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HomeMy WebLinkAboutDrainage Reports - 07/05/2012ROTH ENGINEERING ' GROUP, LLC May 15, 2012 Mr. Wes Lamarque City of Fort Collins Stormwater Engineering Division 700 Wood Street Fort Collins, CO 80521 RE: Prospect 7-Eleven Store No. 35506 Drainage Letter REG No. 111101 Dear Mr. Lamarque: City of Ft. Collin rov Plans Approved By �.: Date The purpose of this letter is to discuss the drainage system improvements and erosion control measures proposed for the development of this project located in the southeast quadrant of the intersection of South Overland Trail and West Prospect Road. More specifically this project is comprised of the Elliot -Miller Foothills West Subdivision, Third Filing, located in the northwest 1 /4 of the northwest ''/. of Section 21, Township 7 North, Range 69 West of the 6`h Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. A vicinity map is included in Appendix A. ' As defined in the City of Fort Collins, Stormwater Utility, Storm Drainage Design Criteria and Construction Standards, Section 1.3: "All new multi -family and commercial development with an increase in impervious area of greater than 350 shall submit drainage and erosion control ' reports and plans to be approved by the Stormwater Utility". This project will decrease the imperviousness from approximately 98% impervious to approximately 75% impervious with the addition of landscape treatment on portions of the project. An Impervious Area Comparison is ' included in Appendix B. This percentage is based upon the net remaining area after a right of way dedication is conveyed. If the right of way land were included the impervious value would drop even more, as much of the existing right of way which is paved will be replaced with ' landscaped surface. As a formal drainage and erosion control is not required this letter will detail site stormwater runoff and conveyance capacity conditions in addition to the construction and post construction water quality considerations. This letter is divided into two sections. 1) will describe the historic and proposed stormwater characteristics and detail the efforts proposed to provide permanent storm water runoff quality This letter and accompanying calculations describe the impacts to the drainage system, quantify the 100 year stormwater runoff through the site, and propose actions to mitigate the impacts and safely convey the storm water runoff through and from the site. The design is compliant with ' City of Fort Collins (City) requirements and regulations. and, 2) will detail the erosion control planning and effective and performance standards. 21111 Unbridled Avenuc c Parker, Colorado 11111 , o: 303.841.9365 • f: 303.648.5212 • www.rothcnginecring.com Prospect 7-Eleven Store No. 35506 May 15, 2012 Drainage Letter DRAINAGE The Prospect 7-Eleven Store No. 35506 (Project) is a 0.315 acre (after right of way is dedicated to the City, which is a condition of the development) parcel of land. The land is zoned NC and is currently functioning as a convenience store and fueling station and is almost exclusively covered by paving and building. The land falls gently (1% — 21/o) from the south to the north. A small strip of landscaped area (about 5 feet by 125 feet) contributes stormwater runoff from the ' south. The adjacent parcel to the east has a connecting parking lot to the Project and may contribute minor surface runoff onto the site. ' The proposed development will remove all existing improvements (parking lot, structure and fuel service and build a new 7-Eleven convenience store with appurtenant parking, utility services and landscape. This letter and the supporting documentation are based upon the following assumptions: ' 1) No detention storage is required for this site. 2) Onsite water quality mitigation is required for this site, following the recommendations and criteria of the Urban Drainage and Flood Control Districts, Storm Drainage Criteria Manual (Manual), Volume 3, to the maximum extent practical. The full development of this project will be consistent with the approved Zoning for NC. This t zoning requires a five foot parking lot setback from adjacent parcels and a 10 foot — 25 foot build to line along the two arterial frontages. Furthermore the requirements for maximum parking counts and interior parking landscape requirements have been followed. The predominant soil is ' Altvan- Staanta loams, according to the NRCS, which is Type B hydrologic soil group. Soil maps and soil properties are included in Appendix C. The Project does not propose to change the existing drainage patterns of the site. The Project is considered, for hydrological purposes, a single subbasin that is tributary to the inlet located just off site in the southeast comer of the intersection of Prospect Road and Overland Trail. Runoff calculations and supporting documentation are included in Appendix D at the back of this report, and a Drainage Map is included in Appendix E. Any tributary offsite runoff from the east will be intercepted_ by a shallow grasslined swale and conveyed to Prospect Road, the last fifteen feet within a curb and gutter. The tributary runoff from the south will pass through the site and will enter the water quality swales, or if it enters far enough to the west it will be conveyed to the Overland Trail right of way street, curb and gutter. The runoff from the site will drain overland and via downspout or curb and gutter will enter a ' shallow grass lined swale (designed per the Manual's criteria for a grass lined swale BMP) on either the west or north side of the convenience store. This water will be conveyed to the northwest corner of the site where it will be intercepted by a sidewalk curb chase and conveyed ' into the curb and gutter of West Prospect Road. Note: The City has directed this project to not connect directly into the existing inlet, but rather to drain overland to the right of way. While ' Page 2 1 Prospect 7-Eleven Store No. 35506 May 15, 2012 Drainage Letter there is no 100-year storm detention requirement, the capacity of all of the conveyances to the right of way can handle the 100-year developed runoff of approximately 2.4 cfs. POST CONSTRUCTION WATER QUALITY ' The Manual defines a four step process to minimize the adverse impacts of urbanization. While this project is a redevelopment of an urbanized parcel, the proposed improvements have considered and employed the recommendations of this process and provide significant improvement to the existing condition. Step 1 is to "Employ Runoff Reduction Practices". To reduce runoff peaks, volumes and pollutant loads this project has implemented Low Impact Development (LID) strategies, including Minimizing Directly Connected Impervious Area (MDCIA). ' Historically, all runoff from this site, which is almost 100% paved, and the small amounts of offsite drainage from paved surfaces, drained overland to the public right of way conveyance system, as Directly Connected Impervious Area to the public storm system. This project will increase the pervious area by about 25% from existing conditions. In addition, this project will direct all on -site and offsite tributary flows into and through landscaped areas and grass lined swales. The effective impervious is reduced, and runoff velocities are slowed within the grass swales which promotes infiltration, thereby potentially reducing the capacity requirements of downstream facilities. Step 2 is to "Implement BMP's that Provide a Water Quality Capture Volume with Slow ' Release". This project does not include water quality capture volume ponds. However, the grass lined swales are designed with specified soil and underdrains to facilitate infiltration. This will allow for some retention volume with in the soil in the form of infiltration. rStep 3 is to "Stabilize Drainageways". This project does not include modification to any existing drainageways. It is anticipated that the LID measures defined in Step 1, above will decrease the amount of runoff leaving the site. This will place •less of a burden on downstream public facilities. A visual inspection of the nearby receiving storm system and roadside ditches did not indicate existing erosion concerns. The on site grass lined swales will be stabilized with thick stands of blue grass. CONSTRUCTION WATER QUALITY The project will follow City standards to prevent erosion and sediment transport during construction. An Erosion Control Plan has been prepared for approval by the City. The project will include perimeter controls to prevent sediment transport including silt fence and straw wattles. Also included is a vehicle tracking control entry at the access from Overland Trail. The concrete wash out and stabilized staging area will be located in the vicinity of the vehicle tracking control. 1 Page 3 I 1 Prospect 7-Eleven Store No. 35506 May 15, 2012 Drainage Letter 1 A sediment trap will be located on the site to capture sediment laden runoff. The site is 0.357 acres of disturbed land and requires 100 cubic yards per acre. Therefore the sediment trap must be 964 cubic feet. Calculations for the sediment trap are included in the Appendix D The Project will disturb approximately 0.357 acres. Therefore no Colorado Discharge Permit will be required with this project. CONCLUSION The Site has been laid out to accommodate the offsite and site generated storm water runoff up to 1 the 100-year recurrent event. Further, water quality mitigation in the form of grass lined swales has been considered for the Project Site. The drainage system has been designed to safely convey the tributary offsite and onsite generated storm runoff to the existing conveyance system within Overland Trail and Prospect Road. Thank you for your consideration of this matter. Should you require any additional information or have any questions, please do not hesitate to contact me at 303-841-9365. 1 Sincerely ROTH ENGINEERING GRO LLC Kevin : oth, P.E., E AY'7�)Zts Managing Member1 1 i 1 1 1 1 1 Page 4 1 1 CI I I I I I Prospect 7-Eleven Store No. 35506 May 15, 2012 Drainage Letter Appendix A - Vicinity Map APP A N - - - a Plum gt g r a a; W.EIiranetba4 5 Arancia Qr r THP D P*ptar C•r o E3lan:c Dr �`onetlov.a�r,T Pleasarl VbRpy Rd > Grattree Gr - C lewvleN Ava y Qye rj [h Z-rl�ttridge Fi Go5den Corr r a^J1yp g�` Pondsal Overland-u. ©rrrJtrury Co d p � SITE— 4 W Lake 51 Wj Lake St Af N O ].i 3 a .. 4M Pr*iiPecl Rd m W Proved Cr SP e t •� 4' - % Nudhb we5tgate u � WestwoodAZahm MVb'S cU Or�1a)lfls(pn Sumac 51 . Fairbrooke �oc�` �,,,x+<e ;l• w Rio S Stadium - Heights Hughes : O a .. �ti -. ., ... -Y ... Maw Lane ry h Tratl West' yn! W.Itxt $t . t = N l Pr Brawn Farm a .. VICINITY MAP SCALE 1" = 1000' ' Prospect 7-Eleven Store No. 35506 May 15, 2012 Drainage Letter ' Appendix B - Impervious Area Comparison ' APP B 1 0 � V W I I m II z� I I w • o w w a (� O_ • Q - 0- ! (n WZo rlOO - 0LL�J >QgZ co M I - , . c oQ GAO z I W ��Z� O I o 0:0 aa—ln O Q ------- — — ------ a Z O a V W Q y O C) U w Woa w v � L LU W I� IV g ao IV LLJ <w a V 0wQQz ca Y a °aQ C9 LOY o IV IV Jo ZNOO m w m LU I� F- Q W m XlllZr F Z to `Z $ D 07 W� ..m a o o O ® � � N ® W 7 O " W road, N W L� O a 410H uIAGN u Bou -ZIOZ '4L Aen llnoRe-!:gel &v-NOS!M.wdnOa SnO!ALl3dn!\s1!q!gX3\OOVO\IOLLLL\sloefad\dnaO Buuew,BU3 glom wm u!neAsiesn\:O Fl '(Sawal 00'a X 00'l1) O Pblq Reg ISNV `!NV S£5v11 ZIOZJ61/S `3MP'NOSrddV&WP SI101AY3dM$)!glgx3\QQVO11011111sW(a+d\dnu+O 8mwu!Sug gloN\gWb M+a71\&sll\:O m W m m m m m m m m m m m m m ' Prospect 7-Eleven Store No. 35506 May 15, 2012 Drainage Letter Appendix C - Soils Information APP C tL ,. , cwllsba onolsbb oosonba n 0 .£Z .L .901 N m m o � � a UM N in e T N 2 U) m Z 3 E e i .# W §KE __ jd § %ir » a fk§ I � 7{|( §/z {I )§ \A G0- ƒ2]K o2Wc § 0) ;) {ƒ ®7E#/!\N 3 {\ Qf )- k {|ƒ | { M k= �� -® f §)7) } 2 .cf-0E\ -0 w ƒ| - �_ f fE |EmE/// L i} )�n -0 00 � q \ \ q _ $ / / \ I! Q� g q�7 P q 4 q@ m g� m # ) ■ _ ` ! §ggqqqq/ggqEq■■e�| VO _ § ® » ! ( 4:�-L ' K Factor, Whole Soil-Larimer County Area, Colorado 7-Eleven Prospect K Factor, Whole Soil K Factor,Whole Soil —.Summary by Map Unit'— Larbner Coonly Area ;colorado (60644) .Map unit symbol !As un name ' =Rating Acres in AOI .'Percent of A 1, 3 Altvan-Satanta foams, 0 to 3 percent slopes .28 93.7 43.6% 4 AltvanSatanta hams, 3 to 9 percent slopes .28 60.3 28.0% 54 Kim loam, 3 to 5 percent slopes .32 5.2 2.4% 63 Longmont day, 0 to 3 percent slopes .17 0.8 0.4% 65 Midway day loam, 5 to 25 percent slopes .24 2.1 1.0% 67 Minnequa-Laporte comple), 3 to 15 percent slopes .43 02 0A% 74 Nunn day loam, 1 to 3 percent slopes .20 482 22A% 76 Nunn day loam, wel, 1 to 3 percent slopes .17 4.5 2.1% Totals for Area of Interest 215.1 100.0% Description Erosion factor K indicates the susceptibility of a soil to sheet and rill erosion by water. Factor K is one of six factors used in the Universal Soil Loss Equation (USLE) and the Revised Universal Soil Loss Equation (RUSLE) to predict the average annual rate of soil loss by sheet and rill erosion in tons per acre per year. The estimates are based primarily on percentage of silt, sand, and organic matter and on soil structure and saturated hydraulic conductivity (Ksat). Values of K range from 0.02 to 0.69.Other factors being equal, the higher the value, the more susceptible the soil is to sheet and rill erosion by water. "Erosion factor Kw (whole soil)" indicates the erodibility of the whole soil_ The estimates are modified by the presence of rock fragments. Rating Options Aggregation Method: Dominant Condition ' Component Percent Cutoff., None Specked Tie -break Rule: Higher ' Layer Options: Surface Layer ' USDA Natural Resources Web Soil Survey 1/192012 am Conservation Service National Cooperative Soil Survey Page 3 of 3 C-3 n 9 m: g m . . W• jq. m. m a. O O U m mm Cm. p O _y W O N � u Z Z 6 N YI 6 d N N N 1fl eD 0 O ap N �O N N O O O O 00 O � N 0 0 m O 1h O N m w r 22=��Im a m' c "U �: UJ NLL iJ c' c a .�. E r E c E m o > i L E, W J U J fA J LL (n (J (I U JiL: s. d m o W E W W Bo.-, W O d m C C W t,, t m Ili m a ' RUSLE2 Related Attributes-Larimer County Area, Colorado 7-Eleven Prospect ' RUSLE2 Related Attributes ' This report summarizes those soil attributes used by the Revised Universal Soil Loss Equation Version 2 (RUSLE2) for the map units in the selected area. The ' report includes the map unit symbol, the component name, and the percent of the component in the map unit. Soil property data for each map unit component include the hydrologic soil group, erosion factors Kf for the surface horizon, erosion factor T, and the representative percentage of sand, silt, and clay in the surface horizon. Report—RUSLE2 Related Attributes RUSLE2 Related Attributes- Latimer county Area, Colorado Map symbol and soil name, Pct. ov Slope:, Hydrot ogic group Kf. T faofor Represent11 ative value . ' map'unit `length ley . % sand % sift .%:Clay . 3—Altvan-Salanta loams, 0 to 3 percent slopes AINan 45 — B 28 4 42A 38.11 19 5 Satanta t 30,, — B r - 28 5 43.0 > 395 ' 4--Allvan-Satama loams, 3 to 9 percent slopes AINan 55 — B 28 4 42.4 38.1 19.5 34.5, 17,.5 54--Gm loam, 3 to 5 percent slopes ' IGm 90 — B .32 5 41.6 37.4 21.0 63—Longmont clay, 0 to 3 percent slopes ' Longmont----_—__— _ 85 — C .17 5 _-- -_ 22.1 27.9 50.0 6"idway clay loam, 5 to 25 percent slopes Midway 90 — D .24 2 333 31.7 35.0 ' 67—Minnequa-Laporte complex, 3 to 15 percent slopes ' Mmnequa 55 C 43 3 11.3 67.7 21.0 -,Leporhe "s 30.-;160`I �.. 74-Nunn day loam, 1 to 3 ' percent slopes Nunn 85 — C .20 5 35.4 33.6 31.0 76—Nunn day loam, wet, 1 to 3 percent slopes Nunn,, wet90 — C .17 5 35.41 33.6 31.0 ' USDA Natural Resources Web Soil Survey 1/192012 Conservation Service National Cooperative Soil Survey Page 1 of 2 ' Prospect 7-Eleven Store No. 35506 May 15, 2012 Drainage Letter Appendix D - Drainage Calculations P L w Z LL, -3-;(J) aaOf N O Y� W a Z W U d' W m H Z N W •- (j cn OD LL W O U M LL m V- a O Z D c W U N T LL O m o a o :o N O 1 U U ddU) a 0 m c R m m Y U m c co c L �C G 0 Y w L M w 0 L Y c O o O 0 U o 0 0 0 c m cc,),� C m (� O7 ] � � CVO7 I O O co:)O !6 5 O w Y 0 w O y 0 G R Y Kc7cm.. 0-1 w of n m Z NO U- ~4 F 2 Ow a LL U f1 C Q U C LL QCO LLI � C LL E v�rowo N DZ 1 1 1 1 1 t 1 1 Y Q w w Of (ww) w (Sd3) ,UIDOl3 m} w d (13) HlON3l w F o o (NI) 3ZIS 3dld d� o w W 3dOlS 0-0 a r co (S30) MOl3 NOIS30 pWz z W (Sd0) MOId J 3381S m0 00 w Sao w w F W 3dOlS co (Sd0) O LL LL (MH/NI) I z z z w ¢ (0v) (v X 0)3 F M p O N W U (NIW)' H O a rn 0 (Sd0) O Qul N = Q Z U (UH/NI) I LL Q Q z (0v) v X 0 N N 20 o 0 V (ww) 01 1-2 " w u�i o d4300 d30Nnu 01 0 (0v) via o N Ci 0 0) 1NIOd NOISW Y W" m f- W m F g Y � U Z U U m Q D-3 ' Channel Report ' Hydraflow EVress Extension for AutoCAD® Civil 3D® 2011 by Autodesk, Inc. Water Quality Grass Swales ' Triangular Side Slopes (z:1) = 16.00, 16.00 ' Total Depth (ft) = 0.67 Invert Elev (ft) = 100.00 (%) = 1.00 'Slope N-Value = 0.030 ' Calculations Compute by: Q vs Depth No. Increments = 2 1 Elev (ft) 101.00 1 100.75 100.50 100.25 1 100.00 99.75 1 0 5 10 15 Highlighted Depth (ft) Q (cfs) Area (sgft) Velocity (ft/s) Wetted Perim (ft) Crit Depth, Yc (ft) Top Width (ft) EGL (ft) Thursday, Jan 19 2012 = 0.34 /'� A = 2.697 �' = 1.80 tOQ = 1.50 = 10.74 = 0.01 = 10.72 = 0.37 Sfi-e, -,.4-e cAnAss Section (infAT40 TO NOATµ -4- Reach (ft) Depth (ft) 1.00 pk DETENTION POND SIZING NKVJEt:I NAME: 7-11 Ft. PROJECT DESCRIPTION: TSB PROJECT NO.: 111lot BY: KSR ELEVATION AREA INC. VOL INC. VOL. TOTAL VOL. (FT2) FT) CY AC- 21.00 107 0.00 0.0000 0.000 22.00 457 261.71 261.7104 261.710 22.90 915 605.59 867.3051 1,129.016 Disturbed area 0.32 acres Water Surface El Sediment Pond 0.003 ac-ft 5670.9 0.085 cf 5671.5 100-YR Volume 0.04 ac-ft 5671.80 Total Volume 0.13 Stage vs. Storage 23.0 22.5 c 22.0 0 w m W 21.5 Z 210 20.5 0.000 200.000 400.001) 600.000 800.000 1,000.000 1,200.000 Storage (ae-ft) b J ' Prospect 7-Eleven Store No. 35506 May 15, 2012 Drainage Letter ' Appendix E - Drainage Plan 1 1 F 1 u 1 1 1 ' APP E 11 IR N SECTION LINE ■ ■ ■ ■ I I \ _ PROPOSED 0.0W �--S�T.S' MEASURED FltpI8ECTNNI LIRF/CERiER UNE) EXIST PTI I \ 54111111111111111 0 r\ � J / / A 0. AC T AC Q J — •. I PROPERTY uxE_ STING RO V e A 4 Toa ENSTNG ROW RUNOFF SUMMARY SUB- DESIGN DIRE00-CT RUNOFULATIVE RUNOFF N BASINS POINT R(CFF CUMS) 100-YR(CFS) A 1 2A1 2.41 A LEGA ND BASIN DESIGNATION qWB � AREA IN ACRES B AC 100 100— 100 YR RUNOFF COEFFICIENT D - DESIGN PONT DESIGNATION l" DRAINAGE ROW BASIN BOUNDARY — —5570 — EXISTING CONTOUR 5870— PROPOSED CONTOUR $WALE Ol INLET: Y SQUARE OLDCA8TLE 2 X 2 CATCH BASIN WITH 20' SQUARE FRPME A ORATE (OR APPROVED EW AL) OPPERFORNTEDHWE PIPE. SLCPETOFMTCHSWALE. O3 SIDEWALK CHASE RE: PAVING PLAN FOR DETAIL RIGHTa WAYDEDICATIgI — SECTION AA- GRASS LINED SWALE SCALE V=5' UTIL ESPl.NI ROTH ENGINEERING GROUP, Lu 2170 UNBRIDLED AVENUE PARKER.COWlM PHONE: 2D1BA1-9385 FAX 301&b5212 FQE Xm,,IIor.beI=. Celln MIwmB. CALLR BUSIXE85 DATB IN ADVANCE BEFORE YOU DIG, co 0 LO Lo GM O z ILI LL 0 z 3 cn EL N m Z (D `: u FACE > Z y W _> U.I w w a W 1 F UF W a W 0 s I I SECTION DB SCALEI'=V CEyo FI;Ilt WMF.ORIwtle UTILITY PLAIN APPROVLL PVN SCALE 10 0 10 HORIZONTAL SCALE: 10= 1D' W S 2 WEI W W & NI APPROVE): CRY EIIEIeeN ore — PRELIMINARY CHECKED BY: wWa Awrwr«wBy Deq NOT FOR CHECKED ON: BTammomw MANY om CONSTRUCTION CHECKED BY PeNB Recree)m Da CHECKED BY. Trexlc ENII on SHEET NUMBER: CHECKEDBY: Etlrlw.m..DI PI..Mr -mlimi DP OF CHECKEDBY: DNI