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Home My WebLink AboutDrainage Reports - 11/05/2008November 5, 2008 Mr. Wes Lamarque City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, CO 80521 RE: Thorland Subdivision Drainage Study To whom it concerns, (Sdgo-?oS8 City of Ft. Collin s A •rove . �' ; Approved By- Di" - We are pleased to submit for your review and approval, this letter describing the drainage design requirements for the Thorland Subdivision. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria dated May 1984, revised April 1997. As a result of a preliminary design review requested by the Thorland family, the city responded with a letter dated June 11, 2007. In said letter, the stormwater department states "since this is a very large site, the property owner's design engineer can compare the overall site imperviousness, including %2 of Kechter Road, to the 35% imperviousness used in the drainage master plan. If it is equal to or less than the 35%, then on -site detention and water quality treatment are waived since the 35% imperviousness is accounted for in the drainage master plan" The attached calculations indicate very conservative estimates of future impervious coverage including %2 of the ultimate ROW for Kechter Road being fully paved, the full width of the ROW required by the city in the middle of the site being fully paved, all existing structures, and a conservative estimate of the proposed future building. Since the calculations indicate that under this conservatively estimated condition the total site impervious substantially less than 351/o, JR Engineering requested and was granted a variance to the detention requirement with the Utility Plan approval dated 10/16/08 At that time a note was added to the plans requiring that increased runoff from the proposed house would be required to flow directly to the existing Stetson Creek channel, the approved major drainage way that ultimately is to receive planned flows, along the north lot line without crossing neighboring properties. The purpose of this letter is to address this comment. Due to the fact that the attached plot plan indicates runoff will reach the ultimate receiving drainageway in accordance with the master plan, JR Engineering respectfully requests that the drainage design proposed by this letter and accompanying plan be accepted for the purpose of obtaining a building permit. We greatly appreciate your time and consideration in reviewing this submittal. If you have any questions or required additional information please call (970) 491-9888. Sincerely, JR Engineering Prepared by, Reviewed by, Jahn Meyers Jr. Michael S. Brake, PE Design Engineer Principle e@: Jill lo Ili; P3 i pa S E pis 6$ d a °gy�� 9 a Billy afil M €s a � 6 f on Tjg- QT__ll Vqq i ' tli �f I� h-' � A ys p$ pppp ap p t t 5 ____�!!O_�a_ __________ _______________ E� b 1NGIC.AND s1mMs0N ''•so' •, Puauuo ma ja ➢Y6NO aMIY ponn �� caie aicsrtN cr. rmr mews m eosu GRADING AND DRAINAGE PLAN $ � aclemwmm.om.m� moO.r. nsN fam)me�s: .w RUNOFF COEFFICIENTS & % IMPERVIOUS LOCATION: Thorland Subdivision PROJECT NO: 39580.00 COMPUTATIONS BY: jmj DATE: 312712008 Recommended Runoff Coefficients from Table 3-3 of City of Fort Collins Design Criteria Recommended % Impervious from Urban Storm Drainage Criteria Manual Streets, parking lots (asphaH)] 0.95 I 100 Sidewalks (concrete): 0.95 96 Roofs: 0.95 90 Lawns (flat <2%, sandy Equations - Calculated C coefficients & % Impervious are area weighted C, = runoff coefficient for specific area, A, A, = areas of surface with runoff coefficient of Ci n = number of different surfaces to consider A = total area over which C is applicable; the sum of all A is OVERALL SITE BASIO IN TOTAL TOTAL ROOF PAVED SIDEWALK LANDSCAPE RUNOFF % DESIGNAT AREA AREA AREA AREA AREA AREA COEFF. Impervious NUMBER (ac.) (SCIA) (800 (sq.ft) (sq.ft) (sq.ft) (C) 1 2.80 121,929 4,194 18,482 0 282,688 0.39 16.61 2 3.89 169,320 8,000 4,343 0 15Q977 0.15 5.75 November 5, 2008 Mr. Wes Lamarque City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, CO 80521 RE: T6ortand Subdivision Drainage Study To whom it concerns, We are pleased to submit for your review and approval, this letter describing the drainage design requirements for the Thorland Subdivision. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria dated May 1984, revised April 1997. As a result of a preliminary design review requested by the Thorland family, the city responded with a letter dated June 11, 2007. In said letter, the stormwater department states "since this is a very large site, the property owner's design engineer can compare the overall site imperviousness, including %2 of Kechter Road, to the 35% imperviousness used in the drainage master plan. If it is equal to or less than the 35%, then on -site detention and water quality treatment are waived since the 35% imperviousness is accounted for in the drainage master plan" The attached calculations indicate very conservative estimates of future impervious coverage including '/2 of the ultimate ROW for Kechter Road being fully paved, the full width of the ROW required by the city in the middle of the site being fully paved, all existing structures, and a conservative estimate of the proposed future building. Since the calculations indicate that under this conservatively estimated condition the total site impervious substantially less than 35%, JR Engineering requested and was granted a variance to the detention requirement with the Utility Plan approval dated 10/16/08 At that time a note was added to the plans requiring that increased runoff from the proposed house would be required to flow directly to the existing Stetson Creek channel, the approved major drainage way that ultimately is to receive planned flows, along the north lot line without crossing neighboring properties. The purpose of this letter is to address this comment. Due to the fact that the attached plot plan indicates runoff will reach the ultimate receiving drainageway in accordance with the master plan, JR Engineering respectfully requests that the drainage design proposed by this letter and accompanying plan be accepted for the purpose of obtaining a building permit. We greatly appreciate your time and consideration in reviewing this submittal. If you have any questions or required additional information please call (970) 491-9888. •I V p I I I / I I " QEE ]Aj f[SY"{1.�u Z"iM1 y ;ylJ; y� S� i'. •`'�f .ia v`(•F. f� ♦_e / � I L 11$$Q3 R9 y!e 9agQ8 �98 Y:pQa is IS i app. 'it zA a S a 3 2 f} .I - �. I Ia---------------- �� 4 a� g a Fg ------------ is g A Ep V � ' --------------- O 1 I• t M I E: �s g � nm)aum s)mmsoH r.lc •. ......n S "i" ®J,g )pag m.Alo E.aY GRADING AND DRAINAGE PLAN Mi'fAU�'6.'R'm SOu mlm woc 9 IS. (9T) B99-9153 Q s MOl N� lu • PLIDT PLAN THORLAND RESIDENCE 2224 KECHTER ROAD FORT COLLINS, COLORADO PROJECT NO. 28186 10-2-08 3 WEEKS & ASSOCIATES 4700 S. COLLEGE FORT COLLINS, COLORADO (970) 225-2422 t 30' REA ESMT T0F=4944.0 GARDEN LEVEL N89d32'56"E 223.53' 'I lo 1 " = 80'-0" BERM UP SIDE TO PREKNT WNW FROM IEANNG TIE PROPERTY WHERE NECESSARY ENSTHG IRPoGATd DI 20UTUTY IV EXISTING AND REA EASEMENT DRAINAGEi0 BE VACATED EASEMENT BY PLAT -__x.----- x__ __ --- _____x-___t LOT 2. BUI M SRpN51d (UNINCORPORATED IARYER COUNTY) 62 EMSTWG CONTOUR TYP $ 2 3.89 APPROPRATE HOUSE LAYOUT f___ _ __ Xt _ _ ..RED o0 •-----x-----x-----x-----x-----x-----•-----_-----x----'K-----x-----x- LEQMQM -XOV _ - EMSTMG MINOR CONTOUR -'.500D EXISTING MAJOR CONTOUR —� PROPOSED ROW ONE EASTING BOUNDARY — — EXISTING EASEMENT -------x EXISTING FENCE W� M� IIIIII M M I• EX. AND PROP. DRAINAGE BASINS 1. ALL WORK TO BE ACCOMPLISHED IN STRICT ADPUMENCE WIN ALL LOCAL ORDINANCES. CITY OR STATE. 2. CONTRACTOR TO COORDINATE ALL WORK WITHIN PUBOC RIGHT -OF WAY WITH ME APPROPRIATE UTILITY COMPANIES. ]. ME TOO OF FOUNDATION ELEVATORS BAUM ARE ME MINIMUM EI£VATdS WOUIRm FOR PROTECTOR FROM THE 100-YEAR STORM. MINIMUM FINISHED FLOOR UEVATNM ABOW ME IOD-YE'.Vt WATER SURFACE IN STREETB. CHANNELS DIVMM SWAUS. OR OT1ER DAMMAM FACILITIES AS ILLUSTRATED BY A MASTER GRADING FILM ARE TO BE SHOW. 4. A DETAILED LOT (FADING @ DRAINAGE PLAN MD. BE REQUIRED FOR LOT 2 BUM A BUILDING PERMIT CAN BE ISSUED, INCREASED RUNW FRd NEW CONSIRUCTON OF BUILDINGS. PATIOS. DRIWWAYS. ETC. SHALL NOT UAW THE PROPERTY AT MY POINT DTHER THAN ME NORTHERN PROI BOUNDARY DRUGS DETAINED TO HISTORIC PEAK FLOW RATES, 9' IIIILITY 1� W[ �EASEMENT II rII II e I L_____________IY $€ I 1 {� �9 uTutt , DDITCH EUDI O '`�.��T EAA SEMENT BUI NY UTRITY W EXISTING AND REA EASEMENT DRAINAGE TO BE VACATED EASEMENT BY PLAT I CXIy. 20'M1T W Ru'�nNC EASEMEN E ROW PPEERPIAT o� pl it PROP_ M'_ EjU;]p1EER1 I I I I I I I I I I I I I I I I I I I I I I I sl II g, I I I I I I I I eisAidr 1` i I II I I I (UNINCORPORATED LARIMER COUNTY) I )OD �I !I 5D 25 D SD SCALE: 1' = SO' CALL UTILITY NOTIFICATION CENTER OF COLORADO 1-800-922=1987 GALL 2-BUSINESS DAYS IN ADVANCE BEFORE YOU DIG GRADE. OR EXCAVATE FOR THE MARKING OF UNDERGROUND MEMBER UTILITIES. NOTE: THE ONLY INFRASTRUCTURE PROPOSED BY THESE PLANS IS THE ELECTRIC UNE AND POSSIBLY CABLE TV PHONE SERVICES. ALL OTHER IMPROVEMENTS ARE SHOMN ONLY AT THE REQUEST OF THE CITY FOR THE PURPOSE OF LOCATING EASEMENTS. AS SUCH, THEY ARE PURELY CONCEPTUAL AND NOT INTENDED FOR CONSTRUCTION. PREPARED UNDER THE DIRECT SIH OM OF TW ATp0. RCCAsi � 'URVRY':FP 0�26262�� MICHAEL, SHAWN BRAKE DATE C0.gfADO RE NO, 2BM2 Fd ND d BBWf d A BIOmWK Wpwa 6 � �N $3OJ� FZ€p�p6TZZ LLtti�VFOO WE OOUO ZO F;�4IXZ& y c ZF 3«<Oo - 0 N CO N jUWMNT CDO V Omj S�mzOO OO 3 GJpJp X F, m U XOD ON O \ n 3 2 2 � � O - Y w O Z Q J 0_ 0 N W S Q O Z DO of z p Z Z J Q It 0 O z Of SHEET 7 OF B JOB No. 39580.00 V MATCH LIRE A NATION UNE B w w o 7HAS SHEET THIS SHEET a<Wwz Mai J - 1 15""x20"" Fz€ww_ I I CONC. A Nam x I I 1 ) �I}� CUL PERT a 0 0o�ZO I I Y IX F mixzix Z�Zox I I X I I PEON Y - x I I BERM to APR �mTY \� n I PREVENT MOM LEANXC _ / x N I I I) BOUND YY } U U N PRONOE SWNE TO XCFTFIdI LOT I - BOUND T m m u7 LINE DRAINAGE RI PROPOSED I I 09FIL I O W IMPRO VENEWTS SHA L ONLY LEAVE j{r.� PROPOSED ME PROPERTY THROUGH ME NgfM 4 %I x LOT uc I I 1+ I t\ Q J z m pm00 ] I xl I it 1 d U m DRAINAGE 4936.5 ��...--�.—�_ l swA E 4936.40 a I I 49328t l l ell .. I ,4936.58 I x I I x a939.20 I 1 I 4939.20 493920 11 PROPERTY BOUNDARY I I I 6 939.20 4919.20 I I II {y I x T I Y l y PROPERTY f� x 4 3 .20 L ' I I� I l III BDMMT 1 4941.25 4 43.T0 4938.7 1 1 1 - DITCH TOFw494&70 4 1I { I Z l 4941.25 FFm49G I 1 W 4943.20 4 4 .7 4943,20 49 20 X I 494170 I r.. 494370 11 1 4 20 �' OARAO! 4III / 1 I l (�//\/, ;,y llLAh/Wi.70 I x I I 'V/� x _. 4843.7G I I III I -�� I I L/ I I 49., I d IICY R t, % I I I I I I' 11 )Q� S \ x S MATCH UNfi NE \ I THISISHEOT \ l 49 7 I j J I 'I z� 1 41 I 71I1 I % rc e Nii�• - EMBIHG FENCE 1 IlI If l y l lz ` . I I - YA A > 10 > ' m l —__ _��x•--•--1 ;,— \. \ 7HI5 SHEET i z m W yy UU z x .� XI �{.yam-.-}_-_ _________T_______ I Z> ib Ne w 0 z J LEGENDI NOTESE z a E%ISTINC MINOR CONTOUR 1 Q I. ALL WORK TO BE ACCOMPLISHED IN STRICT ADHERENCE WITH ALL LOCAL EASING MAJOR CONTOUR ORDINANCES, CITY OR STATE. --- PROPOSED ROW UNE z 2 ME APPROPRIATE IA COORDINATE ALL INNER WITHIN PUBl1C RIGHT-OF-WAY M1X m Q E%ISTINC BOUNDARY ME APPROPRIATE UTILITY COMPANIES. - — — E%ISTNG EASEMENT 3 ME TOP 0E FOUNDATION ELEVATIONS SNONN ARE ME MINIMUM EUWATONS REGIIRM 10 5 0 10 20 PREPARED UNDER ME DIRECT APEFIMS N Cf V) � - - --- % EXISTING E£NCE FOR PROT=CRON FROM ME Im-YEAR STORY. MINIMUM IMISIED POOR ELEVATOR Q Q ABOVE ME NCO -YEAR WATER SURFACE IN STREETS, CHANNELS. DITCHES WALES. OR SCALE: 1 10' Q 4x 5M SPOT ELEVATION OMER DRAINAGEDRAINAGEFACILITIES AS RLUSMATED BY A MASTER GRADNG PLAN ARE TO BE z 3.0% SLOPE ARROW 91oxN. Q p0 REgJ J ypp{ PROPOSED CONTOUR A INCREASED RUNOFF FROM NEW CMSMLICD NR O BUILDNGS. PATIOS DRIVEWAYS. M. F .ir SHALL NOT LEAME ME PROPERTY AT MY PUNT OMER MAN ME NORTHERN CALL UTILITY NOTIFlCATON �' ��M" � p z Sm5 PROPOSED INDEX CONTOUR PROPERTY BOUNDARY UNLESS DETNNED TO HISTMIC PEAK ROW RATES CENTER OF COLORADO 5 HOU I R� SCHEME E SOREST MAYFOUNDATIONBE01T- A11MOD011EPENDING BE NO YD2IMALN 4 FEET -O�9GG-aieJ BELOW EASING MADE PR NORTHOM GEOTCH RECDNMENDAMONS.I `: 2828E Q .•5 EXCAVATE CELL 2-BIIS IN 6, SPOT EIEVAVON ARE FINISH SS GRADE UNLENOTED OMERWM ADVANCE FORE DAY$ YOU DIG. PF ANp F� GRADE. OR EEXCAVATE FOR THE IsHAM1 MAKE SHEET 7 COF B MARKING OF UNDERGROUND aaRAOPM oo PE. xo 28262 MEMBER UTILITIES. FM .VR M 6TAlF 6 A FNptEOMO JC9 NO. JHSBO.00