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1 0 a) Every effort should be made to re-armor the channel after construction to prevent uncontrolled degradation. b) Alternate bridge designs that would provide for designed failure in the event of plugging should be considered. I I I I I I I I I I I I I I I I I I I Street to 55th Street but the magnitude and impact of this increase is not thought to be significant. Further detailed study to answer these concerns is needed during final design. E. STATEMENT ON FLOOD FLOW CHARACTERISTICS AND WATER QUALITY Construction of the proposed excavated floodway will confine the esti- mated lOO-year discharge of l2,000 c.f.s. to the main channel area between the canyon mouth and l]th Street. The proposed excavated floodway will not affect the quantity or quality of urban storm water runoff. Consequently, the proposed excavated floodway will neither enhance nor degrade the water quality of Boulder Creek. F. STATEMENT ON FLOOD PLAIN MANAGEMENT The proposed improved crossings downstream of 17th Street at 24th, 28th, and 30th Streets will accommodate the estimated 100-year discharge of 12,000 c.f.-s.; lower the anticipated water surface profi les immediately upstream of the existing crossings approximately four feet; and will decrease the quantity of floodwaters diverted from the main channel area between 17th Street and 30th Street. FLOOD INSURANCE Federally subsidized flood insurance would be available to all residents. FLOOD PLAIN REGULATIONS Flood plain regulations would be administered to prevent an increase in flood damage potential by prohibiting development in the regulatory floodway and by flood-proofing all other new development to the level of the 0.2%/500-year flood. The proposed channel excavation between 24th and 28th Streets, presented in this report as an alternate improvement, together with the improved crossings at 24th, 28th and 30th Streets would prevent inundation of the commercial area to the south of Arapahoe Avenue between 24th and 28th Streets and would prevent the diversion of floodwaters associated with the estimated 100-year discharge of 12,000 c.f.s. from the main channel area to the north immediately upstream of 28th Street. FLOOD HAZARD NOTIFICATION The residents within and adjacent to the 100-year flood plain would be notified annually of flood hazards. The proposed excavated floodway from the canyon mouth to l7th Street together with the proposed improved crossings at 24th, 28th, and 30th Streets would increase the main channel discharge downstream of 30th G. BENEFIT/COST SUMMARY FOR PROPOSED MASTER PLAN In Summary, the 50-year 6-7/8 percent annualized improvement cost of the selected alternative with channel ization between 24th and 28th Streets