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HomeMy WebLinkAboutMASON STREET MOTEL - PDP/FDP - 7-98 - REPORTS - DRAINAGE REPORT (3)z. EROSION CONTROL: This site is located in a high rainfall erodibility zone and in a low wind erodibility zone. A portion of the existing wetland will be retained during the filling process and a gravel sediment filter will be placed over the existing outlet pipe during construction. During the construction of the parking lot and building pad, a silt fence will be installed along the east side of the site behind the walk on Mason Street, and in the wetland area all along the toe of the fill for the parking lot. Straw bale inlet filters will be placed around the area inlets prior to paving. The existing development around the site provides adequate wind barriers. All erosion control methods comply with City of Fort Collins criteria. railroad right-of-way and the westerly portion of the property to the north. A copy of the City's map of the area showing Basin No. 4 is included in this report. Calculations of the runoff from Basin No. 4 and the capacity of the swale along the north side of the parking lot are included in this report. This site has been flooded a few times in the past. The cause of the flooding was that the New Mercer Ditch overflowed and then the railroad embankment overflowed and flooded this and adjoining sites. The site and adjoining sites are in a low basin with the only drainage outlet being the McClelland Drive Interceptor Storm Sewer. The Burlington Northern Railroad has raised their embankment about six inches which may provide some protection from this overflow flooding, and the City Stormwater Utility has a long range plan to provide relief from the New Mercer Ditch overflowing. The building floor has been set at approximately 2 '/z feet above the adjacent sidewalk along Mason Street to provide protection from flooding. The floor elevation has been set at elevation 5037.50. AYRES has made a study of the basin, and determined that after the Mason Street Motel is constructed, the 100 year water surface elevation in this area during the worst condition will be 5036.11, so the floor will be about 1.4 feet above the possible 100 year water surface elevation. The overall drainage concept for this site is to detain and restrict the release from the new hard surfaced areas and to let the wetland areas outflow without restriction, after about 12" of ponding. ' The calculations of required detention volumes, release rates, restricted outlet sizing and detention pond volumes are included in this report. OFFSITE FLOWS: There are offsite flows onto this site from about 0.06 acres of lawn area to the south, from about 1050 feet of the west 1/2 of Mason Street (about 1.0 acres) which enters the northeast comer of the site through a sidewalk culvert, and from approximately 0.94 acres of the railroad right-of-way and from 0.48 acres of the rear portion of the site to the north. The offsite flows from the south, west and northwest will enter the wetland area. The offsite flow from Mason Street through the sidewalk culvert will flow into the wetland sump at the northeast corner of the site and then out through the existing 15 inch pipe and into the McClelland storm sewer, just as it has done historically. A water quality outlet structure will be placed over the 15 inch outlet pipe, so all of the runoff from the motel site, railroad right-of-way and the west half of Mason Street will go through this outlet structure. This will cause the water quality ponding to back up into the wetland, but that should be acceptable. i; . The water quality pond and outlet works will be designed based on the area of the motel site and the 6 west half of Mason Street. This will be Basins No. 1 and 3, which is a total of 1.70 acres. DRAINAGE AND EROSION CONTROL REPORT FOR MASON STREET MOTEL EXISTING SITE: The Mason Street Motel site is located on the west side of S. Mason Street just north of the intersection of S. Mason and Boardwalk. S. Mason Street is fully improved with curb, gutter, sidewalk and pavement, and all utilities lines are installed. The Ramada Limited Motel is on the south side of the site and Harms Sound Lab is on the north side of the site. The Burlington Northern Railroad right-of-way runs along the west side of the site. The railroad tracks are on a 10 foot high embankment located in the center of the 100 foot wide railroad right-of-way. The east edge of the right-of-way is a low wetland area. This wetland extends east about three fourths of the way across the South Mason Motel site. The site is located in the Mail Creek Drainage Basin and stormwater outflow is through the "McClelland Drive Interceptor Storm Sewer." This storm sewer, which was built in 1979, carries flows east on Boardwalk to College, then south to Mail Creek. The allowable release into this storm sewer from new development is 0.5 c.f.s. per acre, per the criteria established for this basin by the Stormwater utility. PROPOSED NEW DEVELOPMENT AND DRAINAGE FACILITIES: The Mason Motel site will be developed by the construction of a building, parking lot and walks. It is proposed to maintain some of the existing wetland areas around the edges of the site. The parking lot areas will be constructed bowl shaped to provide detention ponding for the runoff from the new pavement and from the entire motel building. A swale will be provided along the south side of the building. This swale will pick up the runoff from the landscaping along the south side of the building as well as some offsite flow from approximately 0.06 acres or grassed area on the site located to the south. A six foot wide concrete sidewalk for pedestrian access from the railroad to Mason Street will be constructed adjacent to the south property line, and the swale will be located north of the sidewalk. This swale will drainto the west and carry the runoff into the wetland area along the westerly and northerly portions of the site. A calculation of the runoff through this swale and the capacity of the swale is included in this report. The side slopes of this swale and the slopes from the top of the parking lot curbs into the wetland area will be 3 to 1 slopes. A variance is requested for these slopes that are steeper than the allowable 4 to 1. The wetland area around the west and north sides or the parking lot will not have a direct outflow into the McClelland storm sewer, but as the water surface increases the wetland can overflow through a swaled area along the north side of the parking lot. The original design had a pipe extended into the wetland area to allow a direct outflow, but now it appears, that pipe is not necessary and it will be better to keep more ponding in the wetland area. The swale along the north side of the parking lot will carry the 100 year runoff from Basin No. 4, which includes about 800 feet of the Q 1 1 1 r 1 $TEWART$, kWCIATE$ Consulting Engineers arxi Surveyors October 30, 2000 Mr. Basil Hamdan Storm Water Utility City of Fort Collins P.O. Box 580 Fort Collins, CO 80522 Dear Basil, The included drainage report and calculations have been prepared for the Mason Street Motel located at 3935 S. Mason Street, which is Lots I and 2 of the South College Investments Subdivision. This area is located in the Mail Creek Basin. ' The present site is mostly a low wetlands area which will require filling prior to development. The City has issued a letter stating it is permissible to fill the site as necessary for development. A copy of this letter is included in this report. This report has been prepared in compliance with the City of Fort Collins Criteria. 1 I Sincerely, eg Phillip I. Robinson, P.E. & L.S. 4 .502 PIR/meh a % James H. Stewart and.Associates, Inc. 103 S. Meldrum Street • P.O. Box 429 - Ft. Collins, CO 80522 970/482-9331 • Fax 970/482-9382 wn- ..13.1.,Uebjo ird ct. Or Affkwwd CL Rd. Am Bonita l Am 1 Ap Pkins Ct eii U, 4t C lboard aockmcn or.. somdm* DE j v? ro Trout n an Pkwv, c Npow Kww n IDrr. r.] VICINITY MAP SCALE: 1"= 1000' ct Table of Contents 1 Vicinity Map 2 Cover Letter 3-4-5 Teat of Report 6 Net and Gross Site Developed Runoff 7 Required Detention 8 Volume of Proposed Pond 9 Pond Release and Restriction Sizing 10 Swale along South side of Site 11 Offsite Basins 12 Swale along North side of Site 13-14-15 Erosion Control Calculations 16 Erosion Control Collateral 17-18-19 Water Quality Calculations 20 Copy of Letter Regarding Wetland 21 Rip Rap Calculations 22 Kutters Chart 23 Map of Offsite Basins Pocket Grading, Drainage and Erosion Control Plan STORM DRAINAGE AND EROSION CONTROL REPORT FOR MASON STREET MOTEL 3935 S. MASON STREET LOCATED IN THE MAIL CREEK DRAINAGE BASIN PREPARED FOR HATTMAN AND ASSOCIATES PREPARED BY STEWART & ASSOCIATES, INC. 103 SOUTH MELDRUM STREET FORT COLLINS, COLORADO 80521 970-482-9331 OCTOBER 30, 2000