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benefits will accrue to the district to compensate for the cost of constructing and <br />operating the facility. Without the credits, recovery of recharge water would be counted <br />as an increase in Tucson Water Department's gallons used per capita per day. <br />To obtain economic benefits from the recharge project, the district or other entities must <br />either recharge imported water at the site or relocate the project to an area where storm <br />or effluent flows would otherwise leave the Tucson Active Management Area. <br />Results and Conclusions <br />The ALERT System <br />The Rillito Recharge Project enabled the district to expand the existing ALERT system. <br />The expanded coverage of stream and precipitation gauges in the Rillito watershed <br />improves the National Weather Service's ability to issue special weather statements and <br />allows Pima County Emergency Services to direct field personnel during floods. The <br />ALERT system was critical during 1993 floods in predicting flood hazards and directing <br />the district's field operations. <br />Besides its flood warning capability, the ALERT system is generating an increasingly <br />valuable data base. ALERT data are used by universities, private consultants, and <br />governmental agencies. The National Park Service and USGS have direct telephone <br />access to the ALERT data base. It is anticipated that the ALERT system will be used by <br />the National Weather Service in testing and improving the predictive capabilities of the <br />new Doppler Radar System. <br />The Rillito Recharge Project dam operations plan demonstrated how the ALERT system <br />could be used to operate an inflatable rubber dam placed on an unregulated ephemeral <br />stream. For large, complex watersheds, the operation system should primarily use <br />hydraulic modeling of stream gauge data rather than rainfall- runoff methods. This, in <br />turn, demands a high level of accuracy in detecting and measuring low flows unless <br />sufficient flood plain conveyance is available to allow safe overtopping while the dam is <br />deflating. The Rillito Recharge Project dam operations plan could be used elsewhere as a <br />blueprint for developing an operating system. <br />Yield Estimates <br />The Rillito Recharge Project successfully tested a new method to obtain specific yield <br />estimates of various portions of the aquifer. The microgravity surveys conducted by <br />USGS used subtle changes in gravity to detect changes in storage and movement of <br />recharged groundwater. The USGS used the 1993 flood to examine the recharge of large <br />volumes of water in the study area. In all, over 6,000 acre -feet were recharged in the <br />study area. The results show that recharge in the Rillito downstream of Swan Road <br />would be more effective in replenishing Tucson's central well field than recharge east of <br />Swan Road. The ADWR is now funding a similar microgravity survey for another <br />portion of the Tucson basin. <br />Program Summary Report Part 111— Demonstration Project Summary Reports 17 <br />