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Last modified
11/23/2009 12:58:13 PM
Creation date
10/4/2006 10:13:51 PM
Metadata
Fields
Template:
Floodplain Documents
Designation Number
46
County
Denver
Community
Denver
Title
Flood Hazard Boundary Map - Supplementary Report, Sanderson Gulch & Weir Gulch, Denver, Colorado
Date
3/1/1975
Designation Date
7/1/1975
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />I <br />I <br />I <br />I <br />1 <br />I <br />I <br /> <br />1 <br />I <br />I <br />I <br />I <br />I. <br /> <br />Exhibit A <br /> <br />SECTION III <br /> <br />HYDROLOGY <br /> <br />GENERAL <br /> <br />As required by the contract, hydrologic studies were completed <br />for both the Sanderson and Weir Basins. Through the hydrologic <br />studies the magnitude of the peak rate of storm runoff and volume <br />of storm runoff were determined for the six required storm <br />frequencies. The frequencies analyzed are the 2, 5, 10, 25, <br />50 and 100 year return periods. The 10 year and 100 year <br />frequencies were selected for a basis of final design. The <br />determination of the peak flow rates and volumes was done for <br />two different degrees of basin development. Land use under <br />existing conditions was analyzed to provide an indication of <br />the adequacy or inadequacy, as the case might be, of the existing <br />system. An estimate of future land use was then projected, with <br />the aid of local planning officials, so as to establish the <br />requirements of the total drainage system for the ultimate <br />development in the basins. With the requirement of analyzing <br />six storm frequencies for two different conditions of basin <br />development, the need was evident for a computer hydrograph <br />model. Therefore, a program was developed by Frasier & <br />Gingery which is designed to generate the storm hydrograph <br />for each sub-basin with a minimum of .input. The program, <br />referred to as HYDRO, was built around the Colorado Urban <br />Hydrograph Procedure as outlined in the Urban Storm Drainage <br />Criteria Manual. A discussion of the program input and opera- <br />tion is given in the HYDRO Section. <br /> <br />Upon the completion of the development of HYDRO, the model was <br />tested in a number of areas where runoff had been recorded or <br />estimated through earlier studies. One particular instance <br />where the model satisfactorily duplicated the recorded run- <br />off was the June 8, 1969 storm on Harvard Gulch. With minor <br />manipulation of the rainfall storage and loss parameters, the <br />recorded hydrograph at Logan Street was duplicated well within <br />hydrological accuracies. Other basin analyses tested also <br />showed very good comparison. <br /> <br />With the unusually high number of reservoirs within the Sanderson <br />and Weir Gulch Basins, it was evident that hydrographs would <br />have to be routed through the reservoirs to reflect the actual <br />overflow conditions. A program was developed which followed <br />the simple reservoir routing procedure outlined in most hydrology <br />texts. The location of the reservoirs made it difficult to <br />totalize the tributary basin into a larger single basin at each <br />design point, so a computerized method of hydrograph lagging and <br />adding was also developed. Both the routing and lagging and <br />adding programs were tied into the HYDRO Program. <br /> <br />-20- <br />
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