Management of the Colorado River: Water Allocations, Drought, and the Federal Role

Congressional Research Service (CRS) | April 4th, 2024

From its headwaters in Colorado and Wyoming to its terminus in the Gulf of California, the Colorado River Basin covers more than 246,000 square miles. The basin spans sev

From its headwaters in Colorado and Wyoming to its terminus in the Gulf of California, the Colorado River Basin covers more than 246,000 square miles. The basin spans seven U.S. states (Wyoming, Colorado, Utah, New Mexico, Arizona, Nevada, and California) and two countries (the United States and Mexico). Pursuant to federal law, the Bureau of Reclamation (Reclamation), a component of the Department of the Interior (DOI), plays a prominent role in the management of the basin’s waters. In the Lower Basin (i.e., Arizona, Nevada, and California), Reclamation also serves as water master on behalf of the Secretary of the Interior, a role that elevates the status of the federal government in basin water management. The federal role in managing Colorado River water is magnified by the multiple federally owned and operated water storage and conveyance facilities in the basin, which provide low-cost water and hydropower supplies.

Managing diversions in unregulated streams using a modified percent-of-flow approach

Freshwater Biology (Wiley) | August 22nd, 2017

In Mediterranean-type river systems stream flows are naturally low in summer and autumn. This pattern is often exacerbated by over-exploitation of water resources during

In Mediterranean-type river systems stream flows are naturally low in summer and autumn. This pattern is often exacerbated by over-exploitation of water resources during the dry season, which has implications for managing flows for both environmental and human needs. Mediterranean systems are characterised by strong inter- and intra-annual variability with almost all precipitation occurring in winter months followed by summer droughts with little or no rainfall, and extreme year-to-year variation ranging from intense winter storms to year-round drought (Gasith & Resh, 1999; Power, Kupferberg, Cooper, & Deas, 2015; Power, Parker, & Dietrich, 2008). The seasonal pattern of precipitation in Mediterranean climatic regions results in water availability and demand being out-of-phase; precipitation and runoff occur (almost exclusively) in winter when human demands are lowest, and precipitation is virtually non-existent in summer months when human demand is greatest (Kondolf & Batalla, 2005; Merenlender & Matella, 2013). As a result, rivers in Mediterranean climates tend to have a high degree of alteration with streamsdiverted and dammed to provide scarce water for human use (Kondolf, Podolak, & Grantham, 2013; Marr et al., 2009; Moyle, 2013). While the biophysical responses to alterations of land use, vegetation and hydrology are similar in Mediterranean and other climatic regions, the magnitude of responses tends to be intensified in Mediterranean systems. For example prolonged dry season flows may result in lower dissolved oxygen, higher temperatures and concentration of contaminants among other impacts (Cooper, Lake, Sabater, Melack, & Sabo, 2013). Climate change and increasing frequency and severity of drought promise to increase the conflict between human needs and ecological needs over time (Arthington, 2012).

Managing to End Groundwater Overdraft in California’s Central Valley with Climate Change

University of California, Davis (UC Davis) | July 14th, 2016

Several water management cases with climate change are modeled to assess the effects of ending long-term groundwater overdraft in the Central Valley using the Cal

Several water management cases with climate change are modeled to assess the effects of ending long-term groundwater overdraft in the Central Valley using the California Value Integrated Network (CALVIN) model, a hydro-economic optimization model of California’s water system. CALVIN optimizes water management decision-making for the lowest net operating and water scarcity cost over an 82-year period of unimpaired inflows. Recent updates to the CALVIN model include, input hydrology, network representation, agricultural demand and shortage penalties, and hydropower improvements. Management cases evaluated include changes in outflow and inflow requirements for the Sacramento-San Joaquin Delta (Delta), and prohibiting long-term groundwater overdraft. Cases were analyzed over an 82-year modified historical record with a warmer, drier climate, and compared to historical hydrology results. A modelled warmer, drier climate reduces average inflows overall by about 28% and shifts stream flows towards winter and away from spring. Results show large water scarcities south of the Delta without Delta exports, especially for agriculture. Allowing for increased water transfers, Delta exports, conjunctive use, and water recycling and desalination reduces the water supply effects of groundwater overdraft and climate change.

Mark/Recapture Experiments at Clifton Court Forebay to Estimate Pre-Screening Loss to Juvenile Fishes: 1976-1993

California Department of Fish and Wildlife (CDFW) | September 30th, 1997

From October 1976 through November 1993, the California Department of Fish and Game conducted mark/recapture experiments at Clifton Court Forebay, designed to estimate pr

From October 1976 through November 1993, the California Department of Fish and Game conducted mark/recapture experiments at Clifton Court Forebay, designed to estimate pre-screen loss to entrained juvenile fishes. Ten studies were conducted; eight evaluated losses to hatchery-reared juvenile chinook salmon, and two evaluated losses to hatchery-reared juvenile striped bass. Pre-screen loss was calculated from the proportion of marked fish released at the radial gates that were subsequently recaptured during salvage operations at Skinner Fish Facility. The proportion was adjusted for handling mortality, fish facility louver effiCiency, and any subsampling at the facility. Studies were conducted across a wide range of environmental conditions and State Water Project operations, with a wide range in the size ofexperimental fish. Pre-screen loss estimates for juvenile chinook salmon were 63-99%. Potential biases in estimates of pre-screen loss may be due to (1) the calculation for pre-screen loss, (2) underrepresentative and over-representative salvage of experimental fish at Skinner Fish Facility, and (3) the introduction of experimental fish directly into Clifton Court Forebay. A multiple-regression analysis of pre-screen loss to juvenile salmon showed that 91% of the variance in pre-screen loss can be explained by export rate, experimental fish size, and water temperature. 

Mean and Extreme Climate Change Impacts on the State Water Project

California Department of Water Resources (DWR) | August 27th, 2018

Warming temperatures, shifting hydrology, and rising sea levels will challenge management of California’s water resources. This study quantifies climate change risks t

Warming temperatures, shifting hydrology, and rising sea levels will challenge management of California’s water resources. This study quantifies climate change risks to California’s State Water Project (SWP) and federal Central Valley Project (CVP). This study uses the California Department of Water Resources’ (DWR’s) newly developed water planning model, CalSim 3.0, as a risk assessment tool. Impacts were assessed for 20 climate change scenarios (10 global climate models and two emission scenarios, representative concentration pathway (RCP) 4.5 and RCP 8.5). Water supply and water quality metrics evaluated include Delta exports, North of Delta Carryover storage, reservoir dead storage (i.e. when reservoir levels fall below the lowest outlets), and Delta salinity. Results for the driest future scenario were also analyzed to examine future drought impacts. In addition, a series of sensitivity tests were implemented to assess individual impacts of four climate change factors: flow seasonal pattern shift, sea level rise, annual flow volume change, and water demand change on the State Water Project and Central Valley Project operations. It was found that flow seasonal pattern shift will become a major climate change factor and sea level rise a secondary factor, leading to a half million‐acre feet of Delta export reduction as well as a roughly 25% decrease of North‐of‐Delta carryover storage by around 2060. The results also indicate that the extra runoff from early snow melting and higher percentage of rain in the winter and early spring is not conserved in reservoirs and thus cannot be used to meet the higher summer demand in the current SWP/CVP system. This extra water is released as flood water in the winter and early spring to become Delta outflow.

Memorandum of Understanding by and among Colorado River Basin Municipal and Public Water Providers

Southern Nevada Water Authority (SNWA) | November 15th, 2022

Methodology for Flow and Salinity Estimates in the Sacramento-San Joaquin Delta and Suisun Marsh

California Department of Water Resources (DWR) | June 1st, 2017

This is the 38th annual progress report of the California Department of Water Resources’ San Francisco Bay-Delta Evaluation Program, which is carried out by t

This is the 38th annual progress report of the California Department of Water Resources’ San Francisco Bay-Delta Evaluation Program, which is carried out by the Delta Modeling Section. This report is submitted annually by the section to the State Water Resources Control Board pursuant to its Water Right Decision D-1485, Term 9, which is still active pursuant to its Water Right Decision D-1641, Term 8. This report documents progress in the development and enhancement of computer models for the Delta Modeling Section of the Bay-Delta Office. It also reports the latest findings of studies conducted as part of the program. This report was compiled under the direction of Tara Smith, Program Manager for the Bay-Delta Evaluation Program.

Missing Water: The Uses and Flows of Water in the Colorado River Delta Region

Pacific Institute | September 1st, 2001

The Pacific Institute for Studies in Development, Environment, and Security is pleased to announce the release of Missing Water: The Uses and Flows of Water in the Color

The Pacific Institute for Studies in Development, Environment, and Security is pleased to announce the release of Missing Water: The Uses and Flows of Water in the Colorado River Delta Region. This new study describes the fate of the millions of acre-feet of water diverted from the Colorado River at and below Imperial Dam, and the total inflows to and outflows from the Colorado River delta region more generally. This study uses the classic hydrologic boundaries of the delta region described by Godfrey Sykes in 1937, encompassing some 3,325 square miles (8,611 square kilometers) in the states of Arizona, Baja California, California, and Sonora, including the Imperial, Mexicali, and San Luis valleys, Yuma Project lands, and the lower Coachella Valley. The study period examines the flows and uses of water in the years 1991-1998, divided into Flood and Non-Flood years to reflect the tremendous variability of mainstem Colorado River flows. Missing Water compiles flow data along the mainstem and along diversions within the delta region, the first time such data has been compiled for the region as a whole. The study also report consumptive uses of water in the agricultural and urban sectors, and estimates such use by the environment. Agricultural use is also reported for the major crops in the region, both by acreage and by water use.

Modeling Functional Flows in California’s Rivers

Frontiers in Environmental Science (Frontiers) | March 11th, 2022

Mono Basin Runoff Year 2024-25 Annual Operations Plan

Los Angeles Department of Water & Power (LADWP) | May 20th, 2024

The purpose of the AOP is to describe how operations will commence for the current year-type to accomplish exports and stream releases in accordance with the Li

The purpose of the AOP is to describe how operations will commence for the current year-type to accomplish exports and stream releases in accordance with the Licenses. The AOP will provide specific information about the flow schedule, export, and facility operations for the year ahead. The AOP will also review the prior year’s plan and compare it to actual runoff and operations.