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COMMENTARY - SHEET 12 At the confluence of Tributary B with the main stem of Little Dry Creek, Sta. 189 + 00, several structures are situated within the limits of the 100 year floodplain. The enlarged concreted-lined channel section proposed for the tributary will conduct the flow past these structures, removing them from the 100-year floodplain as shown in the plan TOTAL IMPROVEMENT COSTS - SHEET 12 view of Sheet 12. Details about these improvements appear on Sheet 27. Item Channel Improvements Street Improvements Utili ty Relocation Downstream from the tributary confluence and upstream of Sheridan Boulevard, the channel is to be left in its present state and improved when the adjacent land is developed. Under existing channel conditions, the 100-year flood would overtop Sheridan at a depth of one foot, exceeding the Urban Storm Drainage Criteria Manual (Reference E) recommendations for allowable flow depths of major arterials. Because of its critical SUB-TOTAL Contingencies (25% of Sub-Total) importance in the emergency vehicle access network, twin 10' x 6' box culverts are TOTAL CONSTRUCTION COSTS Right-of-Way Acquisition Annual Operation and Maintenance Costs Arvada Westminster Present Worth Operation and Maintenance Costs proposed for construction beneath Sheridan to eliminate overtopping. This design would utilize the existing four 10' x 4' concrete box culverts to convey the 100-year flow beneath Sheridan. Following a 3.1 foot drop at the culvert outlet, a 100-year grass-lined channel would direct flow to the West 76th Avenue crossing, shown on Sheet 13. TOTAL IMPROVEMENT COSTS Debris and other possible obstructions should be cleared from the channel regularly during the flood seasons and after all major storms. The floodplain should continue to be regulated and property owners who would be adversely affected by the 100-year flood should be encouraged to acquire flood insurance. Residents in the vicinity of the 100-year floodplain should be notified annually of the potential flood hazards. Cost $ 57,200 $ 52,600 $ 1,600 I I I I I I I I I I I I I I I I I I I $111,400 $ 27,900 $139,300 $ 17,700 $ (630) $ 0,700) $ 33,700 $190,700