HomeMy WebLinkAboutMOSAIC NEIGHBORHOOD CENTER - PDP210003 - - STORMWATER-RELATED DOCUMENTSPage 1 of 2
5265 Ronald Reagan Boulevard, Suite 210
Johnstown, Colorado 80534
Phone: 970.800.3300
January 20th, 2021
Galloway Project No. HFH27
WES LAMARQUE FROM CITY OF FORT COLLINS
The following is Galloway & Company Inc.’s (Galloway) conformance letter supporting that developing
East Ridge Fifth Filing Lot 2 Block 1 – Mosaic Neighborhood Center (ERMNC) has no greater impact to
the storm drain infrastructure than originally estimated at the time East Ridge Second Filing (ERSF) was
designed and approved.
• Final Drainage Report East Ridge Second Filing by Galloway & Company Inc., dated June 1st, 2016
• Final Drainage Report East Ridge Fifth Filing Mosaic Condominiums by Galloway & Company Inc.,
dated August 19th, 2020
ERMNC (hereafter referred to as ‘the site’, or ‘project site’) proposes to develop a portion of Phase 9 of
ERSF and bounded on the north by the East Ridge Fifth Filing – Mosaic Condominiums (ERFFMC); on the
east by Conquest Way; on the south by Sykes Drive; on the west by undeveloped land and Timberline
Road. The project site interacts with developments done for ERSF and ERFFMC. The larger ERSF project
is in the Northeast Quarter of Section 8, Township 7 North, Range 68 West in the city of Fort Collins,
County of Larimer, and State of Colorado.
The project site, ±1.25 acres, is currently an undeveloped tract of land that drains into the existing,
southeast F.E.S (referred to herein as the design point), built in the ERSF. It is slightly larger than the
original allocation of 1.071 acres because the project site’s proposed design redirects a portion of the
flow from ERFFMC’s basins (P10) onto our site. The exhibit, page 4, shows the newly delineated basin
(P15) for the project site in green. Basin P15 includes the area from the southern-most part of ERFFMC’s
basins, which are shown as red in the exhibit, page 4.
The approved ERSF drainage report dictated that basin Fut-G2 drains 19 cfs into the design point, as
previously defined. The northern portion of Fut-G2 was developed in ERFFMC, which effectively split
ERSF’s basin Fut-G2, effectively reducing tributary area draining to project site’s design point. In
addition, the ERSF project calculated the runoff coefficients of C2 = 0.90 and C100 = 1.00 in preparation of
the future condition, summarized in Table 1. Galloway calculated new runoff coefficients for the project
site, shown in composite runoff coefficients table on page 3 and summarized in Table 1. The newly
calculated runoff coefficients for Basin P15 are lower than the originally calculated estimates, which
effectively lessens the volume of water seen at the design point. Thus, the original storm drain
infrastructure, from ERSF, is not impacted and the proposed site plan’s drainage patterns are generally
acceptable if the recommendations are followed.
Page 2 of 2
Table 1. | Drainage Basins
Basin ID Area Runoff Coeff. | C2 Runoff Coeff. | C100
Ac
New P15 1.25 0.62 0.78
Original Fut-G2 2.41 0.9 1
If you have questions or require additional information, please call.
Sincerely,
Galloway & Company, Inc.
Jeffrey Ditty, EIT
Civil Engineer
Subdivision:East Ridge Fifth Filing Lot 2 Block 1 -- Mosaic Neighborhood Center Project Name: Mosaic Neighborhood Center
Location:CO, Fort Collins Project No.:
Calculated By: JKD
Checked By: HHF
INPUT User Input Date: 1/20/21
OUTPUT Calculated Value Single-Family Alley-Loaded SF Duplex/AttachedMulti-Family
95%5%100%
C2*1.25
P15 1.25 95 0.54 41 25 0.60 12 100 0.12 9 0.62 0.78
Σ Basins 1.25
C2 C100Area (ac)
Lots (e.g., Single-Family, Alley Loaded)
Runoff
Coefficient
COMPOSITE RUNOFF COEFFICIENTS
Area (ac)Area
Weighted
Asphalt + Concrete Walks Lawns, Heavy Soil: Flat <2%
Area Weighted Runoff Coefficient Area (ac)
HFHLV27
Area
WeightedBasin ID Total Area (ac)
Runoff
Coefficient
Page 1 of 1 1/20/2021
P10
acres
P10
0.60
0.75 0.78
acres
P15
0.62
0.78
1.25
P15
MOSAIC POOL
-
FORT COLLINS, COLORADO
-
CONFORMANCE LETTER - DRAINAGE
HFH000027
JKD
HHF
01/20/2021
Checked By:
Project No:
Drawn By:
Date:
5265 Ronald Reagan Blvd., Suite 210
Johnstown, CO 80534
970.800.3300 •GallowayUS.com