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I I I I I I I I I I I I I I I I I I I The dam would reduce the 100-year peak discharge at Pioneer Park from 4,400 cfs to about 225 cfs. Figure 4 presents the 100-year residual floodplain asswning that both the Sand Creek and Pawnee Creek improvements have been constructed. Pioneer Ditch: The improvements proposed in the 1995 COE Report were determined to be the best plan for the Pioneer Ditch. These improvements are planned to convey the lO-year peak discharges (1040 cfs) and include a detention pond located north of the intersection of Division Avenue and Filmore Street (Division Avenue Detention Pond). The City currently owns the land where the proposed pond would be located. The pond would eliminate the need for expensive bridge and channel improvements downstream by reducing the lO-year peak discharge from 1,040 cfs to about 300 cfs. Existing culverts at the following locations would be replaced with larger structures designed to convey peak discharges developed by the lO-year storm. . Burlington Northern Railroad . Phelps Street . State Highway 14 The existing culverts at these locations are undersized and create severe backwater conditions even during minor storms. Secondary channel improvements and erosion protection are required for existing bridges at the following locations. · In a parking lot about 1,000 feet upstream ofHWY 14 · The intersection of Franklin Street and North Seventh Avenue . Seventh A venue . Sidney Avenue The proposed channel improvements typically involve widening the channel bottom and re-grading the channel sideslopes. Fairly steep sideslopes are proposed through the bridges and soil cement erosion protection would be provided at these locations. In addition, the banks of the Pioneer Ditch will need to be raised in some locations by berming to contain the 10-year flows, It should be noted that since these berms are intended to confine storm water generated by the lO-year storm instead of the 100-year storm, they are not required by FEMA to have 3 feet of freeboard like the levees proposed for Pawnee Creek, Finally, a re-alignment of a portion of the Pioneer Ditch is proposed to permit a steeper grade. The channel would be realigned through a vacant field beginning at the southwest comer of Franklin Street and Seventh Avenue and continuing to the southwest for approximately 3,800 feet. the estimated project cost for all of the improvements along the Pioneer Ditch is $2,306,900. Because the proposed improvements for the Pioneer Ditch are planned for the lO-year storm, there is only a minor affect on the 100-year floodplain caused by local drainage. The approximate limits of the 100-year residual floodplain assuming that all of the proposed improvements (Pawnee Creek, Sand Creek, and Pioneer Ditch) have been constructed are presented on Figure 5. 6