HomeMy WebLinkAboutSALUD FAMILY HEALTH CENTER - ODP - ODP150003 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT1
Overall Development Plan (ODP) Drainage Report
Date: November 13, 2015
Project: Salud
Fort Collins, Colorado
Attn: Mr. Wes Lamarque
Fort Collins Utilities
700 Wood Street
Fort Collins, Colorado 80524
Mr. Lamarque:
This letter report accompanies the submittal for the Salud 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 northeast of the intersection of Laporte Avenue
and Taft Hill Road in Fort Collins, Colorado (Please see Figure 1, below). The project involves
site improvements including parking, roadway, and utilities. The large existing building located
on the project site is planned to remain and to be renovated.
The west Vine Floodplain encroaches a portion of the property as shown in Figure 2, below. A
notable feature of the West Vine floodplain is the spill entering the floodplain in vicinity of the
current project site from the Larimer Canal No. 2 irrigation ditch. Current floodplain mapping
changes are under way by the City of Fort Collins, and we are working with City Stormwater
Utility Staff to incorporate the changes regarding this spill from the Larimer No. 2. A future
submittal to the City involving modeling of the spill from the ditch and grading the project site
to allow for this spill to safely pass along the western perimeter of the site (just west of the
large existing building that is to remain and to be renovated). The West Vine flood zone is a
City-designated floodplain; there is no FEMA designated flood zone in vicinity of the project
site.
The proposed development site is in the City of Fort Collins West Vine 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. However, due to site constraints, the proposed
drainage concept for the site is to place an interim pumped detention pond in the area shown
on the ODP Drainage Exhibit. This pond is to be located so that in the future a gravity tie-in to a
future City of Fort Collins Regional Pond, which is anticipated to be constructed just northwest
of the project site. A rough anticipated construction date for this pond is the year 2025. In the
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interim period, the onsite detention pond will be pumped. The pump will be sized to discharge
at a rate that adequately evacuate all storm runoff from the pond to meet State of Colorado
revised Statute 37-92-602(8). This states that 97% of all the stormwater runoff from a 5-year or
less event be released within 72 hours of the storm event, and 99% of all of the stormwater
runoff from greater than a 5-year event be released within 120 hours of the storm event.
Calculations will be provided at Preliminary and Final stages of the design process to show
proper pump sizing meeting these criteria. Additionally, the pumped detention pond will be
required to obtain a variance from the City, as pumped detention is not allowed per the Fort
Collins Stormwater Criteria Manual.
FIGURE 1
Vicinity Map
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FIGURE 2
City Floodplain Map
(Floodplain shown is a City Designated Flood Zone-No FEMA Flood Zones encroach project site)
Developed runoff from the southern portion of the project site, as shown on the ODP Drainage
Exhibit, will be detained and released into the Larimer Canal No. 2 irrigation ditch at a historic
2-year rate. There is an area of the Laporte Avenue frontage that has historically drained into
Laporte Avenue. This area is composed of an existing parking lot as well as landscaped areas.
We will maintain historic runoff rates from this area and ensure no increase in runoff going into
Laporte Avenue.
All water quality treatment requirements and LID requirements will be satisfied with the
proposed development. Means of providing for these requirements will be worked through at
the Preliminary and Final stages of the design process.
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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