HomeMy WebLinkAboutFISCHER PROPERTIES - FDP230010 - DOCUMENT MARKUPS - ROUND 1 - DRAINAGE REPORT
PRELIMINARY DRAINAGE REPORT
FISCHER PROPERTIES
FORT COLLINS, COLORADO
OCTOBER 19, 2022
NORTHERNENGINEERING.COM
970.221.4158
FORT COLLINS
GREELEY
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NORTHERNENGINEERING.COM |
970.221.4158
FORT COLLINS | GREELEY
PRELIMINARY DRAINAGE REPORT: FISCHER PROPERTIES
10 | 11
Sub-Basins OS-4
Sub-Basins OS- is an offsite basin containing existing single-family residential lots. Stormwater runoff
from this basin will be routed through Basins 200. The underground stormtech chambers will provide
LID treatment for this basin. 100-year stormwater runoff from this basin will be routed through Basins
300 and 200 to Westward Drive and ultimately Shields Street. This is the historic drainage path for this
basin. No detention is provided for this basin with this project.
Rational Flow Summary | Developed Basin Flow Rates
BASIN
TOTAL
AREA
(acres)
Tc2
(min)
Tc100
(min)
C2 C100 Q2
(cfs)
Q100
(cfs)
100 0.60 5.3 5.3 0.64 0.80 1.10 4.80
200 1.83 5.0 5.0 0.83 1.00 4.33 18.20
300 1.17 6.7 6.7 0.54 0.68 1.63 7.12
301 0.96 5.0 5.0 0.68 0.85 1.86 8.13
302 0.52 5.0 5.0 0.59 0.74 0.87 3.79
OF-1 0.23 7.2 7.2 0.33 0.41 0.19 0.82
OF-2 0.04 5.0 5.0 0.70 0.88 0.08 0.36
OS-1 0.13 5.0 5.0 0.81 1.00 0.31 1.32
OS-2 0.52 10.8 10.8 0.44 0.55 0.49 2.16
OS-3 0.40 8.1 8.1 0.43 0.54 0.41 1.79
OS-4 0.93 10.1 10.1 0.33 0.41 0.68 2.95
Table 2 – Proposed Rational Summary
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of this report.
C. LID AND WATER QUALITY
Water Quality Concept
1. Stormwater runoff from this site is proposed to be treated through a combination of rain garden,
underground chambers and traditional Water Quality.
2. This site is required to treat 100% of the site through an approved water quality measure. Due to
site constraints stated previously, Basins OF-1 and OF-2 are unable to be captured and treated for
water quality. In order to meet the water quality requirement, the existing impervious area of off-
site basins OS-2 and OS-4 are proposed to be treated in exchange.
Rain Gardens/Underground Chambers
3. Rain Garden A provides Low Impact Development (LID) for Basins 301, 302 and OS-2. This rain
garden was sized to provide 120% of the calculated 12-hour volume.
4. Stormtech Underground Chambers provides Low Impact Development (LID) for Basins 200 and OS-
4. This underground chamber system was sized to provide 120% of the calculated 12-hour volume.
5. An overflow weir will be provided both in the rain garden and underground chambers to pass
storms greater than the WQCV to their respective detention ponds.
6. The site is required to treat 75% of new impervious area with LID treatment. Due to site constraints
stated previously, Basins OF-1 and OF-2 are unable to be captured and treated for water quality. In
order to meet the water quality requirement, the existing impervious area of off-site basins OS-2
and OS-4 are proposed to be treated in exchange. This site treats 72.4% of the on-site impervious
areas with by LID and an additional 10,721 ft2 of offsite area for an effective percent of impervious
area treated of 79.91%.
7.
CHARACTER OF SURFACE1:
Percentage
Impervious
2-yr Runoff
Coefficient
10-yr Runoff
Coefficient
100-yr Runoff
Coefficient
Developed
Asphalt .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………100%0.95 0.95 1.00
Concrete .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………100%0.95 0.95 1.00
Rooftop .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………90%0.95 0.95 1.00
Gravel .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………40%0.50 0.50 0.63
Pavers .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………40%0.50 0.50 0.63
Residential (Low Density).…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………50%0.55 0.55 0.69
Landscape or Pervious Surface
Playgrounds .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………25%0.35 0.35 0.44
Lawns Clayey Soil .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………2%0.25 0.25 0.31
Lawns Sandy Soil .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………2%0.15 0.15 0.19
Notes:
Basin ID Basin Area
(ac)
Area of
Asphalt/Con
crete
(ac)
Area of
Concrete
(ac)
Area of
Rooftop
(ac)
Area of Single
Family (ac)
Area of
Gravel
(ac)
Area of
Pavers
(ac)
Area of
Playgrounds
(ac)
Area of Lawns
(ac)
Composite
% Imperv.
2-year
Composite Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
H1 2.742 0.00 0.06 0.26 0.28 0.00 0.00 2.49 17% 0.39 0.39 0.46
H2 2.653 0.00 0.00 0.00 0.00 0.00 0.00 2.65 2% 0.25 0.25 0.31
OS-1 0.133 0.105 0.03 80% 0.81 0.81 0.86
OS-2 0.518 0.141 0.38 26% 0.44 0.44 0.50
OS-3 0.397 0.00 0.097 0.30 25% 0.43 0.43 0.49
OS-4 0.928 0.01 0.095 0.82 12% 0.33 0.33 0.39
EXISTING CONDITION BASIN % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
2) Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Chapter 3. Table 3.2-1 and 3.2-2
1) Percentage impervious taken from the Fort Collins Stormwater Criteria Manual, Chapter 5, Table 4.1-2 and Table 4.1-3
Offsite Basins