HomeMy WebLinkAbout301 PARKER STREET - TWO FAMILY - FDP210026 - DOCUMENT MARKUPS - ROUND 3 - DRAINAGE REPORT
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FORT COLLINS | GREELEY 1 | 2
DATE: December 22, 2021
PROJECT: 301 Parker Street
Fort Collins, Colorado
PROJECT NO. 1892-001
ATTENTION: Stormwater Staff
City of Fort Collins Stormwater
700 Wood Street
Fort Collins, CO 80521
Stormwater Staff
This letter serves to document the proposed drainage impacts for improvements at 301 Parker Street in Fort
Collins, Colorado. The site is in the Old Prospect Neighborhood, and it is bounded by Parker Street to the north,
an unpaved alley to the south, and single-family homes to the east and west. The project site is Lot 8 and a
portion of Lot 9, Block 1, Alpert Subdivision.
Project Overview
The proposed project is to replace a single-family home with a duplex with walkways and a gravel parking lot in
the back. Walkways towards the front of the lot will be concrete. Walkways towards the rear of the lot will be
crusher fines. The developer proposed to keep an existing honey locus tree on the property.
Existing Site/Drainage
The existing site functions as a “B” lot, with runoff first sheet flowing out from the home to the side lot lines,
which then convey the drainage to both the front and back of the lot. Existing grades in the front yard range
between 4% to 15%, and the grades in the back of the rear yard vary between 0.5% to 3.0%. There are some
small steep areas of 5:1 to 4:1 slope in the southwest corner of the lot, along the alley. In addition to the existing
home, the existing lot consists of a gravel driveway in the front and a detached shed in the rear. There is a 2.5’
wide concrete path from the gravel driveway to the existing home, and some bare spots around the detached
shed. The remainder of the site is Kentucky Bluegrass lawn with several mature trees. The alley is bare dirt with
the flowline in the center conveying runoff west towards the Mathews Street curb and gutter.
The total existing impervious area for the lot is 1,319 square feet.
Proposed Site/Drainage
The proposed site will continue to function as a “B” lot, with drainage from the new duplex being directed to the
side lot lines, then to both the front and back of the via swales. A swale along the west lot line is proposed to
collect and convey drainage to the front and rear without impacting the neighboring properties. Because of the
flat grades, a valley pan and curb along the southeast quarter of the lot is provided along the east lot line to
convey stormwater to the alley. The curb is required to protect the neighbor’s garage along the east property
line.
The total proposed impervious area for the lot is 2,205 square feet. This is a net increase of 887 square feet.
There will be an increase of 0.04 cfs and 0.16 cfs during the 2-Year and 100-Year storm events respectively within
the Parker Street curb and gutter from the increased impervious area. There will be an increase of 0.02 cfs and
0.06 cfs during the 2-Year and 100-Year storm events respectively within the alley from the increased impervious
area. The additional 0.06 cfs results in a negligible increase of the flowrate and flow depth within the alley.
NORTHERNENGINEERING.COM | 970.221.4158
FORT COLLINS | GREELEY 2 | 2
Basin Existing Flowrate (cfs) Proposed Flowrate (cfs) Net Increase (cfs)
2-Year 100-Year 2-Year 100-Year 2-Year 100-Year
Front 0.05 0.21 0.09 0.37 0.04 0.16
Rear 0.11 0.52 0.13 0.58 0.02 0.06
Detention
According to Fort Collins Stormwater requirements, an increase of less than 1,000 square feet are not required
to provide detention, water quality, and LID improvements. The attached exhibit documents the existing vs.
proposed impervious areas for the site.
Water Quality
Water quality for the site is being provided by releasing concentrated flows from the roof into landscaped areas
allowing stormwater to infiltrate into the surrounding soils. Stormwater unable to infiltrate is slowly passed
through vegetated areas, further removing stormwater contaminates before leaving the property.
Erosion and Sediment Control
During construction, the contractor will follow the appropriate and applicable Fort Collins standards for erosion
and sediment control. Even though the project will disturb less than 10,000 square feet, the contractor will be
required to sweep and maintain the site to prevent dirt, saw cuttings, concrete wash, trash and debris,
landscape materials and other pollutants from leaving the site. City inspectors may require the installation of
erosion and sediment control measures dependent on site inspections or neighbor complaints.
Floodplains
There are no regulatory floodplains associated with the project.
Conclusions
The proposed grading concept closely matches the original drainage patterns and comply with the City of Fort
Collins Stormwater Manual. There will be no adverse impacts to downstream properties and City of Fort Collins
infrastructure from the proposed improvements for 301 Parker Street.
Please feel free to contact me if you have any questions.
Sincerely,
NORTHERN ENGINEERING SERVICE, INC.
Frederick S. Wegert, PE
Project Engineer
Project Number:1892-001 Calc. By:F. Wegert
Project Name:301 Parker St Date:December 22, 2021
Project Location:Fort Collins, Colorado
Description Surface Area (ft2)Percent Impervious Impervious Area (ft2)
Rooftop 896 100%896
Concrete 109 100%109
Asphalt 0 100%0
Pavers 0 40%0
Gravel 784 40%314
Landscaping 5,072 0%0
Total 6,861 19%1,319
Description Surface Area (ft2)Percent Impervious Impervious Area (ft2)
Rooftop 1,472 100%1,472
Concrete 437 100%437
Asphalt 0 100%0
Pavers 0 40%0
Gravel 741 40%296
Landscaping 4,211 0%0
Total 6,861 32%2,205
887
IMPERVIOUS AREA CALCULATIONS
Historic Impervious Areas
Developed Impervious Areas
Net Increase in Impervious Area
NORTHERNENGINEERING.COM | 970.221.4158
FORT COLLINS | GREELEY
XW
T
X X
XX XXXXXXXXXVAULT
ELEC
X X XW
T XXXXXXXXVAULT
ELEC
X X
ROOFTOP
CONCRETE
ASPHALT
PAVERS
SURFACE
AREA (SF)% IMPERV.IMPERV.
AREA (SF)
896
109
0
0
100%
100%
100%
40%
TOTALS 6,861 1,319TOTAL=
ROOFTOP
CONCRETE
PAVERS
GRAVEL
SURFACE
AREA (SF)% IMPERV.IMPERV.
AREA (SF)
TOTALS 6,861 2,205TOTAL=
EXISTING PROPOSED
P:\1892-001\DWG\DRNG\1892-001_IMPV.DWG301 PARKER STREET
FORT COLLINS
COLORADO
Fort Collins: 301 N. Howes St., Ste. 100, 80521
Greeley: 820 8th Street, 80631
E N G I N E E R N GI
EHTRON R N
PHONE: 970.221.4158
www.northernengineering.com
DESCRIPTION
EXISTING VS. PROPOSED
IMPERVIOUS AREA - BASIN B1
DRAWN BY
F. WEGERT
DATE
DEC 22, 2021
PROJECT
1892-001
DR-A1
DRAWINGSCALE
1"=20'
LANDSCAPE
GRAVEL 784 40%314
LANDSCAPE 5,072 0%0
ASPHALT
896
109
0
0
1,472
437
0
0
100%
100%
100%
40%
741 40%296
4,211 0%0
1,472
437
0
0
TOTAL PERCENT IMPERVIOUS = 19%TOTAL PERCENT IMPERVIOUS = 32%
Runoff Coefficient1
Percent
Impervious1 Project:
Location:
0.95 100%Calc. By:
0.95 90%Date:
0.50 40%
0.50 40%
0.20 2%
0.20 2%
Basin ID Basin Area
(sq.ft.)
Basin Area
(acres)
Asphalt, Concrete
(sq.ft.)Rooftop (sq.ft.)Gravel (sq.ft.)Pavers (sq.ft.)
Undeveloped:
Greenbelts,
Agriculture (sq.ft.)
Lawns, Clayey Soil,
Flat Slope < 2%
(sq.ft.)
Percent
Impervious
C2*Cf
Cf = 1.00
C5*Cf
Cf = 1.00
C10*Cf
Cf = 1.00
C100*Cf
Cf = 1.25
Front 2,773 0.06 1.43 0.00 691.53 0.00 0.00 2,080.33 12%0.28 0.28 0.28 0.34
Rear 4,088 0.09 108.07 896.17 91.99 0.00 0.00 2,991.49 40%0.50 0.50 0.50 0.63
Total 6,861 0.16 109.50 896.17 783.52 0.00 0.00 5,071.82 40%0.50 0.50 0.50 0.63
2) Composite Runoff Coefficient adjusted per Table 3.2-3 of the Fort Collins
Stormwater Manual (FCSM).
Lawns, Clayey Soil, Flat Slope < 2%
USDA SOIL TYPE: C
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.
Combined Basins
EXISTING RUNOFF COEFFICIENT CALCULATIONS
Asphalt, Concrete
Rooftop
Gravel
Pavers
Streets, Parking Lots, Roofs, Alleys, and Drives:
Character of Surface:301 Parker Street
Fort Collins
F. Wegert
December 22, 2021
Lawns and Landscaping:
Page 1 of 3
Where:
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
(%)Surface n
Flow
Area3
(sq.ft.)
WP3 (ft)R (ft)V
(ft/s)
Tt
(min)
Max.
Tc
(min)
Comp.
Tc 2-Yr
(min)
Tc
2-Yr
(min)
Comp.
Tc 10-Yr
(min)
Tc
10-Yr
(min)
Comp.
Tc 100-
Yr
(min)
Tc
100-Yr
(min)
front Front 57 90.80 87.00 6.67%6.19 6.19 5.67 N/A Swale (8:1)0.04 8.00 16.12 N/A N/A 0.00 10.32 6.19 6.19 6.19 6.19 5.67 5.67
rear Rear 50 90.80 90.40 0.80%8.55 8.55 6.77 61 90.40 89.40 1.64%Swale (8:1)0.04 8.00 16.12 0.50 3.42 0.30 10.62 8.84 8.84 8.84 8.84 7.06 7.06
Notes
S = Longitudinal Slope, feet/feet
R = Hydraulic Radius (feet)
n = Roughness Coefficient
V = Velocity (ft/sec)WP = Wetted Perimeter (ft)
EXISTING TIME OF CONCENTRATION COMPUTATIONS
Location:
Maximum Tc:Overland Flow, Time of Concentration:
Channelized Flow, Velocity:Channelized Flow, Time of Concentration:
301 Parker Street
Fort Collins
F. Wegert
December 22, 2021
Project:
Calculations By:
Date:
Design
Point Basin ID
Overland Flow Channelized Flow Time of Concentration
(Equation 3.3-2 per Fort Collins Stormwater Manual)𝑅𝑖=1.87 1.1 −𝐶∗𝐶𝑓𝐿
𝑅ൗ13
𝑉=1.49
𝑛∗𝑅2/3 ∗𝑅(Equation 5-4 per Fort Collins Stormwater Manual)
𝑅𝑐=𝐿
180 +10 (Equation 3.3-5 per Fort Collins
Stormwater Manual)
𝑅𝑡=𝐿
𝑉∗60
(Equation 5-5 per Fort Collins
1)Add 4900 to all elevations.
2) Per Fort Collins Stormwater Manual, minimum Tc = 5 min.
3) Assume a water depth of 6" and a typical curb and gutter per
Larimer County Urban Street Standard Detail 701 for curb and gutter
channelized flow. Assume a water depth of 1', fixed side slopes, and a
triangular swale section for grass channelized flow. Assume a water
depth of 1', 4:1 side slopes, and a 2' wide valley pan for channelized
flow in a valley pan.
Page 2 of 3
Tc2 Tc10 Tc100 C2 C10 C100 I2 I10 I100 Q2 Q10 Q100
front Front 0.06 6.2 6.2 5.7 0.3 0.3 0.3 2.7 4.6 9.6 0.05 0.08 0.21
rear Rear 0.09 8.8 8.8 7.1 0.5 0.5 0.6 2.4 4.0 8.8 0.11 0.19 0.52
Design
Point Basin
Intensity, I, from Fig. 3.4.1 Fort Collins Stormwater Manual.
Rational Equation: Q = CiA (Equation 6-1 per MHFD)
Area
(acres)
Runoff CTc (Min)Intensity (in/hr)Flow (cfs)
301 Parker Street
F. Wegert
December 22, 2021Date:
Fort Collins
Project:
Location:
Calc. By:
EXISTING DIRECT RUNOFF COMPUTATIONS
Page 3 of 3
Runoff Coefficient1
Percent
Impervious1 Project:
Location:
0.95 100%Calc. By:
0.95 90%Date:
0.50 40%
0.50 40%
0.20 2%
0.20 2%
Basin ID Basin Area
(sq.ft.)
Basin Area
(acres)
Asphalt, Concrete
(sq.ft.)Rooftop (sq.ft.)Gravel (sq.ft.)Pavers (sq.ft.)
Undeveloped:
Greenbelts,
Agriculture (sq.ft.)
Lawns, Clayey Soil,
Flat Slope < 2%
(sq.ft.)
Percent
Impervious
C2*Cf
Cf = 1.00
C5*Cf
Cf = 1.00
C10*Cf
Cf = 1.00
C100*Cf
Cf = 1.25
Front 2,805 0.06 252.12 736.00 0.00 0.00 0.00 1,817.24 34%0.46 0.46 0.46 0.58
Rear 4,056 0.09 185.19 736.00 741.19 0.00 0.00 2,393.72 40%0.50 0.50 0.50 0.63
Total 6,861 0.16 437.31 1,472.00 741.19 0.00 0.00 4,210.97 40%0.50 0.50 0.50 0.63
2) Composite Runoff Coefficient adjusted per Table 3.2-3 of the Fort Collins
Stormwater Manual (FCSM).
Lawns, Clayey Soil, Flat Slope < 2%
USDA SOIL TYPE: C
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.
Combined Basins
DEVELOPED RUNOFF COEFFICIENT CALCULATIONS
Asphalt, Concrete
Rooftop
Gravel
Pavers
Streets, Parking Lots, Roofs, Alleys, and Drives:
Character of Surface:301 Parker Street
Fort Collins
F. Wegert
December 22, 2021
Lawns and Landscaping:
Page 1 of 3
Where:
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
(%)Surface n
Flow
Area3
(sq.ft.)
WP3 (ft)R (ft)V
(ft/s)
Tt
(min)
Max.
Tc
(min)
Comp.
Tc 2-Yr
(min)
Tc
2-Yr
(min)
Comp.
Tc 10-Yr
(min)
Tc
10-Yr
(min)
Comp.
Tc 100-
Yr
(min)
Tc
100-Yr
(min)
front Front 25 91.30 90.48 3.28%4.00 4.00 3.27 67 90.48 87.60 4.30%Swale (4:1)0.04 4.00 8.25 0.48 5.45 0.20 10.51 4.21 5.00 4.21 5.00 3.48 5.00
rear Rear 25 91.30 90.79 2.04%4.42 4.42 3.50 117 90.79 89.40 1.19%Valley Pan 0.04 6.00 10.25 0.59 3.25 0.60 10.79 5.02 5.02 5.02 5.02 4.10 5.00
Notes
S = Longitudinal Slope, feet/feet
R = Hydraulic Radius (feet)
n = Roughness Coefficient
V = Velocity (ft/sec)WP = Wetted Perimeter (ft)
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Location:
Maximum Tc:Overland Flow, Time of Concentration:
Channelized Flow, Velocity:Channelized Flow, Time of Concentration:
301 Parker Street
Fort Collins
F. Wegert
December 22, 2021
Project:
Calculations By:
Date:
Design
Point Basin ID
Overland Flow Channelized Flow Time of Concentration
(Equation 3.3-2 per Fort Collins Stormwater Manual)𝑅𝑖=1.87 1.1 −𝐶∗𝐶𝑓𝐿
𝑅ൗ13
𝑉=1.49
𝑛∗𝑅2/3 ∗𝑅(Equation 5-4 per Fort Collins Stormwater Manual)
𝑅𝑐=𝐿
180 +10 (Equation 3.3-5 per Fort Collins
Stormwater Manual)
𝑅𝑡=𝐿
𝑉∗60
(Equation 5-5 per Fort Collins
1)Add 4900 to all elevations.
2) Per Fort Collins Stormwater Manual, minimum Tc = 5 min.
3) Assume a water depth of 6" and a typical curb and gutter per
Larimer County Urban Street Standard Detail 701 for curb and gutter
channelized flow. Assume a water depth of 1', fixed side slopes, and a
triangular swale section for grass channelized flow. Assume a water
depth of 1', 4:1 side slopes, and a 2' wide valley pan for channelized
flow in a valley pan.
Page 2 of 3
Tc2 Tc10 Tc100 C2 C10 C100 I2 I10 I100 Q2 Q10 Q100
front Front 0.06 5.0 5.0 5.0 0.5 0.5 0.6 2.9 4.9 10.0 0.09 0.15 0.37
rear Rear 0.09 5.0 5.0 5.0 0.5 0.5 0.6 2.9 4.9 10.0 0.13 0.23 0.58
Design
Point Basin
Intensity, I, from Fig. 3.4.1 Fort Collins Stormwater Manual.
Rational Equation: Q = CiA (Equation 6-1 per MHFD)
Area
(acres)
Runoff CTc (Min)Intensity (in/hr)Flow (cfs)
301 Parker Street
F. Wegert
December 22, 2021Date:
Fort Collins
Project:
Location:
Calc. By:
DEVELOPED DIRECT RUNOFF COMPUTATIONS
Page 3 of 3
Channel Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Tuesday, Dec 21 2021
Existing 100-Year Flowrate in Alley from 301 Parker Street
Trapezoidal
Bottom Width (ft) = 12.00
Side Slopes (z:1) = 5.00, 3.00
Total Depth (ft) = 0.25
Invert Elev (ft) = 100.00
Slope (%) = 7.60
N-Value = 0.022
Calculations
Compute by: Known Q
Known Q (cfs) = 0.52
Highlighted
Depth (ft) = 0.03
Q (cfs) = 0.520
Area (sqft) = 0.36
Velocity (ft/s) = 1.43
Wetted Perim (ft) = 12.25
Crit Depth, Yc (ft) = 0.04
Top Width (ft) = 12.24
EGL (ft) = 0.06
0 2 4 6 8 10 12 14 16 18
Elev (ft)Depth (ft)Section
99.75 -0.25
100.00 0.00
100.25 0.25
100.50 0.50
100.75 0.75
101.00 1.00
Reach (ft)
Channel Report
Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Tuesday, Dec 21 2021
Developed 100-Year Flowrate in Alley from 301 Parker Street
Trapezoidal
Bottom Width (ft) = 12.00
Side Slopes (z:1) = 5.00, 3.00
Total Depth (ft) = 0.25
Invert Elev (ft) = 100.00
Slope (%) = 7.60
N-Value = 0.022
Calculations
Compute by: Known Q
Known Q (cfs) = 0.58
Highlighted
Depth (ft) = 0.03
Q (cfs) = 0.580
Area (sqft) = 0.36
Velocity (ft/s) = 1.60
Wetted Perim (ft) = 12.25
Crit Depth, Yc (ft) = 0.05
Top Width (ft) = 12.24
EGL (ft) = 0.07
0 2 4 6 8 10 12 14 16 18
Elev (ft)Depth (ft)Section
99.75 -0.25
100.00 0.00
100.25 0.25
100.50 0.50
100.75 0.75
101.00 1.00
Reach (ft)