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HomeMy WebLinkAboutLARKS NEST - PDP - 36-00 - REPORTS - DRAINAGE REPORTNo Text C DEVELOPED SITE: We are proposing to develop six four-plex buildings with attached garages, private access roads, private parking, and a detention pond. The project is scheduled to begin construction in early spring, 2001. At present there is no proposed phasing for this project. All runoff from this site will be to the proposed detention pond North of the existing drainage channel on the South side of the project. The runoff will then be to the existing drainage channel in a 15" pipe and be released at this site's two-year historic runoff rate. There are three sub -basins on this site. Sub -basin "A" is located in the Northeast comer of this site and is 0.29 acres. Runoff from this basin is to Starflower Drive, then North to a proposed 10 foot curb inlet on grade, then Northwest in a 15" pipe to a proposed area inlet that will also catch runoff from this basin, then South in a 15" pipe to the proposed detention pond. Sub -basin `B" is most of the developed site. It is 1.45 acres more or less. Runoff is directed from the most Northwest corner of the site overland and in grass swales to the North -South access road, then South in curb and gutter, and also sheet flow to a proposed two foot curb opening in the South parking area, then in a two foot concrete pan to the area inlet in the detention pond. Sub -basin "C" is located along Starflower Drive. It is 0.26 acres. All runoff from this basin is to a proposed 10 foot curb inlet on grade East of the detention pond, then piped to the detention pond. The detention pond is designed to hold the developed 100-year runoff plus 120% of the Water 1 Quality Capture Volume (WQCV). The inlet will be raised in the pond to WQCV level. Holes will be drilled through a steel plate placed in the area inlet. The holes will be 5/8" diameter and be drilled every 4" up beginning at the pond bottom to the top of the inlet which is 12" above the pond bottom for the 40 hour release rate. At the WQCV water level runoff will be allowed over the top of the Her. A restriction plate will be placed on the outlet pipe in the area inlet. It is designed to let runoff be released at the two-year historic rate. EROSION CONTROL: ' This site is in the City's Moderate Wind Erodability Zone and in the Moderate Rainfall Erodability Zone. A silt fence will be constructed before beginning construction and left in place until all construction is completed. A straw bale dike will also be constructed around both area inlets and left in place until construction is completed. Because the top of the area inlet in the pond is above the pond's bottom because of the WQCV, this area will act. as a sediment trap during construction. Prior to seeding, the pond bottom will need to be regraded. The detention pond and any disturbed area in the existing 30' swale area will need to be reseeded as shown on sheet 4 of 10 of the utility drawings. Required escrow to the City of Fort Collins for erosion control is $4170. IV FINAL DRAINAGE & EROSION CONTROL REPORT s FOR LARKS NEST P.D.P. INTRODUCTION: This project is for developing six four-plex buildings, parking areas, access drives, and a detention pond on a 2.00 acres site. This site is an infill project. It is located in the City's McClelland/Mail Creek Drainage Basin. The site located in the Southwest 1/4 of Section 35, Township 7 North, Range 69 West of the Sixth P.M., City of Fort Collins, County of Larimer, Colorado. Developed "Woodlands Subdivisions" are on the West, North, and East sides of the project. Front Range Community College is located on the South. EXISTING CONDITION: The site is bounded on the North by Wakerobin Lane, on the East by Starflower Drive, on the South by Harmony Road, and on the West by an apartment complex. A six foot high block wall separates this site from the apartments. All roads are constructed. There is an existing drainage channel along our South property line. It is about 30 feet wide and flows West to East at about 1.0% slope. The flow in the channel is controlled by an existing 36" R.C.P. at the West side of our site. West of this site is a 30 foot wide dike constructed in the swale with the 36" pipe through it. According to the Mail Creek Master Plan, 100-year flow in the swale is 91.9 c.f.s.. A cross section of the Swale at our release point in the swale shows the 100-year High Water line to be at elevation 5064.5. On the East side of our site in the swale are two existing 42" RC.P.. They flow East under Starflower Drive to the existing swale on the East side of the street. Runoff on the North side of Harmony Road flows to an existing 8 foot long curb inlet on Harmony Road and then into the existing swale at Starflower Drive. Also runoff from the West side of Starflower Drive flows to this inlet, about 300 feet. The remaining 160 feet of the West side of Starflower Drive along with all of the South side of Wakerobin Lane which is about 290 feet, flow to an existing pan at the intersection of Starflower Drive and Wakerobin Lane, then flows in the pan Northeasterly across the street, then Northeasterly along Starflower Drive. The existing site slopes Southeast to the existing drainage channel or to Starflower Drive then back to the existing drainage channel. The average slope is about 1.06 percent. This site is covered by native grasses, weeds, and bare ground at. this time. t TESSOCIATEC S LWARTQ Q X� J Consulting Engineers and Surveyors January 2, 2001 Mr. Basil Harridan Stormwater Utilities City of Fort Collins P.O. Box 580 1 Fort Collins, CO 80522-0580 ® Dear Basil, RE: LARKS NEST P.D.P. This project is to construct six four-plex buildings with off street parking and a detention pond area. Construction for this project is scheduled for early Spring 2001. This project is in the McC1ellands Mail Creek Basin. The site is located in the Southwest 1/4 of Section 35, Township 7 North, Range 69 West of the Sixth P.M., Fort Collins, Larimer County, Colorado. The project is bordered by "Woodlands" developments on all sides. This is the last undeveloped area in the "Woodlands." Harmony Road is on the South side, Wakerobin Lane on the North side and Starflower Drive on the East. The West side is separated along the property line by a six foot high concrete block wall. Part of this site is an existing drainage channel that flows West to East along the South side of this site. All design and calculations within this report are in compliance with the City of Fort Collins Storm Drainage Design Criteria and Construction Standards. All basins in this project use the rational method for the runoff. U.D. Inlet is used to size the inlet. If you have any questions or need any more information regarding this report please let me know. Sincerely, Franklin D. Blake, P.E. FDB/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 ' TABLE OF CONTENTS A-C Cover Letter and Teat D Vicinity Map 1-31 Storm Drainage & Erosion Control Calculations Pocket Overall Grading, Drainage & Erosion Control Plan i FINAL DRAINAGE AND EROSION CONTROL REPORT FOR LARKS NEST P.D.P. PREPARED FOR ARMHOL, LTD JANUARY 02, 2001 PREPARED BY STEWART & ASSOCIATES 103 SOUTH MELDRUM STREET P.O. BOX 429 FORT COLLINS, CO 80522 TEL. 970-482-9331 FAX. 970-482-9382