The URL can be used to link to this page

Home My WebLink AboutAPPLEBLOSSOM - 712 W. LAUREL ST. - PDP - 22-10 - REPORTS - DRAINAGE REPORTEXISTING PROPOSED 4 LAUREL STREET NORTHERN ENGINEERING 200 South Colle8e Anme, Suite 100 PNONE970.221A158 FAA. 970.221.4159 FM Coffins, Colorado W524 w .nm0u:mugwg .ing.c SURFACE AREA (SF) %1MPERV. IMPERV. AREA (SF) ROOFTOP 1.837 100% 7,837 CONCRETE 388 100% 388 ASPI(ALT 0 100% 0 PERMEABLE 0 PAVERS 40% 0 LANDSCAPE 10,2BB O% 0 TOTALS 12,521 TOTAL= 2,223 EXISTING & PROPOSED IMPERVIOUS AREA LAURELSTREET SURFACE AREA(SF) %IMPERV. IMPERV. AREA(SF) ROOFTOP 3.528 100% 3,528 CONCRETE SBi 100% 583 ASPR L 7.768 10D% 1,788 PERMEABLE 2,908 PAVERS 40% 1,1& LANDSCAPE 3,755 O% 0 TOTALS 12,521 TOTAL= 7,021 712 W. Laurel Street DRAWN BY: A. Reese EXHIBIT SCALE: 1 in=20R ISSUED: 03 SEPT 10 1 J INORTHERN ENGINEERING • 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. 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 receives regional water quality mitigation in the Udall Natural Area; therefore, on -site water quality treatment in not required. However, sustainable design practices and environmental stewardship are part of the goals and vision of this project. As such, this development will go above and beyond the minimum requirements for stormwater management. A permeable paver system will be employed, not only to limit the increase in total impervious area, but also to help cleanse and treat runoff prior to leaving the site. A depressed rain garden adjacent to the Laurel Street right-of-way will also provide additional water quality treatment and encourage on -site infiltration. Although not required, other opportunities may be explored during the Final Plan phase. While a good portion of historic runoff does travel north and east towards existing single-family residences, a slight modification to current drainage patterns for the site is proposed in an attempt to improve this condition. First and foremost, on -site infiltration will be encouraged to the maximum possible extent. However, sub -surface soils conditions, combined with the proximity to building foundations, demand an underdrain system. Therefore, a shallow underdrain will relieve near surface waters and discharge into the proposed rain garden adjacent to the sidewalk along Laurel Street. The rain garden itself will allow 6 to 12 inches of ponding / infiltration prior to spilling through a sidewalk chase and into the existing flowline of Laurel Street. The grading plan allows safe surface passage of excess stormwater towards the alley and Laurel Street in emergency situations. The proposed grading concept closely matches existing elevations and drainage patterns, and only varies in an effort to improve the existing condition and to help ensure that adjacent properties are not adversely impacted. On -site detention is proven to be unnecessary. Stormwater quality has been considered, and will be addressed in a manner well above and beyond the minimum requirements. Therefore, it is my professional opinion that the triplex and duplex proposed at 712 W. Laurel Street (Replat of Lot 17 and Lot 18, Block 5, Westlawn Addition) satisfy all applicable stormwater criteria. Please do not hesitate to contact me if you have questions or require additional information. Sincerely /03/ '4QftftmmGW0 LEED Nicholas W. Haws, PE AP cc: Mark Goldrich & Prue Kaley — Owners Dave Derbes, LEED AP — Brinkman Construction Ian Shuff, AIA, LEED AP — Aller-Lingle-Massey Architects Jim Birdsall, ASLA, RLA — The Birdsall Group Page 2 of 2 D`:F'rofecs57A-OOri6ra!naa=_\Reoods\Dainaee Reunrturalna.e-Letter 03-03-lOdoc J NORTHERN ENGINEERING Drainage Letter Report Date: September 3, 2010 ADDRESS: PHONE:970.221.4158 : 200 S. College Ave. Suite 100 WEBSITEWEBSITEnengineering.com Fort Collins, CO 80524 FAX: 970.221.4159 Project: 712 W. Laurel Street Replat of Lots 17 and 18, Block 5, Westlawn Addition Fort Collins, Colorado Attn: Mr. Wes Lamarque City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 Dear Wes: Project No. 574-001 This letter serves to address the stormwater impacts of the above referenced residential redevelopment. The existing home is situated towards the western portion of the site, but does occupy portions of both lots. The site currently consists of rooftop, concrete walks and patio, turf, trees, and other vegetation. It presently functions similar to a 'B' lot, with historic drainage being split towards the northeast and southeast. The unpaved alley adjacent to the western properly line has a high point such that it too drains to the north and towards Laurel Street on the south. The total impervious area of the existing site is approximately 2,223 square -feet. The proposed redevelopment will completely remove all existing above -grade structures and hardscape. The new project will consist of a triplex on the western lot, a duplex on the eastern lot, and a permeable paver courtyard between the two. A new parking lot will be constructed north of the residential units, over half of which will consist of permeable pavers. The pedestrian connections from the units south to Laurel Street will be made with shallow boardwalks, allowing 100% of the rainwater to pass through the decking material. The total impervious area of the proposed redevelopment is roughly 7,021 square -feet. The off -site alley adjacent to the project will get paved with a cross-section according to LCUASS Figure 7-12F. The existing curb cut and concrete apron to Laurel Street will remain as -is. The area of paved alley draining south across the Laurel sidewalk will be approximately 650 square - feet, which is less than the maximum 750 square -feet allowed by LCUASS. 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 impervious area is less than 5,000 square -feet. The total increase in impervious area proposed with this development is approximately 4,798 square -feet (7,021 — 2,223). A detailed breakdown of the existing and proposed impervious areas, along with graphical site depictions can be found on the attached Exhibit 1. Page 1 of 2 0:\Proiects\574-001�Oravtaee\ReoorslDrainaee Reo,MDminaoe-Letter 09-03-10.dos