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Home My WebLink AboutPLANTATION MANOR - PDP - 39-00 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORThistoric rate. The outlet will be in a pipe that flows East about 500 feet; then South across Horsetooth Road to a drain swale; then in the drain swale to the Westfield Park Detention Pond. The existing drain swale on the South side of Horsetooth will require lowering and a concrete pan constructed as part of this project. Sub -basin 6 is the North side of Horsetooth Road lying East of Big Ben Drive. The concentration point will be at the proposed 16 foot wide sidewalk chase and curb opening. Flows will be into the detention pond. EROSION CONTROL: The site is in the high rainfall erodibility zone and in the moderate wind erodibility zone. The site will be divided into two phases for erosion control. The first phase that will be constructed is Big Ben Drive and the utilities that are in the street and all of the units on the East side of Big Bend Drive. The detention pond will be constructed at the beginning of the grading of the first phase. The water quality extended detention will be constructed with the detention pond. A silt fence will be constructed along the East line of the site. Two straw bale dikes will be placed in the swale in the detention pond. The existing ground cover on the West side of Big Bend Drive will not be disturbed until the units on the East side of the site are completed. At that time, a silt fence will be placed along the i West side of Big Bend Drive. I� The extended detention calculations and erosion control calculations are enclosed as part of this report. This drainage report and the design, of the drainage system are in compliance with the City of Fort Collins Storm Drainage Design and Criteria. If you have any questions regarding this report, please call. Sincerely, G. Richard A. Rutherford, P.E. & L.S. RAR/meh 'J,''••.,,. ��,•`,"CORD .............. 00 C\1 ,acO s ':• 0 JJ 11t 11111' developed site will be detained in the proposed detention pond and released at one c.f.s. as determined by the City because our runoff is into the Wesfield Park PUD Pond Southeast of this site. The Master Plan identified the maximum release rate of 2.8 c.f.s. of which our portion is one c.f.s.. DEVELOPED SITE: This project is proposed to develop 38. single family attached homes, private drives and parking areas, Big Ben Drive and an onsite detention pond. All runoff from this site will be directed to the detention pond to be constructed in the Southeast comer of this site; then released at one c.f.s. as identified by the above mentioned master plan into a piping system that will take the runoff to the Westfield Park Detention Pond which is on the South side of Horsetooth Road about 800 feet East of this site. The Westfield Park Detention Pond is constructed. This developed site is divided into six sub -basins. Sub -basin 1 is located in the Southwest comer of the project. It will also include runoff from Horsetooth Road that flows onto this site. The offsite portion is constructed. There is also an existing two foot curb chase that takes 1.04 c.f.s. of runoff from Horsetooth and routes it through the Rossborough Subdivision. The concentration point for this basin is located at the proposed 10 foot curb inlet on the West side of Big Ben Drive at Horsetooth Road. This inlet will be in a sump condition. Runoff from this inlet is in a pipe to the East under Big Ben Drive to the proposed pond. Sub -basin 2 is located in the Northwest part of this site. The concentration point for this basin is the 10 foot curb inlet located on the West side of Big Ben Drive at the North side of this Project. This inlet is ongrade and will handle the 2 year runoff rate. However, flows from the 100-year storm will not be captured in this inlet but will overflow into Rossborough Subdivision. Sub -basin 3 is located along the East side of Big Ben Drive on the North side of this project. The concentration point is on the East side at Big Ben Drive of the North end of this project. This inlet handles the 100-year runoff. Flows from the inlet are East in a pipe, the same as for Sub -basin 2. Sub -basin 4 is located along the East side of Big Ben Drive on the South end of this site. The concentration point is at a 10 foot curb inlet on grade at the East side of Big Ben Drive at the Horsetooth Road Intersection. This Inlet will handle the 100-year runoff. All flows from this inlet are piped East to the detention pond. Sub -basin 5 is along the East side of this project and is where the detention pond is located. All runoff from this project will be to this pond. The pond is sized to store the 100-year runoff less the historic two year runoff and the extended detention pond volume. The spillway for this pond will be 25 feet wide and will be directed to flow to Horsetooth Road. It will be located at the Southeast corner of the pond on the South side. An outlet structure is proposed and located in. the Southeast corner of the pond. It is designed to detain and release for the 40-hour extended detention, then overtop into the structure but still being restricted on the outlet pipe to release at the two-year STEWART&ASSOCIATES Consulting Engineers and Surveyors 1 July 16, 2001 Mr. Basil Harridan Stormwater Utilities _ City of Fort Collins P.O. Box 580 Fort Collins, CO 80522-0580 Dear Basil, EXISTING SITE: The following is the Final Drainage, Erosion Control & Extended Detention Report for Plantation Manor P.D.P. which is situated in the Southwest 1/4 of Section 27, Township 7 North, Range 69 West of the 6th P.M., Fort Collins, Colorado. The site contains 4.78 acres and is located in the City's Foothills Drainage Basin and the Spring Creek Drainage Basin. The site is bounded on the South by West Horsetooth Road and on the West and North by Rossborough Third Filing, and on the East by an existing horse boarding establishment. The site has two older frame houses and nine out buildings that are existing. There are many existing Chinese Elm trees on the site. The ground cover is grass and weeds. The historic site is divided into two sub -basins. Historic Basin -I is the South 1.93 acres of the site, and also 0.92 offsite acres from Horsetooth Road that now flows West to East in the curb and gutter and dumps onto this site. There is an existing ridge in the site that runs East to West. Historic Basin-1 slopes from Northwest to Southeast at about 2.2%. The Southeast corner of the site is approximately two feet lower than Horsetooth Road. The Major Basin Map shows this sub - basin being in the Spring Creek Drainage Basin but it is actually in the Foothills Basin. Historic Basin -II is the North 1.95 acres of the site and is on the North side of the ridge. Historic Basin -II slopes from Southwest to Northeast and historically drains offsite to the Pleasant Valley and Lake Canal. The two year runoff rate from Historic Basin -I is 2.19 c.f.s. and the 100 year runoff rate is 9.88 c.fs.. The two year runoff rate from Historic Basin -II is 1.08 c.f.s. and the 100 year runoff rate is 4.90 c.f.s.. ' DRAINAGE CRITERIA: Due to the small size, the Rational Method has been utilized to determine peak runoff rates and required detention pond volumes. Design factors used are in accordance with the recommendations of the City of Fort Collins Storm Drainage Criteria and Construction Standards Manual. In accordance with the City of Fort Collins drainage policy, the 100-year runoff from the James H. Stewart and Associates, Inc. 103 S. Meldrum Street • P.O. Box 429 91 Ft. Collins, CO 80522 970/482-9331 • Fax 970/482-9382 L�) Nit w Swallow Id. I Linmfflw Dr. r- sr��. F a : D9ra J a Milt 7m: a _', 've 1L:ItIQ v �. `• ' . M •-� S Fe.•cr o 1■ — l a C. C� DtunsklrLDs. i_ Ciz. .4� Ct. t a�Casj �- •a .��. �.� .. _a �� v i ej Newcastle C,l-'. a sr O. Ora` o6 �.• . iLl34Se �I o� od'•/ roasa� St. 7 e, ..:. o p o�• 1 1 ` DAM.s �� ?ztts tf 4 J�N rl - .ac i:; LM w a VICINITY MAP SCALE.• 1 " = 1000' N TABLE OF CONTENTS 1 Vicinity Map 2-4 Text of Report 5-8 Historic Drainage Calculations 9-20 Developed Drainage Calculations 21-23 Detention Pond and Spillway Calculations 24-27 Extended Detention Calculations 28-31 Erosion Control Calculations 32-35 Drainage Criteria Manual Charts Pocket Grading, Drainage and Erosion Control Plans FINAL DRAINAGE, EROSION CONTROL & EXTENDED DETENTION REPORT PLANTATION MANOR P.D.P. SITUATE IN THE FOOTHILLS DRAINAGE BASIN AND SPRING CREEK DRAINAGE BASIN PREPARED FOR BRET LARIMER JULY 169 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