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Home My WebLink AboutDrainage Reports - 04/22/1996January 23, 1996 Mr. Matt Fater Stormwater Utility City of Fort Collins PO Box 580 Fort Collins, Colorado 80522 Dear Matt, Attached is the Final Storm Drainage Report that accompanies the construction of a single duplex located in the Old Town drainage basin at 613-112 South Sherwood Street. All design is in conformance with the latest edition of the City of Fort Collins' Storm Drainage Design Criteria and Construction Standards. FINAL STORM DRAINAGE and EROSION CONTROL REPORT DUPLEX CONSTRUCTION 613-112 SOUTH SHERWOOD STREET CITY OF FORT COLLINS, CO January 23, 1996 Revised February 27, 1 996 Prepared For: Midwestern Homes of Colorado PO Box 621815 Littleton, Colorado, 80126 Phone (303) 972-7200 Prepared By: Structured Engineering 31 8 East Oak Street Fort Collins, Colorado, 80524 Phone (970) 495-0810 Fax (970) 224-1 314 , > 1/ ' --~-i E Vine Drive 0 •"' St L~ Ct .. £. Myrtle s, .;; .;; ;; .;; ;; E . Laurel SI. [ Plu"' St. t..oc11et St. SI. [, E 111 aDetfl Gerfieltl 0 ... : Ed••r•t C ! 'i " £.::I Pltll1ft E .l.Okl INTRODUCTION FINAL STORM DRAINAGE and EROSION CONTROL REPORT for Duplex Construction 613-112 South Sherwood January23, 1996 A single duplex is proposed for construction on a residential lot within the Old Town Drainage Basin between Laurel and Myrtle Streets at 613-112 South Sherwood. 613 Sherwood is an existing residence. This report sums up the analysis that was undertaken to determine what, if any, impacts the proposed construction will have on the historical drainage patterns in each area. The report will address the following: 1 .Site Descriptions 2.Storm Drainage A. Design Criteria 8. Conformance With Existing Master Drainage Plans C. Hydrology 3.Erosion Control A. Erosion Control Measures It is i ntended that the recommendations found in this report become an integral part of the design and construction phases of the project. 1. SITE DESCRIPTION The property is also known as Lot 6 of Block 76 of the City of Fort Collins. The area is established and mature with landscaping and an older house. The duplex site will be in the back half, or western part, of the lot. With the exception of a water service installation, little disruption is planned for the front half of the lot. Duplex construction will be tight inside the lot lines, and several trees will need to be removed. Existing grading is at approximately 1 .2%, generally from the back, (west) of the lot towards the front. The alley along the west lot line will be paved adjacent to the lot. The alley will have an inverted crown of 2% to 4%, and there will be a 3' wide concrete pan flow line with a 5/8" invert. The specific pan shape is as requested by city engineering staff. The primary existing drainage improvements at the site consists of curb and gutter along Sherwood Street. There are no pronounced natural drainage features on the site. The soils group making up both sites are primarily ML and CL-ML according to the Larimer County Soils Survey by the Soil Conservation Service. 2-STORM DRAINAGE A. Design Criteria The City of Fort Collins has prepared a Storm Drainage Design Criteria and Construction Standards (SDDC) which provides the basis for the analysis used in predicting storm runoff and the recommended drainage improvements. B. Conformance With Existing Master Drainage Plans The Old Town Master Drainage Plan was prepared for the City of Fort Collins by RCE Engineers on January 7, 1993. RCE assumed a runoff coefficient of .60 for the area proposed for construction of the duplexes. Stormwater Utility has said that if the developed percentage of imperviousness of a site is less than 60%, then on-site detention is not required. Calculations included with this report confirm that neither site has an imperviousness percentage greater than 60%, hence detention is not analyzed nor provided. Additional related drainage reports are the Final Storm Drainage and Erosion Control Report for 605-1 /2 South Meldrum and 627-1 /2 and 629-3/4 South Sherwood, May 16, 1995, Revised June 29, 1995, and Addendum No. 1 to that report, and the Final Storm Drainage and Erosion Control Report for 619-1 /2 South Sherwood, January 17, 1996, Revised February 27, 1996. Both reports were prepared by Structured Engineering. C. Hydrology The Rational Method is used to predict the amount of runoff. The 1 00-year return frequency was used in this report to predict major peak discharges, and 2- year storm is analyzed to predict minor flows. The difference between historical and developed conditions has been analyzed and the findings can be found in this report. One investigation was to see if the inverted crown capacity in the alley was adequate for the anticipated 1 00yr flows. Calculations included with this report verify alley capacity is adequate to contain those flows. Basin D2, which includes the front portion of the lot (see included basin map), is meant to be final graded to prevent an increase in runoff from encroaching onto neighboring lots. This is done by primarily maintaining the existing flow pattern, which is sheet flow to the front and middle of the lot. Should this lot ever be subdivided in the future, the minor subdivision process will be required at that time, and minimum 5' wide drainage easements will need to be provided as necessary to pass runoff from the back lot across the front lot. .3.... EROSION CONTROL The SDDC outlines the causes and results of soil erosion due to wind and rain. Because each site is less than 1 acre in size, they are exempt from wind erosion control requirements. The SDDC shall be considered in it's entirety for guidelines to aid in preventing rainfall soil erosion. The SDDC will govern requirements and specifications for earth moving at the construction site. A cost estimate for erosion control measures is included with this report. SUMMARY OF STORM DRAINAGE AND EROSION CONTROL MEASURES The following is a summary of the storm drainage improvements and erosion control measures that will become part of project construction. GENERAL EROSION CONTROL NOTES 1. Keep disturbed areas to a reasonable minimum at any one time. 2. Stabilize all disturbed areas. 3. Keep runoff to velocities not causing erosion. 4. Provide diversion channels to direct runoff around and away from disturbed areas. 5. Keep all cut and fill slopes stabilized with terracing or scarifying furrows perpendicular to the slope. 6. Protect stockpiled materials from wind erosion. Stockpiles are not to be higher than 8'. 7. Permanent ground cover is to be established on all disturbed areas. Areas to be seeded which have been compacted by construction activities are to be ripped or otherwise loosened prior to seeding. 8. Provide a temporary cover crop or an application of mulch to areas to remain unseeded greater than one month. Disturbed areas which have topsoil removed may require an application of fertilizer prior to temporary seeding. 9. Inspect, clean and repair all erosion control measures the following work day after each storm event. 10. Additional erosion control construction details and specifications shall be taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards. Mr. Matt Fater Stormwater Utility City of Fort Collins PO Box 580 Fort Collins, Colorado 80522 Dear Matt, Attached is the cost estimate for erosion control measures associated with the construction of a duplex (Unit "B"), at 613 South Sherwood Street. Perimeter Barrier -210 If @ $2 .50 /If Alternate; Seeding -.22 ac @ $1300/ac Security required = $525 .00 x 1.5 = $525 .00 $286.00 $787.50 However, city policy requires a minimum escrow of ... $1000 00 Matt, please feel free to call with any questions, comments or suggestions you may have. Very Truly Yours . Joseph P. Marcisofsky, P.E . Structured Engineering I I I I I I I I I I I I I LEGEND <tl.) = POWER POLE IC) = CABLE BOX 0 = CATCH BASIN C8j = ELECTRIC TRANSFORMER DRAINAGE REPORT LEGEND 0 DESIGN POINT L @ = ELECTRIC VAULT 181 = ELECTRIC BOX ¢ = LIGHT •Cf = WATER SHUT OFF ~ '\-!!!} BASIN DESIGNATION AREA (ACRES) I I EXIST. GRAVEL SURFACE GRADED ++ TO MAINTAIN INVERTED CROWN ~,-2 I") TO MYRTLE STREET. I , 1 \ I I I I STA. 2+70; END NEW PAVEMENT AT P.L. BASIN BOUNDARY USED TO DETERMINE DEVELOPED RUNOFF I i-,'1-\·4·;.:-. I i ' ::::l'\ · :. · · :/t:W NEW HBP ALLEY PAVEMENT W/DRAIN PAN : · ::-,1-:-_.:· '):_; PAVEMENT TO BE PLACED UP TO :, ·:.'" ·."'. ::: AND AROUND ALL EXIST. UTILITIES, · (:·: < ·"' ..... FENCES. AND OTHER FEATURES. I :.,.-;,: :: PAVE FULL 20' WIDTH WHERE POSSIBLE. ff'· SEE ALLEY PROFILE AND CROSS SECTION ■ ;: . DETAILS SHT. C-2 STA. 2+20; BEGIN NEW PAVEMENT AT P.L. __.J I EXISTING GRAVEL ALLEY SHOULDERS -.:.::J: I I .J NOTE: IF THIS LOT IS EVER SUBDIVIDED INTO A FRONT AND A BACK LOT IN THE FUTURE, THE MINOR SUBDIVISION REVIEW PROCESS WILL BE REQUIRED AND MINIMUM 5' DRAINAGE EASEMENTS WILL NEED TO BE PROVIDED ALONG EACH SIDE LOT LINE. (AS REQ'D) · 5002.4 120 LF EROSION CONTROL FENCE 609 S. SHERWOOD -~ 'i:lci 1t ~-l\:) <'+-~ :c:: C i ,,1.4 "-'l ! , 5001 6 I I · 5001 . .3 tETAIL rt.Nl.;t. A, 1-'.L.J I \ . 5002.1 / . . soo1.6 I I ~ 5HT .. 5002.1 \ / LARGE BUSH\. 5001.9 I I 1 I Z I / . r\.-, 6" DECIDUOUS I I · 500l.O '-._/ rv 5001.1 <9~ ~1.4 (INSIDE EXIST. -· ·--• --. 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( t)-z.) ~ .9o pz-~ ( C) 3 , i -0 I , I ) / Z Z. 0 ""' \, L "/0 V 613 SOUTH SHERWOOD HYDROLOGIC CALCULATION WORKSHEET RATIONAL METHOD PROCEDURE 9603 JPM 16-Feb-96 BASIN DATA INITIAUOVERLAND TIME Ti TRAVEL TIME Tt BASIN DESIGN ATIONA SIGNATI STORM COEFF C [ENTER] [ENTER] [ENTER] H-1 2 yr 0.32 H-1 100 yr 0.32 D-1 2 yr 0.34 D-1 100 yr 0.34 D-2 2 yr 0.52 D-2 100 yr 0.52 RUNOFF SUMMARY EVENT AREA LENGT SLOPE COEFF Cf acres ft % [ENTER] [ENTER] [ENTER] [ENTER] 1 0.287 220 1.1 1.25 0.287 220 1.1 1 0.047 50 2.0 1.25 0.047 50 2.0 1 0.251 220 1.2 1.25 0.251 220 1.2 613 SOUTH SHERWOOD NOTE: MINIMUM VALUE OF Tc IS 10.0 MINUTES BASIN DESIGN DESIGN DIRECT RUNOFF POINT STORM Tc AREA COEFF RODUC mins acres C*Cf C*Cf*A H-1 1 2 yr 21.0 0.287 0.32 0.09 H-1 1 100 yr 18.8 0.287 0.40 0.11 D-1 2 2 yr 10.0 0.047 0.34 0.02 D-1 2 100 yr 10.0 0.047 0.42 0.02 D-2 1 2 yr 15.1 0.251 0.52 0.13 D-2 1 100 yr 11.8 0.251 0.65 0.16 Tc LENGT SLOPE VELOCITY min ft % [ENTER] [ENTER] 21.0 18.8 10.0 10.0 15.1 11.8 I Q in/hr cfs 1.70 0.16 5.40 0.62 2.50 0.04 7.40 0.15 2.10 0.27 6.70 1.09 f,es [ENTER] TOTA REMARKS TIME Tt Tc min min 0 21.0 0 18.8 0 10.0 0 10.0 0 15.1 0 11.8 "'"'"' I-.. 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