To effectively manage and ensure long-term water supplies for Napa County, local municipalities and regional agencies regularly estimate water supply and demand numbers.
Studies and water management plans are developed to compare available water supplies to existing and future water demands of the County's municipal, rural, and agricultural water users. These technical reports recommend management actions and identify specific water supply project options to fulfill any future water supply shortfalls.
Municipal water supplies for normal years are adequate through the year 2050. Water supply shortages occur in the cities for multiple dry years in the year 2050 and for single dry years for all study periods through the year 2050. Single dry years were modeled using a worst-case year equivalent to the 1977 drought and multiple dry year events were modeled using the droughts in the 1930s and late 1980s.
Agricultural and rural water supplies may run short in single dry years and for multiple dry years. Agricultural and rural water supplies for normal rainfall years may begin to show a deficit by the year 2020. In 2009, to better understand, predict and account for our local groundwater supplies, Napa County began conducting additional groundwater studies and expanded the County's groundwater well monitoring network. The WICC's groundwater information pages are the best source for up to date information on local groundwater supplies.
Various water supply options have been studied including recycled water, groundwater, local surface water, imported surface and groundwater, and water conservation. Projects identified to supplement water supplies for municipalities and rural agricultural areas include the further development of recycled water in the Milliken-Sarco-Tulocay area, the Carneros region, and in and around each of the cities. These and other recycled water projects are currently being taken up by the North Bay Water Reuse Program.
The preferred water supply option for the larger municipalities is to pursue dry year supplies through contracts and/or purchases from outside of Napa County to ensure the North Bay Aqueduct is kept full when cutbacks from the State Water Project occur. These dry year purchase options are being pursued by other state water contractors and opportunities exist to partner in these purchases.
Increased use of groundwater will continue in the rural areas and is being considered by municipalities and must be done carefully to ensure overdraft and depletion of this resource does not occur.
Projects including Napa River diversions, new dams, and raising the City of Napa's Lake Hennessey were found to be infeasible in today's regulatory environment. The listing of salmonid fish species, such as steelhead trout, has made the modification of existing diversion structures and construction of new diversion structures infeasible in the Napa River watershed.
In 2003 the Napa County Flood Control and Water Conservation District authorized the preparation of the 2050 Napa Valley Water Resources Study. The study, completed in 2005, was funded and prepared cooperatively with the cities of American Canyon, Calistoga, Napa, St. Helena, Town of Yountville, Napa County, and the Napa Sanitation District.
A fact sheet and the Technical Memos that comprise the 2050 Study can be viewed in the Related Content section of this page.
Questions about the 2050 Study should be directed to the Napa County Flood and Water Conservation District Engineer at (707) 259-8600.