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I I I I I I I I I I I I I I I I I I- I Design Hydrographs In the Phase A report, we prepared tabulations of the maximum flows at each design poi nt for present and future conditions, for each design frequency. In this report, we hove completed the finol hydrology for preliminary designs by preparing hydrographs af the IOO-year flood at each of the 16 design points; these hydrographs are shown an Plates 11-2, 11-3 and 11-4. The peak flows from these hydrographs are alsa shown in the right-hand column of Table 11-2, reprinted from the Phose A report. Plate 11-2 shows the hydrographs far Tributaries Land M, Plate 11-3 shows them far the upper portion of Niver Creek to 88th Avenue, and Plate 11-4 shows them for the remainder of Niver Creek downstream to the South Platte River. Each hydrograph shows the total effect of the tributary contributions up- stream from it, taking inta consideration the natural storage and conveyance characteristics of each reach. In addition, the hydrographs for Niver Creek at 88th Avenue and for Tributary L at 1-25 show the outflow hydrographs with de- tention facilities installed. Design Criteria The detailed design criteria used in this study are basically the same as presented in the Urban Storm Drainage Criteria Manual. The design philosophy used in this study varied from reach to reach depending on the type of development in that reach. Basically, it was assumed that all structures must pass a 1 O-year storm without damage. If on existing struc- ture was found to be undersized for a IO-year flood, the decision whether to up- grade it to IO-year or IOO-yeor capacity was dependent on incremental cost, type of adjacent development and magnitude of possible damages. v" Chapter III presents a detailed discussion of the design criteria and phi losaphy used for each reach of the creek. 11-5