monthly Flow Pattern for Whitewater River near Mecca.........................................H2-103 H2-35 Average Monthly Flow Pattern for Gaged Streams Flowing into the Salton Sea...............................................................................................................H2-105 H2-36 Monthly Reference Evapotranspiration Rates near Brawley...................................H2-107 2006 H2-vi Salton Sea Ecosystem Restoration Draft PEIR APPENDIX H-2 HYDROLOGY AND HYDROLOGIC MODELS This appendix describes the development of historical and future hydrology of the Salton Sea to support the Draft Programmatic Environmental Impact Report (PEIR) and Ecosystem Restoration Study. A comprehensive analysis of the hydrology of the Salton Sea watershed is necessary to approximate the water and salt budgets at the Salton Sea under both existing and future conditions. The PEIR alternatives were developed with consideration of the water and salt budgets, including uncertainty related to future changes in these conditions. This is particularly critical with respect to future proposed Salton Sea elevation and salinity goals. As part of the PEIR effort, a technical Inflows/Modeling Working Group conducted meetings in 2005 and 2006 relating to the hydrology of the Salton Sea. The purpose of the Working Group meetings were to collect information, present draft technical analyses, receive comments, and allow for discussion regarding Salton Sea hydrology. The components of the hydrology and future hydrologic scenarios presented herein have been previously presented at the Working Group meetings. DESCRIPTION OF STUDY AREA The Salton Sea is a terminal, saline lake located in the southeastern corner of California and within one of the most arid regions in North America. The Salton Sea is the largest lake in California, measuring about 35 miles long and 9 to 15 miles wide with about 360 square miles of water surface area and 120 miles of shoreline. The Salton Sea lies in a geographic depression known as the Salton Basin located about -278 feet mean sea level (msl). The water surface elevation on January 1, 2005, is about -228.7 feet msl (USGS, 2005). At this elevation the Salton Sea has a maximum depth of about 50 feet, an average depth of 30 feet, and water storage volume of about 7,200,000 acre-feet. Background The Salton Basin is the northern arm of the former Colorado River delta system. Throughout the millennia, the Colorado River has deposited water and sediments across the delta through many distributaries sometimes discharging south to the Gulf of California and sometimes discharging floodwater north into the Salton Basin. The floodwaters in the Salton Basin periodically formed a large, temporary lake known as Lake Cahuilla (Pomeroy and Cruse, 1965; Ogden, 1996). The Colorado River would eventually return to the southerly path and, without a water supply, the lake waters would evaporate leaving behind millions of tons of salts. The last transient existence of Lake Cahuilla may have been as recent as 300 or 400 years ago and is described in native American folklore and verified through carbon dating (Ogden, 1996). Eventually the floods of the Colorado River built a slight natural berm that created a topographically separate Salton Basin from the Gulf of California. During large floods of the Colorado River, however, flood flows are reported to have reached the Salton Basin in at least 8 years during the 19th century (Ogden, 1996). The current Salton Sea was formed during 1905 to 1907 as a result of a failure of a diversion structure on the Colorado River in which the Colorado River flowed uncontrolled into the Salton Basin (Ogden, 1996; Hely et al., 1966). The water surface elevation of the Salton Sea rose to a maximum of -195 feet msl by the time the diversion dike was repaired in 1907, but rapidly receded to about -250 feet msl in 1925 as evaporation exceeded the rate of agricultural drainage flows to the Salton Sea. In 1925, the elevation of the Salton Sea started to increase due to increased discharge of drainage from agricultural areas in Imperial, Coachella, and Mexicali valleys. Salton Sea Ecosystem H2-1 2006 Restoration Draft PEIR Appendix H-2 Hydrology and Hydrologic Models The Salton Sea is saline due to the accumulation of salts left behind through evaporation. The Colorado River water which formed the Salton Sea during 1905 to 1907 is estimated to have had an average salinity of about 500 milligrams/liter (mg/L) (Hely et al., 1966). However, the large amount of salts that had accumulated during previous inundations in past centuries rapidly dissolved into the fresh water. This redissolution of salts, combined with high evaporation rates and minimal inflows, caused the salinity to rapidly rise to above 40,000 mg/L total dissolved solids by 1925. The salinity decreased in the late 1920s as irrigated agriculture expanded and caused greater drainage flows to enter the Salton Sea. During the 1930s, agricultural activity and agricultural drainage flows declined, and the salinity increased to more than 43,000 mg/L. The salinity declined during the 1940s and 1950s to near ocean salinity (35,000 mg/L), and then slowly rose to about 46,550 mg/L in the early 2000s (Hely et al., 1966; Tostrud, 1997; Holdren, 2005). Salton Sea Watershed The Salton Sea watershed encompasses an area of about 8,360 square miles from San Bernardino County in the north to the Mexicali Valley (Republic of Mexico) to the south. The Salton Sea lies at the lowest point in the watershed and collects runoff and agricultural drainage from most of Imperial County, a portion of Riverside County, smaller portions of San Bernardino and San Diego counties, as well as the northern portion of the Mexicali Valley, as shown in Figure H2-1. Mountains on the west and northeast rims of the basin reach elevations of 3,000 feet in the Coyote Mountains to over 11,000 feet in the San Jacinto and San Bernardino mountains. To the south, the basin extends to the crest of the Colorado River Delta. About one-fifth of the basin is below or only slightly above mean sea level (Hely et al., 1966). Annual precipitation within the watershed ranges from less than 3 inches near the Salton Sea to 40 inches in the upper San Jacinto and San Bernardino Mountains. The maximum temperature in the basin exceeds 100 degrees Fahrenheit (°F) for more than 110 days/year. The open water surface evaporation rate at the Salton Sea is estimated at about 69 inches/year and average crop reference evapotranspiration rate at Brawley is reported to be about 71 inches/year (DWR, 2005). Average monthly patterns of the precipitation, temperature, and evapotranspiration near the Salton Sea are shown in Figure H2-2. Long term annual precipitation is shown in Figure H2-3. Agriculture in Imperial and Coachella valleys is sustained by Colorado River water diverted at Imperial Dam and delivered via the All-American and Coachella canals. In recent years, total diversions from the Colorado River at the Imperial Dam have ranged from about 3,000,000 to 3,600,000 acre-feet/year to support irrigated agriculture in the Imperial and Coachella valleys (Reclamation, 1999-2003). Agricultural drainwater from these areas and parts of the Mexicali Valley, as well as municipal and industrial discharges in the watershed, feed the major rivers flowing to the Salton Sea. The principal sources of inflow to the Salton Sea are the Whitewater River to the north, New and Alamo rivers to the south, and direct drainage from agricultural areas in both Imperial and Coachella valleys. Smaller contributions to inflow come from San Felipe Creek to the west, Salt Creek to the east, direct precipitation, and subsurface inflow. Total average inflow to the Salton Sea over the 1950 to 2002 period is estimated to be 1,300,000 acre-feet/year. Due to a variety of conditions ranging from implementation of the Quantification Settlement Agreement (QSA) which includes Imperial Irrigation District (IID) water transfers to the San Diego County Water Authority (SDCWA), potential transfers to the Metropolitan Water District of Southern California (Metropolitan), water management planning in the Coachella and Imperial valleys, and water conservation/reuse in Mexicali, inflows to the Salton Sea will be reduced in the future. The reduced inflows will result in declining water surface elevations in the Salton Sea and will further contribute to increases in Salton Sea salinity, as described below. 2006 H2-2 Salton Sea Ecosystem Restoration Draft PEIR FIGURE H2-1 SALTON SEA WATERSHED AND MAJOR CONTRIBUTING STREAMS ES112005003SAC figure_H2_1.ai 08-09-06 dash FIGURE H2-2 LONG-TERM AVERAGE MONTHLY TEMPERATURE, PRECIPITATION, AND EVAPOTRANSPIRATION AT BRAWLEY (1927-2005) ES112005003SAC figure_H2_2.ai 08-10-06 dash FIGURE H2-3 ANNUAL PRECIPITATION AND PERCENT CUMULATIVE DEPARTURE FROM THE MEAN VALUES AT BRAWLEY (1927-2005) ES112005003SAC figure_H2_3.ai 08-14-06 dash