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Home My WebLink AboutHAMPSHIRE POND PUD PRELIMINARY - 44 93 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT:. 0 Hampshire Pond P.U.D. Preliminary Drainage Report page 3 VI. DEVELOPED DRAINAGE Off -site flows that enter the northwest corner of the site amount to 2.5 cfs for the 100-year storm and 0.69 cfs for the 2- year event. The total contribution of runoff for the developed site is 39.89 cfs and 10.90 cfs for the 100-year and 2-year storms, respectively, as shown in Table A for sub -basin D-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 sites runoff to the regional detention area. VII. EROSION CONTROL 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. Preliminary Drainage Report page 2 III. HISTORIC DRAINAGE the site drains to the east or southeast and Historically, 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 and conveys it east to the adjacent property (see plan and calculations for sub -basin H-6). Six sub -basins have been identified as H-1 through H-6 on the preliminary drainage and grading 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-6). The peak runoff that is concentrated. - at the 36" diameter RCP culvert that passes Spring Creek a cthe southeast corner of the Regional Detention Area, is Q100= and Q2=3.77 cfs. IV. DESIGN CRITERIA The drainage design criteria established by the Stormwater Utility Department of Fort Collins are the guidelines used for the study. The developed runoff for the site (sub -basin D-1) concentrates at Spring Creek and is compared to the historic peak (H-5). Prior to the construction of the regional detention basin, temporary measures would be taken to alleviate the increased runoff from the site. An additional storage area would be excavated from single restrictive 36" culvert to he creek bank upstream from the t negate the expected increase in water surface elevation. 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 procedure will be to change the input file to model the developed site. Then the depth/volume curve for Spring Creek will be adjusted and the model run until the appropriate volume of excavation is determined. modelThe l be run submitted, butwilltbefore be completedfor the efinal review submittal. V. PROPOSED IMPROVEMENTS The development of the site would consist of single-family homes with new local streets. Curb and Gutter would carry most of 3 flows that enter the site at the the drainage. The off -site northwest corner would be conveyed by a Swale that spills out to would have to cross the proposed Hampshire Road. The Swale Featherstar Way in a 15" RCP culvert. I Preliminary Drainage Report for Hampshire Pond P.U.D. Fort Collins, Colorado July, 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. 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. Dr. Suttolk St. \ me t� al axing $hr shire 3 Kingsb P'omenadP ��_ Goro Ryelard Ave. °.° a S Rums 5• o c� I c o ¢ Pecon a illeDr• Dorset c a Ct ct Ro 9h Dr. a a. 0j o mne W.- Stuart St, Ct. i 0k r, Ava St Ory Ross�O� v Ct Sr m Dr. =Z< Ct. °e Glet i ro a x� 3� �pmppO o 1 2 nirh zF = m � Gt. �� Cr C C t r. Merino oClwold prtv� W, St art t. Cl. Panama O Neil Dr. Morgan Bei90n n Dc. V. 4 i o ` ■ - _ Clydesdale C1. ¢' ree o o N . ti ` 4 CI desdole Vr ot4 Fo d o h Q c 1 Ct. F Gt �o`o t m `+ 7 F Pipeslone 0 8 is ti m Sca borough ¢ Chao s . Dr. h-- GpcOec � o�� P e 3 C?r. Ct os o Jy;s�^ Ur. ¢ _ C1 vall� F r Ci �O to a —E G " ` •o a COn °°t n m 4A� Ave. m 3 .V 4j c 5�r� vhPos Dr. o ValleTi 0 0 l d d C i > rOSS Dr. c° Cane �A ompshire 50 Ct. �. O Blue ss Dr. c , o 1 ti4 - Y 1 _ E I dt. yal Cl. ' c o Lodi Cl, p in = V 0. N Seccomb " - ��TE Cie inCt. OtIgh �— '� c�eP^` Frrmoni kcmcn c t. 1 II t 1 om of Zendt Dr. 1' Falcon nr1 1 61 a Ct. Michner Dr. G{t��w 1 II ..nc V) o Oda' H I i n e Dr. 1 m i 1 Pl�� • 1 v Dewee; c Kinnison Drive 1 Dora J mmmmmmmmmr��r•� Moffet Drive 1 Biming/� o �, •. Efhng of 1 e in 1 ` Bed Devonshire o Primrose I or. � w Cir. 1 v � � Cheshire St / = J Derby _Ct. r VICINITY MAP Northern Engineering Services, Inc. July 2, 1993. Mr. Glen Schleuter i Stormwater Utility I City of Fort Collins 235 Mathews P.O. Box 580 Fort Collins, Colorado 80522-0580 re: Hampshire Pond P.U.D. Fort Collins, Colorado Project No. 9317.00 Dear Glen: i Northern Engineering is pleased to submit this Drainage Study j for your review. It represents a study of the existing and proposed runoff characteristics of Hampshire Pond P.U.D., a single- family residential development. 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. Sincerely, NORTHERN ENGINEERING SERVICES, INC. terry P. McEnany V / / bael F. Jones P E. 11 420 S. Howes • Suite 106 • fort Collins, Colorado 80521 • (303) 221-4158 • Fax (303) 221-4159 I Li PRELIMINARY DRAINAGE REPORT for H A M P S H I R E P O N D P. U. D Fort Collins, Colorado July,.1993 prepared by t' NORTHERN ENGINEER = NG S ERV I C E S 420 South Howes, Suite 106 Fort Collins, Colorado 80521 (303) 221-4158 Project No. 9317.00