Imperial Irrigation District, California

Client: Imperial Irrigation District
Project: Imperial Irrigation District, California

Imperial Irrigation District (IID) is a large irrigation district located in the Imperial Valley of Southern California. IID is in charge of ordering and distributing roughly 3.1 million acre-feet per year from the Colorado River. The conveyance and distribution system serving IID is complex and includes nearly 1,700 miles of canals serving about 500,000 irrigated acres.

Review of IID Water Conservation Projects

NRCE has reviewed and analyzed IID’s history of water conservation. The water use in IID has been the subject to numerous conservation efforts due to the competition for lower Colorado River water by California’s agricultural and municipal water users. The objectives of the review were to document water conservation efforts and their effectiveness and help develop a water conservation and management plan for the District.

Results of water conservation efforts conducted by IID over the past 50 years were evaluated and summarized by NRCE. The water conservation activities included efforts on the district, agricultural producer, state, and federal levels. Major categories of water conservation efforts that were evaluated include canal and lateral lining, seepage recovery programs, regulating reservoirs, interceptor canals, water structure operations and control, water ordering procedures, tailwater recovery systems, irrigation scheduling databases and programs, operator training programs, field leveling, and on-farm water management.

Each conservation program was evaluated for its effectiveness in reducing irrigation water requirements. NRCE analyzed IID’s water use, conveyance and distribution system efficiencies, and on-farm irrigation efficiencies. NRCE summarized expenditures by the various conservation program participants. The conservation program analysis was documented in a report to IID.

Water Use Assessment

NRCE conducted an extensive analysis of the irrigation water use practices and conditions in IID. The analysis provided an overall summary of the IID canal and delivery system, including the physical attributes of the system and the operations and scheduling of water deliveries. Detailed studies of crop ET and climatic effects were undertaken for a variety of crop types grown in the District. Field studies of soils within the District indicated an elevated water demand, and studies were undertaken to evaluate tailwater, irrigation efficiency, salinity management, and leaching requirements. These studies resulted in a water budget accounting for IID at the District, canal/ditch, and field levels for estimating the overall irrigation efficiency. The report concluded that the Imperial Irrigation District practices are relatively efficient in comparison to other irrigation districts in the region.

Review and Analysis of Colorado River Surplus Criteria and Impacts

The Colorado River is operated in accordance with a set of Federal laws, interstate compacts, international treaties, court decrees, and other documents relating to the use of the waters of the Colorado River. For example, in years with sufficient water supply, the operation of Lake Mead is governed by the surplus criteria wherein the surplus water is released and used by water users in the Lower Basin states (California, Arizona, and Nevada) in accordance with applicable laws and regulations. At the time NRCE was hired by IID, the surplus criteria were undergoing revision and development. An alternative surplus criteria was developed and proposed by the State of California/Metropolitan Water District (California/MWD Proposal) and the other six basin states (Six States Proposal). The U.S. Bureau of Reclamation (USBR) also developed and analyzed several alternative surplus criteria.

NRCE was hired by IID to review and analyze the different options for the Colorado River surplus criteria and their impacts to IID. NRCE first collected and reviewed all relevant documents, reviewed historical operations of the Colorado River Reservoirs, existing surplus criteria, and the application of the criteria during historical operations. NRCE also reviewed the USBR’s CRSSez model and the input and assumptions made by the State of California Metropolitan Water District and prepared comments and recommendations.

After the thorough review of the existing model and all alternative surplus criteria proposed by various parties, NRCE performed independent modeling and analysis of these alternatives using the CRSSez model. Additionally, NRCE performed risk assessments for the various alternatives and estimated the probability of adverse impacts to IID. NRCE developed and recommended an implementation plan for the Imperial Irrigation District that would minimize any potential risks.

System Improvement Study

In 2005, NRCE conducted a System Improvement Study to evaluate and improve the performance of its water delivery system. The study completed the following tasks: 1) identified irrigation service needs; 2) documented existing service levels; 3) reviewed performance of existing water conservation projects; 4) defined current operating procedures; 5) analyzed the irrigation system structures and layout; 6) identified and developed planning tools; 7) assessed existing automation of irrigation facilities; 8) developed and defined an irrigation system baseline and metrics to measure performance improvements; and 9) provided recommendations for improvement of the irrigation system performance. As part of the System Improvement Study, conceptual designs were completed for canals, reservoirs, and water control structures as part of water conservation opportunities, and cost estimates were developed for each recommended conservation opportunity.

Integrated Water Resource Management Plan

The IID has an annual consumptive Colorado River water right of 3.1 million acre-feet. Approximately 97% of IID’s water deliveries are to irrigate over 450,000 acres of highly productive farmland. Due to the high water demand in Southern California, several agreements have been established over the past 10 years that transfer water from IID to municipal water users. The transfer water will nearly all be generated through agricultural water conservation, and IID is required to reduce district water use. At the same time, non-agricultural water demands in IID are increasing; with geothermal electric power generation and municipal water demands of particular importance. NRCE was contracted by IID as part of a team to develop an Integrated Water Resource Management Plan to evaluate opportunities for the district to meet increasing water needs for non-agricultural uses without utilizing agricultural water conservation. NRCE’s tasks within the Plan included: (1) documentation of existing non-agricultural water uses; (2) development of future water demand scenarios; (3) identification and quantification of local, regional and imported water supply sources; (4) recommendations on water use practices and drought management strategies; (5) water quality and reliability evaluations; (6) identification of regulatory and environmental compliance requirements; and (7) providing recommendations on priority water supply and demand planning.

Review and Modeling of the Colorado River Interim Surplus Criteria

On behalf of the IID, NRCE performed a review and model of the interim surplus criteria for the Lower Colorado River operations that were developed by the Colorado River Basin states. The purpose of the interim surplus criteria is to assist the State of California in reducing its use of Colorado River water to its allocated amount of 4.4 million acre-feet. Using the CRSSez model, NRCE evaluated impact risks to the IID and assisted them in negotiations with the Metropolitan Water District of California and other parties. In addition, NRCE reviewed and prepared comments on the Environmental Impact Statement developed by the U.S. Bureau of Reclamation (USBR). As part of this review, NRCE reviewed and prepared comments on the modeling and analysis of the Colorado River operations that were performed by the USBR using the RiverWare model. This model simulates the operation of the entire Colorado River Basin under increasing demands and various alternative operating rules, including the proposed interim surplus criteria.

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