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Home My WebLink AboutGrading Plans - 02/27/2023�� -- �� ; _-- _�---- - -_ _ `�t� � � ,� . • �� February 24, 2023 KEEFE CIVIL, INC 3125 Crockett Street Fort Collins, Colorado 80526 (970) 215-6808 meg@keefecivil.com Keefe Civil Project Nuinber: 2022-013 Grading/Stormwater Plan Accepted Water Utilities Engineering City of Fort Collins (Building Permit Released) 700 Wood Street Accepted by: Dan Mogen Fort Collins, Colorado 80522 Date: 02/27/2023 RE: 1028 Akin Avenue Drainage Meino Prospect PlaceBlock Parcel # 9711319008 8 Lot 2 To Whom it May Concern: The purpose of this letter is to describe the proposed site iinprovements and potential drainage impacts at 1028 Akin Avenue (Exhibit A). The 0.137-acre project site is an undeveloped single- family residential lot with established groundcover located on the north side of Akin Avenue between South Shields Street and South Mack Street in Fort Collins, Colorado. The site is located within the Old Town drainage basin. The lot is bound by existing single-family residential properties on the east and west lot lines, Akin Avenue right-of-way to the south, and a dirt alley way to the north. Per the NRCS Soil Survey of Larimer County (Exhibit B), the site entirely consists of Fort Collins loam and is classified as being within hydrologic soil group C. These soils are anticipated to have a slow infiltration rate when thoroughly wet and a slow rate of water transmission. CDS Engineering Corporation (2017) completed field investigations at the site, which included a boring drilled to 16 ft below ground surface. Groundwater was not observed during investigations and subsurface conditions were observed to consist of lean clay soils. Since use of dry wells for stormwater management is only feasible where subsoil is sufficiently pernleable, infiltration is not a viable option with this site. Per the flood insurance rate map, the lot is located within Zone X. Zone X is defined as an area of minimal flood hazard and does not have a base flood elevation associated with it. Also, the site is outside of all Ciry of Fort Collins inapped floodplains. (Exhibit C) Historic and developed drainage basins are shown in E�iibit D. Historically, site stormwater has drained with average slopes from the north to south into Akin Avenue right-of-way (historic basin A). Stonnwater froin the northern portion of the site has historically flowed from the south to the north, onto adjacent private property, with gentle slopes and ultimately discharge stormwater into the alley (historic basin B). Based on field survey and visual inspections, the alley drains east froin the project site towards Mack S�reet. -��- 7� Q� �� eo Q� 4� 9� O� �� a3 ��- �3 � Q� Q�' II�' v�- �� Qo �3 D� �� - , � a e e e d d d d d d d a d d d d d d d d a a d a C G C� G � G G G Q G Q a v G�0 q Q Q G a a G Q G G G G �� G' �� E7 fl4 pC �d �b aD ab dtr pD �b d!7 d�b �D QD �G nt7 C Q Qb dC �C � 4C�AA�AG3A'AAA.AAAG3 �►�AA��A�A�G�AG 1028 Akin Avenue Drainage Memo Pa�e 2 of 3 Keefe Civil Project No.: 2022-013 February 24, 2023 Proposed site improvements include a two-story single-family residential home with a basement and detached garage with alley access out to Shields and Mack Streets. All house roof drains and all, but one garage roof drain shall drain towards Akin Avenue right-of-way (developed basin A). A small anlount of landscape area, the proposed concrete driveway, and outside concrete parking area will drain towards the alley (developed basin B). Where possible, iinpervious areas and downspouts shall be routed into pervious areas with landscaping to allow for project stonnwater infiltration and increased water quality with site runoff. Since the site is currently a vacant lot, total adjusted impervious area will increase by 3,571 sf, as indicated by calculations shown below. Adjusted Developed Adjusted Historic Lot Historic Lot Area Developed Hardsca e or Hard Surface Area s Area s s Area s Concrete 0 0 63 5 63 5 Rooftop (90%) 0 0 3,262 2,936 Total Impervious Area 0 0 3,387 3,571 Adjusted Basin 3,571 Im erviousness The composite runoff coefficient and drainage basin runoff calculations for the historic and developed site are included in the enclosed tables (Exhibit E). Using the Fort Collins Stonnwater Criteria Manual (2018), the proposed stornlwater runoff will increase towards Akin Avenue right- of-way, but will decrease towards the alley way, as indicated in the summary table below. 2-year 10-year 100-year Basin A Historic Runoff 0.02 cfs 0.03 cfs 0.09 cfs Basin A Developed Runoff 0.24 cfs 0.41 cfs 1.05 cfs Basin B Historic Runoff 0.06 cfcs 0.10 cfs 0.27 cfs Basin B Developed Runoff 0.04 cfs 0.06 cfs 0.15 cfs Through the construction of retaining walls and drainage swales, the project's proposed drainage design will liinit potential dainage associated with its proposed storinwater runoff by forcing more storinwater towards Akin Avenue and less towards the alley. Based on visual inspections of the alley and field survey by others, it is my professional opinion the proposed improvements presented in this drainage memo will not negatively impact downstream private properties adjacent to the alley before draining into Mack Street right-of-way to the east. Conclusions Based on the enclosed design, it is my professional opinion the additional runoff generated by these site improvements will not cause adverse impacts to downstream private properties. I herby attest that this letter for the final drainage design for 1028 Akin Avenue was prepared by me or under my direct supervision, in accordance with the provisions of the Fort Collins Stormwater Criteria Manual. I understand that the City of Fort Collins does not and will not assume liability for drainage facilities designed by others. ' ��' ?�' �� v3 �3 II�'' �r.' 4� 9i� v3 �3 a3 ��' ?3 � �3 �3 �C' Q�' �� Q� �3 Q�"�" �i3 ��" ' o a e e e a e a a e e e e a a e e a e e a e e a a c a q v v a o a a v v a a v a c a a v a a a o v v a c > °v °� °o °c °� °� °c °v °c °c °a �� °o °d °a °v °c d °c °Q °o °c °c °o °c ' AAAG��AAAt�s�AG�G�AL�CsL�.AA�A.4,C�►�'A6 1028 Akin Avenue Drainage Memo Pa�e 3 of 3 Keefe Civil Project No.: 2022-013 February 24, 2023 Thank you for the opportunity to submit this drainage memo. Please do not hesitate to reach out to me if you have any questions or comments regarding the above items. Best regards, Megan L. Keefe, PE / Manager Keefe Civil, Inc. c��o�P p 0 UCF�s �........ O :•N �. �•.�FO : �<v�'02/24/23�� : : 39378 's f Digllally signetl by � Meyen L Ke��fe � � acusacl st�o� � � r yantlipn�e�n��y�//,� C �ate152023 C�Z� v rsS�ONAL N�� Enclosures Cc: Taylor Meyer, VFLA Tom and BJ Miller, Property owners References CDS Engineering Corporation. 2017. Geotechnical Exploration for 1028 Akin Avenue, City of Fort Collins, Lariiner County, Colorado for Rucker Design Build. Project nuinber 17-8569. April 14, 2017. Fort Collins Stormwater Criteria Manual. 2018. ' ��' ?�' �� v3 �3 II�'' �v 4� 93 v3 �3 a3 ��: ?3 � �3 Q3 �3 Q� �3 Q� �3 Q�' �� ' , o a e e e a e a a e e e e a a e e a e e a e e a a c a q v v a o a a v v a a v a c a a v a a a o v v a c > °v °� °o °c °� °� °c °v °c °c °a �� °o °d °a °v °c d °c °Q °o °c °c °o °c ' AAAG��AAAt�s�AG�G�AL�CsL�.AA�A.4,C�►�'A6 i ' i � �� -"� '� �� --- � � _�, i i � i i i i ; ii i � � I � � �I I , � �I �� I 3 � I. �� _� 1 I — �� lir-- 1 I � I I� �E �\ \�� .c � R � � I � � " � � � � .o w�r �'' I w I1il I I �� E � `� I z � W�� I � � a— �--- � I � � � ��I I 1 _ ��$ z �, i _ iA � � f � , , . o,> ,,, � �� . � e 56 _ , , � � r �.: � ..� r - � A � 1 , i � '� � , uwi. ra�cM v�ar � � �s _ o �� ,� �' as : � . , � s o —d� � i � � � �I � s �s Asc�-� � s- 50 � PROPOSEO �� aeam i I`� � � � .� � � � � PROP06ED ��, � DARAGE ,� � �°ao e � ��,�:� a � �� .� �_� HOUSE � �w , , - i i �I�.� � � � �",. � . 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E RF F��f,�f n.+�.. r o.�a,i�� mr sv., aE oe iFen e, TMe� or�raarmR eeF aF nnr rorvsrR ou oa o1Hea maerneMen*s. .�nwr_ .c N�, cF �.N_� E E..�uc �it w _ un n:orv�RE1E raa�� sc.Nni_ Nn,E. ,_mu.m - au2s.sa �u nsE Nme *t - owsa Foe n vEur�ca� oarum. s uaouvoirvc oc�a��ocMenir; HavE usco ticvoz9 uw�u�u,.E� c- :m .-R��a cmr or Fu .,�i.i.u�� . �) �.a ra:e �Fzrcni ra.urns� �. r- . .,o �_ .�.. �r , ..�_� .a_ � e.�v�.. ��n � � �,. ��•�. .. v�, �. � ., s iM �n�-ooe o �,u �. ,.I', Ki'� I W ' —_ ro�+ � � ..,aar� � ` I- � �I o��, e. o.��F_ �_ SECTION A-A � �b l ��I --, a l � u� ~f — � ¢I 0 5 10 20 t—tT �.. �I i,N ��Ns � c � � � i � _ _ i.. L II �� \ \ ? � _. �.� . �. _,s w. / SECTION B-8 I' 'L�. �� .x SECTION GC zwo U J p O � Uyzow Yo°�� :� � V 1� I� `V � w Q � J � a Q, � Z' Z Y'. Q'. Q m, Q N O;I �/R V o,x.,e „n .,i,��l .aon e,e�i O oo�wo�i _ _ — . -wrv:�.as�.,, a.m � F� 1 b�^� 4 OF 5 � Calloe�wero�ax. � Hydrologic Soil Group—Larimer County Area, Colorado � � (1028 Akin Avenue) N 0 0 4915i8 491945 491952 491�159 4919E6 491973 491�0 40° 35 T' N� � � 40° 3S 7" N � � Nf o �.. � � � � � ~� � 4 � �. r}'�� ' ,� � ; � , � •� i � �� ! � �_ ,. _ � . - �� , � , - � m � � �_ _ ; �'�_ � , �� - � . . � - ,� � N I + � , N � � - � ,� � � � ,� . _ � ' � s t— ► � � 7 • � � � � � ' i I 1 � � �� .'�� - • � • +� ` . �� w�.+ �- # . � + �� _ � � � �x- �- � � ,. � :� �� r. , �� „ � �. � + - - w' —� p i k� r `� � r � - - _�: � � Soil M�p rii;��y,�,i be valid at this scale. 40° 35' S' N�` I . I... I I � 40° 35 5" N 491938 491945 451952 491959 491�f& 491973 491� � 3 -��, Map Scale: 1:281 if printed on A porbait (8.5" x il") sheet. -��, ° N Meters ° � 0 4 8 16 24 � n Feet �\ 0 10 ZO 40 60 N Map projection: Web Mercator Comer coordinates: WGS84 Edge tics: lffM Zone 13N WGS84 Usb� Natural Resources Web Soil Survey 8/4/2022 � Conservation Service National Cooperative Soil Survey Page 1 of 4 Hydrologic Soil Group—Larimer County Area, Colorado (1028 Akin Avenue) MAPLEGEND Area of Interest (A01) Area of Interest (AOI) Soils Soil Rating Polygons � A Q A/D 0 B � B/D Q C 0 C/D � D 0 Not rated or not availabie Soil Rating Lines . � A o � � C/D � D � Not rated or not availabie Water Features Streams and Canais Transportation � Rails �..i Interstate Highways US Routes Major Roads Local Roads Background � Aeriai Photography .�.i A/D ..� B �r B/D . . C . r C/D .�.♦ D .. Not rated or not availabie Soil Rating Points o A 0 A/D ■ B � B/D MAP INFORMATION The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 16, Sep 2, 2021 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Aug 11, 2018—Aug 12, 2018 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. USbn Natural Resources Web Soil Survey 8/4/2022 � Conservation Service National Cooperative Soil Suroey Page 2 of 4 Hydrologic Soil Group—Larimer County Area, Colorado Hydrologic Soil Group Map unit symbol 35 Map unit name Fort Collins loam, 0 to 3 C percent slopes Totals for Area of Interest Description Rating 1028 Akin Avenue Acres in AOI Percent of AOI 0.2 100.0% 0.2 100.0% Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition USDn Natural Resources Web Soil Survey 8/4/2022 � Conservation Service National Cooperative Soil Survey Page 3 of 4 Hydrologic Soil Group—Larimer County Area, Colorado Aggregation is the process by which a set of component attribute values is reduced to a single value that represents the map unit as a whole. A map unit is typically composed of one or more "components". A component is either some type of soil or some nonsoil entity, e.g., rock outcrop. For the attribute being aggregated, the first step of the aggregation process is to derive one attribute value for each of a map unit's components. From this set of component attributes, the next step of the aggregation process derives a single value that represents the map unit as a whole. Once a single value for each map unit is derived, a thematic map for soil map units can be rendered. Aggregation must be done because, on any soil map, map units are delineated but components are not. For each of a map unit's components, a corresponding percent composition is recorded. A percent composition of 60 indicates that the corresponding component typically makes up approximately 60% of the map unit. Percent composition is a critical factor in some, but not all, aggregation methods. The aggregation method "Dominant Condition" first groups like attribute values for the components in a map unit. For each group, percent composition is set to the sum of the percent composition of all components participating in that group. These groups now represent "conditions" rather than components. The attribute value associated with the group with the highest cumulative percent composition is returned. If more than one group shares the highest cumulative percent composition, the corresponding "tie-break" rule determines which value should be returned. The "tie-break" rule indicates whether the lower or higher group value should be returned in the case of a percent composition tie. The result returned by this aggregation method represents the dominant condition throughout the map unit only when no tie has occurred. Componenf Percent Cutoff.� None Specified Components whose percent composition is below the cutoff value will not be considered. If no cutoff value is specified, all components in the database will be considered. The data for some contrasting soils of minor extent may not be in the database, and therefore are not considered. Tie-break Rule: Higher The tie-break rule indicates which value should be selected from a set of multiple candidate values, or which value should be selected in the event of a percent composition tie. 1028 Akin Avenue USbn Natural Resources Web Soil Survey 8/4/2022 � Conservation Service National Cooperative Soil Survey Page 4 of 4 National Flood Hazard Layer FI RMette �: FEMA Legend 105°6'1"W 40°35'20"N SEE FIS REPORT FOR DEfAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT s � � � i �i �- Without Base Flood Elevation (BFE) � � '- . 1 - I r Zone A. V. A99 � � �I �� i � SPECIAL FLOOD WIYFI BPE Of D@ptll Zone AE. AO, AH. VE. AR � 7 � HAZARD AREAS Regulatory Floodway � - �� s , , - _ , iT � � ,� � �",� � 0.2% Annual Chance Flood Hazard, Areas - �� of 1% annual chance flood with average ; depth less than one foot or with drainage �� _ � i areas of less than one square mile zo„e x A' '� -"'� . . v , - - � - � �. � Future Conditions 1%Annual ti � ¢ �,� �h � C =-- Chance Flood Hazard zo�,� x ��. �' �� Area with Reduced Flood Risk due to OTHER AREAS OF Levee. See Notes. zo�,e x - FLOOD HAZARD Area with Flood Risk due to Leveezo„e o �� Q i i r y NO SCREEN Area of Minimal Flood Hazard zone x �, a � "i � Effective LOMRs �" , � 4� � �� '� i� r` o '� '� OTHER AREAS Area of Undetermined Plood Hazard zo„e o • # , i - -� • - - � �I � � GENERAL '--' Channel, Culvert, or Storm Sewer STRUCTURES � i i t i i t Levee Dike or Floodwall � �� , , - ' �' i - . T I i z '� la,� so.z i I �� Cross Sections with 1% Annual Chance f- � � � ��5 Water Surface Elevation } ��'.Ei� �F rt��r`-��rti��.l�L �L��'}[}a�[��e�� -�, e- - - CoastalTransect � �" ` n {� - • � � �t+3� Base Flood Elevation Line (BFE) ��Ti r'.I faF+ri: r"S� '- ,� � �� - � TT�`� Kr �' , �. � , � 1�.�' �{Sf�� Jt iA � L�lillt,i 1� � � ' ^ � �"�"' - � Limit of Study � f ♦ (YI,��) �. �� . u �s i i n ounBa ( J r" d'ct'o B dary � _ � ! --- --- Coastal Transect se ine � i� a :' �1 F ; M�.`' �. �"` � ' 1 : � .' �u� a �� OTHER _ - Profile Baseline 1 �, FEATURES Hydrographic Feature I • � 4 li' • ,I � � � �� ° - Digital Data Available � � � � � ' No Digital Data Available � �� _ " i � MAP PANELS Unmapped ili, �' � I '� J � � ! � � � � y � .,,� • ? The pin displayed on the map is an approximate Y point selected by the user and does not represent y � �, � an authoritative property location. + .� � I � i fi � � "� � `+ �I �� This map complies with FEMA's standards for the use of � _ � t,. _ digital flood maps if it is not void as described below. � � � � - The basemap shown complies with FEMA's basemap '� � _ � ,� � �� accuracy standards F � � , _� The flood hazard information is derived directly from the �- �' - " authoritative NFHL web services provided by FEMA. This map ' � � �'# � � was exported on 8/4/2022 at 3:36 PM and does not �� " ' r�,� e� � '� � reflect changes or amendments subsequent to this date and �� t� �� i ,� ,� � ` time. The NFHL and effective information may change or �j' � y � � ��+.( become superseded by new data over time. ' �I �� ` 7� ' ,� � �4 � ` This map image is void if the one or more of the following map - ' ` k` � � .. • � �� elements do not appear. basemap imagery, flood zone labels, ' T7PJ F��C�4"d 51 v �� ' � f•��r� ��ti�+ ry.°.1� � � � legend, scale bar, map creation date, community identifiers, 105°523"w a0°34'S3"N FIRM panel number, and FIRM effective date. Map images for Feet 1.6, o0o unmapped and unmodernized areas cannot be used for 0 250 500 1,000 1,500 2,000 regulatorypurposes. Basemap: USGS National Map: Orthoimagery: Data refreshed October, 2020 �t��ns 1028 Akin Floodplain Vicinity Map �f� � � ��o � � n �■ 4i � � l I .,. W �ST � �� f � � , �,1!� A+: ,TERA7CSU —' �•� _ I I � + � W OA�K ST �� n �� -�— Y t� R � ti� �4 � � w 4�r :i, � A � �� i�, � � �� Legend Parcels FEMA Floodplain ■ FEMA High Risk - Floodway FEMA High Risk - 100 Year FEMA Moderate Risk - 100 / 500 Y� FEMA Map Panel City Floodplains ■ City High Risk - Floodway City High Risk - 100 Year City Moderate Risk - 100 Year ❑ Growth Management Area Parks Schools Natural Areas �_; City Limits I I ��.� � r � � ., • " ' ' • ' 1:1,715 � Notes '.86.0 0 143.00 286.0 Feet This map is a user generated static output from the City of Fort Collins FCMaps 'VGS 1984 Web_Mercator_Auxiliary_Sphere Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. ;ity of Fort Collins - GIS r�. n i cP ko �� .c (-_oe�c,.� i �F ,� ce �m�isNen ��cos v�w -,�< , � . . ";ve�s' ■�■■■■■ N, e. 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' ' , °ory � � � ; � ' � I i I . , - � 1 , , ' . �-, ' .,,. ; � �...' � �` L - � 1.-��__1.��_�__��- ��__��-��__��_J � �� «� ,� � � i �� a �� i— � � R� �� aAOPE�.��E u �5e.� � i -- � . � � . . � �L� / � ,. � � — �i � I HISTORIC DRAINAGE BASINS �. i- P` W � Z W a z Y Q I .a,�.�.a •, wi� i im5 nn' Imoerv,a,�� 3..,� � �� \ L�� .,,� ,o��E ��sv �� vaopeAry �me � � i-s ��s-�_��a �� ' / k I' .�� RESOIDOENL�E �� A � � �,�� ,os ,� _ ��r��a�� i ��«�� aaaPEa,.��E f�� , \ 1 -� � �� -��■ . F��s , PROPOSEDGARAGE NOTE�. ONLY ONE ROOF ' N � � oftPIN PERMITTEo To eE �. ', ��RECTEDTOWAROSALLEY � �. 1— — �� clNi °� � „ ..-.�; �� DEVELOPED DRAINAGE BASINS ,�.�v�� L� FOR DRAINAGE REVIEW ONLY NOT FOR CONSTRUCTION I I L_—_ ZwN o Jr� ��o`�U Y'n�m� , 'j; V I� 1� I� `V � PlioPEPrvLNE � �- — � x � � > w a O.OiS i Y,. � AC �- � a o', Z , Q � � a � � � ��-. � b�^� 1 OF 1 �� ca�ie�orew�a4. Composite Runoff Coefficient Calculations 1028 Akin Avenue, Fort Collins, CO �(c,.,�a, ) � _ ,-� A, Where: C= Composite Runoff Coefficient C, = Runoff Coefficient for Specific Area (A;�, dimensionless A; = Area of Surface with Runoff Coefficient of C;, acres or square feet n= Number of differe�t surfaces to be considered A,= Total Area over which C is applicable, acres or square feet Equation 5-2 Historic Drainage Basin A Developed Drainage Basin A Historic Dreinage Basin B Developed Dreinage Basin B Minor (2- and Minor (2- and Minor (2- and Minor (2- and Runoff 10-yr) Major�100-yr) 10-yr) Major�100-yr) 10-yr) Major�100-yr) 10-yr) Major�100-yr) Surface Type Coefficientsl Area �sf) Composite CZ Composite C3 Area (sf) Composite CZ Composite C3 Area (sf) Composite CZ Composite C3 Area �sf) Composite CZ Composite C3 Hardscape or Hard Concrete 0.95 0 340 0 300 Rooftop 0.95 0 3,032 0 230 Total Impervious Area 0 3,372 0 530 Landscape or Pervious Surface Lawns, Clayey Soil, Avg 0.25 1,384 1,936 4,599 145 Slope 2-7% Total 1,384 0.25 031 5,308 0.69 0.87 4,599 0.25 0.31 675 0.80 1.00 Notes: 1. Runoff coefficients per Fort Collins Stormwater Criteria Manual Table 3.2-2. 2. Composite runoff coefficient per Fort Collins Stormwater Criteria Manual Equation 5-2. 3. Frequency adjustment factor per Fort Collins Stormwater Criteria Manual Table 3.2-3. Table 3.2-3. Frequency Adjustment Factors Storm Return Period Frequency Adjustment (years) Factor (t�) 2, 5, 10 1.00 25 1.10 50 1.20 100 1.25 Table 3.2-2. Surface Type - Runoff Coefficients Surface Type Runoff Coefficients Hardscape or Hard Surface Asphalt, Concrete 0.95 Rooftop 0.95 Recycled Asphalt 0.80 Gravel 0.50 Pavers 0.50 Landscape or Pervious Surface Lawns, Sandy Soil, Flat Slope < 2% 0.10 Lawns, Sandy Soil, Avg Slope 2-7% 0.15 Lawns, Sandy Soil, Steep Slope >7% 0.20 Lawns, Clayey Soil, flat Slope < 2% 0.20 Lawns, Clayey Soil, Avg Slope 2-7% 0.25 Lawns, Clayey Soil, Steep Slope >7% 0.35 1028 Akin Ave - dreinage.xlsx Drainage Basin Runoff Calculations 1028 Akin Avenue, Fort Collins, CO Area Minor Major Initial/Overland Timel Travel TimeZ Final T� Intensit (in/hr 4 Basin Flow cfs)5 Basin Length Slope Minor to Major to Length Slope Channel Velocity tt Minor Tc Major Tc (acres) Composite C Composite C 2-yr 10-yr 100-yr 2-yr 10-yr 100-yr (ft) (%) (min) (min) (ft) (%) Type (fps) (min) (min) (min) Historic A 0.032 0.25 0.31 35 2 7.5 6.9 NA 7.5 6.9 2.47 4.23 8.85 0.02 0.03 0.09 B 0.106 0.25 0.31 50 2 8.9 8.3 NA 8.9 8.3 2.31 3.95 8.31 0.06 0.10 0.27 Developed A 0.122 0.69 0.87 20 2 2.4 1.5 140 2%o swale 2.1 1.1 5.0 5.0 2.85 4.87 9.95 0.24 0.41 1.05 B 0.015 0.80 1.00 25 4 1.8 0.6 5.0 5.0 2.85 4.87 9.95 0.04 0.06 0.15 Notes: 1. Per Fort Collins Stormwater Criteria Manual Section 3.3.2. i.s��i.i-cxc�� T' 3� Where: C= Runoff Coefficient, dimensionless Cr = Frequency Adjustment Factor, dimensionless L= Length of Overland Flow, feet S = Slope, percent 2. Per Fort Collins Stormwater Criteria Manual Section 3.3.3. V _ 1.49 R2/3S]/2 n Where: V = Velocity, feet/second n = Roughness Coefficient, dimensionless R= Hydraulic Radius, feet (Hydraulic Radius = area / wetted perimeter, feet) S = Longitudinal Slope, feet/feet And L T� - vxeo 3. Per Fort Collins Stormwater Criteria Manual Section 3.3.4. A minimum T� of 5 minutes is required. T�-iao+10 4. Per IDF Table for Rational Method, Table 3.4-1 Fort Collins Stormwater Criteria Manual. 5. Per Fort Collins Stormwater Criteria Manual Equation 5-1. Q = CIA Where: Q= Peak Rate of Runoff, cfs C = Runoff Coefficient, dimensionless I = Rainfall Intensity, in/hr A= Area of the Basin or Sub-basin, acres 1028 Akin Ave - drainage.xlsx