Orestimba Creek Hydrology - Stanislaus County

Table 9 shows the ratios of Orestimba Creek’s(ORES1) and Crow Creek’s (CROW1 andCRSUB2) 5-day main wave used to produce the 1percent 30-day series. Orestimba Creek’s 5-dayvolume was a little less than the frequency curve’s5-day volume, so the second 5-day wave ratio wasincreased to make the 10-day volume match thefrequency 10-day event. The same was done on theremainder of the main wave ratios so that theresulting volumes matched the Orestimbafrequency curve. Orestimba Creek’s ratios to themain wave are listed in Table 10. Crow Creek’smain wave is the product of a concurrent 1 percentstorm over its basin. The main wave is less than aspecific centering over the same area. Ratios inTable 9 are derived from Del Puerto Creek’svolume flow frequency curves without any furtheradjustment.StartDayTable 91 Percent 30-Day Flood Seriesfor Orestimba and Crow CreeksRatios of Main WavesUsed to Develop 30-Day SeriesRelative WaveSizeORES1LocationCROW1 &CRSUB21 6 0.166 0.1736 4 0.188 0.19111 2 0.438 0.29816 1 1.000 1.00021 3 0.184 0.23626 5 0.166 0.173Note: Wave 1, the largest wave, occurs as the fourthwave. Wave 6 is the smallest wave.The main 5-day wave for each of the additional five floods, 0.2, 0.5, 2.0, 10, and 20 percent, areratios of their 5-day volumes to that of the 1 percent (100-year) 5-day volume, as shown below, andat the top of Table 11 as the “Main Wave Ratios to the 1 Percent Probability Flood.”The main wave for each frequency floodis computed first and then ratios of thatmain wave are computed to fill in theremaining 5 of the six waves. Table 11shows the entire Orestimba Creek 30-day flood, 6-wave 5-day flood seriesratios. Figure 9, Orestimba Creek nearNewman, CA, (at the damsite) showsthe main 5-day waves for the 20, 10,2.0, 1.0, 0.5, and 0.2 percent probabilityflood. An example of the six 5-daywaves (the Orestimba Creek nearNewman (ORES2) 1 percent 30-dayflood series) is shown in Figure 10. Thesame floods for Crow Creek (CROW1)are shown in Figures 11 and 12,respectively.Table 10Orestimba Creek 1 Percent Flood Hydrograph FlowsDurationUnitsFrequencyCurveFlowsAdjustedHydrographFlowsPercent ofFrequencyValuesPeak cfs 13,831 13,831 1003-day (72-hr) day-cfs 3,250 3,194 984-day (96-hr) day-cfs 2,498 2,586 1045-day (120-hr) day-cfs 2,498 2,213 897-day day-cfs 2,052 1,962 9610-day day-cfs 1,591 1,591 10015-day day-cfs 1,196 1,199 10020-day day-cfs 1,001 1,001 10025-day day-cfs 875 875 10030-day day-cfs 790 790 10028