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TOTAL IMPROVEMENT COSTS - SHEET 15 Item Cost Channel Improvements $ 294,600 Street Improvements $ 145,400 Utili ty Relocation $ 99,600 SUB-TOTAL $ 539,600 Contingencies (25% of Sub-Total) $ 134,900 TOTAL CONSTRUCTION COSTS $ 674,500 Right-of-Way Acquisition $ 107,400 Annual Operation and Maintenance Costs $ (5,300) Present Worth Operation and Maintenance Costs $ 76,800 TOTAL IMPROVEMENT COSTS $ 858,700 I I I I I I I I I I I I I I I I I I I COMMENTARY - SHEET 15 A grass-lined channel designed for the 10-year event is proposed for the Little Dry Creek channel in Westminster upstream from about Sta. 90 + 00. The channel should be constructed on the northern edge of the Westminster School District property, and the only right-of-way required will be downstream from Sta. 90 + 00. There is an existing 24" sanitary sewer trunk line which parallels the channel and has been constructed at shallow depths and at nearly flat slopes. Because of the presence of this trunk sewer, utility relocation costs could be hig):!. The final channel design may need to be altered to accommodate this trunk sewer, but there is insufficient field data at this point in the study to accurately determine the actual extent of the utility conflicts. At Lowell Boulevard, the channel is to transition to a 234 square foot rectangular bridge opening. Upon emerging from the bridge opening, the channel should again transition to a grass-lined channel which should follow the existing channel to West 69th A venue. The upstream end of the 69th Avenue bridge is the Westminster City Limits and the terminating point for the 10-year design. The open channel and related structures downstream are in Adams County and are designed for the 25-year storm. A bridge will conduct flow beneath 69th Avenue, after which the channel is to transition to a 25-year grass-lined channel that will parallel the 69th Avenue right-of-way for approximately 500 feet (See Sheet 16). Two drop structures of varying heights are to be incorporated into the channel to reduce channel grades and consequently lower flow velocities to within permissible limits. The existing floodplain should 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. Since the improvements are designed for either the 100 or 25- year event. The continued enforcement of floodplain regulations and an ongoing program of floodplain management will be necessary after the proposed improvements are built to compensate for larger floods.