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The 100-year peak flow per unit area is highest in the Core Area because of the high imperviousness, with values up to 3100 cfs per square mile. The 100-year peak flow per unit area in the Buffer Zone is highest in basins that include steep valleys adjacent to the creeks, with values ranging from about 600 cfs/sq mi for large basins to about 1600 cfs/sq mi for small basins, The western portion of the plant and tributary areas west of the plant have low runoff per unit area because of the high soil infiltration characteristics. Many of these basins have no surface runoff for up to the 50-year storm event. The 100-year peak flow per unit area is about 200 cfs/sq mi for these basins. TABLE IV-S PEAK FLOW AND RUNOFF VOLUME AT SELECfED LOCATIONS' PRESENT DEVELOPMENT CONDITIONS (6-Hour SIOnu) SWl\tM 2-Year Ewat s..Year EftIlit l~Year Event 25-Year Event SO-Vear Event tOO-Year Eveat ........ Area "'I I ,I, I '" I at Loatl.. Nomber (""") at '" at '" at '" at at STANDLEY LAKE BASIN Woman Creek 119 570 0 0 0 0 0 0 0 0 31 6 130 21 Basin at sooe Woman Creek at 113 1,414 10 1 62 7 ]JIJ 22 3"-' 52 "" 77 690 116 Pond C-2 Bypass Inflow to Pond C-2 1"-' 192 6 2 39 6 77 10 150 18 190 22 250 28 Woman Creek at 108 ~880 29 9 150 30 370 78 830 162 1,100 221 1,600 301 Indiana Street Upper Big Dry 106 1,261 32 10 ]JIJ 30 250 53 440 84 580 109 800 144 Creek Basin at saoe Upper Big Dry 105 ~995 27 12 240 68 530 135 970 277 1,300 291 1,700 377 Creek at Indiana Street GRHAT WESI'ERN RESERVOIR BASIN , Walnut Creek 139 154 0 0 0 0 0 0 0 0 6 2 23 6 Basin at SHeD Walnut Creek 348 "" 51 5 74 7 90 8 ]JIJ U 170 19 240 31 Basin at Walnut Creek Diversion D= McKay DiversiOD 134 550 28 5 42 7 54 8 78 12 1"-' "-' 210 33 Canal at Oullet Inflow to Pond A-4 169 371 87 13 160 21 240 29 420 44 5"-' 53 650 64 Inflow to Pond 8-5 151 346 140 22 230 31 310 40 470 52 560 61 690 71 Walnut Creek at 129 2,374 210 42 4&l 78 800 118 1,400 183 1,800 232 2,300 296 Indiana Street IlQ!;l\, QUlEK BASIN ~__- ---.4 Rock Creek Basin 186 224 0 0 0 0 0 0 0 0 33 2 99 8 atSBDC Rock Creek at 185 ~862 68 19 94 24 Z70 60 660 122 890 163 1,200 215 Highway 128 The 100-year peak flow per unit area data is plotted in Figures IV-3 to IV-6 for sub-basins with low percentage imperviousness for four ranges of soil infiltration. This data was plotted to verify the consistency of CUHP model peak flow results. This is only possible when comparing basins with like infiltration and percentage imperviousness characteristics, The small number of basins with relatively high percentage imperviousness (greater than 20 percent) had too great a variation in the percentage imperviousness to allow comparison. The unit runoff is highest in the Core Area with 100-year values of 2.21 to 3.69 inches (58 percent to 97 percent of rainfall), The unit runoff from Buffer Zone basins having steep valleys have values ranging from approximately 1.4 to 1.8 inches. The unit runoff from the western portion of the plant and areas west of the plant boundary generally have unit runoff of less than 0.5 inches for the lOO-year event, with many having no runoff for up to the 50- year event. The unit runoff drops significantly for lower recurrence intervals for areas outside of the developed Core Area. There is negligible unit runoff for the 2-year storm, except in the Core Area. 1 The values listed arc the peak flow and volume of nmoff occurring at the downstream end of the SWMM element. SWMM Model Results. The calculated peak flow and volume of runoff for selected locations design points on Walnut Creek, Woman Creek, Upper Big Dry Creek, and Rock Creek are presented in Tables IV-5 and IV-6 for present and future basin development. A full listing of these values for each modelled design point is presented in Tables IV-7 and IV-8 (also for present and future basin development). Hydrographs for various design points of interest are presented in Appendix IV-C.