Programs

Hydrology Monitoring

Hydrologic cycle

water enters the system as rainfall and leaves the system as either runoff to the Bay or evapotranspiration
water balance for Napa River watershed includes imported water from Delta
surface water storage significant, but not enough for city demands
need to increase conservation efforts, groundwater recharge and recycling

Rainfall varies with elevation, from 25 to 55 inches per year

in Napa River watershed, average annual precipitation is greater upvalley and at higher elevations
Snow falls occasionally on Mt Veeder. Carneros & American Canyon get the least rain. Putah Creek, Suisun Creek watersheds less extreme
classic Pacific coast hydrology: rain mainly in the winter, summers are dry

Surface runoff increases as infiltration decreases, with intensified land use.

Channel flow leads to Napa River, Putah Creek (Lake Berryessa), Suisun Creek

follows the pattern of rain, but differences are magnified
total annual flow in Napa River varies from near zero (1977) to over 400,000 acre feet (1983)
concentrated in winter; summertime flows are low
spring and summer flows in river & creeks may be critical for fish
Napa River and many creeks have unstable bed & banks

Groundwater is important to agriculture and increasingly in demand

sparse long-term monitoring by state Department of Water Resources
identified groundwater basins include Napa Valley main basin, Milliken-Sarco-Tulucay basin, and Carneros basin
human use is primarily for irrigation and rural residential wells
recharge of groundwater not keeping up with human use
groundwater levels especially threatened in Milliken-Sarco-Tulucay

Evapotranspiration is the process by which water return to atmosphere (evaporation from free surfaces + transpiration by plants)