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835 Wood Street Drainage Report
Page 4 of 7
HISTORIC DRAINAGE
The existing site consists of two basins. The runoff from the existing site sheet flows to the north
through concrete pans into the existing detention pond. Flows enter the storm system located in
Wood Street via an existing outlet structure and storm infrastructure located at the south end of the
existing pond.
PROPOSED DRAINAGE
Proposed drainage patterns are to remain generally the same as the current with the exception of
the flows along the northern redeveloped portion of the site being routed to the proposed rain
garden before discharging into the existing detention pond. The bioretention system will be utilized
for low impact development (LID) treatment requirements of the site. With the added
imperviousness area for the project being 0.25 acres and the rain garden being sized to treat 0.63
acres of the contributing area the 75% treatment requirement is exceeded. The bioretention
systems will reduce runoff, treat and slowly release the water quality capture volume as part of the
four step process for the City of Fort Collins criteria on BMP selection. Detention will be
maintained within the existing detention facility.
For the purposes of calculations, the site was divided into 2 basins. Basin P1 includes a portion of
the proposed building addition, portions of repaving, and part of a new concrete drainage pan.
Historically Basin P1 includes the existing drainage facilities for the site. Historical drainage
patterns will be maintained for this basin and flows are considered to be equal to existing
conditions. Basin P2 will include the proposed additional asphalt parking area, a portion of the
proposed building addition, a majority of the repaved area, and a rain garden with its appurtenant
flow conveyance facilities. Flows gathered for treatment in the rain garden will be discharged into
the existing detention pond and follow historical drainage patterns.
There are four downspouts draining into various drainage pans or trench drains. The downspouts
along the southern portion of the proposed addition will drain into the rebuilt concrete pan and
follow historical drainage patterns to the existing pond. An existing downspout along the northern
portion of the existing building and a proposed downspout along the northern section of the
proposed addition will be routed through trench drains into the rain garden to be pretreated before
release into the existing pond.