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between gauges. In general, HEC -2 velocities compare reasonably well with travel times <br />estimated from stream gauge records (CH2MHill, 1994). The HEC -2 based average <br />velocities suggest travel time decreases with discharge. Travel time estimates were used <br />for refining the distribution of stream gauge sensors and for prioritizing gauge <br />maintenance needs. <br />Preliminary Design Considerations <br />Five foundation alternatives were analyzed for the fuse plugs and inflatable dam. A <br />stability analysis was performed to test the structures' stability against sliding and <br />overturning. Preliminary seepage analysis determined the uplift pressures below the <br />dam. The analysis found that the grade - control structure along with the dam on top of it <br />would not be stable unless scour could be prevented. Therefore, a reinforced concrete top <br />slab and cutoff wall added to the grade - control structure for the dam foundation was <br />recommended. A soil- cement grade - control structure would suffice for the fuse plug <br />foundation. Estimated cost for the foundation would be $671,000. <br />Based on review of existing geotechnical data, the fuse plugs could be constructed from <br />processed river material. Coarser material for the upstream and downstream faces of the <br />fuse plugs would come from offsite. A geomembrane would create an impervious zone <br />within the fuse plugs. The crest of the fuse plugs would be notched to enhance the rate <br />of erosion once the fuse plug is overtopped by water. <br />Dam Operations Plan <br />The Rillito Dam Operations Plan would use data from the ALERT flood warning system <br />in conjunction with other data for decisionmaking for normal operation of the inflatable <br />dam and recharge facilities. The stated goals of the dam operation plan are to optimize <br />recharge volumes, rates, and water quality within the following constraints: <br />• Ensure the structural integrity of the recharge facilities <br />• Minimize risk to site visitors and operations staff <br />• Minimize the need for maintenance <br />• Meet applicable Federal, State, and local agency requirements <br />In addition, the operations plan considered ways to reduce capital and maintenance costs <br />for the ALERT system components of the proposed Rillito Recharge Project. <br />Scour Analysis <br />The district sponsored an analysis of the impact of the proposed fuse plugs and inflatable <br />dam on the Corps' grade - control structure. The analysis indicated that the total depth of <br />the grade - control structure needed to be increased from 13.1 feet to at least 24.2 feet. The <br />volume of material to construct the invert stabilizer at the district's preferred location <br />would be about 7,500 cubic yards. If the grade - control structure were located at the <br />Corps' preferred location and without the dam, the volume would be 3,350 cubic yards. <br />10 High Plains States Groundwater Demonstration Program <br />