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Home My WebLink About617 WOOD ST. (MORIE AT CAPITOL HILL) - PDP - 22-06 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT617 Wood Street Preliminary Drainage Report Ft. Collins, Colorado IV. SUMMARY & CONCLUSIONS In summary, the Project will make use of existing grades to the greatest extent Possible, minimize impacts to On -Site environmental amenities, provide. conveyance of On- and Off -Site storm flows through the Site, and provide water quality and storm detention in manner consistent with Best Management Practices. Under the Plan, no adverse impacts to the local community or environment are expected. -5- n 617 Wood Street Preliminary Drainage Report Ft. Collins, Colorado Q3 C. Water Quality & Detention As significant landscaping is programmed, and where the total impervious area.is not increased to or above 5,000 s.f., no water quality or detention is proposed. It is expected that downstream natural process will continue to function such that any residuals will be mitigated. D. Erosion Control Erosion control will be provided and will be consistent with the standard practice. More specifically, BMPs will be installed as appropriate to minimize erosion due to aeolian and surface runoff affects. BMPs during construction may include tracking pads, silt fencing, inlet protection, revegetation, and contour roughening. Post -Construction BMPs may vegetation, and proper maintenance of open areas. -4 617 Wood Street Preliminary Drainage Report Ft. Collins, Colorado III. DRAINAGE FACILITY DESIGN — PROPOSED CONDITIONS The general concept for drainage includes the use of surface and subsurface stormwater conveyance systems, including curb & gutter, swales, detention ponds, and storm sewers at select locations, such that both aesthetics and economy are maintained. A. Design Criteria Drainage design and computations are based on the City's criteria, as well as Urban Drainage & Flood Control District's Drainage Criteria Manuals. Minor design storms for residential systems shall be based on the local 2- year event, while the major design storm shall be based on the 100-year recurrence storm interval. Detention releases from On -Site ponds shall be based on the 5-year historic event. Where the site will not increase the level of impermeability above 5,000 square feet, no detention or water quality systems are proposed. Further drainage patterns will remain consistent as existing conditions. B. Sub -Basin Descriptions For purposes of hydrologic analysis, Basin OS-1 (On -Site) is further subdivided into four (82) sub -basins, with each based on specific topographic characteristics. Basin I Being approximately 0.02 acres and located on the west 1/8 of the site, stormwater is routed west to an alley where it conveyed to the Elm Street gutter systems and ultimately to the Cache La Poudre River. Storm runoff is considered to be minimal under developed, and no adverse impact due to drainage is expected for on- or off - site properties along the drainage paths to Elm Street and beyond. Basin 2 Being 0.38 acres and located on the east 7/8 of the site, stormwater is routed east to the Wood Street gutter system where it conveyed south to the Elm Street gutter systems and ultimately to the Cache La Poudre River. Storm runoff is considered to be minimal under developed, and no adverse impacts are expected for on- or off -site properties along the drainage paths to Elm Street and beyond. -3- 617 Wood Street Preliminary Drainage Report Ft. Collins, Colorado II. DRAINAGE BASINS This section discusses existing and proposed, developed basin hydrology. Time of concentration and runoff calculations performed in analyzing drainage under both conditions are based on the 2003 City of Thornton Standards and Specifications for the Design and Construction of Public Improvements (TSSDCPI, 03). A. Major Basin Description — Existing Conditions The Site is in unincorporated Adams County, and the Developer ultimately proposes to annex the subject area to the City of Thornton. Based on the Adams County, Colorado Flood Insurance Rate Map (FIRM) Community Panel Number 08001 C0035G (8/95), the Site is not influenced by floodplains (see attached). The nearest region which may be inundated by a 100-year flood event would be to the north of the site in Todd Creek and its tributaries. Todd Creek is a tributary of the South Platte River. Area's identified as being inundated by a 100-year flood are approximately 1000 feet away from the Site. Due to the nature of the Site, no wetlands are identified On -Site. B. Sub -Basin Description — Existing Condition Sub -basins which influence the Site include, the Site' itself, property to the west, the neighboring roadways (140`h Avenue, 144`h Avenue, and Holly Street). Sub -Basin OS-1 Sub -Basin OS-1 is the approximate northern 3/4 of the Site. This region is approximately 128.2 acres which is currently used for agriculture. In its current condition, existing grade is split towards the north by the ridge running through the site. The slope of the northern region is roughly a 5 percent grade to the north. The historic outfall for the north On -Site area is Todd Creek. Sub -Basin OS-2 Sub -Basin OS-2 is the approximate southern 1/4 of the Site. This region is approximately 31.4 acres which is currently used for agriculture. In its current condition, existing grade is split towards the south by the ridge running through the site. The slope of the southern region is roughly an 8 percent grade to the south. The historic outfall for the southern On -Site area is Brantner Gulch. -2- I 617 Wood Street Preliminary Drainage Report Ft. Collins, Colorado I• GENERAL LOCATION & PROJECT DESCRIPTION This section contains information relative to Project location and general description of facilities and intent. A. Project Location The Project Site is located in the NW %a of Section 11, Township 1 North, Range 69 West of the 6`h P.M., and is currently within City of Ft. Collins city limits and Larimer County, Colorado. The Developer ultimately proposes to redevelop the subject site such that demolition of the existing residence will lead to the construction of 2 duplexes on site. The Project area occupies approximately 0.40 acres. The Site is bounded on the north and south by residential lots, on the east by Wood Street and on the west by an alley. A Project Vicinity map and Drainage Plan are included with this Report. B. Project Plan & Phasing The Project Plan demolition of the existing residence and replacement with two duplexes, as well as landscape improvements and water/sewer services. The Developer intends to utilize the natural grade and terrain to facilitate adequate drainage of stormwater to the two proposed drainage basins located on the east and west sides of the property. The Project will be constructed in 1 phase. C. Site Features, Existing Land Use & Constraints The Site is presently zoned as residential and will remain as such. In its current condition, existing grade is split towards the east and west, with roughly a 1 to 6 percent grades on site. The historic outfall for the site is the Cache La Poudre River approximately '/a miles to the northeast. D. Existing Easements & Right -of -Way Existing easements and ROWS within subject area include the Wood Street ROW and standard utility easements for services. E. Floodplains, Groundwater & Wetland Areas Based on review of the Larimer County, Colorado Flood Insurance Rate Map (FIRM) Community Panel Number 08001 C0035G (8/95), the Site is not influenced by floodplains. Further, no wetlands are identified On -Site. While no current geotechnical study is provided with this Project, soils in the area are considered to be moderate to well draining of the Ulm soils class. No groundwater is anticipated, but should be verified prior to construction of the units as basements are programmed for the project. I CERTIFICATION I hereby certify that this drainage report for the 617 Wood Street Property was prepared by me (or under my direct supervision) for the Owners thereof and meets or exceeds the criteria in the City of Fort Collins Storm Drainage Design Criteria & Construction Standards Manual. Stanley E. Dunn, P.E. Registered Professional Engineer State of Colorado No. 33827 N Preliminary Drainage Report 617 Wood Street Ft. Collins, Colorado August 2006 Prepared for: McKee Brothers, LLC 221 East Lincoln Avenue Ft. Collins, Colorado 80524 Prepared by: Alpine Consulting Engineers, Inc. 2000 South College Avenue, Ste. #308 Ft. Collins, CO 80525