OCWD provided several lines of evidence for the determination that depletions of interconnected surface water in the Santa Ana Canyon area are insignificant (i.e., de minimis).
1. The large disparity in the supply of surface water to the Santa Ana Canyon area compared to the amount of pumping. The annual flow in the Santa Ana River is much greater than the amount of annual groundwater production. When the 2017 Alternative was prepared, some production wells in the Santa Ana Canyon were estimated, namely production wells supplying irrigation water to the Green River Golf Course. OCWD and Orange County Department of Public Works have worked together to install meters on wells supplying the Green River Golf Course. Now all production wells in the Santa Ana Canyon are metered. This effort resulted in a reduction in pumping as prior estimates were too high. For the 2022 Update, the 5-year water budget is presented in Table 1-2 in the Santa Ana Canyon section (reproduced below). This water budget is a combined surface and groundwater water budget for the Santa Ana Canyon Management Area. As shown on this table, groundwater production over this five-year period is approximately 0.6 percent of the total inflow to the canyon area. Table1-2: Water Budget, 5-Year Average (2016-21)
Flow Component
5-Yr Avg: 2016-21 (afy)
INFLOW Santa Ana River Base Flow Santa Ana River Storm Flow
76,860 78,750
Subsurface Inflow
6,000
TOTAL INFLOW
161,610
OUTFLOW Santa Ana River Base Flow Santa Ana River Storm Flow
76,120 78,750
Evapotranspiration
740
Groundwater Production
1,000 5,000
Subsurface Outflow
TOTAL OUTFLOW
161,610
2. The second line of evidence is the stability of groundwater levels as shown in Figure 3-3 in the Santa Ana Canyon section of the report. This figure is reproduced below. The consistent, stable nature of groundwater elevations in the Santa Ana Canyon Management Area shows that the aquifer is generally full and at equilibrium, which is consistent with the finding that here are no measurable losses of flows between Prado Dam upstream and OCWD’s diversion to its recharge system just below Imperial Highway. 3. The third line of evidence, mentioned above, is the finding that there are no measurable losses of flows between Prado Dam and OCWD’s diversion at the Imperial Rubber Dam. The location of these two measuring locations is shown in the figure below. The measuring location below Prado Dam is operated by the United States Geological Survey (USGS) and is identified as US11074000, Santa Ana R BL Prado Dam, CA. The USGS carefully reviews data from this location and publishes it annually as it is of interest to multiple stakeholders, including OCWD, the US Army Corps of Engineers, and a number of agencies upstream of Prado Dam.
Appendix F - 279
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