HomeMy WebLinkAboutDrainage Reports - 05/24/20212900 South College Avenue, Ste. 3D
Fort Collins, CO 80525
303-740-9393 • Fax: 303-721-9019
www.jrengineering.com
Memorandum
To:Wes Lamarque
From:JR Engineering
Date:4/28/2021
Subject:Lot 1 of the Warren Federal Credit Union – East Drake – Final Drainage Report 1ST Amendment
This memo has been prepared to certify that the drainage and proposed improvements for the re-plat of lot 1 of
the Warren Federal Credit Union –East Drake, is in compliance with Lot 1, 3 and Tract A, of the Warren
Federal Credit Union – East Drake - Final Drainage Report; as prepared by Interwest Consulting Group.
Introduction:
Lot 1 of the Warren Federal Credit Union – East Drake (Site), is located in the northwest quarter of Section 29,
Township 7 North, Range 68 West of the 6th Principal Meridian, in the City of Fort Collins, Larimer County,
Colorado. Refer to the attached Vicinity Map.
The site is bounded to the north by East Drake Road, Illinois Dive to the west, Lot 2 of the Warren Federal
Credit union to the south, and the existing parking lot of the Warren Federal Credit Union – East Drake
development to the east.
The total area of the site is 0.25 acres of land. The proposed development includes the construction of an office
building and a future commercial/retail building, walks, patios, and a landscape area. A walk going north-south
has been proposed to connect to an existing walk within the East Drake Road ROW.
Existing Conditions:
The site is within a property that is part of the approved Warren Federal Credit – East Drake – Final Drainage
Report. Detention for the site has been provided by an off-site existing water quality and detention pond as
stated in the Final Drainage Report for Rigden Farm Northwest Roads, as prepared by JR Engineering. The site
is currently undeveloped and is composed primarily of dry vegetation, with the exception of an existing
drainage pan on the site. The site is located in a FEMA flood zone X in the non-published FIRM panel
08069C1000F, dated 12/19/2006. The soils on the site are primarily composed of type B soils - with Satanta
loam, 3 to 5 % making up 94.7% of the site. A minority of the soils on the site are characterized as type C soils
– with Nunn clay loam, 3 to 5% slopes making up 5.3% of the overall site. For additional information on the
soil-groups, refer to the attached Hydrologic Soil Group map.
City of Fort Collins Approved Plans
Approved by:
Date:
2900 South College Avenue, Ste. 3D
Fort Collins, CO 80525
303-740-9393 • Fax: 303-721-9019
www.jrengineering.com
Proposed Development:
Lot 1 of the Warren Federal Credit Union - East Drake will be re-plated into two separate lots. Lot 1 will be
developed into the Bachus and Schanker law office building, and lot 2 will be developed into a
commercial/retail building.
Basin 1A is 0.15 Acres and 59.0 % impervious, includes lot 1 of the re-plat, the Bachus and Schanker law
office building, proposed walk, landscape area. Runoff from basin 1A is collected with nyloplast landscape
drains and roof drains, which drain to design point 2, as shown in the attached Bachus and Schanker Office
Building Drainage Plan (Attached).
Basin 2A is 0.02 Acres and 37.0% impervious, included within lot 1 of the re-plat is an existing concrete pan,
and landscape area. Basin 2A drains into the existing parking lot at design point 1, as shown in the attached
Bachus and Schanker Office Building Drainage Plan. The runoff is then treated by LID pervious pavers and
drains into an inlet represented as design point B2 in the attached Interwest drainage map.
Basin 1B is 0.07 Acres and 72.9% imperious, included within lot 2 of the re-plat designated to be a future
office/ commercial/retail building. Basin 1B drains to design point 3, as shown in the attached Bachus and
Schanker Office Building Drainage Plan. Runoff from basin 1B confluences with the upstream runoff from
basin 1A at design point 3.1. The runoff is ultimately conveyed into an existing manhole and is represented as
design point C, as shown within the attached Interwest drainage map.
Basin 2B is 0.01 Acres and is 2.0 % impervious. This basin is part of lot 2 of the replat. Runoff from basin 2B
drains south off the property and onto the undeveloped lot 2 of the Warren Federal Credit Union - East Drake at
design point 4, as shown in the attached Bachus and Schanker Office Building Drainage Plan.
Basin 3B is 0.01 Acres and is 25.3% impervious. This basin is part of lot 2 of the replat. Runoff from basin 3B
drains west off the property onto Illinois drive at design point 5, as shown in the attached Bachus and Schanker
Office Building Drainage Plan.
Basins 1A, 2A, 1B, 2B, and 3B are part of basins C and B2, from the Interwest drainage report. Additional
impervious area will be added to basin B2 from the site connection to the existing sidewalk along the East
Drake ROW, with walks along the building(s) eastern parking. The net percent impervious of the proposed
improvements to the site is 58.1 % percent. The proposed site imperviousness is well below the Interwest future
assumed imperviousness of 73% impervious for Basin C as well as the 72% impervious for Basin B2. Therefore
the proposed additions to the site are anticipated to not adversely affect the LID measures put in place during
the development of the East Warren Federal Credit Union subdivision or the downstream stormwater
infrastructure.
Low Impact Development
Approved LID measures were designed by Interwest to treat 51% of the runoff, as shown in the attached
Interwest LID exhibit. The sidewalk extension to the East Drake Road ROW within Basin 2A is tributary to the
LID pervious pavers. The required LID treatment determined by Interwest was 30,130 sq-ft. The provided
treatment area was for 30,477 sq-ft. of total impervious area. The new walk adds 236 sq-ft. of impervious area,
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