HomeMy WebLinkAbout609 S COLLEGE AVE MIXED USE - BDR200004 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTDrainage Memo
February 5, 2020
Project: 609 South College Avenue Project No. 564-005
Attn: Stormwater Staff
City of Fort Collins Stormwater Utility
700 Wood Street
Fort Collins, CO 80521
Stormwater Staff:
This letter serves to document the proposed drainage impacts of the addition to the existing building
proposed at 609 South College Avenue in Fort Collins, Colorado.
Project Overview
The project proposes to add an addition to the rear (west side) of the existing building adding ~800 sf.
Construction activities will also include the removal of the existing garage. A concrete patio area, concrete
walks, and alley parking will also be added as a part of these improvements, as well as planters to provide
LID treatment to the site. A dedicated fire service will also be added as part of this project.
Existing Site
The existing site is relatively flat (0% - 1%) in the front and rear yards, and functions as an “A” Lot, with
drainage generally draining from back to front along the side lot lines. In addition to the existing home, the
lot consists of a garage, a concrete driveway, concrete entry walk, and concrete walks around the entire
home. The remainder of the site is Kentucky Bluegrass lawn, with small landscaping beds and mature
trees.
The total existing impervious area for the lot is 2,781 sf.
Proposed Site
The proposed site will generally maintain the existing site drainage. Drainage from the rear yard and
proposed planters directed overland via concrete pan along the southern lot line to College Avenue. The
parking area will maintain the existing drainage pattern and flow west to Dalzell Alley. Existing grades
outside of our improvements will remain unchanged, including along the north side of the existing house
where no improvements are proposed.
The total proposed impervious area for the lot is 4,731 sf. The proposed change in imperviousness will
add an estimated 0.46 cfs to College Avenue and 0.1 cfs to Dalzell Alley in a 100-yr event. We do not
foresee the additional runoff causing any issues with the existing inlets intercepting the flow at Myrtle Street
and College Avenue, but additional information regarding the inlet’s capacity will need to be obtained from
the City and verified. No adverse effects to adjacent properties are anticipated due to the increased
imperviousness of the site.
Detention
Since the impervious area increase is than the 5,000 sf allowed in the Old Town Master Drainage Basin, no
detention is required for the site.
Floodplain
A portion of the property is currently located in the City of Fort Collins 100-yr Old Town floodplain.
Northern Engineering is currently working on a LOMA remove the building from the floodplain.
Water Quality
Water Quality for the site is being provided by releasing the concentrated flows from the roof into two
planters in the front and rear of the house. The planters will contain Bioretention Soil and landscape.
Water will infiltrate the soil, removing stormwater contaminates, and exit the planters through knockouts at
the base of the planters into sidewalk chases. Flows will then travel, via concrete pan to a proposed
sidewalk chase onto College Avenue.
An exhibit has been provided to illustrate the existing and proposed impervious areas. Please feel free to
contact us if you have any questions.
Northern Engineering Services, Inc.
Benjamin Ruch, PE
Project Engineer
Project: 609 S. College Avenue
Calculations By:
Date:
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)
Up Stream
Elevation
Down
Stream
Elevation
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Up
Stream
Elevation
Down
Stream
Elevation
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Project:
Calculations By:
Date:
Existing A Existing A 0.14 22 22 21 0.25 0.25 0.31 1.53 2.61 5.53 0.05 0.09 0.24
Existing B Existing B 0.01 6 6 5 0.25 0.25 0.31 2.76 4.72 9.95 0.01 0.01 0.03
Existing OS Existing OS 0.04 5 5 5 0.25 0.25 0.31 2.85 4.87 9.95 0.03 0.04 0.11
Flow,
Q100
(cfs)
Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8
Design
Point
Sub-Basin(s)
Area, A
(acres)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
C2
C10
C100
Intensity,
i2
(in/hr)
Intensity,
i10
(in/hr)
Intensity,
i100
(in/hr)
Flow,
Q2
(cfs)
Flow,
Q10
(cfs)
Rainfall Intensity:
EXISTING RUNOFF COMPUTATIONS
Rational Method Equation: 609 S. College Avenue
B. Ruch
February 5, 2020
Q = C f ( C )( i )( A )
Project:
Calculations By:
Date:
Proposed A Proposed A 0.14 13 13 12 0.55 0.55 0.69 1.98 3.39 7.16 0.16 0.27 0.70
Proposed B Proposed B 0.02 6 6 5 0.55 0.55 0.69 2.67 4.56 9.95 0.03 0.05 0.13
Proposed OS1 Proposed OS1 0.03 5 5 5 0.60 0.60 0.75 2.85 4.87 9.95 0.04 0.08 0.20
B. Ruch
609 S. College Avenue
PROPOSED 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)
Sub-Basin(s)
Rational Method Equation:
Rainfall Intensity:
Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8
February 5, 2020
Intensity,
i10
(in/hr)
C10
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
Q = C f ( C )( i )( A )
CHARACTER OF SURFACE:
Runoff
Coefficient
1
Percentage
Impervious
1
Project:
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By:
Asphalt …………………......................... ............................................................................... 0.95 100% Date:
Concrete ………………. ......................... ............................................................................... 0.95 100%
Gravel (packed) ………. ......................... ............................................................................... 0.50 40%
Roofs………………….. ......................... ............................................................................... 0.95 90%
Pavers…………………. ......................... ............................................................................... 0.50 40%
Recycled Asphalt ......................... ............................................................................... 0.80 80%
Lawns and Landscaping
Playgrounds 25%
Sandy Soil
Flat <2% ………….. ......................... ............................................................................... 0.10 2%
Average 2% to 7% ......................... ............................................................................... 0.15 2%
Steep >7% ………… ......................... ............................................................................... 0.20 2%
Clayey Soil
Flat <2% ………….. ......................... ............................................................................... 0.20 2%
Average 2% to 7% ......................... ............................................................................... 0.25 2%
Steep >7% ………… ......................... ............................................................................... 0.35 2% 2-year Cf
= 1.00 10-year Cf
= 1.00
USDA SOIL TYPE: C
Sub-Basin ID
Sub-Basin
Area
(sq. ft.)
Sub-Basin
Area
(ac.)
Area of Asphalt
& Concrete
(ac.)
Area of Roofs
(ac.)
Area of Gravel
(ac.)
Area of
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
Existing A 6,085 0.140 0.014 0.025 0.000 0.101 0.25 0.25 0.31 28%
Existing B 488 0.011 0.002 0.000 0.000 0.009 0.25 0.25 0.31 20%
CHARACTER OF SURFACE:
Runoff
Coefficient
1
Percentage
Impervious
1
Project:
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By:
Asphalt ………………… ......................... ............................................................................. 0.95 100% Date:
Concrete ………………. ......................... ............................................................................. 0.95 100%
Gravel (packed) ………. ......................... ............................................................................. 0.50 40%
Roofs………………….. ......................... ............................................................................. 0.95 90%
Pavers…………………. ......................... ............................................................................. 0.50 40%
Recycled Asphalt ......................... ............................................................................. 0.80 80%
Lawns and Landscaping
Playgrounds 25%
Sandy Soil
Flat <2% ………….. ......................... ............................................................................. 0.10 2%
Average 2% to 7% ......................... ............................................................................. 0.15 2%
Steep >7% ………… ......................... ............................................................................. 0.20 2%
Clayey Soil
Flat <2% ………….. ......................... ............................................................................. 0.20 2%
Average 2% to 7% ......................... ............................................................................. 0.25 2%
Steep >7% ………… ......................... ............................................................................. 0.35 2% 2-year Cf = 1.00 10-year Cf = 1.00
USDA SOIL TYPE: C
Sub-Basin ID
Sub-Basin Area
(sq. ft.)
Sub-Basin Area
(ac.)
Area of Asphalt
& Concrete
(ac.)
Area of Roofs
(ac.)
Area of Pavers
(ac.)
Area of
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
Proposed A 6,206 0.14 0.039 0.038 0.005 0.060 0.55 0.55 0.69 54%
Proposed B 824 0.02 0.016 0.000 0.000 0.003 0.55 0.55 0.69 84%
Proposed OS1 1,139 0.03 0.002 0.012 0.000 0.013 0.60 0.60 0.75 47%
PROPOSED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
609 S. College Avenue
B. Ruch
Project: 609 S. College Avenue
Calculations By:
Date:
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Velocity,
V
(ft/s)
Tt
(min)
2-yr
Tc
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
Existing A Existing A No 0.25 0.25 0.31 22.1 22.1 20.5 N/A N/A 22.1 22.1 20.5
Existing B Existing B No 0.25 0.25 0.31 5.9 5.9 5.5 N/A N/A 5.9 5.9 5.5
Existing OS Existing OS No 0.25 0.25 0.31 1.9 1.9 1.8 N/A N/A 5.0 5.0 5.0
EXISTING TIMES OF CONCENTRATION COMPUTATIONS
B. Ruch
February 5, 2020
Design
Point
Sub-Basin
Overland Flow Gutter/Swale Flow Time of Concentration
Velocity (Gutter Flow), V = 20·S½
Tt = L / 60V
Tc = Ti + Tt (Equation RO-2)
Velocity (Swale Flow), V = 15·S½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Overland Flow, Time of Concentration:
Gutter/Swale Flow, Time of Concentration:
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
C.O. G
W
C
S
E
VAULT
ELEC
TELE
T
VAULT
ELEC
CONTROL
IRR
VAULT
ELEC
/ / / / / / / /
/ / / / / / / /
/ / / / / / / /
/ / / / / / / / / / / / / / / /
X
605 COLLEGE LTD
605 S COLLEGE AVE
FORT COLLINS, CO 805243003
GATON III INC
DBA CANINOS ITALIAN RESTAURANT
613 S COLLEGE AVE
FORT COLLINS, CO 805243003
SOUTH COLLEGE AVENUE
DALZELL ALLEY
EXISTING 100-YR FLOODPLAIN
(CITY OF FORT COLLINS)
EX A
0.140 ac
EX A
EX B EX OS EX OS
0.037 ac
EX B
0.011 ac
HISTORIC DRAINAGE EXHIBIT
FORT COLLINS, CO
609 S. COLLEGE
E NGINEER ING
N O R T H E RN
FEBRUARY 5, 2020
P:\564-005\DWG\DRNG\564-005_EXST DRNG.DWG
( IN FEET )
0
1 INCH = 20 FEET
20 20
DRAINAGE SUMMARY TABLE
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
2-yr
Tc
C.O. G
W
C
S
E
VAULT
ELEC
TELE
T
VAULT
ELEC
VAULT
ELEC
/ / / / / / / /
/ / / / / / / /
/ / / / / / / /
/ / / / / / / / / / / / / / / /
E
E
E
X
X X X
X
X
X
X
X
X
X X
A
0.142 ac
A
OS
B OS
0.026 ac
B
0.019 ac
605 COLLEGE LTD
605 S COLLEGE AVE
FORT COLLINS, CO 805243003
GATON III INC
DBA CANINOS ITALIAN RESTAURANT
613 S COLLEGE AVE
FORT COLLINS, CO 805243003
SOUTH COLLEGE AVENUE
DALZELL ALLEY
EXISTING 100-YR FLOODPLAIN
(CITY OF FORT COLLINS)
PROPOSED DRAINAGE EXHIBIT
FORT COLLINS, CO
609 S. COLLEGE
E NGINEER ING
N O R T H E RN
FEBRUARY 5, 2020
P:\564-005\DWG\DRNG\564-005_DRNG.DWG
( IN FEET )
0
1 INCH = 20 FEET
20 20
DRAINAGE SUMMARY TABLE
C.O. G
W
C
S
C
E
VAULT
ELEC
TELE
T
VAULT
ELEC
CONTROL
IRR
VAULT
ELEC
/ / / / / / / /
/ / / / / / / /
/ / / / / / / /
G
G
SOUTH COLLEGE AVENUE
DALZELL ALLEY
X X
X
X
X
X
X
C.O. G
W
C
S
E
VAULT
ELEC
TELE
T
VAULT
ELEC
VAULT
ELEC
/ / / / / / / /
/ / / / / / / /
/ / / / / / / /
SOUTH COLLEGE AVENUE
DALZELL ALLEY
ROOFTOP
CONCRETE
ASPHALT
PAVERS
SURFACE
AREA (SF) % IMPERV.
IMPERV.
AREA (SF)
1,928
853
0
0
100%
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 = 1,463 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 49 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 = 3 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 = 29 sq ft
D) Actual Flat Surface Area AActual = 237 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 237 sq ft
F) Rain Garden Total Volume VT= 59 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 = N/A 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)
Benjamin Ruch
Northern Engineering
February 4, 2020
609 S. College
Fort Collins, CO
UD-BMP (Version 3.06, November 2016)
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
RG_UD-BMP_v3.06.xlsm, RG 2/4/2020, 4:16 PM
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
PROVIDE A 30 MIL (MIN) PVC LINER WITH CDOT CLASS B
GEOTEXTILE ABOVE IT. USE THE SAME GEOTEXTILE BELOW
THE LINER IF THE SUBGRADE IS ANGULAR
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
Benjamin Ruch
Northern Engineering
February 4, 2020
609 S. College
Fort Collins, CO
Choose One
Choose One
Choose One
Sheet Flow- No Energy Dissipation Required
Concentrated Flow- Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
RG_UD-BMP_v3.06.xlsm, RG 2/4/2020, 4:16 PM
100%
100%
40% 86
TOTALS 2,781 TOTAL= 2,781
ROOFTOP
CONCRETE
ASPHALT
PAVERS
SURFACE
AREA (SF) % IMPERV.
IMPERV.
AREA (SF)
2,164
2,488
0
198
100%
100%
100%
40%
TOTALS 4,850 TOTAL= 4,731
EXISTING PROPOSED
2,164
79
1,928
853
0
2,488
0
P:\564-005\DWG\DRNG\564-005_IMPERVIOUS.DWG
609 S. COLLEGE AVE.
FORT COLLINS
COLORADO
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
DESCRIPTION
EXISTING VS. PROPOSED
IMPERVIOUS AREA
DRAWN BY
B. Ruch
DATE
February 5, 2020
PROJECT
564-005 SK-C1
SCALE DRAWING
1"=30'
DESIGN
POINT
BASIN
ID
TOTAL
AREA
(acres)
C2 C100
2-yr
Tc
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q100
(cfs)
Existing A Existing A 0.14 0.25 0.31 22.1 20.5 0.05 0.24
Existing B Existing B 0.01 0.25 0.31 5.9 5.5 0.01 0.03
Existing OS Existing OS 0.04 0.25 0.31 5.0 5.0 0.03 0.11
Proposed A Proposed A 0.14 0.55 0.69 13.2 12.3 0.16 0.70
Proposed B Proposed B 0.02 0.55 0.69 6.1 5.4 0.03 0.13
Proposed OS1 Proposed OS1 0.03 0.60 0.75 5.0 5.0 0.04 0.20
(min)
100-yr
Tc
(min)
Q2
(cfs)
Q100
(cfs)
Existing A Existing A 0.14 0.25 0.31 22.1 20.5 0.05 0.24
Existing B Existing B 0.01 0.25 0.31 5.9 5.5 0.01 0.03
Existing OS Existing OS 0.04 0.25 0.31 5.0 5.0 0.03 0.11
Proposed A Proposed A 0.14 0.55 0.69 13.2 12.3 0.16 0.70
Proposed B Proposed B 0.02 0.55 0.69 6.1 5.4 0.03 0.13
Proposed OS1 Proposed OS1 0.03 0.60 0.75 5.0 5.0 0.04 0.20
C Cf L
Ti
= −
February 5, 2020
1) Runoff coefficients are taken from the Fort Collins Stormwater Criteria Manaual, Table 4.1-3and Table 3.2-2.
100-year Cf = 1.25
Composite Runoff Coefficient with Adjustment
Existing OS 1,594 0.037 0.003 0.019 0.000 0.014 0.25 0.25 0.31 57%
1) Runoff coefficients are taken from the Fort Collins Stormwater Criteria Manaual, Table 4.1-3and Table 3.2-2.
EXISTING COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
609 S. College Avenue
B. Ruch
February 5, 2020
100-year Cf
= 1.25
Composite Runoff Coefficient with Adjustment
Proposed A Proposed A No 0.25 0.25 0.31 67 96.96 96.11 1.27% 12.0 12.0 11.1 136 96.11 94.92 0.87% 1.87 1.2 13.2 13.2 12.3
Proposed B Proposed B No 0.35 0.35 0.44 27 97.25 96.79 1.70% 6.1 6.1 5.4 0 96.79 84.93 N/A N/A N/A 6.1 6.1 5.4
Proposed OS1 Proposed OS1 No 0.00 0.00 0.00 7 96.40 95.76 9.14% 2.6 2.6 2.6 0 0.00 0.00 N/A N/A N/A 5.0 5.0 5.0
Tc = Ti + Tt (Equation RO-2)
Velocity (Gutter Flow), V = 20·S½
Velocity (Swale Flow), V = 15·S½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Design
Point
Sub-Basin
Overland Flow Gutter Flow Time of Concentration
Tt = L / 60V
PROPOSED TIME OF CONCENTRATION COMPUTATIONS
Overland Flow, Time of Concentration:
B. Ruch
February 5, 2020
Gutter/Swale Flow, Time of Concentration:
(Equation RO-4)
( )
3
1
1 . 87 1 . 1 *
S
C Cf L
Ti
= −