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I I I I I I I I I I I I I I I I I I I COMMENTARY - SHEET 8 The predominant feature along the stretch of channel shown on the facing sheet is Pomona Lakes 2 and 3. The pond is an effective retention facility, and public acquisition of this reservoir would create an excellent multiple-use facility and insure its long term availability for flood control. Storm runoff from existing and future developments can be detained in the reservoir, which provides as much as 60 acre-feet of flood storage capacity, significantly reducing downstream flood peaks. The structural adequacy of the existing pedestrian bridge, which doubles as a diversion structure when it forces peak flows into the reservoir, should be investigated to ensure its proper performance. The structure must be anchored satisfactorily to withstand the full dynamic load which might be imposed upon the structure in the event of major debris plugging. Its failure would nullify the flood control capabilities of the reservoir. The existing 24-inch diameter pipe beneath West 80th Avenue is hydraulically inadequate to convey all but trickle flows. Consequently, flow depths of storm water overtopping West 80th Avenue exceed the recommended maximum depths set forth in the Urban Storm Drainage Criteria Manual (Reference E). Separate from this flood control plan, however, plans are being made to enlarge the culvert beneath West 80th to a double 10' x6' box. Debris and other potential channel obstructions should be removed and kept out of the creek. Floodplain use should continue to be monitored and regulated. TOTAL IMPROVEMENT COSTS - SHEET 8 Item TOTAL CONSTRUCTION COSTS Annual Operation and Maintenance Costs Present Worth Operation and Maintenance Costs Cost $ 0 $ (840) $12,200 TOTAL IMPROVEMENT COSTS $12,200