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Home My WebLink AboutGrading Plans - 06/06/2023DRAINAGE LETTER 1224 W MAGNOLIA STREET FORT COLLINS, CO June 2, 2023 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: 1224 W MAGNOLIA STREET RESIDENCE FORT COLLINS, COLORADO PROJECT NUMBER: U23O1O Dear Staff, ��'�`\ UNITED CIVIL Design Group Grading/Stormwater Plan Accepted (Building Permit Released) Accepted by: sagenbroad Date: 06/06/2023 United Civil Design Group, LLC. is pleased to submit this Drainage Letter for the 1224 W Magnolia Street Residence in Fort Collins, Colorado. In general, this summary serves to document the stormwater impacts associated with the proposed site improvements. SITE LOCATION AND PROJECT DESCRIPTION The 1224 W Magnolia Street Residence site (referred herein as "the site") is situated in the Southeast Quarter of Section 10, Township 7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins, Larimer County, State of Colorado. More specifically, the site is located at the northeast corner of W Magnolia Street and Scott Avenue. The planned improvements consist of the demolition of existing features and construction of a residence and accompanied garage structure. EXISTING CONDITIONS Hydrology The site, located within the Old Town Drainage Basin, is approximately 0.22 acres. Draining by way of overland flow, runoff from the site generally drains to the southeast and the northwest. Runoff is ultimately conveyed to street inlets in both Magnolia Street and Scott Ave, and is ultimately further conveyed downstream within the Old Town Basin Portions. Floodplain The site is not located within a FEMA floodplain or — FEMA Map No. 08069C0978G (see attachments). The site is also not located within a City of Fort Collins regulatory floodplain (see Fort Collins Floodplain mapping attached). CITY REQUIREMENTS As discussed above, the site is located within the Old Town Drainage Basin. Per information provided by the City of Fort Collins, drainage requirements for residential projects state that, "The water quantity detention requirements can be waived if less than 5,000 square feet of hard surface is being added in the Old Town Drainage Basin or if the final percentage of hard surfaces including one-half the adjacent streets or alleys is equal to or less that the percentage the City's master drainage plan for your area of town." Given these criteria, detention is not proposed with the site improvements. IMPROVED CONDITIONS The proposed site improvements include the re-construction of a single-family residence and garage, in addition to the replacement of the existing driveway and concrete walks in support of the residence. The proposed residence is larger than that of the existing home, resulting in an overall increase in impervious area. The table on the following page summarizes the hydrologic impact associated with the proposed site improvements relative to existing conditions. Refer to the attached Impervious Area Exhibits to see the location of the existing and proposed impervious areas. 19 OLD TOWN SQUARE #238 � FORT COLLWS, CO 80524 � 970-530 4044 � www.unitedciviLcom DRAINAGE LETTER 1224 W MAGNOLIA STREET FORT COLLINS, CO HYDROLOGIC SUMMARY TABLES ��'�'\ UNITED CIVIL Design Group Note that the area used in these calculations considers area within the 0.22-acre property. Runoffflows and drainage patterns for the improved site remain largely unchanged from existing conditions. A breakpoint exists at the intersection of W Magnolia St and Scott Ave, therefore on-site drainage flows are directed generally southeast to northwest to existing discharge locations offsite within the Old Town Basin. Downspouts from the proposed residence are planned to be piped by the contractor away from the proposed buildings. Runoff does drain to the neighboring properties immediately to the north and east in accordance with historic conditions, however, the net increase in hard surface area that ultimately drains to the neighboring lots is less than 350 s.f. Refer to the attached Impervious Area Exhibits for further information. DETENTION S� WATER QUALITY Provided that the net increase in hard surface area (i.e., 1,742 s.f.) is less than 5,000 s.f., detention requirements are waived for this residential project per City of Fort Collins drainage criteria for residential lots within the Old Town Drainage Basin. Proposed improvements include disconnected impervious areas separated by landscaped areas. Runoff from proposed impervious areas discharge to landscape areas that act as grassed buffers before reaching existing discharge locations offsite. EROSION CONTROL Erosion control, both temporary and permanent, is a vital part of any development project. For this project, the site disturbance is less than 1 acre; therefore, a CDPHE Stormwater Management Plan (SWMP) is not required. However, comprehensive erosion control measures are included with the site improvements. Refer to the Civil Construction Plans for additional information. At a minimum, the following temporary BMP's will be installed and maintained to control on-site erosion and prevent sediment from traveling off-site during construction: • Sediment Control Log — a linear roll made of natural materials to trap sediment from sheet flow. Sediment Control Log is a temporary BMP placed at the perimeter of disturbed area. The contractor shall store all construction materials and equipment and shall provide maintenance and fueling of equipment in confined areas on-site from which runoff will be contained and filtered. Temporary Best Management Practices (BMP's) will be inspected by the contractor at a minimum of once every two weeks and after each significant storm event. CONCLUSIONS The drainage system proposed within this Drainage Letter provides adequate conveyance of the developed stormwater runoff from the proposed improvements to existing discharge locations. Existing drainage patterns remain with the proposed site improvements; negative impacts new to the site are not anticipated to the City of Fort Collins Master Drainage Plan or adjacent properties and infrastructure due to the proposed improvements; the net increase in hard surface area that ultimately drains to the neighboring lots is less than 350 s.f. No detention is required for onsite runoff per City of Fort Collins requirements for this residential development as the proposed site increase in imperviousness is less 5,000 square feet. Water quality considerations are being provided by the grassed buffers on the site. 19 OLD TOWN SQUARE #238 � FORT COLLWS, CO 80524 � 970-530 4044 � www.unitedciviLcom DRAINAGE LETTER 1224 W MAGNOLIA STREET FORT COLLINS, CO ��'� UNITED CIVIL Design Grou� We understand that review by the City of Fort Collins is to assure general compliance with standardized criteria contained in the Fort Collins Stormwater Criteria Manual (FCSCM). This summary was prepared in compliance with technical criteria set forth in both the Mile High Flood District (MHFD) Urban Storm Drainage Criteria Manual and the FCSCM. If you should have any questions or comments as you review this drainage summary, please feel free to contact us at your convenience. Sincerely, United Civil Design Group, LLC Prepared by: �� ,,��Z�l�-�G[� Brady Kirkbride Design Engineer �,�� Sam Eliason, PE Principal ATTACH M E NTS - Existing Impervious Area Exhibit - Proposed Impervious Area Exhibit - FEMA Firmette (covering FEMA FIRM Panel 08069C0978G) - City of Fort Collins Floodplain Map 19 OLD TOWN SQUARE #238 � FORT COLLWS, CO 80524 � 970-530 4044 � www.unitedciviLcom TTACHMENTS � EXISTING ROOF EXISTING CONCRETE _ 1.746 SF 802 SF TOTAL = 2,548 SF � � � 0 wQ I �� Z a WQ � Q LL III �° � � O � `, U � I �� i PROPERTY BOUNDARY IMPERVIOUS AREA CONVEYED TO � 326 SCOTT AVENUE 730 SF TOTAL = 730 SF 326 SCOTT AVENUE � �� I 5037 �� i�` i�'��j�� +�� I�� r�� BASIN BOUNDARY (TYP) - � I � /� IMPERVIOUS AREA CONVEYED TO 1218 W MAGNOLIA STREET � 260 SF � 620 SF � I I �► � TOTAL = 880 SF I � .,. I 1218 W MAGNOLIA o �� STREET � � � � �... .:.� I MAGNOLIA STREET 70'-80' RIGHT OF WAY (PLAT) I I � �� UNITED CIVIL ° Design Group '� DATE: June 2, 2023 PREPAREO FOR: ARCNER HOMES INC. JOB NUMBER'. U23070 NOTE�, THIS EXHIBIT WAS PREPARED FOR INFORMATION ONLY AND THE ENGINEER PREPARING THESE PLANS WILL NOT BE RESPONSIBLE FOR UNAUTHORIZE� USE OF THEM. SHEET � OF 1 � PROPOSED ROOF PROPOSED CONCRETE _ 3.800 SF 490 SF TOTAL = 4,290 SF NET INCREASE IN HARD SURFACE AREA = 1,742 SF ' 326 SCOTT IAVENUE _� � 5p'S � � R , � , � DOWNSPOUT I W Q = a z} a Q LL �o H� O� U� �� PROPERTY BOUNDARY DOWNSPOUT 1218 W MAGNOLIA STREET � �� UNITED CIVIL ° Design Group '� DATE: June 2, 2023 PREPAREO FOR: ARCNER HOMES INC. JOB NUMBER'. U23070 NOTE�, THIS EXHIBIT WAS PREPARED FOR INFORMATION ONLY AND THE ENGINEER PREPARING THESE PLANS WILL NOT BE RESPONSIBLE FOR UNAUTHORIZE� USE OF THEM. SHEET 1 OF 1 IMPERVIOUS AREA CONVEYED TO � ggg SF 326 SCOTT AVENUE TOTAL = 888 SF NET INCREASE = 158 SF I BASIN BOUNDARY (TYP) �J I _. - '._. ' ------ - - �so� - - ' \ � IMPERVIOUS AREA CONVEYED TO 'OUT � 1 °% 1218 W MAGNOLIA STREET DOWNSPOUT � ,�',� \ � � � � 635 SF DOWNSPOUT � � � TOTAL = 880 SF I � � NET DECREASE = 245 SF I I �, i MAGNOLIA STREET 70'-80' RIGHT OF WAY (PIAT) National Flood Hazard Layer FI RMette � FEMA Legend 105°6'9"W 40°35'12"N SEE FIS REPORT FOR DEfAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT n - � s � -�.r , = Without Base Flood Elevation (BFE) Zone A. V. A99 ' • �-' ` � � SPECIAL FLOOD WIYFI BPE Of D@ptll Zone AE. AO, AH. VE. AR '� `� � t HAZARD AREAS Regulatory Floodway iR • - i � � t � � �� 0.2% Annual Chance Flood Hazard, Areas - �� of 1% annual chance flood with average s � depth less than one foot or with drainage a ,.,�, � �, �• ' areas of less than one square mile zo„e x � �fi � �' '� r � - � Future Conditions 1% Annual -� � ; _-- Chance Flood Hazard zo�,� x � -�� - � 1�,,y � �, ,R � ,� Area with Reduced Flood Risk due to _ _ � "� Levee. See Notes. zo�,e x � OTHER AREAS OF I �-.� �� a � h ,� ,� FLOOD HAZARD Area with Flood Risk due to Leveezo„e o ! • ,� • • �lr� '��,.' • i 6 I � � �'� � � � NO SCREEN Area of Minimal Flood Hazard zone x _ • � , � i � � Effective LOMRs �' a' �� _ � OTHER AREAS Area of Undetermined Plood Hazard zo„e o T'�;! R "1 ; T?G•d Re. �,' `=,lq � � ! I � GENERAL '--' Channel, Culvert, or Storm Sewer � �� • � r, � � � _ � � _ STRUCTURES � i i t i i t Levee, Dike, or Floodwall • � • i� f ` •� . _ � Cross Sections with 1% Annual Chance � u � ��5 Water Surface Elevation ,�',�'.E/�,��F'�^��r''��r4�15'yL ��(}[1 f-�{.�,�,t'�� 1 I e- -- CoastalTransect �1[p��f'�t�.��L�l�l� � L � i �F+.�+. �� "� "�� ' r �t+3� Base Flood Elevation Line (BFE) ��If��' ,i * - - LimitofStudy * * � � = � � � � Jurisdiction Boundary r � ` �►'� � 1 � - � # �� ' .� i • --- --- Coastal Transect Baseline .� i - _ � � � a', � . � � � 7i -; „ OTHER - - Profile Baseline I � � � � � � p� -`��`s -�Y *, � � FEATURES Hydrographic Feature . s'i - �� fk M � � 1 '�� F? � �� t �� ~ ' � � p � � � ��ih Digital Data Available � ,� n- � ,�� " i � � �.� �� No Digital Data Available � i. � � � � � � � _ ` � _� .� ,�� , MAP PANELS Unmapped .� , � " _ ,►1 +d�, �� . � � � � � i � '� i � " M ' �'� Q The pin displayed on the map is an approximate �� f- � +� - oint selected b the user and does not re resent � � _ P Y P F � � � _� � �, `� � � I � � _ � � an authoritative property location. � � „� � � � � � 1 � ��. ,� � �± �� ( M � � ,� � ,� I This map complies with FEMA's standards for the use of � � s '�� ,� � �' � i � di gi ta l f loo d maps i f i t is no t voi d as descri be d be low. - ` i�, { The basemap shown complies with FEMA's basemap � � , �t�' 7 y I accuracystandards � T?�J Rr�:h1 S9� � }� � _ � � � � T i hd R� + i�1= The flood hazard information is derived directly from the � � - '� authoritative NFHL web services provided by FEMA. This map N,,� � � „'�! + ��' �,��r was exported on 5/24/2023 at 3:48 PM and does not � � r� reflect changes or amendments subsequent to this date and � _ � • � � `� • time. The NFHL and effective information may change or � ,,� - � .� • become superseded by new data over time. �� r .r �p � � ;� This map image is void if the one or more of the following map ��+ �- elements do not appear. basemap imagery, flood zone labels, 4 *�� '� �' legend, scale bar, map creation date, community identifiers, 105°5'32"w a0°34'45"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�1s FCMaps � i , i � � L i �in �i�� _ � 1: 3,430 � 572,0 0 286.00 572.0 Feet This map is a user generated static output from the City of Fort Collins FCMaps WGS 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. City of Fort Collins - GIS Legend Parcels 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 L..i World Hillshade Notes 1224 W Magnolia St EXISTING IMPERVIOUS AREA RooF 1,7Gb 5F CONCRETE 8025F PROPOSEDIMPERVIOUSAREA ROOF 3,800 SF CONCRETE 4905i TOTALNEWLYA��E�IMPERVIOUSAREA = i,i425F I I vi�ui or wn.r � 326 SGOTT AVENUE I I su cre��: I EXISTINGGARAGE - I� / i , . ._ . . ,_I f -.:. I I sc� ' E,��F,ow �NE�� II � / s „ w xAHs.o t � �� / � �a�oEs��,�Ra � �\ �, ' � ~ PROPOSE�HOUSE I GvczoenecE.�nv \ � I j4 } � T — > s • .. . .. y I 1218 W MAGNOLIA o� STREET � o � sF nu . t.rvA �P -- PR6PDSED �^ GARAGE w�v....a.>N.,oao � . v .� ^� �� . oesi naoe�ui . 1 _v_�..E L� i . _ _ _ i xisnrvcrwa 1 � � � � I�� ;�— --_ _ -- � PROPOSED � 4��+ � CDNCRETE vcnioFwnv 1 ORIVEWAV I PROJECTCOORDINATES 1. TNISPROJECTISAMOOIFIEDSTATEPLANECOOR�INHTE SYSTEM (GROUN� DISTANCES) IMTHA GRIDTO GROt1ND SCALE FACTOR OF 1.0002629665 APPLIEO TO POINT 150 (SOUTH WEST CORNER OF BLOCK 8) HAVING A STATE PLANE COOR��NATE OF N1455511.242. E3111826.299AN0 NAV088 ELEVATION OF 5031 35 BASE� ON AN OPUS SOLl1TION. ELEVATIONSAT1VJOFORTCOLLINS BENCHMARKS WERE CHECKED. (BM31-9] AND BM03-OB) 2. ALL PROJECT CONTROL LISTEO HEREON IS PROVIOED AS A GOURTESV. IT IS THE ftESPONSIBILITY OF THE RECIPIENT TO VERIFV TEH ACCURACV OF THE COORDINATES AN� ELEVATIONS SHOWN PRIOR TO USING THEM FOR ANY PtIRPOSES. \ % — — — i / ws✓ % � .. / — _� / . SCl ta ___ ....: �.� , . . .; ...:. '. � ..-..1. � —�— :�. _f . ;'.� _. ._ i_—_ � << _t-. �� .., . LaArnrcvo¢�r ��qsiirvcr�wr,.ier i ' � � MA�GN OLlorw v�Ptin IEGE jN0'Nc c nroupPpor-.�+rs�urvwk� //r \ ' --�„s— �o � "°a IJNITED CIVIL .. - �nsn.��,oA��,o��re �esign Group � � � $CL �o Ja�rmn eo vaa - � ��OfES "� � o- �o�k` .. . . __ _ .�_ :.0 .. : � . r+ ' I rvo �nv� y U � W w o � � ��,�.aMA�t��,.=.ae�,A.�� w ME,�,�= �L o m r Z vsry W Q uan� .. orvrvo `- N a � Z Q ❑ �E�,E�_E �vs _,o,�FFErA�,aFN Z � � � ��. QC � G p ��,n�«,.. ��a�R�� Ao �.,w�E�, � � v < N ° � a tt o OOHE,�S ?� Ew a tFss O�j� e �_\ C1.00 � � 0 � scAi[ � _.p ��