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Home My WebLink AboutHAMPSHIRE POND PUD FINAL - 44 93A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTHampshire Pond P.U.D. Preliminary Drainage Report page 3 V. PROPOSED IMPROVEMENTS The development of the site would consist of single-family homes with new local streets. The off -site flows that enter the site at the northwest corner would be conveyed by a swale that spills out to the proposed Hampshire Road. The swale would have to cross Featherstar Way in a 15" RCP culvert. Curb and Gutter would carry most of the runoff to the corner of Marshwood Drive and Willow Fern Way at the southeast corner of the site. A drainage swale would divert the flows to the temporary detention basin to the east. VI. DEVELOPED DRAINAGE Off -site flows that enter the northwest corner of the site amount to 3.12 cfs for the 100-year storm and 0.85 cfs for the 2- year event. The peak runoff leaving the developed site is 43.52 cfs and 11.98 cfs for the 100-year and 2-year storms, respectively, I as shown in Table A for design point 1. The various concentration points quantify on and off site runoff for the design of storm drainage facilities. A small drainage swale with trickle pan is proposed along the landscape buffer near Drake Road to.convey the point discharge from an existing 12" driveway culvert west of the site. The flow would pass under Featherstar Way in a 15" culvert, continue in the swale to a sidewalk culvert, and enter the gutter on Hampshire Road. Flows from Drake Road would follow the curb returns into the subdivision and follow the gutters and cross -pans to meet at the intersection of Marshwood Drive and Willow Fern Way, as would most all the site runoff. Flow would then exit the gutter through a sidewalk culvert and flow into a swale that would carry the site's runoff to the regional detention area. The project will be constructed in three phases as indicated in the Site Plan. At the ends of each curb and gutter a channel must be constructed to carry the runoff to the excavated area of the regional detention pond. Refer to the Drainage and Erosion Control Plan for locations. VII. EROSION CONTROL Temporary erosion control will consist of a soil sealant to be applied to bare ground just after overlot grading. Straw bales are to be placed in the temporary channels constructed for Phase I and II development. Permanent vegetative erosion .control will be used in conjunction with landscaping. Permanent revegetation of areas disturbed by construction will be the responsibility of the contractor. Seed will be applied by drilling and protected by crimped straw mulch. Straw shall be applied at a.rate of two tons per acre (minimum). Erosion control performance standards and specific erosion control measures :will be completed in the final drainage report. ' Hampshire Pond P.U.D. i' Final Drainage Report page 2 III. HISTORIC DRAINAGE Historically, the site drains to the east and southeast into Spring Creek. Off -site runoff flows onto the west side of the property. A driveway culvert conveys a portion of the off -site runoff to the northwest corner. The remainder sheet flows onto the site along the north half of the west property line. An existing roadside swale collects runoff from the south side of Drake Road g and conveys it east to. the adjacent property (see plan and 1 calculations for sub -basin H-6). Five sub -basins have been identified as H-1 through H-5 on the final drainage plan. Drainage on the entire site will be affected by the proposed development. The runoff coefficient for grass land (C = 0.20) was used to obtain 2 and 100 year peak stormwater flows at the concentration points. Table A in the appendix shows the results of peak historical runoff calculations (H-1 to H-5). IV. DESIGN CRITERIA The drainage design criteria established by the Stormwater Utility Department of Fort Collins are the guidelines used for the study. The required ponding volume for the increased runoff from the site is compared to the historic using the mdoel UDSWM2-PC. Peak runoff is quantified at various design points as shown on the final drainage plan. Prior to the construction of the regional detention basin, temporary measures are to be taken to alleviate the increased runoff from the site. Storage will be obtained by increasing the capacity of a natural sump area to the east of the site where the future regional detention basin will be. The volume of excavation will be determined by modifying the Stormwater Departments current data from the Urban Drainage Storm Water Management Model (UDSWMM) for Spring Creek Basin. The increased storage volume required for the developed site is modeled by separating the Hampshire Pond P.U.D. site from the originally modeled subcatchment (see notes for Det'ention Analysis in the appendix). A conveyance element was created to store the runoff from the new subcatchment that represents the historic condition of the site.. This data set was input to UDSWMM to obtain the base storage volume. Then, a second data set was created to model the developed condition of the site. The new subcatchment was changed by increasing the impervious area. Another conveyance element representing a new channel from the site to the storage basin was added, and the model run. The required volume of excavation is the difference between the storage as determined for the two runs (volume = 0.2 ac-ft.). r .. Final Drainage Report for Hampshire Pond P.U.D. Fort Collins, Colorado August, 1993 I. GENERAL This report summarizes the results of a storm drainage study conducted for the proposed development of Hampshire Pond P.U.D., to be located in the Northeast quarter of Section 28, Township 7 North, Range 69 West of the 6th Principal Meridian, in Fort Collins, Colorado. Methods outlined in the Fort Collins Storm Drainage Design Criteria were used in the calculations for the stormwater runoff portion of this study. The Rational Method was used to estimate peak stormwater runoff from the site. Summary calculations and other supporting material are contained in an appendix to this report. II. SITE DESCRIPTION The existing site is pasture land that slopes gently down toward the east at approximately one percent grade. Native grasses grow over the entire site with a large cottonwood tree growing approximately 500' south of Drake Road along the west property line. Several choke cherry trees grow along the fence on the north side of the site. Existing improvements on the site are irrigation laterals and structures, and a roadside swale along Drake Road. A six inch diameter ADS pipe from an off -site irrigation lateral extends 5 feet onto the site approximately 510 feet south of Drake Road. A diversion structure exists in line and east of the ADS pipe. Both are to be abandoned. A paved bike path has recently been constructed in an access and utility easement along the south edge of the property. sumac St. L e Oc. $uFfolk bourn Promendd, Shro shire 3 n Kingsb \ n. ��• Cor;. Ryeland Ave. °'o a Rom- c� o cr ¢ Pecan er illeDr. r° o Ct 6 R ugh Dr. e a i °. Q ° Dorset C)� g W, mne Ova W. Stuart S}, Q cf. Sr r Z 0 ¢ u°r m c c e ° Sf " o Ross y G �i/�P Cn i pr• ro CI. Glee 3o Lor^ono o 2 nirh ~ o o Gt. u ... Cr Z = m Cpfswpr C i r. Merino Cf. d Or'IVp W, Stuart A ro iQ Ct. Panama . Neil Dr n Bel9 Morgan o Ct. Ct. �o r Clydesdale e cl desdole / Cr orge t� w o 5~ Ct. Pipestone 9 g O Charo s o Sca boro h Dr. �' Gprdec Q • /prs yO°ir �e o nr. Ct as Cr V d I I F r v Aej c� c °ado\te n ��E Con Ave. V � o ! 5�r� °nrPos pr. oy c J Valle e d •- uu b L w Forti 4 81u .t o . N �% N V e .,_O >° rOss Dr. c° C�cP ` �P -ompshire 5� Q Ct. r &ue ss Dr. o o 0 0 1 0 d E At. yol Cl. = ro i odi Ct. p N o. co Seccomb T o'\ , MCKep o' 1 I 1 E Cie m Qny r0i, c� StjCt. Frrmcnl o _ u ktmm r.t Dr. `.Hull SL Ct. i orr Zendt Dr. Faicon Dr ' 81 a Lac Cf. Michner Dr. ' ..nc in p ' �rsette C� Or�O'C o 'r yOQ: I H I i ne Dr. 'Hiw= 17 ' PIS DEwee, e Kinnison , Drive " Dora t Moffet Drive Binning (rep. • O _ v � tf mg at m 1 L Devonshire U 0 Primrose Dr. Cir. 1 Cheshire S \ �' °•� 0 1 � / = J Der by_Ct. i VICINITY MAP i Northern Engineering Services, Inc. July 29, 1993 Mr. Glen Schleuter Stormwater Utility City of Fort Collins 235 Mathews P.O. Box 580 Fort Collins, Colorado 80522-0580 re: Hamshire Pond PUD Fort Collins, Colorado Project No. 9317.00 Dear Glen: Northern Engineering is pleased to submit this Drainage Study for your review. It represents a study of the existing and proposed runoff characteristics for a commercial site. Soil erosion has also been included as an item of study in this report. Your input during the initial design of this project have been greatly appreciated. If you should have any questions or comments as you review this report, please feel free to contact me at your earliest convenience. rSincerely, NORRTHERN ENGINEERING SERVICES, INC. /Tbrry P McEnany 11 Michael F. Jones, P.E. 11 420 S. Howes - Suite 106 • Fort Collins, Colorado 80521 • (303) 221-4158 • Fax (303) 221-4159 rig FINAL DRAINAGE REPORT for H AM P S H I RE POND P_ U_ D Fort Collins, Colorado August 2, 1993 prepared by NORTHERN ENGINEERING SERVICES, INC. 420 S. Howes, Suite 106 Ft. Collins, Colorado 80521 (303) 221-4158 Project No. 9317.00