Loading...
HomeMy WebLinkAboutDrainage Reports - 02/22/2013NORTHERN ENGINEERING Drainage Letter Report Date: February 20, 2013 Project: Canyon Place Fort Collins, Colorado City of Ft. Collins rove ;lens Approved By_ Date ADDRESS: PHONE:970.221.4158 WEBSITE: 200 S. College Ave. Suite 10 www.northernengineering.com Fort Collins, CO 80524 FAX: 970.221.4159 Attn: Mr. Wes Lamarque City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 Dear Wes:, Project No. 838-002 This letter serves to address the stormwater impacts of the above referenced project. The site currently consists of rooftop, concrete walks and patio, asphalt parking areas, some turf, trees, and other vegetation. The majority of the site presently drains to an area inlet located in the center of the main drive aisle. This area inlet releases into the City's storm sewer system within West Magnolia Street. Historic drainage patterns will generally be preserved. The total impervious area within the limits of construction of the existing site is approximately 22,387 square -feet. The proposed redevelopment will completely remove all existing above -grade structures and adjacent hardscape. The new project will consist of a larger building, as well as a courtyard area and modified parking area. Concrete pedestrian connections will be maintained along South Meldrum Street, West Magnolia Street and Canyon Avenue. The total imperious area within the limits of construction of the proposed redevelopment is roughly 21,637square-feet. The two existing curb cuts and concrete aprons to West Magnolia will be removed. A proposed curb cut is designed at Canyon Avenue to meet current code requirements and minimize the amount of area draining across the pedestrian path. The area within the court yard has been designed with a ridge routing stormwater north and south. The stormwater routed to the south is intercepted by a trench drain which outfalls into the City's stormwater system. The stormwater routed to the north is intercepted by a trench drain which out falls into Canyon Avenue. The area within the existing parking area is designed to be routed into a proposed area inlet. There is design only routes runoff within the Canyon Avenue right-of- way into Canyon Avenue. The site is located in the Old Town master drainage basin, and therefore, on -site detention is not required so long as the increase in imperious area is less than 5,000 square -feet. The total imperious area proposed with this development will be decreased by approximately 750 square -feet (22,387 — 21,637). A detailed breakdown of the existing and proposed imperious areas is attached to this letter. Page 1 of 2 D:'%Proiec&S3S-0021Drainaee\Reoorts:Draina¢ Remd1838-002 Drainage -Letter 2012-09-18.docr Although stormwater quantity detention is not required, stormwater quality mitigation will be addressed by both temporary and permanent Best Management Practices (BMPs). During construction, the Contractor will follow the appropriate and applicable City of Fort Collins standards for erosion and sediment control. A comprehensive. Stormwater Management Plan has been prepared for this project, and a copy has been supplied to the Environmental Regulatory Specialist with Fort Collins Utilities. 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. This portion of the Old Town basin does receive regional water quality treatment; therefore, on -site water quality mitigation is not required. However, much of the existing landscaped buffers on the north, south and east sides of the building will be preserved as permeable areas to promote infiltration and treat surface runoff prior to entering the adjacent gutters and inlets. The project site is also located in the Old Town Basin floodplain. This is a City of Fort Collins regulatory floodplain. The entire site is currently located within the Old Town Basin floodplain, but the majority of the site is located within the 100-year moderate risk floodplain. The entire proposed structure is located within the 100- year moderate risk floodplain and this area does have risk of flooding. Since a small portion of the development falls within a 100-year high risk flood fringe or floodway, a Floodplain Use Permit (FUP) shall be obtained prior to commencing with any construction within this area. The only proposed improvements within the 100-year high risk flood fringe or floodway consists of site work. As such, this project seeks to obtain a FUP with the initial Development Construction Permit (DCP), which would then cover all work to take place within the floodplain. It is important to note that the floodway currently follows the back of sidewalk along the project's West Magnolia Street frontage. This means that some of the driveway and streetscape modifications will occur within the floodway. A No -Rise Certification is required for all work within the floodway. Further details and supporting documentation for the No -Rise Certification shall accompany the FUP application. The proposed grading concept closely matches existing elevations and drainage patterns, and only varies in an effort to improve the existing condition. On -site detention is proven to be unnecessary. On -site stormwater quality is not required as runoff will be treated at the Udall Natural Area water treatment facility. The project is designed in accordance to the governing floodplain regulations contained within Chapter 10 of the City Code, and the Floodplain Use Permit and necessary certifications shall ensure that construction remains compliant with Chapter 10. Therefore, it is my professional opinion that the new building and site improvements proposed with Canyon Place satisfy all applicable stormwater criteria. Please do not hesitate to contact me if you have questions or require additional information. Sincerely, N&&IYU, Nicholas W. Haws, PE LEED Project Manager AP JCod�/Snowclon Project Engineer DdProiects\838-002VDrainaee\Reoort5\Drainave Feoort\838-002 Drainaee-Letter 2012-09-18.dxx Page 2 of 2 ( J m i§ (( 0 / cn C « E & g = koN & %%)_$ �■cn ƒ0 J /� -\ \A -,u a a\) \ \M m CD00 \0 0 u u Q _ 0�E � )}}§%%k«r, U = 2/J§\\ � — Lai bo _ §) - J k�\/kj j � ±! ! 2 g® — ] / tt\ - %• §§ %)| e(((( J0 Lai m — "a cj k2 ) § :§ ® \ ° 0 ) � � ©! UM � Cc u q �:a 2] \— :\ �:::: @7 o0 co §): / 00 �2 k # � 'U cli CV 4.. ...a & {§# f) (Efi` 1�|=0{ \})3 cWM o)/ a ! u En � I EXISTING PROPOSED S EXISTING AREA .-v INLET LIMITS OF--,-" CONSTRUCTION (TYPICAL) _ to FFE = 97.55 _ 6 EXISTING CITY OF FORT COLLINS FLOODWAY FORT COLLINS FLOOD FRINGE TVC W. MAGNOLIA ST.ISTORM SEVER IlrrFrrrflrrlr It It /}frPllrr Ifl7rrr HI Mr ltt" NORTHERN ENGINEERING 200 SwM College Avenue. Suite 10 PHONE: 970.221.4158 FAX: 970.221.41159 Fort Collins, Cho 0 80524 www.northemenglr�eing.cpn OMITS OF caNsrnucnoN LINE FFE = 95.93 EXISTING CITY OF FORT COLLINS FLOODWAY U 0Lu \ I (n a T I A � r \ CURB INLET ST— SURFACE AREA(SF) %IMPERV. IMPERV. AREA(SF) ROOFTOP - - 3,231 100% 3,231 CONCRETE 4.781 100% 4,761 ASPHALT 14,375 100% 14,375 LANDSCAPE T 5.672 0% 0 TOTALS 26,059 TOTAL= 22,387 2' SIDEWALK CHASE — / 2' CURB /GiASEV SIDEWALKCHASE10' TRENCH nrrrrrMrrrlMr// /AM/lpr MMrrr MrrMr //e F }}ff f//fi/ EXISTING & PROPOSED IMPERVIOUS AREAS 0 EXISTING CURB INLET SURFACE AREA (SF) %IMPERV. IMPERV. AREA (SF) ROOFTOP 11.541 1011% 11,541 CONCRETE 7,479 100% 7,479 ASPHALT 2.617 10D% Z617 LANDSCAPE 6.422 0% 0 TOTALS 26.059 TOTAL= 21.637 Canyon Place DRAWN BY: C. Snowdon EXHIBIT SCALE: 1 in=20ft ISSUED: 02.20.13