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Home My WebLink AboutGrading Plans - 12/05/2023DATE: PROJECT: December 4, 2023 Bodenhamer Residence 210 S. Grant Street Fort Collins, CO 80521 PROJECT NO. 1328-038 ATTENTION: Stormwater Department City of Fort Collins 700 Wood Street Fort Collins Colorado 80521 Dear City Staff: Grading/Stormwater Plan Accepted (Building Permit Released) Accepted by: sagenbroad Date: 12/05/2023 B2308539 This letter memo accompanies the submittal for the Bodenhamer Residence, 210 S. Grant Street. Grading Plan dated December 4, 2023. Specificalfy, this letter report serves to document the drainage impacts associated with the proposed developments. The proposed development consists of the demolition of the existing buildings, sidewalks, driveways, and patios. Existing impervious areas total 2374.46 (SF). The proposed development will incfude one single famify residential home (Building 1) and a garage (Building 2). The proposed development also includes some sidewalk and patio areas. The total impervious footprint for the proposed development is 3607.85 (SF), which is an addition of 1233.39 (SF) of impervious area. The proposed Grading Plan for the proposed development of 210 S. Grant Street allows for the lot drainage to remain substantially unchanged and follow existing drainage patterns. A swafe wilf convey runoff from Buifding 1 east to the rear alley, following the existing grade of the site. The rear alley generafly slopes from north to south at about 0.5% grade. However, there is a very minor localized low area along the east of the ally where runoff has historically been conveyed to. This localized low area will then pond roughly 0.4' before it overtops and runoff then continues to sheet flow south to W. Olive Street. Once in W. Olive Street runoff is then conveyed via curb and gutter to an inlet located near the NW corner of W. Olive Street and S. Loomis Avenue. The runoff from the front of the lot remains unchanged. Vertical curb and gutter along S. Grant Street conveys runoff from the front of the lot to nearby curb inlets. The proposed development is increasing the total impervious by 12%. This 12% increase in area results in an increase in runoff during the 100-year event by 0.43 cfs (see attached Rational Calcs). This increase in 0.43 cfs is negligible and will have no adverse impacts on downstream infrastructure. A regional drainage map has also been included to show the conveyance from the proposed devefopment to the nearby inlets. For additional information please refer to the Grading Plan dated December 4, 2023. Please feel free to contact me if you have any questions. Sincerely, NORTHERN ENGINEERING SERVICE, INC. �\ _ BLAINE MATHISEN, PE Project Manager NORTHERNENGINEERING.COM � 970.221.4158 FORT COLLINS � GREELEY DRAINAGE MEMO: 3235 Moore Lane Attachments: 1. Rational Calculations 2. Regional Drainage Map NORTHERNENGINEERING.COM � 970.221.4158 FORT COLLINS � GREELEY 1 � 2 � NORTHERN ENGINEERING DEI/�OPED BASIN CHARACTER OF SURFACE1: IMPERVI�!!'l�NESS AND R Asphalt........................................................................................... . Concrete............................................................................................ Rooftop...................................................................................................... Gravel...................................................................................................... Pavers...................................................................................................... Landscape or Pervious Surface Playgrounds................................................................................................ LawnsClayey Soil ................................................................................................ LawnsSandy Soil ................................................................................................ Notes: 1) Percentage impervious taken from the Fort Collins Stormwater Criteria Manual, Chapter 5, Table 4.1-2 and Table 4,1-3 2) Runoff Coefflcients are taken from the Fort Colllns Stormwater Criteria Manual, Chapter 3. Table 3.2-1 and 32-2 Basin Area Area of Area of Area of Area of Lawns Basin ID �a�� Concrete Rooftop Gravel (ac) (ac) (ac) (ac) Existing 0.24 0.01 0.04 0.01 0.19 Pronosed 0.24 0.01 0.07 0.00 0.16 ENT CALCULATIONS ercen age 2-yr Runoff Impervious Coefficient 100% 0.95 100% 0.95 90% 0.95 40% 0.50 40% 0.50 25% 0.35 2% 0.25 2% 0.15 Composite % Impero. 21% 33% u-yr rcuno• Coefficient 0.95 0.95 0.95 0.50 0.50 0.35 0.25 0.15 2-year "- '-"' Composite Runoff Composite Coefficient Runoff Coefficient 0.39 0.39 0.49 0.49 uu-yr rcunc Coefficient 1.00 1.00 1.00 0.63 0.63 0.44 0.31 0.19 Composite Runoff Coefficient 0.49 0.61 �; � NORTHERN ENGINEERING l-H]il.l Cxli��_L T, � (Equation 33-2 FCSCM) y :hannelized Flow, Time of Concentration: Ti = �,;�o F (Equation 5-5 FCSCM) 1 V = ��4 H��ti�-� } (Equation5-4FCSCM) Freauencv Adiustment Factor: 5torm RetuM Verlotl Frequency AdJustment (Years) FectorlG) 2. 7. 10 1.00 a.10 so i.zo 300 1.25 Table 3.23 FCSCM Therefore Tc2=Tc10 7,. —=- 10 } (Equation 33-5 FCSCM) �� is the lesser of the values o! Tc calculated using T�= T; + T i Overland Flow Channelized Flow Time of Concentretion Design Basin Point Length, Slope, Length, Slope, Rou hness Assumed Velotity, T C2 C�oo L S T;z T��oo L S g Hydraulic V T� (Eq. 3.3•5) T�2 = T; +Ti T�� = T; +T� T�z T�ioo ,,,. ,,,,, ,,,, ,,,,. CoeHicient „ ._.. ,,,, . (min) � NORTHERN ENGINEERING S Q = c, (c)(�)(A) IDF Table for Rational Method - Table 3.4-1 FCSCM Design Basin(s) Point Area, A T�2 (acres) (min) 0.24 10.5 0.24 6.6 T�ioo (min) 10.5 6.6 CZ 0.39 0.49 Intensity, Intensity, Intensity, Flow, Flow, Flow, �ioo �z �io �ioo 4z Qio Qioo (in/hr) (in/hr) (in/hr) (cfs) (cfs) (cfs) �.49 221 3J8 7.72 0.21 0.35 0.90 0.61 2.60 2.60 9.06 0.31 0.31 1.33 9/4/23, 10:56 AM �O �le M��S 210 S Grant Ave Bodenhamer Resitlence 210 S. Grant Street Fort Collins, CO 80521 • — � T — �- � �� `�� ."t�� • A�. -- . e �.--- ; -- -� , �. �. 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[�i�• � -1 � � . � `�� _ -�C � / _ �.____ _ __ __ _ ___ ____ - _____ .� �- ____ ________ ___ ____ .�E`- _ .� �\' � �� m'o ��_--_ _ =- --- N ' � �---�__ � _- - �o�-�a— —�,� . � l � ,i� i �� , ��, ■I � i � � ■� �'I � NORTH �Ii LEGEND roPervP�uxEORiw+we��.�,>o�raa+ou>nou •/ / a Qa�_o ��o.��w � NOTES. PROJECTINFORMATION: PROJECT�ADDRESS�. 210 GRANT AVENUE FORT COLLINS, CO 80527 BUILDING PERMIT#: CONTACT INFORMATION� HAMMERSMITH STRUCTURES 201 COMMERCE DR. #2 FORT COLLWS, CO 80524 (303j250-7182 ERIC@HAMMERSMITHSTRUCTU RES.COM EXISTING IMPERVIOUS AREA: HOUSE = 1283.67 SF GARAGE = 488.36 SF CONCRETE = 245.37 SF GRAVEL 357.06 SF PROPOSEDIMPERVIOUSAREA: HOUSE = 2377.55 SF GARAGE=628.23SF CONCRETE FLAT WORK = 602.07 SF 8�� Z� �_� W � = W �� oj Q = ] g Z W u � �� 3 f �_ J �E z Q J d � Z � � :� i snea� Iof7 1