Is the modern historical record sufficient to account for variation in water availability to be used for planning purposes?
Will drought or other factors likely affect water availability or system demands and, if so, in what ways?
This section is dedicated to considering these types of questions to better inform the conclusions reached elsewhere in this report, and ultimately to assist the City in understanding the long-term water supply and demand characteristics of their system inclusive of these types of considerations.
The City pumps its wells well below its available water rights due to the groundwater contamination plume discussed previously. At the lower levels of pumping, the City has not observed any long-term trends of declines in the groundwater table. Therefore, there is little current concern regarding groundwater availability at the levels assumed for planning in this document. For planning purposes, it has been assumed that this volume will continue to be available, even during periods of drought. Even with that, the City should continue to monitor groundwater levels due to pumping from surrounding agencies. The City should also continue to closely track potential contamination issues. Due to the small percentage of total supply, it is expected that the City could adjust to a groundwater supply disruption if it were to occur.
The City's existing contract with JVWCD is generally considered reliable for planning purposes because JVWCD has its own contingencies to account for source interruption. However, JVWCD has recently produced a Drought Contingency Plan (still in draft form as of the writing of this chapter). This contingency plan includes drought mitigation and response actions for each community within its service area. JVWCD has created Water Supply Availability Levels and corresponding Drought Response Action Levels ranging from 1 to 4 (4 being the most severe drought level). If enacted by JVWCD, these response actions will result in a reduction in the water that will be delivered to member agencies and JVWCD retail customers. Table 4-1 shows these levels with the associated reduction in water deliveries for each level.
Drought Level | % Reduction in JVWCD Contract | Annual Volume from JVWCD (Acre-ft) | Groundwater Remediation from JVWCD (Acre-ft) | Total Annual Volume from JVWCD (Acre-ft) |
0 | 0% | 18,500 | 1,500 | 20,000 |
1 | 5% | 17,575 | 1,500 | 19,075 |
2 | 10% | 16,650 | 1,500 | 18,150 |
3 | 20% | 14,800 | 1,500 | 16,300 |
4 | 30% | 12,950 | 1,500 | 14,450 |
While annual delivery volumes may be reduced in drought years, the plan does not identify any reduction in the delivery capacity from JVWCD. Thus, it has been assumed that the peak delivery capacity from JVWCD will remain about the same, even in drought years. Correspondingly, the remainder of this chapter will focus primarily on the annual supply implications of drought.
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