Since the early twentieth century, DWR and Metropolitan have constructed surface water reservoirs to meet emergency, drought/seasonal, and regulatory water needs for Southern California. These reservoirs include Pyramid Lake, Castaic Lake, Elderberry Forebay, Silverwood Lake, Lake Perris, Lake Skinner, Lake Mathews, Live Oak Reservoir, Garvey Reservoir, Palos Verdes Reservoir, Orange County Reservoir, and Metropolitan’s Diamond Valley Lake (DVL). Metropolitan’s Live Oak and Garvey Reservoirs serve exclusively as regulating facilities and have a combined capacity of approximately 4,100 AF. The remaining reservoirs are primarily used to meet emergency, drought, and seasonal demands, with a total gross storage capacity of 1,760,200 AF. However, not all of this capacity is available to Metropolitan; accounting for dead storage and volumes allocated to other entities, Metropolitan’s effective storage capacity is approximately 1,665,200 AF. Conjunctive use of the aquifers offers another important source of dry year supplies. Unused storage in Southern California groundwater basins can be used to optimize imported water supplies, and the development of groundwater storage projects allows effective management and regulation of the region’s major imported supplies from the Colorado River and SWP. Over the years, Metropolitan has implemented conjunctive use through various programs in its service area.
Metropolitan Demand Management Programs
Demand management costs are Metropolitan’s expenditures for funding local water resource development programs and water conservation programs. These Demand Management Programs incentivize the development of local water supplies and the conservation of water to reduce the need to import water to deliver to Metropolitan’s member agencies. These programs are implemented below the delivery points between Metropolitan’s and its member agencies’ distribution systems and, as such, do not add any water to Metropolitan’s supplies. Rather, the effect of these downstream programs is to produce a local supply of water for the local agencies and to reduce demands by member agencies for water imported through Metropolitan’s system. The following discussions outline how Metropolitan funds local resources and conservation programs for the benefit of all of its member agencies and the entire Metropolitan service area. Notably, the history of demand management by Metropolitan’s member agencies and the local agencies that purchase water from Metropolitan’s members has spanned more than four decades. The significant history of the programs is another reason it would be difficult to attempt to assign a portion of such funding to any one individual member agency.
Local Resources Programs
In 1982, Metropolitan began providing financial incentives to its member agencies to develop new local supplies to assist in meeting the region’s water needs. Because of Metropolitan’s regional distribution system, these programs benefit all member agencies regardless of project location because they help to increase regional water supply reliability, reduce demands for imported water supplies, decrease the burden on Metropolitan’s infrastructure, reduce system costs and free up conveyance capacity to the benefit of all the agencies that rely on water from Metropolitan.
Appendix B - 17
IRWD – 2025 Urban Water Management Plan – Reduced Delta Reliance
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