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structures may be desirable because they are a single structure, they are believed to be <br /> less accurate than standalone measurement structures such as long-throated flumes or <br /> other comparable flumes and weirs. <br /> Depending on the conditions of the site, it may be more cost effective to deliver water to <br /> the recharge pond with pumps, despite the added cost associated with their operation. <br /> Pumps and meters may be relatively inexpensive when compared with the additional <br /> infrastructure that may be needed to deliver water at a site that may be higher in <br /> elevation than the ditch. <br /> Recharge Operational Procedures <br /> The water balance method should be used to determine the amount of ground water <br /> recharge at each recharge pond and canal segment. The general approach of the water <br /> balance method is to subtract consumptive water losses that occur during the process of <br /> recharge (e.g. evaporation) from the volume of water flow into the recharge structure, <br /> over some time interval. The net result of this calculation is a total volume of ground <br /> water recharge. Inflow and losses should be measured and calculated on a daily time <br /> interval, but may only be accounted for on a monthly basis. <br /> Consumptive Water Losses <br /> When water is conveyed through a canal or is placed in a recharge pond, water will be <br /> lost to surface water evaporation and phreatophyte evapotranspiration3. Evaporation <br /> losses from the surface of the pond should be estimated daily according to the daily <br /> evaporation rates presented in Table 4 and according to changes in the surface area of <br /> the pond. A field survey should be performed on each recharge pond for purposes of <br /> determining a relationship between staff gage height and the surface area of the pond. <br /> Surface area estimates for canal segments should be based on capacity flow in the <br /> canal. <br /> Because phreatophyte evapotranspiration is difficult to determine without field surveys <br /> on the characteristics of the local vegetation, it should be accounted for by increasing <br /> daily evaporation estimates by some percentage, such as 40%. <br /> Calculation of Net Recharge from Recharge Ponds <br /> The following equation should be used to calculate the net recharge to the aquifer from <br /> recharge ponds. Net recharge can be calculated on a daily or monthly basis with this <br /> equation. <br /> R = 1 + Si— ET— Sf <br /> Where, <br /> R = net recharge to aquifer <br /> / = inflow to recharge ponds <br /> 3 Phreatophyte evapotranspiration is the evapotranspiration from plants that habitually obtain their water supply from <br /> saturated soil(Schwab et al., 1993). <br /> Aqua Engineering, Inc. Recharge Project Potential <br /> February 17, 2004 - 12 - <br />