HomeMy WebLinkAboutWEST SIDE HOUSE - PDP/FDP - FDP160021 - REPORTS - DRAINAGE REPORT301 N. Howes Street, Suite 100, Fort Collins, CO 80521 970.221.4158 www.northernengineering.com
Drainage Letter and LID Report
Date: July 29, 2016
Project: West Side House Project No. 970-001
Project Development Plan/Major Amendment
Fort Collins, Colorado
Attn: Mr. Wes Lamarque
City of Fort Collins Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
Dear Wes:
This letter serves to address the stormwater impacts of the West Side House project. The existing building
is situated towards the northern portion of the site. The site currently consists of rooftop, concrete walks,
asphalt parking areas, turf, trees, and other vegetation. It presently functions similar to a ‘B’ lot, with
historic drainage being split towards Plum Street to the north and towards Shields Street to the east.
Calculations using the rational method to determine the proposed runoff are attached to this letter, as is a
drainage exhibit.
The total impervious area of the existing site is slightly reduced due to the removal of an existing concrete
pad along the north face of the building. For this reason, the total runoff was assumed to also be reduced
and, therefore, no stormwater detention is proposed. Although stormwater quantity detention is not
required, stormwater quality will be addressed by permanent Best Management Practices (BMPs).
There is one existing bio-retention pond (Rain Garden) that is located along the south face of the building.
Currently, this site is deficient with the City’s Low Impact Development Standards. In order to bring the
site into compliance, two Rain Gardens will be installed along the north face collecting building
downspouts and one additional rain garden will be located in the southeast corner of the site to collect
runoff from the parking lot. These Rain Gardens will have an engineered section designed to remove
particulates and contaminants from the stormwater. While most minor events are expected to infiltrate
into the ground, weep holes and subdrains will be provided to drain the Rain Gardens should they become
overburdened. During major events, runoff will spill through designed depressions in the top of the
concrete retaining walls.
During construction, the Contractor will follow the appropriate and applicable City of Fort Collins standards
for erosion and sediment control. Since the approximately 1,250 sf area of disturbance for the project is
less than 10,000 sf, a comprehensive Stormwater Management Plan will not be prepared for this project.
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.
There are no regulatory floodplains associated with the project.
The City LID requirements specify that either 75% of all impermeable areas are provided LID treatment OR
50% LID treatment by which 25% is treated by permeable pavers. In the case of this project, we will
meet or exceed the 75% treatment of impermeable areas through the use of LID. The combination of
treatment provided by the 4 infiltration Rain Gardens will treat 10,679 square-feet of impervious area on
the site, which is 83.5% of the total impervious areas with the project, which again far exceeds the
amount required by city code. A LID Treatment Exhibit is provided with this report.
To summarize, the proposed grading concept closely matches existing elevations and drainage patterns.
On-site detention is proven to be unnecessary. Stormwater quality has been provided, and exceeds the city
requirements for Low Impact Development treatment. Therefore, it is my professional opinion that the
West Side House satisfies all applicable stormwater criteria.
Please do not hesitate to contact me if you have questions or require additional information.
Sincerely,
Danny Weber, PE
Project Engineer
enc.
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: West Side House
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: D. Weber
Asphalt ……....……………...……….....…...……………….………………………………….0.95 . 100 Date:
Concrete …….......……………….….……….………………..….………………………………… 0.95 90
Gravel ……….…………………….….…………………………..……………………………….0.50 . 40
Roofs …….…….………………..……………….…………………………………………….0.. 95 90
Concrete Pavers…………………………...………………..…………………………………………….0.40 . 22
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0 2-year Cf
= 1.00 100-year Cf
= 1.25
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Concrete
Pavers
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
NW 3,180 0.07 0.02 0.01 0.02 0.00 0.00 0.02 0.77 0.77 0.97 70.6
NE 3,192 0.07 0.00 0.01 0.02 0.00 0.00 0.05 0.51 0.51 0.64 33.4
S 10,777 0.25 0.15 0.02 0.04 0.00 0.00 0.04 0.85 0.85 1.00 83.3
Total 17,149 0 0 0 0 0 0 0 0.77 0.77 0.97 71.7
DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Overland Flow, Time of Concentration:
Project: West Side House
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt
= L / 60V
Tc
= Ti
+ Tt
(Equation RO-2)
Velocity (Gutter Flow), V = 20·S
½
Velocity (Swale Flow), V = 15·S
½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
Rational Method Equation: Project: West Side House
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
NW NW 0.07 5.0 5.0 5.0 0.77 0.77 0.97 2.85 4.87 9.95 0.2 0.3 0.7
NE NE 0.07 5.5 5.5 5.1 0.51 0.51 0.64 2.85 4.87 9.95 0.1 0.2 0.5
S S 0.25 5.0 5.0 5.0 0.85 0.85 1.00 2.85 4.87 9.95 0.6 1.0 2.5
DEVELOPED RUNOFF COMPUTATIONS
C100
Design
Point
Flow,
Q100
(cfs)
Flow,
Q2
(cfs)
10-yr
Tc
(min)
2-yr
Tc
(min)
C2
Flow,
Q10
(cfs)
Intensity,
i100
(in/hr)
Basin(s)
D. Weber
July 29, 2016
Intensity,
i10
(in/hr)
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
C10
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
Q = C f ( C )( i )( A )
D:\Projects\970-001\Drainage\Hydrology\970-001_Rational-Calcs_Proposed.xlsx\Direct-Runoff
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Thursday, Jul 28 2016
Northwest Driveway Chase
Rectangular
Bottom Width (ft) = 1.00
Total Depth (ft) = 0.24
Invert Elev (ft) = 100.00
Slope (%) = 0.50
N-Value = 0.013
Calculations
Compute by: Known Q
Known Q (cfs) = 0.20
Highlighted
Depth (ft) = 0.12
Q (cfs) = 0.200
Area (sqft) = 0.12
Velocity (ft/s) = 1.67
Wetted Perim (ft) = 1.24
Crit Depth, Yc (ft) = 0.11
Top Width (ft) = 1.00
EGL (ft) = 0.16
0 .25 .5 .75 1 1.25 1.5
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® AutoCAD® Civil 3D® by Autodesk, Inc. Thursday, Jul 28 2016
Southeast Driveway Chase
Rectangular
Bottom Width (ft) = 1.00
Total Depth (ft) = 0.41
Invert Elev (ft) = 100.00
Slope (%) = 0.50
N-Value = 0.013
Calculations
Compute by: Known Q
Known Q (cfs) = 0.60
Highlighted
Depth (ft) = 0.25
Q (cfs) = 0.600
Area (sqft) = 0.25
Velocity (ft/s) = 2.40
Wetted Perim (ft) = 1.50
Crit Depth, Yc (ft) = 0.23
Top Width (ft) = 1.00
EGL (ft) = 0.34
0 .25 .5 .75 1 1.25 1.5
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)
T S
CTV
W
X
X
X X
X X
G
CT
VAULT
ELEC
T
C
S
C
S
ELEC
ELEC
RAIN GARDEN A
EXISTING RAIN GARDEN
RAIN GARDEN B
RAIN GARDEN C
D:\PROJECTS\970-001\DWG\DRNG\970-001_LID.DWG
WEST SIDE HOUSE
FORT COLLINS
COLORADO
301 N. Howes Street, Suite 100
Fort Collins, Colorado 80521
ENGINEER ING
N O R T H E RN
PHONE: 970.221.4158
www.northernengineering.com
DESCRIPTION
LID TREATMENT EXHIBIT
DRAWN BY
D. WEBER
DATE
JULY 29, 2016
PROJECT
970-001 LID-1
SCALE DRAWING
1"=30'
( IN FEET )
1 inch = ft.
30 0 30 Feet
30
LEGEND
RAIN GARDEN
RAIN GARDEN
TREATMENT AREA
On-Site LID Treatment
Project Area
Total Impervious Area 12,790 sf
Target Treatment Percentage 75%
Minimum Area to be Treated by LID measures 9,593 sf
Rain Garden Treatment
Run-on area for Existing Rain Garden 1,600 sf
Run-on area for Rain Garden A 800 sf
Run-on area for Rain Garden B 800 sf
Run-on area for Rain Garden C 7,479 sf
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 100.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 1.000
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.40 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 800 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 27 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum) DWQCV = 4.75 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 0.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin = 16 sq ft
D) Actual Flat Surface Area AActual = 69 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 69 sq ft
F) Rain Garden Total Volume VT= 27 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y = ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft
iii) Orifice Diameter, 3/8" Minimum DO = N/A in
Design Procedure Form: Rain Garden (RG)
D. Weber
Northern Engineering
July 29, 2016
West Side House
Rain Garden A
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
Rain Garden A.xlsm, RG 7/28/2016, 8:49 AM
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 100.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 1.000
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.40 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 800 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 27 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum) DWQCV = 4.75 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 0.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin = 16 sq ft
D) Actual Flat Surface Area AActual = 69 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 69 sq ft
F) Rain Garden Total Volume VT= 27 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y = ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft
iii) Orifice Diameter, 3/8" Minimum DO = N/A in
Design Procedure Form: Rain Garden (RG)
D. Weber
Northern Engineering
July 29, 2016
West Side House
Rain Garden B
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
Rain Garden B.xlsm, RG 7/28/2016, 8:50 AM
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 99.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.990
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.39 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 7,449 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 243 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum) DWQCV = 6.50 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 0.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin = 147 sq ft
D) Actual Flat Surface Area AActual = 455 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 455 sq ft
F) Rain Garden Total Volume VT= 246 cu ft
(VT= ((ATop + AActual) / 2) * Depth)
3. Growing Media
4. Underdrain System
A) Are underdrains provided?
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y = ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft
iii) Orifice Diameter, 3/8" Minimum DO = N/A in
Design Procedure Form: Rain Garden (RG)
D. Weber
Northern Engineering
July 29, 2016
West Side House
Rain Garden C
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
Rain Garden C.xlsm, RG 7/28/2016, 8:51 AM
UD
CTV
CTV
CTV
X X X
X
X
X
X
X X X X
X X
X
X
util
UD
NW
S
NW
S
NE
RAIN NE
GARDEN A RAIN GARDEN B
EXISTING
RAIN GARDEN
RAIN GARDEN C
NORTH
C500
DRAINAGE EXHIBIT
Sheet
Of 9 Sheets
WEST SIDE HOUSE
E NGINEER ING
N O R T H E RN
301 North Howes Street, Suite 010
Fort Collins, Colorado 80521
www.northernengineering.com
Phone: 970.221.4158
These drawings are
instruments of service
provided by Northern
Engineering Services, Inc.
and are not to be used for
any type of construction
unless signed and sealed by
a Professional Engineer in
the employ of Northern
Engineering Services, Inc.
NOT FOR CONSTRUCTION
REVIEW SET
CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU
DIG, GRADE, OR EXCAVATE FOR THE MARKING OF
UNDERGROUND MEMBER UTILITIES.
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
Know what'sbelow.
Call before you dig.
R
LEGEND:
A
1 1
NOTES:
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
UD
A
DEVELOPED RUNOFF SUMMARY TABLE
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C10 C100 2-yr Tc
(min)
10-yr Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q10
(cfs)
Q100
(cfs)
NW NW 0.07 0.77 0.77 0.97 5.0 5.0 5.0 0.2 0.3 0.7
NE NE 0.07 0.51 0.51 0.64 5.5 5.5 5.1 0.1 0.2 0.5
S S 0.25 0.85 0.85 1.00 5.0 5.0 5.0 0.6 1.0 2.5
On-Site LID Treatment
Project Area
Total Impervious Area 12,790 sf
Target Treatment Percentage 75%
Minimum Area to be Treated by LID measures 9,593 sf
Rain Garden Treatment
Run-on area for Existing Rain Garden 1,600 sf
Run-on area for Rain Garden A 800 sf
Run-on area for Rain Garden B 800 sf
Run-on area for Rain Garden C 7,479 sf
Total Treatment Area 10,679 sf
Percent Total Project Area Treated 83.5%
Total Treatment Area 10,679 sf
Percent Total Project Area Treated 83.5%
V
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
NW NW No 0.95 0.95 1.00 30 2.8 2.0 1.1 0.7 47 0.5 1.41 0.6 41 0.5 1.06 0.6 5.0 5.0 5.0
NE NE No 0.25 0.25 0.31 35 5.0 5.5 5.5 5.1 0 0.0 0.00 N/A 0 0.0 0.00 N/A 5.5 5.5 5.1
S S No 0.95 0.95 1.00 58 3.0 1.5 1.5 1.0 132 0.5 1.41 1.6 0 0.0 0.00 N/A 5.0 5.0 5.0
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
D. Weber
July 29, 2016
Time of Concentration
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
C Cf L
Ti
−
=
D:\Projects\970-001\Drainage\Hydrology\970-001_Rational-Calcs_Proposed.xlsx\Tc-2-yr_&_100-yr
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
10-year Cf
= 1.00
July 29, 2016
D:\Projects\970-001\Drainage\Hydrology\970-001_Rational-Calcs_Proposed.xlsx\C-Values