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4,649.5 feet, respectively. The proposed plan is to leave the existi.ng 54- . inch pipe in place. No additional culverts could be economically justified. If a flood greater than SPF would occur, or should the pipe become blocked, water would simply spillover the railroad at Highway 227 and pcond to approximately elevation 4,652 feet. The post-project flood plains for I'onding Area I are identical to the existing condition flood plains as shown on Plate 10 of Appendix A. 3-06. DrainaEe Area G. The existing storm drain system in Area G consi.sts of three 36-inch culverts, one 27-inch culvert, two 18-inch culverts and two 10- inch culverts. These culverts will go under the proposed levees and c~~ pass about a five-year flow. The location of the culverts is shown on Phlte 17. Flow which is not passed by these culverts become street flow and t'ravels south to the southern end of Hudson Street. At this point, the flow cc~bines with the run off from Sub Area H. This combined flow is then conveyed into Fountain Creek by use of two existing 48-inch culverts. Since pondirlg does not occur at Area G, no ponding area is proposed at this point. No additional culverrs could be economically justified. 3-07. PondinE Area H. Under existing conditions, run off from Drainag,e Area H collects at the south end of Hudson Street. This area is currently d,rained through an existing levee by two 48-inch pipe culverts. No provisiolu for closure currently exist at the outlets. The proposed plan is to leave the two culverts in place and extend them through the proposed levee. No additional culverts could be economically justified. The SPF and 100-year floods pond to elevations 4,658.6 and 4,657.8, respectively. The post-project flood :plains . are identical to the existing conditions flood plains as shown on PlatE: 10 in Appendix A. 3-08 DrainaEe Area Kl and K2. Under existing conditions, run off from Drainage Area K2 discharges into Fountain Creek through an existing 2..-inch culvert. Flows exceeding the capacity of the culvert will pond behi.nd the concrete median on Interstate 25 to elevation 4,681.0 and eventually drain through the culvert. The proposed flood wall in this reach will not affect this existing ponding condition. However, flows that spill over the COl1crete median will be trapped between the Interstate and the proposed flood wall. To drain this flow and flows from Area Kl, two 48-inch culverts are proposed. An existing drop inlet into the 24-inch culvert will be left in place,. The proposed culverts would pass the 100-year peak without ponding. The maximum ponding for the SPF would be two acre feet at elevation 4,679.9 feet. 3-09. Hvdraulics General. The level of protection (200-year, 85,000 cfs) established in Phase I studies proved to be the maximum protection attainable using detailed design data in this study. A higher degree of prot,~ction requires bridge replacements which are not economically justified. Data which provided the basis for the hydraulic analysis was obtained from digitized cross sections developed from controlled aerial photography flown in December 1983. Supplemental data on the Fountain Creek low flow channe 1 was obl:ained from a field survey done in February 1984. Topographic mapping from these surveys was done on a scale of 1 inch a 100 feet with 2-foot contour intervals. The new mapping revealed different topographic conditions at ... various locations from the less detailed mapping used in the Phase I r'~port. These conditions plus changes in the design criteria discussed in the minutes 1II-2