Laserfiche WebLink
<br />Projected future land uses were determined from the planning information provided by the City <br />of Lafayette (1990), the City of Louisville (1989), and Boulder County (1985). These future land <br />uses were used to project the "ultimate" percent impervious for the watershed. Figure 5 indicates <br />the location of the various "percent impervious" for future land use conditions. The future land <br />use "percent impervious" was based on charts provided in the Runoff Section of the Urban Storm <br />Drainage Criteria Manual (UDFCD, 1969). Table 4 summarizes the percent impervious used for <br />each land use: <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />3.0 HYDROLOGIC ANALYSIS <br /> <br />3.3 BASIN AND ROUTING DATA <br /> <br />The hydrologic analysis consisted of determining the 10-,50- and lOO-year frequency runoff for <br />future developed basin conditions, The results have been summarized in this report. All technical <br />documentation is provided in a separately published technical addendum (Greiner, 1990) and is <br />available at the offices of UDFCD. <br /> <br />3.1 METHODOLOGY <br /> <br />The basis for this study is the Urban Storm Drainage Criteria Manual, (UDFCD, 1969) and the <br />Boulder County Storm Drainage Criteria Manual (Boulder 1986). The procedure used involved <br />the following three computer programs: Hydrocad (UCD, 1989), CUHPE/PC (UDFCD, 1985a) <br />and UDSWM2-PC (UDFCD, 1985b). Hydrocad is an autolisp program which runs from within <br />AutoCAD and was used to digitize the sub-basin area, soil type, land use and drainage flow path <br />information, This raw data was compiled into a format which was read into CUHPE, along with <br />user input for rainfall depth and depression losses for pervious and impervious areas. Individual <br />storm hydrographs were developed using CUHPE. These hydrographs then were routed and <br />combined using the SWMM computer program. <br /> <br />Table 4 <br /> <br />Percent Impervious for Various Land Uses <br /> <br />Desilmation Land Use <br />A Commercial <br />B Industrial/OfficelEmployment Center <br />C Residential (8 DU*/Acre); Multi-Use Residential <br />D Developing Resource (5 DU/Acre) <br />E Residential (2 DUlAcre) <br />F Non-Urban Residential (1.0 DUlAcre) <br />G Residential (0.75 DU/Acre) <br />H Park <br />I Residential (0.2 DU/Acre) <br />J Open Space/Agricultural/Golf Course <br /> <br />3,2 RAINFALL <br /> <br />The rainfall depth was taken from the Boulder County Storm Drainage Criteria Manual (Boulder, <br />1986). The one-hour point rainfall depths for Zone 1 were used for each rainfall frequency event. <br />These one-hour rainfall depths are listed in Table 3 below: <br /> <br />Table 3 <br /> <br />* DU - Dwelling Units <br /> <br />One-Hour Rainfall Depths for Zone 1, Boulder County <br /> <br />Storm Frequency (year) 2 <br />One-Hour Rainfall Depth (inches) 1.01 <br /> <br />5 <br />1.43 <br /> <br />10 <br />1.73 <br /> <br />50 <br />2.40 <br /> <br />100 <br />2.70 <br /> <br />FLOOD HAZARD AREA DELINEATION <br />BULLHEAD GULCH AND lRIBUTARlES <br /> <br />6 <br /> <br />% ImDervious <br /> <br />95 <br />85 <br />70 <br />40 <br />30 <br />15 <br />10 <br />7 <br />5 <br />2 <br /> <br />FINAL <br />7131191 <br />