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Water Supply Planning

VOMWD recognizes the importance of a long term reliable water supply.  To ensure that we can continue to meet the demands of our current and future customers, the District engages in long-term planning.

  • What is the role of Valley of the Moon Water District (District) in determining if a proposed development will occur?
    The District is a special kind of local government known as a “County Water District”. This means that it only provides this one service. It has a very limited purview when it comes to anything outside of providing water service within its boundaries. The “land use authority” in the area of the District’s boundaries, is the County (County) of Sonoma. The County maintains the General Plan and administers all land use, building, and encroachment permits in the areas where the District operates. Because the District is not the land use authority, it has no right to approve or deny any development. If the District’s State-approved Urban Water Management Plan (or properly conducted Water Supply Assessment [WSA], in cases where development will exceed 500 units) determines water is available, the District cannot discriminate as to who will or will not receive that water. If the District did discriminate, it would be subject to a lawsuit which it would lose. Because the District’s only revenue is from water rates, its customers would ultimately fund the lawsuit through their water rates.
  • Is the former Sonoma Developmental Center (SDC) part of Valley of the Moon Water District (District), and how much authority does the District have regulating the redevelopment of the campus?
    The SDC site is within the District’s “sphere of influence”. This is a Local Agency Formation Commission (LAFCO) term meaning that the site is within the District’s probable physical boundary and service area, but has not yet been fully annexed into the service area. The District is not a land use authority; it has no jurisdiction or authority to set policy or regulations regarding land use, development, or housing type/density.
  • Does the District have any control over the number of hotels or other projects within the District’s service area?
    No, the District does not have control over the type or volume of development that occurs in the District’s service area. These kinds of controls are governed by the local land use authority, which is the County of Sonoma in the case of the District’s service area
  • Is there enough water for all the projects being proposed and/or built in the District’s Service area?
    Yes, the District has plenty of water for all the projects proposed. Please see Q & A 9 and 10 below for further information
  • Why is the District relying on data from the 2020 Urban Water Management Plan (UWMP)? Aren’t those figures out of date at this point? Could the District simply wait until the 2026 figures are available before “approving new projects”?
    The 2020 UWMP is the most up-to-date version of the plan. Urban water suppliers are required to update their plans every five (5) years. The 2020 UWMP takes a “conservative approach”. This means that, if anything, it underestimates the District’s ability to meet the coming demands. Even taking this approach, however, it is predicted that the District will be able to meet all current and future demands as outlined in the plan. The District’s UWMP can be found here. Sonoma Water (the regional water wholesaler) also maintains a UWMP, which can be found here.
  • When a developer proposes a new project, how are the water demands calculated? Can we trust these figures?
    Multiple factors contribute to the calculation of water demand within a given development ranging from population served, to development and water use type, to plant evapotranspiration rates. All of these and more are considered using prescribed methodologies. The resulting figures are used both for the sizing of infrastructure and for estimating system demands. In both cases, the water demand looks at a “worst-case scenario” to ensure there is a safety margin. In short, yes, the figures can be trusted.
  • Where does the District’s water come from?
    About 80% of the District’s water comes from the Russian River, through the Sonoma County Water Agency’s transmission system. The remaining 20% comes from local groundwater wells operated by the District. The District is currently seeking additional groundwater sources, because of the loss of its backup water supply when the Sonoma Developmental Center (SDC) water treatment plant shut down in 2019. The SDC water plant was the valley’s only large-scale, sustainable water supply that was not reliant on the depleting groundwater in the Sonoma Valley Subbasin.
  • How are the groundwater aquifers recharged?
    First, it is important to understand that there are at least two distinct aquifers in the Sonoma Valley Subbasin: the upper aquifer and the lower aquifer. The upper aquifer typically recharges pretty well and does so seasonally with regular rainfall. The lower aquifer, however, is confined from the upper aquifer by a significant, nearly impermeable, clay layer. This means that the water in the lower aquifer is thousands of years old and it takes many human lifetimes to recharge naturally. The District owns one well that is in this lower aquifer. The well is not in use, but the District received a grant from the State Department of Water Resources (DWR) to convert it into an “aquifer storage and recovery” (ASR) well. If successful, this well could be used to inject treated drinking water into the lower aquifer for faster recharge than is possible naturally. For more information on groundwater, please see the Sonoma Valley GSA website.
  • Given the size and scope of many of the proposed developments in the Sonoma Valley, how could the District expect to have enough water to serve the redevelopment of the former Sonoma Developmental Center (SDC) site?
    A Water Supply Assessment (WSA) was conducted assessing the District’s ability to serve the SDC site. That WSA found that the District does not have sufficient water supply to serve the former SDC site without additional supply. However, for over 100 years, SDC operated a water treatment plant that was more than capable of meeting all the water demands of the site. Historically, those demands were as much as three to four times higher than what would be needed to supply water to the site if developed as outlined in the County’s SDC Specific Plan. The WSA assumes that if the District were to serve the SDC site, the existing on-site water resources would be utilized. Furthermore, if the SDC water resources were brought back on-line, this would restore the emergency backup supply of water in the Sonoma Valley that has been missing since the water plant shut down in 2019. This is critical because the SDC water plant was the valley’s only large scale, sustainable water supply that was not reliant on the depleting groundwater in the Sonoma Valley Subbasin. The intertie between the District’s water system and the SDC’s water system was essentially insurance against a failure of the wholesaler’s transmission system that runs from the Russian River to the valley through a series of aqueducts, pumps and storage tanks, which are susceptible to disruption by earthquake, fire, power outages, weather events and more.
  • How do we know if the District will have enough water in the future?
    In the not too distant past (early 2000’s), it was common for the regional wholesale water provider (Sonoma Water) to sell 60,000+ acre feet of water annually, peaking at 66,555.9 acre feet in fiscal year 2003-2004. For reference, an acre foot is equivalent to 325,851 gallons. Since that time, the region has successfully navigated two droughts, and a significant amount of legislation has passed related to water use efficiency in the State. What we have seen is that while population in the County has increased by about 50,000, water demand has fallen significantly. Sonoma Water is now selling between 32,000 acre feet and 45,000 acre feet per year. Sonoma Water still has the right to sell up to 75,000 acre feet per year, or about twice what it currently does. The District and Sonoma Water do not predict a water shortage in a normal precipitation year for the duration of the planning horizon of the 2020 Urban Water Management Plan (through 2045). When there are droughts in the future (as there surely will be), the District will enact its Water Shortage Contingency Plan (WSCP) as it has done successfully in the past. This, combined with the District’s initiative to secure more groundwater capacity means that there is still a lot of room in the water portfolio for development. These measures will help ensure that the District is able to meet all of the water supply demands in spite of possible drought conditions.
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