HomeMy WebLinkAboutHOMESTEAD AT CLARENDON HILLS - PDP190007 - DOCUMENT MARKUPS - ROUND 3 - DRAINAGE REPORTFebruary 14, 2020
DRAINAGE LETTER AND LID REPORT
HOMESTEAD AT CLARENDON HILLS
Fort Collins, Colorado
Prepared for:
Kenneth R. Mitchell
Mosaic Real Estate LLC
1021 Nightingale Drive
Fort Collins, Colorado. 80525
Prepared by:
301 North Mason Street, Suite 100
Fort Collins, Colorado 80524
Phone: 970.221.4158
www.northernengineering.com
Project Number: 1013-008
Page | 4
• The drainage report for Clarendon Hills 4th Filing assumed a runoff coefficient C=0.25 for the
church site, and the church site was subsequently part of a land swap for the northwest corner
of the Clarendon Hills Subdivision.
Detention
Assuming a historic runoff coefficient of 0.25, detention from Basin B was accounted for in the original
Clarendon Hills drainage report provided the overall flow at Design Point B does not exceed 1.9 cfs.
Because of the increased impervious area within Basin B, a detention is required within Basin B2 to
reduce the post-developed flow rates at Design Point to equal or less than 1.9 cfs. Since Basins B1, B3,
and B4 will be released into the surrounding curb and gutter undetained, the detention pond in Basin
B2 is designed to release the 100-year event at 0.24 cfs. A release rate of 0.24 cfs is required to maintain
a 100-year flow rate of 1.9 cfs at Design Point B.
Inlets
By limiting the 100-year flowrate at Design Point B, the flowrate at the existing inlets will match or
decrease from the projected flowrates in the previously approved Clarendon Hills drainage reports.
This results in matching or decreasing runoff to the existing inlets that were designed and approved
with the earlier project, so no additional inlet calculations have been provided as a part of this report.
Water Quality/LID Conformance
City LID requirements specify that 50% of all single-family areas receive water quality treatment from
a LID facility. This project proposes to treat at least 50% of the new impervious areas through two rain
gardens on either side of the detention pond. The rain gardens will also provide water quality
treatment for the project site. Furthermore, there will be a vegetated buffer between the rear lot lines
and the irrigation ditch.
Although exact impervious area is unavailable at this preliminary stage, a majority of the lots area will
drain towards the rain gardens or across the vegetated buffer. The front 2/3rds of the lot will graded
to drain south towards the rain gardens. A LID Treatment Exhibit is provided with this report details
treatment area and method.
Erosion and Sediment Control
During construction, the Contractor will follow the appropriate and applicable City of Fort Collins
standards for erosion and sediment control. Since more than 10,000 sf will be disturbed as a part of
this project, a comprehensive Stormwater Management Plan will be prepared for this project at final
design. Post construction water quality and erosion control will be achieved by a fully established and
stabilized site. All areas disturbed during construction will receive permanent hardscape, landscape,
or building structure.
Floodplains
There are no regulatory floodplains associated with the project.
Conclusions
The proposed grading concept matches the original drainage patterns. The site matches or decreases
the designed imperviousness draining to the existing Clarendon Hills curb and gutter. Onsite
Project:
Calculations By:
Date:
C2*Cf C10*Cf C100*Cf
Length
(ft)
Elev
Up
Elev
Down
Slope
(%)
Ti
2-Yr
(min)
Ti
10-Yr
(min)
Ti
100-Yr
(min)
Length
(ft)
Elev
Up
Elev
Down
Slope
(%)
Velocity
(ft/s)
Tt
(min)
Length
(ft)
Elev
Up
Elev
Down
Slope
(%)
Velocity
(ft/s)
Tt
(min)
Tc
2-Yr
(min)
Tc
10-Yr
(min)
Tc
100-Yr
(min)
ex a EX A 0.25 0.25 0.31 65 93.83 88.55 8.12% 6.4 6.4 5.9 N/A N/A N/A 665 88.55 85.49 0.46% 0.10 108.93 14.06 14.06 114.83
ex b EX B 0.25 0.25 0.31 30 93.00 91.75 4.17% 5.4 5.4 5.0 340 91.75 84.93 2.01 2.83 2.00 N/A N/A N/A 7.41 7.41 7.01
ex os1 EX OS1 0.25 0.25 0.31 195 93.00 86.13 3.52% 14.6 14.6 13.5 N/A N/A N/A N/A N/A N/A 11.08 11.08 13.51
ex os2 EX OS2 0.25 0.25 0.31 45 92.23 88.81 7.60% 5.4 5.4 5.0 N/A N/A N/A N/A N/A N/A 5.42 5.42 5.02
ex a North 0.25 0.25 0.31 65 93.83 88.55 8.12% 6.4 6.4 5.9 N/A N/A N/A 665 88.55 85.49 0.46% 0.10 108.93 14.06 14.06 114.83
Overland Flow, Time of Concentration:
Tc2 Tc10 Tc100 C2 C10 C100
I2
(in/hr)
I10
(in/hr)
I100
(in/hr)
Q2
(cfs)
Q10
(cfs)
Q100
(cfs)
ex a EX A 2.382 14.06 14.06 114.83 0.25 0.25 0.31 1.92 3.29 6.71 1.1 2.0 5.0
ex b EX B 0.684 7.41 7.41 7.01 0.25 0.25 0.31 2.52 4.31 8.80 0.4 0.7 1.9
ex os1 EX OS1 0.147 11.08 11.08 13.51 0.25 0.25 0.31 2.13 3.63 7.42 0.1 0.1 0.3
ex os2 EX OS2 0.064 5.42 5.42 5.02 0.25 0.25 0.31 2.85 4.87 9.95 0.0 0.1 0.2
ex a North 2.594 14.06 14.06 114.83 0.25 0.25 0.31 1.92 3.29 6.71 1.2 2.1 5.4
Combined and Routed Basins
HISTORIC DIRECT RUNOFF COMPUTATIONS
Intensity Flow
Overland Flow, Time of Concentration:
Intensity, I from Fig. RA-2
Rational Equation: Q = CiA (Equation 6-1 per MHFD)
Design
Point
Basin
Area
(acres)
Tc (Min) Runoff C
Tt = L / 60V (Equation 6-4 per MHFD)
Tc = Ti + Tt (Equation 6-2 per MHFD)
Velocity (Gutter Flow), V = 20·S½
Velocity (Swale Flow), V = 15·S½
Homestead at Clarendon
F. Wegert
February 14, 2020
Project:
Gutter/Swale Flow, Time of Concentration: Calculations By:
Date:
(Equation 6-4 per MHFD)
(Equation 6-3 per MHFD)
}
𝑇𝑖 =
1.87 1.1 − 𝐶 ∗ 𝐶𝑓 𝐿
𝑆 ൗ
1
3
Page 1 of 1
Character of Surface
Runoff
Coefficient1
Percent
Impervious1
0.95 100%
0.95 90%
0.50 40%
0.55 50%
0.20 2%
0.25 2%
Basin ID
Basin Area
(sq.ft.)
Basin Area
(acres)
Asphalt,
Concrete (acres)
Rooftop (acres) Gravel (acres)
Residential: Low
Density (acres)
Undeveloped:
Greenbelts,
Agriculture
(acres)
Lawns, Clayey
Soil, Avg Slope 2-
7% (acres)
Percent
Impervious
C2*Cf
Cf = 1.00
C5*Cf
Cf = 1.00
C10*Cf
Cf = 1.00
C100*Cf
Cf = 1.25
A 69,082 1.586 0.000 0.000 0.000 0.000 1.194 0.392 2% 0.21 0.21 0.21 0.27
B1 6,956 0.160 0.000 0.000 0.000 0.119 0.041 0.000 38% 0.46 0.46 0.46 0.58
B2 50,820 1.167 0.081 0.000 0.000 0.825 0.000 0.261 43% 0.51 0.51 0.51 0.64
B3 4,484 0.103 0.000 0.000 0.000 0.096 0.007 0.000 47% 0.53 0.53 0.53 0.66
B4 3,524 0.081 2% 0.25 0.25 0.25 0.31
OS1 5,126 0.118 0.000 0.000 0.000 0.000 0.078 0.039 2% 0.22 0.22 0.22 0.27
OS2 2,806 0.064 2% 0.25 0.25 0.25 0.31
North 77,013 1.768 0.000 0.000 0.000 0.000 1.337 0.431 2% 0.21 0.21 0.21 0.27
South 65,784 1.510 0.081 0.000 0.000 1.039 0.129 0.261 40% 0.49 0.49 0.49 0.61
DEVELOPED RUNOFF COEFFICIENT CALCULATIONS
Asphalt, Concrete
Rooftop
Gravel
Residential: Low Density
Homestead at Clarendon
F. Wegert
February 14, 2020
Project:
Calculations By:
Date:
Undeveloped: Greenbelts, Agriculture Composite Runoff Coefficient2
1) Runoff coefficients per Tables 3.2-1 & 3.2 of the FCSM. Percent impervious per Tables 4.1-2 & 4.1-3 of the FCSM.
Project:
Calculations By:
Date:
C2*Cf C10*Cf C100*Cf
Length
(ft)
Elev
Up
Elev
Down
Slope
(%)
Ti
2-Yr
(min)
Ti
10-Yr
(min)
Ti
100-Yr
(min)
Length
(ft)
Elev
Up
Elev
Down
Slope
(%)
Velocity
(ft/s)
Tt
(min)
Length
(ft)
Elev
Up
Elev
Down
Slope
(%)
Velocity
(ft/s)
Tt
(min)
Tc
2-Yr
(min)
Tc
10-Yr
(min)
Tc
100-Yr
(min)
a A 0.21 0.21 0.27 65 93.83 88.55 8.12% 6.7 6.7 6.3 N/A N/A N/A 665 88.55 85.49 0.46% 0.10 108.93 14.06 14.06 115.18
b B1 0.46 0.46 0.58 65 93.97 92.33 2.52% 7.1 7.1 5.8 326 92.33 84.93 2.27 3.01 1.80 N/A N/A N/A 8.88 8.88 7.61
b B2 0.51 0.51 0.64 71 93.92 92.50 2.00% 7.4 7.4 5.8 350 92.50 84.93 2.16 2.94 1.98 N/A N/A N/A 9.35 9.35 7.76
b B3 0.53 0.53 0.66 70 92.85 91.65 1.71% 7.5 7.5 5.8 305 91.65 84.93 2.20 2.97 1.71 N/A N/A N/A 9.22 9.22 7.50
b B4 0.25 0.25 0.31 20 91.89 90.41 7.40% 3.6 3.6 3.4 167 90.41 84.93 3.28 3.62 0.77 N/A N/A N/A 5.00 5.00 5.00
os1 OS1 0.22 0.22 0.27 172 93.83 86.13 4.48% 13.1 13.1 12.3 N/A N/A N/A N/A N/A N/A 10.96 10.96 12.34
Tc2 Tc10 Tc100 C2 C10 C100
I2
(in/hr)
I10
(in/hr)
I100
(in/hr)
Q2
(cfs)
Q10
(cfs)
Q100
(cfs)
a A 1.586 14.06 14.06 115.18 0.21 0.21 0.27 1.92 3.29 6.71 0.6 1.1 2.8
b B1 0.160 8.88 8.88 7.61 0.46 0.46 0.58 2.35 4.02 8.21 0.2 0.3 0.8
b B2 1.167 9.35 9.35 7.76 0.51 0.51 0.64 2.30 3.93 8.03 1.4 2.3 6.0
b B3 0.103 9.22 9.22 7.50 0.53 0.53 0.66 2.30 3.93 8.03 0.1 0.2 0.5
b B4 0.081 5.00 5.00 5.00 0.25 0.25 0.31 2.85 4.87 9.95 0.1 0.1 0.3
os1 OS1 0.118 10.96 10.96 12.34 0.22 0.22 0.27 2.17 3.71 7.57 0.1 0.1 0.2
os2 OS2 0.064 5.13 5.13 5.00 0.25 0.25 0.31 2.85 4.87 9.95 0.0 0.1 0.2
a North 1.768 14.06 14.06 115.19 0.21 0.21 0.27 1.92 3.29 6.71 0.7 1.2 3.1
b South 1.510 9.62 9.62 8.08 0.49 0.49 0.61 2.26 3.86 7.88 1.7 2.9 7.3
Combined and Routed Basins
DEVELOPED DIRECT RUNOFF COMPUTATIONS
Intensity Flow
Overland Flow, Time of Concentration:
Intensity, I from Fig. RA-2
Rational Equation: Q = CiA (Equation 6-1 per MHFD)
Design
Point
Basin
Area
(acres)
Tc (Min) Runoff C
Tt = L / 60V (Equation 6-4 per MHFD)
Tc = Ti + Tt (Equation 6-2 per MHFD)
Velocity (Gutter Flow), V = 20·S½
Velocity (Swale Flow), V = 15·S½
Gutter/Swale Flow, Time of Concentration:
Project:
Calculations By:
Date:
Homestead at Clarendon
F. Wegert
February 14, 2020
(Equation 6-4 per MHFD)
(Equation 6-3 per MHFD)
}
𝑇𝑖 =
1.87 1.1 − 𝐶 ∗ 𝐶𝑓 𝐿
𝑆 ൗ
1
3
Page 1 of 1
Project:
Calc. By:
Date:
1.586 acres
0.6 cfs
2.0% per City of Fort Collins SWCM
5.0% per City of Fort Collins SWCM
10.0% per City of Fort Collins SWCM
2.5%
8.3%
14 ft per City of Fort Collins SWCM
14 ft to 48 ft
25 ft
14 ft to 52 ft
42 ft
17,060 ft2
23,160 ft2
1.36
Max. Allowable Cross-Slope for LID
Max. Allowable Cross-Slope
VEGETATED BUFFER
Basin A
Design Data & Analysis
Vegetated Buffer Area
Run-on Ratio
Homestead at Clarendon
F. Wegert
February 14, 2020
Basin Area
Design Width (S <= 10.0%)
Average Design Width (S <= 10.0%)
Min. Design Cross-Slope (Smin)
Max. Design Cross-Slope (Smax)
Min. Allowable Width
Design Width (S <= 5.0%)
Average Design Width (S <= 5.0%)
Treatment Area
Design Discharge
Min. Allowable Cross-Slope
Note:
Existing coverage consists of well established native grasses with over 95% coverage. As much existing
vegetation and grading will be preserved as feasibly possible. Disturbed areas within vegetated buffer
will occur along rear lot lines, and this work is necessary to daylight lot grades into existing topography.
Any disturbed areas will be replaced with a native grass seed mixture and landscaping in accordance
with the erosion control and landscaping plans.
Average slopes are around 2.5% towards the south and east and gradually get steeper towards the north
and west. An existing irrigation ditch along the north edge of the grass buffer impacts the slopes along
the north edge of the grass buffer. The steeper slopes, greater than 5.0%, are generally along the
irrigation ditch.
Some minor grading will be required in the grass buffer to daylight proposed lawn grades into existing
grades. However, any disturbed areas within the grass buffer will be revegetated per the erosion control
VAULT
ELEC
E ELEC
E
VAULT
ELEC
CONTROL
IRR
CONTROL
IRR
CONTROL
IRCRONTROL
IRR
CONTROL
IRR
CONTROL
IRR CONTROL
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CLARENDON HILLS DRIVE
LANGDALE DRIVE
VEGETATED BUFFER
TOTAL TREATMENT AREA: 17,060 SF
RAIN GARDEN
TOTAL TREATMENT AREA: 53,025 SF
RAIN GARDEN
TOTAL TREATMENT AREA: 53,025 SF
HOMESTEAD AT CLARENDON HILLS
SHEET NO:
P:\1013-008\DWG\DRNG\1013-008_LID.DWG
301 N. Howes Street, Suite 100
Fort Collins, Colorado 80521
E NGINEER ING
N O R T H E RN
PHONE: 970.221.4158
www.northernengineering.com
DRAWING REFERENCE:
LID TREATMENT EXHIBIT F. Wegert
1 in = 60 ft
February 14, 2020 LID-1
DRAWN BY:
SCALE:
ISSUED:
( IN FEET )
0
1 INCH = 60 FEET
60 60
LEGEND
RAIN GARDEN TREATMENT AREA
VEGETATED BUFFER
VEGETATED BUFFER
TREATMENT AREA
HOMESTEAD AT CLARENDON HILLS ON-SITE LID TREATMENT
Project Summary
Total Developed Site Area 82,469 sf
Target Treatment Percentage 50%
Minimum Area to be Treated by LID
measures 41,234.50
sf
Treatment Area
Vegetated Buffer Treatment Area 17,060 sf
Rain Garden Treatment Area 53,025 sf
Total Treatment Area 70,085 sf
Percent Total Project Area Treated 85.0%
UNTREATED AREA
NOTES:
1. EXCEPT FOR LOTS 1 AND 8, UNTREATED AREA CONSISTS
OF LANDSCAPING AND LAWNS.
2. RAIN GARDEN TREATMENT AREA CONSISTS OF
APPROXIMATELY SOUTH 2
3 OF LOT, ROOFS, DRIVEWAYS,
AND SHARED DRIVEWAY FOR LOTS 2 - 7.
3. APPROXIMATELY NORTH 1
3 OF LOTS WILL DRAIN TOWARDS
VEGETATED BUFFER AREA BETWEEN REAR LOT LINES AND
IRRIGATION DITCH.
os2 OS2 0.25 0.25 0.31 45 92.85 88.81 8.98% 5.1 5.1 4.8 N/A N/A N/A N/A N/A N/A 5.13 5.13 5.00
a North 0.21 0.21 0.27 65 93.83 88.55 8.12% 6.7 6.7 6.3 N/A N/A N/A 665 88.55 85.49 0.46% 0.10 108.93 14.06 14.06 115.19
b South 0.49 0.49 0.61 71 93.92 92.50 2.00% 7.6 7.6 6.1 350 92.50 84.93 2.16 2.94 1.98 N/A N/A N/A 9.62 9.62 8.08
Gutter/Swale Flow, Time of Concentration:
Combined and Routed Basins
Intensity, i (per Table 3.4-1 of the Fort Collins Stormwater Manual)
Velocity (Gutter Flow), V = 20·S½
Velocity (Swale Flow), V = 15·S½
Rational Equation: Q = CiA (Equation 6-1 per MHFD)
Overland Flow, Time of Concentration:
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Channelized Flow Swale Flow
Design
Point
Basin(s)
Tt = L / 60V (Equation 6-4 per MHFD)
Tc = Ti + Tt (Equation 6-2 per MHFD)
Overland Flow Time of Concentration
Homestead at Clarendon
F. Wegert
February 14, 2020
(Equation 6-4 per MHFD)
(Equation 3.3-2 per Fort Collins
Stormwater Manual)
}
𝑇𝑖 =
1.87 1.1 − 𝐶 ∗ 𝐶𝑓 𝐿
𝑆 ൗ
1
3
Page 1 of 1
Lawns, Clayey Soil > 7%: C = 0.35, Percent Impervious = 2%
Combined and Routed Basins
2) Composite Runoff Coefficient adjusted per Table 3.2-3 of the Fort Collins
Stormwater Manual (FCSM).
Lawns, Clayey Soil, Avg Slope 2-7%
Open Space (undeveloped): C = 0.25, Percent Impervious = 2%
USDA SOIL TYPE: B
Page 1 of 1
HISTORIC TIME OF CONCENTRATION COMPUTATIONS
Channelized Flow Swale Flow
Design
Point
Basin(s)
Tt = L / 60V (Equation 6-4 per MHFD)
Tc = Ti + Tt (Equation 6-2 per MHFD)
Overland Flow Time of Concentration
Homestead at Clarendon
F. Wegert
February 14, 2020
Gutter/Swale Flow, Time of Concentration:
Combined and Routed Basins
Intensity, i (per Table 3.4-1 of the Fort Collins Stormwater Manual)
Velocity (Gutter Flow), V = 20·S½
Velocity (Swale Flow), V = 15·S½
Rational Equation: Q = CiA (Equation 6-1 per MHFD)
(Equation 6-4 per MHFD)
(Equation 3.3-2 per Fort Collins
Stormwater Manual)
}
𝑇𝑖 =
1.87 1.1 − 𝐶 ∗ 𝐶𝑓 𝐿
𝑆 ൗ
1
3
Page 1 of 1