Integrated Resource Plan –Water Supply Reliability in Southern California

中国环境学会  2011年 06月22日

  Integrated Resource Plan –Water Supply Reliability in Southern California

  Chuching Wang, Ph.D. P.E. 王竹青博士

  2009 Chairman, Chinese American Professional Society

  Senior Engineer, Metropolitan Water District of Southern California


  Water is the most precious natural resources in California. There is no other resource more important to the 800+ $Billion economy and social wellbeing of Southern California than water. However, the mother-nature only provides Southern Californians with about 380 mm of annual precipitation. The vast water supply needs have been met by deliberated water resources planning and development. When mentioning water supply in the coastal southern California, one has to mention the Metropolitan Water District of Southern California.    

  The Metropolitan Water District of Southern California (Metropolitan) is a revenue-neutral public agency established in 1928 by the state Legislature to import and wholesale water to the coastal southern California region and to educate residents on water related issues. Metropolitan is currently governed by a 37-member board of directors, representing 26 member public agencies and serve 18 million people living in six counties stretching from Ventura to San Diego. It supplies more than 50% of the 5 million acre-feet water demand in its 5,200 mi2 service area.

        Traditionally, Metropolitan gets its water from Colorado River through Colorado River Aqueduct (CRA) and northern California via State Water Project (SWP). With growing population in its service area and increasing competition for the import water supplies to serve the urban, agricultural, and environmental needs has resulted in significant uncertainties in the future deliveries. In 1991, droughts forced water rationing in parts of Southern California. Metropolitan has since then engaged in the Integrated Resources Plan (IRP) to prevent future water shortage.   

  IRP (MWD, 1996, further updated in 2004, on-going 2010 update) represents both a process and a plan. As a process, it achieved the coordination among the many water agencies and providers in the region on hundreds of important initiatives and projects that were being undertaken throughout Southern California. It is an open and participatory process that allowed for valuable input guidance and data exchange with many stakeholders. It gathers representatives from State-wide business, environmental, community, agricultural and water interests. In the 1996 IRP, there were more than 35 IRP workshop sessions, 3 regional assemblies, 6 regional public forums and many member agency workshops. In the 2004 IRP update, there were 15 public outreach meetings, 12 member agency workshop and 9 meeting with local water interest groups. Currently, the 2010 IRP Update is in process.  

  As a long-term water resources plan, it provides a blueprint explicitly links future supply reliability with necessary resources and capital investment. The plan ensures resources diversity and adaptability; recognizes environmental, political, and institutional constraints, and emphasizes on reliability, affordability and water quality. 

  Under the IRP, the future Southern California water demand will be met by a diversified resources mix. Other than the imported CRA and SWP supplies, it includes local groundwater production, water conservation, storage and conjunctive use, recycled (reclaimed) water, groundwater recovery, seawater desalination, water transfer, and other water management plans. The following charts indicate the diversified portfolio for the present and future water supply.


  In the followings are brief descriptions of the status and targets of each resources component.


  Colorado River Supplies


  Metropolitan’s contract with the federal government provides a basic apportionment of 550,000 acre-feet per year of Colorado River water. Metropolitan also possesses a priority for an additional 662,000 acre-feet per year, depending upon the availability of surplus supplies.

   By a 1929 Act of the California Legislature and as affirmed by the U.S. Supreme Court decree in Arizona v California, California is required to limit its annual use to 4.4 million acre-foot basic annual apportionment of Colorado River water plus available surplus water.  

  Metropolitan’s Colorado River Aqueduct (CRA) has the capacity to deliver 1,250,000 acre-feet to water per year into its service area. This entire capacity was used in previous years to deliver surplus and unused water from other agencies in addition to its basic apportionment, but the availability of that water has diminished. The IRP target for Colorado River supplies includes not only Metropolitan’s basic apportionment, but also supplies from storage and transfer programs that will combine to provide full use of the CRA’s capacity when needed by the region.



  The IRP Update set total Colorado River dry-year targets of:

  •  879,000 acre-feet in 2010;
  •  1,250,000 acre-feet in both 2020 and 2025.

  State Water Project Supplies


  The State Water Project, operated by the California Department of Water Resources (DWR), provides water supplies to 29 urban and agricultural agencies throughout California. SWP water supply contracts specify an ultimate firm yield of 4.17 million acre-feet. Metropolitan’s share of the total SWP is about 46% based on its contracted “Table A ” amount of 1,911,500 acre-feet.  

  Metropolitan’s SWP water passes through the San Francisco Bay-Sacramento/San Joaquin Delta (Bay-Delta).The Bay-Delta can pose challenges for SWP supplies due to water quality issues, variable hydrology and environmental standards that can affect pumping operations.  

  The State Water Project (SWP) target includes water delivered through the State Water Contract. This includes Table A contract supplies, use of carryover storage in San Luis Reservoir, and use of Article 21 interruptible supplies.  

  This target also includes exchange and delivery agreements with Desert Water Agency and Coachella Valley Water District. These agreements have the effect of increasing the SWP supplies available to Metropolitan, and providing Metropolitan with access to the two agencies rights to carryover storage and other contractual provisions. Metropolitan does incur an obligation to deliver Colorado River water to these agencies as a result of these agreements (see Colorado /River section).  

  It is important to note that the target does not include flexible storage available to Metropolitan from terminal reservoirs Lake Perris and Castaic Lake (see In-Region Surface Water Storage). Also, storage and transfer programs that use the SWP system for conveyance purposes are captured in the IRP target for Central Valley Storage and Transfer Programs.



  Metropolitan’s Board set goals for SWP supplies with the adoption of CALFED Policy Principles in August 1999. The policy set a long-term average annual supply goal of 1,500,000 acre-feet per year. For dry years, that is relevant for the IRP Update Target, the principles called for:

  •  463,000 acre-feet from the SWP by 2010;
  •  650,000 acre-feet of from the SWP by 2020.

  Note: The 650,000 acre-foot target excludes water from transfer and storage programs that convey water through the SWP facilities.




  Views on water conservation are changing: once associated with mandatory reductions in water use (typically during severe drought), conservation practices are gaining wider acceptance s beneficial, water use efficiency measures. The region’s history of recurrent droughts (such as those in 1976-77 and 1987-1992) support the need to invest in long-term water use efficiency balanced with new supply development and revised management strategies.

   Over the past 20 years, implementation of water-use efficiency programs has heightened individual and public recognition of the importance of conservation and underscores the fact that choices individuals make have an impact on the region’s water resource picture. Metropolitan’s programs are proactive efforts to meet supply needs and help sustain our standard of living without onerous mandatory drought restrictions on water use.

   IRP conservation targets were set based on an estimate of full regional compliance with established Best Management Practices (BMPs). The BMPs encompass active conservation and expand on code-based conservation savings (code-based conservation includes ongoing refinements to plumbing codes and retrofit-on-resale ordinances in many Southern California cities). Total conservation targets for Metropolitan’s service area use 1980 as the base year for measuring savings, and include the effects of increasing retail water rates as well as the code-based water savings from plumbing codes.



  The IRP Update targets for conservation savings include both Metropolitan-incentivized conservation and other conservation savings. The targets are:


Recycling, Groundwater Recovery and Seawater Desalination

  •  865,000 acre-feet by 2010;
  •  1,028,000 acre-feet by 2020;
  •  1,107,000 acre-feet by 2025;


  Water recycling, groundwater recovery, and seawater desalination are regional resources that add balance to Southern California’s diverse portfolio of resource option.   

  Water recycling (reclaimed water) provides extensively treated wastewater for applicable municipal uses. Common uses include landscape irrigation (e.g. golf course, parks, freeway and street medians, etc.), agricultural irrigation, and commercial and industrial purposes (e.g. cooling towers, Laundromats, toilet flushing, carpet dying, etc.)

  Groundwater recovery employs additional treatment techniques to make use of degraded groundwater sources that ere previously not considered viable due to high salinity or other (chemical) contamination.

  Seawater desalination achieves removal of salts from ocean water and provides that water to potable water uses.  

  While recycled water and groundwater recovery projects in the Southern California region are primarily developed by local water agencies, many newer projects have been developed with financial incentives provided through Metropolitan’s Local Resources Program (LRP). The LRP is a performance-based program that provides incentives to expand water recycling and support recovery of degraded groundwater. A similar approach will be used to provide incentives for seawater desalination production. The IRP Target for local resources development is a total regional combined target, and includes programs developed entirely by member and retail agencies without Metropolitan funding, and the programs developed with Metropolitan’s LRP funding program.



  The IRP Update set total regional water recycling and groundwater recovery targets of:

  •  410,000 acre-feet in 2010;
  •  500,000 acre-feet in both 2020 and 2025.
  •  750,000 acre-feet in 2020 and 2025 including half of the planning buffer.

   For seawater desalination, MWD has approved 5 projects totaling 142,000 AF production capacity. Currently, three of the five projects have executed contracts with MWD. The San Diego County Water Authority project is in progress. The City of Los Angeles project is on-hold. The IRP target for 2025 is 150,000 AF.


  Central Valley Storage and Transfer Programs


  A new direction set by the 1996 IRP was to develop additional supply reliability through the California Aqueduct by entering into water storage and transfer agreements with partners in the Central Valley. Metropolitan’s strategy has been to focus on voluntary programs designed to improve regional reliability while benefiting the partners selling the water supply or providing storage. The storage and transfer target includes programs that bank Metropolitan’s SWP water supplies, as well as short and longer-term water transfer programs using SWP facilities.

  Metropolitan’s success in developing dry-year storage and transfer agreements results from changes since the 1996 IRP which include:

  •  Development of significant water storage and transfer program partnerships in the Central Valley;
  •  Recognition by some Central Valley agriculture interests that participation in transfer programs can be a good business practice;
  •  More cooperation between Metropolitan, DWR and federal agencies to facilitate water transfers;
  •  Recognition of the value of groundwater storage strategies.


     The 2004 IP Update set targets of:

  •  300,000 acre-feet by 2010;
  •  550,000 acre-feet by 2010 including half of the planning buffer.

  In-Region Groundwater Storage (Conjunctive Use Programs)


  Groundwater basins within Metropolitan’s service area provide significant water storage and operational flexibility for Southern California. Conjunctive use storage in these groundwater basins is an important part of maintaining and enhancing the reliability of the region’s future water supplies. An example is 2005’s Supplemental Storage Program: Metropolitan’s water supplies were abundant from a wet winter across the state, so to encourage storage in the region, Metropolitan offered discount rates to its member agencies to store more water than previously planned. The water is available at Metropolitan’s call for up to six years.

  The In-Region Groundwater Storage target includes the dry-year yield from groundwater storage programs within the service area, and also includes estimates of yield from existing Cyclic Storage and the Replenishment Rate program.



  The 2004 IRP Update set the following dry-year yield targets for In-region groundwater storage:


In-Region Surface Water Storage

  •  275,000 acre-feet for 2010;
  •  300,000 acre-feet for 2020 and 2025.


  Metropolitan established long-term in-region surface storage guidelines in the 1996 IRP. In that report, storage capacity requirements for dry-year yield and for emergency needs were determined, consistent with Metropolitan’s Emergency Storage Planning Criteria from the Diamond Valley Lake Environmental Impact Report. Development needs for dry-year storage capacity is determined by evaluation total emergency and dry-year yield needs, and subtracting dedicated emergency storage capacity.  

  Surface storage significantly improves Metropolitan’s ability to manage et or dry hydrologic years of imported supplies primarily because of its generally unrestricted put and take capability. In combination with conveyance improvements like the Inland Feeder, surface storage will allow Metropolitan to take advantage of high quantity wet-year SWP supplies, and to manage fluctuating Colorado River supplies.



  The 2004 IRP Update set targets of:

  •  620,000 acre-feet by 2010
  •  620,000 acre-feet by 2025.

  Local Production (Groundwater)


  Groundwater is one of the essential local water supplies in Metropolitan’s 5,200 square mile service area. It supports nearly 40 percent of the total annual water needs. Between 1995 and 2004, an average of 1.56 million AF of water per year was produced from the groundwater basins in the service area. In addition, groundwater represents an important element of Metropolitan’s Integrated Resource Plan, or IRP, which has a target of 275,000 AF of dry-year yield from groundwater basins by 2010 and 300,000 AF by 2020 from within the service area. Since this IRP planning process requires planning for three consecutive dry years, the actual planned targets for dry-year storage are 825,000 AF by 2010 and 900,000 by 2020.   

  The followings are summaries of Southern California groundwater assessment:

  Management: 93 percent of the groundwater production came from adjudicated or formally managed groundwater basins.

  Production: Each year in the Metropolitan service area, groundwater production

  accounts for about 1.56 million AF, meeting nearly 40 percent of the water demands.

  Recharge: Average annual active groundwater recharge is 758,000 AF. Active

  groundwater recharge proportionately is using more local runoff and less imported water than in the past.

  Overdraft: Over the 20-year study period (1985-2004), groundwater production grew 5 percent faster than groundwater recharge suggesting that total groundwater in storage is declining throughout the service area.

  Facilities: Substantial investments have been made in capital infrastructure in support of the use of groundwater. These projects include over 4,000 production wells and nearly 5,000 acres of spreading facilities. Of note, there are 16 groundwater desalters on-line in the Metropolitan service area as of 2006.

  Water Quality: TDS and nitrate contamination is a common issue in service area

  groundwater basins. Other recurring contaminants include VOCs, iron and manganese, and perchlorate.

  Potential for Storage: Groundwater basins throughout the area have 3.2 million AF of space available for possible storage.

  Needs: Using additional storage opportunity requires: capture, delivery and recharge of additional local and imported surface supplies; improved capability to match availability of surplus surface supplies with conveyance and recharge capacity; and resolution of constraints including: remediation of contamination, institutional and legal issues, funding for significant investment in capital infrastructure, and mismatches in aquifer capability with overlying demand for water supplies.




  Though the long term average precipitation in the coastal southern California is only about 15 inch/year, for the past 7 decades it has enjoyed nearly 100% water supply reliability. This is a result of deliberated long term water resources planning and continuous capital improvement of water supply infrastructures. With more and more stringent requirements on environment and water quality, with still growing population in Southern California, with climate change realities, Metropolitan is facing a great challenge to continuously supply reliable water to its customer. A fully collaborated IRP, that looks for solutions cover multi-dimensional issues including technical, economical/financial, environmental, institutional and political, definitely provides a good vehicle for Metropolitan to reach its mission “to provide its service area with adequate and reliable supplies of high-quality water to meet present and future needs in an environmentally and economically responsible way.” For the near 20 million Southern Californians, it is good to know that their ever-challenging water supply future is in a good hand. Furthermore, each Southern Californian should also recognize that he or she is also part of the solution in achieving the desired water use efficiency.


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