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<br />Bosley Wash Drainage Master Plan Phase I: Watershed Floodplain Delineation
<br />.,c- iI!Il !i\J!_-E~,('fir'0I"" "';;;;~;"",.wy'(;:;S~t#0"'s';;;;;,";":;~,, ",' 'c'; ':,
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<br />
<br />1.1 Define Needs and Collect Information
<br />
<br />Representatives of the County, local sponsors, and local residents were contacted concerning the
<br />nature and extent of the existing flooding issues within the basin, A by, product of this task was
<br />to communicate to the local residents the overall direction of this project and to solicit their
<br />feedback and involvement. These tasks entailed an initial meeting with the County and project
<br />sponsors followed by a public meeting where HDR presented the general scope of the project
<br />and discussed basin issues, Photos taken during the site visits, and those provided by the
<br />sponsors, are included in Appendix 1.
<br />
<br />1.2 Data ColI~ction and Mapping
<br />
<br />HDR collected, compiled and evaluated the available existing material related to flooding in the
<br />
<br />Bosley Wash Basin, Sources of infonnation include previous studies and reports, GIS
<br />
<br />
<br />infonnation, future growth projections and land use development infonnation, typical cross-
<br />
<br />sections from topographic data, and water quality data. Sources are listed in the Bibliography
<br />
<br />section,
<br />
<br />1.3 Hydrologic Model Development
<br />
<br />A model was developed that quantified stonnwater hydro graphs, volumes and flow rates within
<br />
<br />the Bosley Wash Basin under existing conditions, The County and GJDD concluded that the
<br />
<br />existing land use would remain unchanged for the foreseeable future; so the representation of
<br />
<br />future land use would be an inconsequential change, Subbasins were delineated based on
<br />
<br />
<br />mapping provided by the County and GJDD. Other infonnation used in the model development
<br />
<br />included site visits, interviews, land use, soil types, and hydraulic structure conditions, A
<br />
<br />hydrologic model was developed using HEC,HMS (V.S, Anny Corps of Engineers, 1999),
<br />
<br />Runoff hydrographs were generated for the 2, 5, 10,50, 100, and 500-year events, HDR used
<br />
<br />the National Oceanic and Atmospheric Administrations Atlas 2 (NOAA, 1973) precipitation data
<br />
<br />for all hydrologic evaluations.
<br />
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<br />Page 2
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