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HomeMy WebLinkAboutDrainage Reports - 11/21/2016City' r-f Ft Collins rov. PI i p' pfoveo, By Date I1- 11-/6 NORTHERN ENGINEERING ' Drainage Letter and LID Report Date: October 28, 2016 Project: West Side House Project No. 970-001 ' Project Development Plan/Major Amendment Fort Collins, Colorado ' Attn: Mr. Wes Lamarque City of Fort Collins Stormwater Utility 700 Wood Street 1 Fort Collins, Colorado 80521 Dear Wes: This letter serves to address the stormwater impacts of the West Side House project. The existing building is situated towards the northern portion of the site. The site currently consists of rooftop, concrete walks, ' asphalt parking areas, turf, trees, and other vegetation. It presently functions similar to a 'B' lot, with historic drainage being split towards Plum Street to the north and towards Shields Street to the east. Calculations using the rational method to determine the proposed runoff are attached to this letter, as is a drainage exhibit. ' The total impervious area of the existing site is slightly reduced due. to the removal of an existing concrete pad along the north face of the building. For this reason, the total runoff was assumed to also be reduced ' and, therefore, no stormwater detention is proposed. Although stormwater quantity detention is not required, stormwater quality will be addressed by permanent Best Management Practices (BMPs). There is one existing bio-retention pond (Rain Garden) that is located along the south face of the building. Currently, this site is deficient with the City's Low Impact Development Standards. In order to bring the site into compliance, two Rain Gardens will be installed along the north face collecting building ' downspouts and one additional rain garden will be located in the southeast corner of the site to collect runoff from the parking lot. These Rain Gardens will have an engineered section designed to remove particulates and contaminants from the stormwater. While most minor events are expected to infiltrate 1 into the ground, weep holes and subdrains will be provided to drain the Rain Gardens should they become overburdened. During major events, runoff will spill through designed depressions in the top of the concrete retaining walls. It has been recommended that an existing tree located within Rain Garden C be ' preserved. As a results, Rain. Garden C is approximately 16% deficient in recommended water quality volume. During construction, the Contractor will follow the appropriate and applicable City of Fort Collins standards for erosion and sediment control. Since the approximately 1,250 sf area of disturbance for the project is less than 10,000 sf, a comprehensive Stormwater Management Plan will not be prepared for this project. ' Post construction water quality and erosion control will be achieved by a fully established and stabilized site. All areas disturbed during construction will receive permanent hardscape, landscape, or building structure. t301 N. Howes Street, Suite 100, Fort Collins, CO 80521 I 970.221.4158 I www.northernengineering.com ■� (NORTHERN ENGINEERING I 1 1 1 U I 1 There are no regulatory floodplains associated with the project. The City LID requirements specify that either 75% of all impermeable areas are provided LID treatment OR 50% LID treatment by which 25% is treated by permeable pavers. In the case of this project, we will meet or exceed the 75% treatment of impermeable areas through the use of, LID. The combination of treatment provided by the 4 infiltration Rain Gardens will treat 10,679 square -feet of impervious area on the site, which is 83.5% of the total impervious areas with the project, which again far exceeds the amount required by city code. A LID Treatment Exhibit is provided with this report. To summarize, the proposed grading concept closely matches existing elevations and drainage patterns. On -site detention is proven to be unnecessary. Stormwater quality has been provided, and meets the city requirements for Low Impact Development treatment. Therefore, it is my professional opinion that the West Side House satisfies all applicable stormwater criteria. Please do not hesitate to contact me if you have questions or require additional information Sincerely, ` Lv OODO ..E„ Danny Weber, PE Project Engineer enc. 10 24M i TONAL 1 I I I I / I I I � 1 I I I / I I I I I 0 0CL §§\/ ■I_Dr- C5cs" @ ƒE ci ( \ b 0 »e» . . §E C5606 y/\ (1 3a 0 " u � U kfCY \ 0 ■2-)r� 3 ��/C:0 k E § LAJ - §#2mr�t \/\° 2 L , O ^000 2 )J/J#ddd° 2e. £p E - S©- §§§° _%ay2 \cA ])# �)§ £ 3 Lo LO \ \Lo�� lo � u � °k0 - k 2 cs CD / . 3)a 222 2on 2 e 3}� k k_ 2 ::\ o §§§ ° � 3 LU : La k ; kj § In co LL o tko AS ' § Ir 2 } \ 11 1 I [J 1 1 t o .+ i. c 'E O l0 O tO c m u o m O U o I6 wi ui O N = CD 0 a`w Nw E N _ 3 N E Ip In In 3 d o � m G N O co_ F . C E 1p o Q z Q z a 'q u U o p x � O O O , 00 d d Ipoo O 00 to L J V O O V% J 2 OF- G 1p Q 1p Q E o z ZI N > O O O a o m W l0 O l0 2 .y p � y y y O o o Q O 0 0 0 1f1 Vpo o.yryN C L J a O N tr) r1 rl n1 r1 r ti C J 2 Q H O c n p ♦♦�� lT E o ui lri .. W r c c E ui O u Q c O 10 l0 p 000 .�Nm .00a .. 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Northwest Driveway Chase ' Rectangular Bottom Width (ft) = 1.00 ' Total Depth (ft) = 0.24 Elev (ft) = 100.00 'Invert Slope (%) = 0.50 N-Value = 0.013 ' Calculations Compute by: Known Q Known Q (cfs) = 0.20 ' 1 ' Elev (ft) Section 1111l 0 .25 Highlighted Depth (ft) Q (cfs) Area (sqft) Velocity (ft/s) Wetted Perim (ft) Crit Depth, Yc (ft) Top Width (ft) EGL (ft) 5 .75 1 Reach (ft) Friday, Oct 28 2016 = 0.12 = 0.200 = 0.12 = 1.67 = 1.24 = 0.11 = 1.00 = 0.16 1.25 1.5 Depth (ft) I 1.00 0.75 0.50 0.25 WE -0.25 II Channel Report Hydraflow Express Extension for Autodesk®AutoCAD® Civil 3D® by Autodesk, Inc. Southeast Driveway Chase Rectangular Bottom Width (ft) = 1.00 ' Total Depth (ft) = 0.41 Invert Elev (ft) = 100.00 ' Slope (%) = 0.50 N-Value = 0.013 ' Calculations Compute by: Known Q Known Q (cfs) = 0.60 ' (ft) 0 .25 Section Highlighted Depth (ft) Q (cfs) Area (sqft) Velocity (ft/s) Wetted Perim (ft) Crit Depth, Yc (ft) Top Width (ft) EGL (ft) 5 .75 1 Reach (ft) Friday, Oct 28 2016 = 0.25 = 0.600 = 0.25 = 2.40 = 1.50 = 0.23 = 1.00 = 0.34 1.25 1.5 Depth (ft) 1.00 0.75 0.50 0.25 9 MI -0.25 No Text Design Procedure Form: Rain Garden (RG) ' Sheet 1 of 2 Designer: D. Weber Company: Northern Engineering Date: October 28, 2016 Project: West Side House Location: Rain Garden A 1 11 1 J 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area. I, 1e = 100.0 % (100% it all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i - I,/100) i = 1.000 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.40 watershed inches (WQCV= 0.8 , (0.91' i3 - 1.19. iz+ 0.78 - it D) Contributing Watershed Area (including rain garden area) Area = 800 sq it E) Water Quality Capture Volume (WQCV) Design Volume Vwocv = 27 cu it Vol = (WQCV / 12)' Area F) For Watersheds Outside of the Denver Region, Depth of de = in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, VWON OTHER ^ cu ft Water Quality Capture Volume (WQCV) Design Volume H) User Input of Water Quality Capture Volume (WQCV) Design Volume VwocvuwR - cult (Only if a different WOCV Design Volume is desired) 2. Basin Geometry A) WQCV Depth (12-inch maximum) Dwocv= 4.75 in B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 0.00 ft / ft (Use'0" It rain garden has vertical walls) C) Mimimum Flat Surface Area AM,n = 16 aq ft D) Actual Flat Surface Area A,,� = 69 sq ft E) Area at Design Depth (Top Surface Area) A,,,,, = 69 sq If F) Rain Garden Total Volume Vr= 27 cult (VT= ((Arm + Anoi,w) / 2) ' Depth) 3. Growing Media choose One O 19" Rain Garden Growing Media O other (Explain): 4. Underdrain System 0loose On* A) Are underdrains provided? O YES ONO B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage Y.-ft Volume to the Center of the Or@ice ii) Volume to Drain in 12 Hours V0112= N/A cult iii) Orifice Diameter, 3/8" Minimum Do = WA in ' Rain Garden A.xlsm, RG I Design Procedure Form: Rain Garden (RG) ' Sheet 1 of 2 Designer: D. Weber Company: Northern Engineering Date: October 28, 2016 ' Project: West Side House Location: Rain Garden B 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, I, (1009/6 if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i - 1./100) C) Water Quality Capture Volume (WQCV) for a 12-lour Drain Time (WQCV= 0.8' (0.91' i3- 1.19 " h+ 0.78' i) D) Contributing Watershed Area (including rain garden area) EI Water Quality Capture Volume (WQCV) Design Volume Vol = (WQCV / 12) ' Area F) For Watersheds Outside of the Denver Region, Depth of Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, Water Ouality Capture Volume (WQCV) Design Volume H) User Input of Water Quality Capture Volume (WQCV) Design Volume (Only If a different WQCV Design Volume is desired) I, = 100.0 % = 1.000 WQCV = 0.40 watershed inches Area = 800 sq ft V W WV = 27 cu ft de - in Vwocv OTHER - cu ft Vwocv USER = cu 1t 2. Basin Geometry A) WQCV Depth (12-inch maximum) B) Rain Garden Side Slopes (Z = 4 min., honz. dist per unit vertical) (Use "0" ff rain garden has vertical walls) C) Mimimunt Flat Surface Area D) Actual Flat Surface Area E) Area at Design Depth (Top Surface Area) F) Rain Garden Total Volume (VT- ((ATm + Am,„a)12) ' Depth) Dwxv - 4.75 in Z = 0.00 ft / ft AM,,, = 16 sq 1t AK,,,,, = 69 sq it ATa = 69 sq it VT= 27 cuff 3. Growing Media Choose One 1 Q 18" Rain Garden Growing Media Q Other(Explain); 4. Underdrain System A) Are underdrains provitled9 B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours iii) Orifice Diameter, 3/8" Minimum One YES 707 NO y= ft V0112 = N/A cu ft DU = N/A in i R Design Procedure Form: Rain Garden (RG) Sheet 1 of 2 Designer: D. Weber Company: Northern Engineering Date: October 28, 2016 ' Project: West Side House Location: Rain Garden C 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, I, la = 99.0 % (1 DO% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i - Id100) I = 0.990 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.39 watershed inches (WQCV. 0.8 ' (0.91' i' - 1.19 - ?+ 0.78 - i) D) Contributing Watershed Area (including rain garden area) Area = 7,449 sq ft E) Water Quality Capture Volume (WQCV) Design Volume Vwocv - 243 cu It Vol = (WQCV / 12)' Area F) For Watersheds Outside of the Denver Region, Depth of d, - In Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, VWeov omen - cU ft Water Quality Capture Volume (WQCV) Design Volume H) User Input of Water Quality Capture Volume (WQCV) Design Volume Vwoovumn = cu ft (Only if a different WQCV Design Volume is desired) 2. Basin Geometry A) WQCV Depth (12-inch maximum) Dwwv = 6.50 In B) Rain Garden Side Slopes (Z = 4 min., honz. dist per unit vertical) Z . 0.00 ft/ft (Use'0' If rain garden has vertical walls) C) Mimimum Flat Surface Area AMn = 147 sq It D) Actual Flat Surface Area Arm„ d = 365 sq ft E) Area at Design Depth (Top Surface Area) A,a - 387 sq It F) Rain Garden Total Volume VT- 2D4 CU ft TOTAL VOLUME < DESIGN VOLUME (Vr ((Arm+Ae )/2)'Depth) 3. Growing Media Goose One Q 18" Rain Garden Growing Medal Other (Dq)laln): 4. Underdrain System A) Are underdrains provided? ChooseOne YES NO B) Urderdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y- ft Volume to the Center of the Orifice III Volume to Drain in 12 Hours Vol,, = N/A Cu h III) Orifice Diameter, 3/8" Minimum Do = N/A in Rain Garden C.xism, FIG 10128/2016, 2:29 PM f a MELOPWSUNOFF SUMMARY TABLE OESION MTIN 2' Tc 10}h 10T066R Oi O10 MIX)POIM ID �� a CID Ct00 (InMD (e1611 ww (AI Iwal (NN ryN afo Dt] BF/ 097 so 5o 59 aZ 0.7 ME ME 0,07 0.51 0,61 0" Ae3Ne Lm T1MmM e1M.a,, Tad ITR•4sAr 12.M IF 1g1iIrlAlVuep )B% IYri�e•Yiwytl4lo®� N3W tl RM. D.e.1r urm� FYtlWYp IFNtl inm�4RtlnWnA SAtl Rn.0 R�r44MB M Ru•m� �4iC )AAa Rtltl u.rve. laps tl IY FrttlA�nW1 HA I ® NORTH IB 0 10 A 30F«I N n) 1m n 0A LEGEND: PMFO6m s m sxEx PPOPOsm UHDERMNN PROPOSED WNIWR G] EKlmxc Cox10UR----eom---- PROPOSED SwNE PRI WRB k MMR PRCVERTY BI OE9d MINT Q r-OW ARROM ✓�-� LABEL B diMNALE ISx A NNI an ..N ae1 MANAM BI BWNJARY • �1 '� • FACPD4D SNAEE MCION u PROPOSm MCOJLAR BI PACERS NOTES: 1. III TO n Z'DRNNAW Sr R REPMT FOR X SCE MI PMECT 070-001' DATED MTOBER 26. 106 BY NORTHERN ENGNEERINO FOR A 704AL MFMM.IBM. FOR DRAINAGE REVIEW ONLY NOT FOR CONSTRUCTION _- c�.LtuTetrrllonNulKNriNePBM caoRrm • N. Call oeDB10 10 ra�. City of Fort Coll . Colorado UTILITY PLAN APPROVAL K OWD: CY) Rylow� Osta CHEGtm BY TM a I�M�eY� 1=7 hY CHII BY eb•m r VWLLy RY CHI BY CHECKED BY: e„m ab CHECKED BY � AY f I;a H w m U) = o w W 0 w N Q W Z 3 Sheet C500 Z9 Sheets