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<br />generate storm hydrographs in the following <br />procedure: <br /> <br />1. Select a numher of rainy days at <br />~ random (or as associated with the desired <br />(:) probability) from Figure 5.4. <br /> <br />c.o 2. Select the dates of these rainy <br />,.j::o. days at random from the number of dates in <br />that month of the year. <br /> <br />3. For each selected date for a rainy <br />day, select a depth at random from Figure 5.5 <br />and an associated durstion from Figure 5.6. <br /> <br /> <br />>- <br />f- <br />iii~ <br />z en <br />W ~ <br />f- 5 <br />z.c <br />- .5 <br />Q .. <br />W E <br />t:l ,- <br />.J - <br /><t:::: <br />:E~ <br />a: <br />o <br />z <br /> <br /> <br />.3 <br /> <br />.2 <br /> <br />,I <br /> <br />o <br /> <br />20 40 <br />PERCENTAGE OF <br /> <br />Figure 5,7. Characteristic storm hyetograph, <br /> <br />, <br /> <br />4. Divide the storm duration into five <br />equal increments and distribute the depth <br />among those increments to form a hyetograph <br />of the shape of Figure 5.7. <br /> <br />For an overview of how well subroutine <br />RAIN matches actual precipitation patterns, <br />simulated and recorded monthly rainfall <br />averages and standard deviations for a <br />24-year period are tabulated in Table <br />5.1. Storm intensity comparisons would be <br />better for assessing how well the model will <br />match runoff peaks and associated sediment <br />and salt loads, but there were no data for <br /> <br />1 <br /> <br />, <br /> <br />60 <br /> <br />80 <br /> <br />100 <br /> <br />STORM LENGTH ("!o) <br /> <br />Table 5.1. Comparison of output from subroutine RAIN with monthly recorded rainfalls. <br /> <br />Month <br /> <br />April <br />May <br />June <br />July <br />August <br />September <br />October <br /> <br />Actual Precipitation4 <br /> <br />Average <br />Precipitation <br />(inches) <br /> <br />0.59 <br />0.72 <br />0.94 <br />0.98 <br />1.11 <br />1.15 <br />1.26 <br /> <br />RAIN Re~ult8 <br /> <br />Standard <br />Devta tion <br />(inches) <br /> <br />Average <br />Precipitation <br />(inches) <br /> <br />Standard <br />Devia tion <br />(inches) <br /> <br />0,52 <br />0.74 <br />0,93 <br />0,74 <br />0.97 <br />1.18 <br />1.29 <br /> <br />0.51 <br />0.65 <br />1.13 <br />1. 21 <br />1.06 <br />1.30 <br />1.55 <br /> <br />0.44 <br />0,79 <br />0.96 <br />1.05 <br />0.91 <br />1.37 <br />1.48 <br /> <br />80btalned from precipitation gages in the Price River Basin. <br /> <br />52 <br />