Location of USGS gauging station below Prado Dam and OCWD Imperial Rubber Dam Inflow from the Santa Ana River to OCWD’s recharge system is measured at the Imperial Rubber Dam (see figure). When flows are less than 1,000 cubic feet per second (cfs), the rubber dam remains fully inflated and all surface flows are either diverted from the river to downstream recharge basins or it is bypassed around the dam and placed back into the river channel. Flows that are diverted from the river pass through a Parshall flume, which measures the flow rate. Flows that are bypassed around the dam are measured using sonic flowmeters installed in the bypass pipelines. This arrangement ensures that all flows received by OCWD under 1,000 cfs are measured accurately. OCWD staff routinely check the accuracy of these two measuring stations. OCWD data from the Imperial Rubber Dam location provide data on total flow of the Santa Ana River on a daily basis. OCWD compiled daily flow measurements for the USGS gauge below Prado Dam (11074000) and at OCWD’s Imperial Rubber Dam for the period July 2015 to October 2021. During the winter months, there can be rainfall that occurs between Prado Dam and the Imperial Rubber Dam, resulting in ungauged inflow in this reach. To screen out these periods, the flow data for May through October is used and shown in the graph below. This graph shows there is very good agreement between the outflow at Prado Dam and what is received at the Imperial
Appendix F - 281
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