San Benito County Water District San Benito County Water District

Table 5. Change in Storage during Water Year 2008 for Zone 6
Subbasin
Area
(acres)
Average Change in
Groundwater Height
(feet)
Average
Subbasin
Storativity
San Juan 11,708 0.30 0.05 174
Hollister West 6,059 3.33 0.05 1,009
Tres Pinos 4,735 -0.67 0.05 -158
Pacheco 7,290 -1.36 0.03 -298
Hollister East 15,367 -0.87 0.03 -403
Bolsa SE 2,690 11.54 0.08 2,483
TOTAL ZONE 6 2,807
Change in
Storage (af)
In recent years, the volume of managed percolation has been decreased in response to high
water levels. The recent annual quantities of managed percolation are very small in comparison
to the peak volumes from the late 1990s. Because managed recharge has been greatly reduced,
storage fluctuations caused by pumping and other sources of recharge can be seen more clearly.
When groundwater levels are high, upward fluctuations in storage are limited because excess
groundwater tends to leak into streams rather than accumulate in storage. Conversely, when
groundwater levels decline, groundwater discharge into streams is affected almost immediately.
Figure 17 illustrates long term changes in groundwater levels in the basin. Water elevations in
key wells from each subbasin for each monitoring event were averaged to produce
representative hydrographs for each subbasin. These key wells are shown on the map in Figure
17. It should be noted that these subbasin hydrographs represent average conditions in each
subbasin and illustrate long term trends, but do not show localized variations in water levels.
Over the past five years, water levels have remained fairly constant in most subbasins. This
includes an interruption in the long-term rising trends seen from 1994 to 2006 in the Hollister
East and Bolsa Southeast (SE) subbasins, where average water levels remained fairly stable
between 2007 and 2008. The increasing trend was related to reduced groundwater pumping and
increased CVP delivery for both agricultural and M&I uses. Water levels in all subbasins show
a seasonal variation with the lowest water levels occurring in the fall and the highest in the
spring. The Bolsa subbasin shows the most variation: 20 to 50 feet of elevation change between
seasons.
Water levels continue to remain generally near their historic highs in most parts of the basin.
Based on these water levels and the stable management of the basin, there was no overdraft in
2008 and overdraft is unlikely to occur in 2009.
Annual Groundwater Report for Water Year 2008 December 2008
San Benito County Water District 32