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<br />A typical input data sheet for the reservoir routing program
<br />is shown in Figure III-2. The objective of this input sheet
<br />is to provide a description of the reservoir and the outlet
<br />control section as well as the methods used in determining
<br />the stage-volume-discharge curves whiCh are Characteristic
<br />of the reservoir and spillway. For the most part, volumes
<br />for the reservoirs were determined from the topographic maps
<br />which were available. In nearly every case the normal water
<br />surface of the reservoir was assumed to be at the spillway
<br />elevation. Spillway overflow and berm overtopping were
<br />computed utili~ing the basic broad crested weir formula.
<br />No input data sheets were made for the lagging and adding
<br />program. Once the input data was established for all phases
<br />of the HYDRO model, the information was transferred to
<br />computer coding sheets from which the input cards were
<br />punched and run. A sample computer output from the HYDRO
<br />model is shown in Figure III-3.
<br />
<br />DESIGN RAINFALL
<br />
<br />The design rainfall for the study area was taken from isohyetal
<br />maps in the Rainfall Section of the Urban Storm Orainaqe Criteria
<br />Manual. These maps provide the rainfall depths for the 2, 10,
<br />and 100 year frequencies and 1, 6 and 24 hour storm durations.
<br />Since the gulChes extended approximately nine miles from the
<br />South Platte River, the storm rainfall typical to each sub-
<br />basin was used, rather than assuming the s~~e design
<br />storm over the total basin.
<br />
<br />From the storm rainfall input, the effective precipitation was
<br />computed following the procedure presented in the Runoff
<br />Section of the Manual. The effective precipitation is a
<br />function of the deGree of imoervious and oervious area. sur-
<br />face detention and depression storage, infiltration, vegeta-
<br />tion interception and an impervious area loss percentage.
<br />
<br />The determination of these abstraction coefficients was based
<br />on an analysis of the recorded rainfall and runoff hydrograph
<br />on Harvard GulCh at Logan Street for the storm of June 8, 1969.
<br />In order to reproduce t~e storm hydrograph, the rainfall ab-
<br />stractions were manipulated to give the required excess pre-
<br />cipitation. A review of the data indicated an infiltration
<br />rate for thi" ~V"nt whir;h vari."d fro1'l 1-1/2 in('h.... "..r hour
<br />in the earlier part of the storm to less than 1/2 inch per hour
<br />toward the end of the storm. The pervious detention-depression
<br />storage for that storm was about 0.80 inches while the impervious
<br />storage was 0.30 inches with a 15% loss factor. These values
<br />were comparatively high yet relatively realistic. Comparing
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