HomeMy WebLinkAboutVINEYARD / FOSSIL CREEK APARTMENTS (FORMERLY GOLDELM) - OVERALL DEVELOPMENT PLAN - ODP170001 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORT1
Overall Development Plan (ODP) Drainage Report
Date: November 21, 2017
Project: Vineyard/Goldelm ODP
Fossil Creek Apartments
Fort Collins, Colorado
Attn: City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
Ms. Hansen:
This letter report accompanies the submittal for the Fossil Creek Apartments Development Plan
(ODP). Specifically, this letter report serves to document the overall drainage impacts
associated with the proposed development.
The proposed development site is located just north west of the intersection of Crestridge
Street and South College Avenue (State Highway 287) in Fort Collins, Colorado (Please see
Figure 1, below). Fossil Creek Drainageway runs along the north side of the project site, but the
associated City of Fort Collins Flood Zone does not encroach on the project site, as discussed
further below.
The proposed development site is in the City of Fort Collins Fossil Creek Master Basin.
Detention requirements for this basin are to detain the difference between the 100-year
developed inflow rate and the historic 2-year release rate (0.20 cfs per acre for the Fossil Creek
Master Basin).
The City of Fort Collins designated Fossil Creek Flood Zone exists to the north of the project site,
as shown in Figure 2, below. This flood zone is a City-designated floodplain; there is no FEMA
designated flood zone in vicinity of the project site. The proposed project will not involve the
placement of any offsite project improvements within the Fossil Creek Flood Zone; however the
project will require storm outfalls to be constructed within this flood zone. It is anticipated that
pre- and post-construction surveys will need to be performed and show that no placement of
fill has occurred in the floodway.
2
FIGURE 1
Vicinity Map
3
FIGURE 2
City Floodplain Map
(Floodplain shown is a City Designated Flood Zone-No FEMA Flood Zones encroach project site)
Portions of the site are encroached by the Fossil Creek Erosion Buffer. The erosion buffer is
shown on the ODP Drainage Exhibit. No site element will be placed within the erosion buffer,
with the exception of detention pond outfalls. Detention ponds are not allowable within the
erosion buffer, thus, all ponds will be located outside of the buffer. However, detention pond
outfall pipes are unavoidably within the erosion buffer.
The proposed site will drain into on-site detention ponds which will release into the Fossil
Creek, located along both the north and southwest sides of the site. All water quality
treatment requirements and LID requirements will be satisfied with the proposed
development. Means of providing for these requirements will be vetted at the Preliminary and
Final stages of the design process.
4
As shown on the ODP Drainage Exhibit, we propose to provide water quality capture volume for
the adjacent half street of Highway 287 within the eastern portion of the overall site according
to conversation with staff. We have accounted for conveyance of this drainage in the release
rate from future planned ponds conceptually shown on the ODP Drainage Exhibit. Future
design of all ponds shown will conform to release rate criteria for the Fossil Creek Master Basin.
In summary, this Overall Drainage Report letter adequately addresses any potential stormwater
changes associated with the proposed development. In general, there are no significant
changes proposed at a major drainage level. The ODP complies with the governing City of Fort
Collins Master Drainage Plans, and the previously approved drainage plans specific for the
subject property.
Please feel free to contact me with any questions you may have.
Sincerely
NORTHERN ENGINEERING
Aaron Cvar, PhD, PE
Senior Project Engineer