|
<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 />III. HYDROLOGIC ANALYSIS
<br />
<br />GENERAL
<br />
<br />A
<br />
<br />Detailed hydrologic analyses were performed to estimate storm runoff peak flow rates and volumes at
<br />various design points within the study area, The CUHP-2000 PC program (Reference 2) was used to determine
<br />storm runoff hydrographs for the sub-watersheds and the UOSWM-2000 PC program (Reference 3) was used
<br />to perform routing of the CUHP-2000 generated hydrographs.
<br />
<br />The total study watershed area as shown in Figure 111-1, is approximately 11,3 square miles, The study
<br />area was divided into a total of 47 sub-watersheds for Kinney Creek, 19 sub.watersheds for North Pinery, 22
<br />sub-watersheds for Fonder Draw and 14 sub-watersheds for South Pinery, The sub-watersheds vary in size
<br />from 16 acres to 130 acres with an average size of 71 acres, Peak flows at each sub-watershed outlet points
<br />were calculated for 10-. 50-,100- and 500-year recurrence intervals based on the future land use conditions,
<br />Peak flows were also calculated for the 1 OO-year event based on the existing land use conditions,
<br />
<br />B, PREVIOUS STUDIES
<br />
<br />The existing floodplain information for Kinney Creek and Fonder Draw shown on the effective Flood
<br />Insurance Rate Map (Reference 6) was prepared based on the FEMA's approximate hydrologic and hydraulic
<br />study method. Therefore, no detailed hydrologic and hydraulic analysis backup data for the study area was
<br />available,
<br />
<br />C. DESIGN RAINFAll
<br />
<br />For the entire study area, the 2-hour design storm distribution recommended by the Urban Storm
<br />Drainage Criteria Manual (USDCM. Reference 1) was used to produce runoff hydrographs, The 1-hour point
<br />rainfall depth for the study area was determined from the Rainfall- Depth - Duration - Frequency Figures in the
<br />USDCM, The standard 2-hour storm distribution was generated based on the guidelines outlined in the
<br />USDCM. The rainfall distributions used in the study are listed for all recurrence intervals in 5-minute increments
<br />in Table 111-1.
<br />
<br />D,
<br />
<br />COLORADO URBAN HYDROGRAPH ANALYSIS
<br />
<br />The Colorado Urban Hydrograph Procedure (CUHP) computer program was used to estimate storm
<br />runoff hydrographs for the sub-watersheds, The model version used for this study is CUHP 2000, Version 1.1
<br />(Reference 2), The sub-watershed input parameters required for GUHP are: sub-watershed identification
<br />number, drainage area, length and centroidallength, drainageway slope, impervious percentage, detention and
<br />retention storage losses, and initial and final infiltration rate losses, A summary of the CUHP input parameters
<br />used for the analysis is presented in Appendix B.
<br />
<br />Sub-watershed parameters were measured directly from the mapping prepared for this study using
<br />digital USGS quadrangle maps, Imperviousness maps were prepared delineating the existing and future
<br />imperviousness percentages based on the zoning information provided by the project sponsors, aerial
<br />photography, USGS quadrangle maps, and site visits, The existing and projected imperviousness percentages
<br />for sub-watersheds were estimated as composite values resulting from a weighted area average computation
<br />using the impervious zones (Figure 111-2 and Figure 111-3, respectively), In addition, several residential areas
<br />were evaluated in more detail to determine the appropriate composite imperviousness values, In order to
<br />account for storage and infiltration losses due to roadside swales, the MDCIA value of 2 was used for the
<br />subdivision areas without curb and gutter (Le, the old Pinery subdivision).
<br />
<br />Detention, retention, and infiltration parameters were assigned to each hydrologic soil group as
<br />recommended in Tables RO-6 and RO-7 of the USDCM, Composite parameters weighted by area were then
<br />determined for each sub-watershed using the soil zones (Figure 111-4), Soil information for the study area was
<br />obtained from an NRCS soil survey ofthe area (Reference 13), Appendix A contains the resultant hydrographs
<br />for several design points and peak flow diagrams,
<br />
<br />E, STORMWATER MANAGEMENT MODEL
<br />
<br />The Urban Drainage and Flood Control District's UDSWM-2000 PC program was utilized in the flow
<br />routing computations of the CUHP-2000 runoff hydrographs. The version of the program used is UDSWM-
<br />2000, Version 1,4,1 (Reference 3), The routing element parameters required for a UDSWM model are: element
<br />numbers, types (e.g. direct flow, channel, pipe, etc.), lengths, slopes, side slopes, and resistance coefficients,
<br />The type of routing elements was determined based on the existing drainageway configurations and shapes.
<br />
<br />III-I
<br />
|