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APPENDIX
B: Groundwater Data and Analysis
Size and Storage of the Groundwater Sub-Basins
The six groundwater sub-basins of Yolo County (see map,
Figure 4) are listed in Table B.1. The potential volume of groundwater
storage available, and the actual amount of deficit in 1974 in
the depth range from 20 ft to 420 ft below the surface (constituting
all of the alluvium and parts of the Tehama Formation) are given
for each sub-basin. These data were taken directly from Scott,
et al. (1975).
Historical Assessments of
Groundwater Pumping
Estimates of groundwater pumping, taken from past studies
are presented in Table B.2. The most recent and comprehensive
data is from the groundwater study by Scott,
et al. (1975) for the average conditions during 1963 to 1972.
In that study, projections for 1990 were also made. These projections
differ from actual conditions in 1990 as follows: 1) since 1983,
19,000 acre-feet/year of additional surface water from the Tehama-Colusa
Canal is available for agriculture in the Dunnigan Water District
area of Colusa sub-basin; 2) 1990 agricultural demands are higher
by 47,300 acres than the 1990 projected level of 255,200 irrigated
acres; 3) actual estimated 1990 M&I water use is substantially
less than the projected 53,400 acre-feet/year due a lower actual
1990 population than projected in 1975 in the Scott study.
In order to try and estimate the spatial distribution of current
estimated average year groundwater pumping, adjustments to the
Scott projections were made to reflect the additional available
surface water and the increases in total irrigation demand. These
estimated levels of pumping by sub-basin for actual 1990 water
usage are given in the last column of Table B.2.
Annual Groundwater Balance,
Assumptions and Calculation
In Table B.3 the contributions to recharge and discharge
to the groundwater basin under Yolo County are detailed at 1990
demand levels for both normal and 'severe' drought conditions
(see Appendix A). The values listed
here are rough estimates taken from other studies, or have been
calculated based on simple assumptions about irrigation and precipitation
recharges. Values for irrigation applications and groundwater
pumping in Table B.3 are taken from the estimates made in this
study.
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