Final Baseline Hydrology Report - October 2012 - Urban Drainage ...

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Sanderson Gulch Major Drainageway Plan Baseline Hydrology Report October 2012 1.5 Data Collection In addition to mapping and survey data described in the previous section, the following sources of data and information on the watershed were utilized in the study: • Major Drainageway Planning, Sanderson Gulch/Weir Gulch (Frasier & Gingery, August 1972). • Flood Hazard Area Delineation, Sanderson Gulch and North Sanderson Gulch (Gingery Associates, Inc., August 1979). • Sanderson Gulch Drop Structure Inventory and Bank Stabilization, South Platte River to Sheridan Boulevard, Engineering Assessment and Maintenance Master Plan (Icon Engineering, Inc., January 2002). • Gulch Master Plan, Denver Parks and Recreation (Matrix Design Group Inc., October 2009). • Final DRAFT Mississippi Gulch Outfall Alternatives Analysis and Scoping Study (Matrix Design Group Inc., December 2010). • River South Greenway Master Plan (Greenway Foundation, 2009). • Soils information for the hydrologic analysis was obtained from the Natural Resources Conservation Service (NRCS). Note that GIS data for soils was only available for the portion of the study area located within Jefferson County. • Future landuse information for the redevelopment of the Green Gables Country Club was taken from the Green Gables Official Development Plan (DTJ Design, Inc., Revised April 11, 2012). • As-Built Drawings of various channel improvement projects from the UDFCD website (http://udfcd.gisworkshop.com/). 1.6 Acknowledgements This report was prepared with the cooperation of UDFCD, City & County of Denver and the City of Lakewood. Representatives who were involved in and contributed to the study are listed in the following Table 1-1. Table 1-1 Project Participants Name Representing Project Role Shea Thomas UDFCD Project Manager Bill DeGroot UDFCD Floodplain Manager Mike Anderson Denver Public Works-Engineering Division Sponsor David Marquardt Denver Parks & Recreation, Planning Sponsor Kevin Lewis Denver Public Works, Wastewater Management Division Sponsor Terry Rogers Lakewood Public Works Sponsor John Paliga Lakewood Community Development Sponsor Robert Krehbiel Matrix Design Group, Inc. Project Manager HungTeng Ho Matrix Design Group, Inc. Project Engineer George Slovensky Matrix Design Group, Inc. Project Engineer Jennifer Newby Matrix Design Group, Inc. Project Engineer Bob Eck Matrix Design Group, Inc./Design Studios West Landscape Architect Ian Anderson Matrix Design Group, Inc./Design Studios West Landscape Architect Jane Kopperl Matrix Design Group, Inc. Landscape Architect Wilson Wheeler Matrix Design Group, Inc. GIS Manager Additional data obtained from the project sponsors included GIS data, drainage reports and design drawings and structure survey data. A complete list of references is provided in Section 9.0 References. Van tours of the drainageway were conducted with the project participants to better understand field conditions. The Denver portion was conducted by Denver Parks and Recreation on August 20, 2012. The tour for the Lakewood portion was conducted by City of Lakewood staff on September 24, 2012. 2
Sanderson Gulch Major Drainageway Plan Baseline Hydrology Report October 2012 2.0 STUDY AREA DESCRIPTION 2.1 Project Area The project study area consists of the Sanderson Gulch watershed including the tributary North Sanderson Gulch. A map of the watershed is provided in the interactive Hydrology Map, Figure B-1 of Appendix B. Sanderson Gulch is a west bank tributary to the South Platte River in Denver. The confluence with the South Platte River is immediately downstream of Florida Avenue. The confluence and lower portion of the Sanderson Gulch watershed are located within the City and County of Denver. The watershed extends west from the South Platte River approximately 7 miles to S. Union Boulevard in the City of Lakewood and Jefferson County. The jurisdictions within the Sanderson Gulch watershed are shown on Figure 2-1. The northern boundary of the watershed varies from Exposition Avenue on the east to Florida Avenue on the west. The southern boundary of the watershed varies from approximately Harvard Avenue on the east to Morrison Road on the west. The Sanderson Gulch watershed has a drainage area of 7.6 square miles. NRCS hydrologic soil types within the basin are predominantly Type C. A soils map is provided in the interactive Hydrology Map, Figure B-1 of Appendix B. The watershed is essentially fully developed. The 152-acre Green Gables Country Club located near the southeast corner of the intersection of Wadsworth and Jewell in Jefferson County is the only significant undeveloped parcel and it is currently under redevelopment as mixed-use commercial and residential. Since development is approved and construction is imminent, this study assumes development of this site under the future conditions model. Watershed elevations range from 5230 feet at the confluence with the South Platte River to 5805 feet at the western limit of the watershed near S. Union Boulevard. Figure 2-2 identifies the parcels within the Sanderson Gulch that are city-owned. Within the City and County of Denver, Sanderson Gulch was one of the first drainageways to preserve the floodplain as open space and the gulch is almost entirely an open channel system contained within linear park and open space areas. Sanderson Gulch is not designated a wildlife corridor by Denver Parks and Recreation, but there are portions of the gulch that are designated as “Park” which means there are some use restrictions for those designated areas. The middle and upper reaches of Sanderson Gulch and the entirety of its tributary, North Sanderson Gulch, are located within Jefferson County and the City of Lakewood. Upper Sanderson Gulch and North Sanderson Gulch are also generally open channel systems, but the number of adjacent parks or open space areas is much more limited. Significant portions of the upper gulches are contained in narrow constructed drainageways. Figure 2-3 depicts the parks and open spaces within the Sanderson Gulch watershed. Map, Figure B-1 of Appendix B. Residential land uses make up a majority of the watershed. Limited commercial and industrial development exists along major arterial streets primarily Federal Boulevard, Sheridan Boulevard, Wadsworth Boulevard and the western part of Jewell Avenue. Land use within the watershed is summarized in Table 2-1. Table 2-1 Watershed Land Use Summary Land Use Percentage of Watershed Residential 75.7% Commercial/Industrial 11.4% Parks/Open Space/Ponds 12.9% Total 100.0% Watershed Area-Weighted Imperviousness 49.6% 2.3 Reach Descriptions For the purposes of the evaluation of alternative improvements, Sanderson Gulch has been divided into 12 reaches and North Sanderson Gulch into 4 reaches. Descriptions of the reaches are provided in the sections below and reach limits are illustrated in Figure 2-5. Major crossings are shown on Figure 2-6 and listed in Table 2-2. An inventory of existing drop structures is shown in Table 2-3. There are currently 35 drop structures on Sanderson Gulch and 16 on North Sanderson Gulch as shown on Figure 2-7. In addition to these existing structures, the previous report Sanderson Gulch Drop Structure Inventory and Bank Stabilization (Icon Engineering, 2002) recommended three new drop structures within the City and County of Denver. Sanderson Gulch Reach 1 – South Platte River to Lipan Culvert Entrance (Denver) There are several irrigation ditches and water storage reservoirs within the Sanderson Gulch watershed. Figure 2-4 shows the ditch locations for the Agricultural Ditch, Welch Ditch, and the Salisbury Lateral Ditch. Smith Reservoir, Ward Reservoir No. 1, Ward Reservoir No. 2 and Ward Reservoir No. 5 within the Sanderson Gulch watershed are privately owned and used for irrigation water storage. The operation of these ditches is described in Section 2-4. 2.2 Land Use Land use and zoning data was provided by the City and County of Denver and the City of Lakewood. A summary of how impervious area values were determined for hydrologic modeling is included in Section 3.3.2 Watershed Imperviousness. Land use in the watershed is illustrated on the interactive Hydrology 3
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