HomeMy WebLinkAboutDrainage Reports - 10/21/2025October 16, 2025
Derek Lutz
Stormwater Engineering
City of Fort Collins
281 North College Avenue
Fort Collins, CO
RE: Spirit of Joy Landscape Improvements Drainage Analysis
Lot 1, Spirt of Joy Lutheran Subdivision
Dear Mr. Lutz:
Bulldog Engineering has completed an analysis of the drainage design for Lot 1, Spirt of Joy
Lutheran Subdivision to determine the changes from the original to the proposed design.
Reference Exhibit A. The original design is defined within the following drainage report:
• Storm Drainage Report for Lot 1, Spirit of Joy Lutheran Subdivision, prepared by
Stewart & Associates, Inc., revised April 19, 1991
• Storm Water Run-off & Water Quality Calculations for the Spirt of Joy Church, prepared
by Forbes Engineering, Civil & Structural Engineering, revised June 1, 2011
The original basin’s composite runoff coefficient from the Storm Drainage Report for Lot 1,
Spirit of Joy Lutheran Subdivision & Storm Water Run-off & Water Quality Calculations for the
Spirt of Joy Church have been compared to the composite runoff coefficient of the site after the
proposed landscape improvements to determine if further analysis would be required. The
original design’s composite runoff coefficient was determined to be 0.57 in the original report
from 1991 and 0.45 in the Drainage Memo from 2011. Reference Exhibits C & D respectively.
The overall composite runoff coefficient of the proposed lot, after the landscape improvements
have been completed, is calculated to be 0.44. Reference Exhibit D. Based on the calculations,
no increase in the developed runoff is anticipated and the proposed percent impervious and
composite runoff value is less than what was used for the original design. Additional water
quality will not be required. The intended drainage patterns will remain the same as the detailed
analysis completed in the Storm Water Run-off & Water Quality Calculations for the Spirt of Joy
Church, so detailed analysis of the changes will not be required. Reference Exhibit D.
The proposed runoff patterns are consistent with the overall drainage report. Runoff from this
site flows to the southwest into the private water quality pond for the site as it was originally
designed. The existing infrastructure will convey the runoff from only the improved
development to the existing private water quality pond. The existing water quality pond has
previously been sized to accept developed runoff from this site and provide adequate storage
based on the runoff coefficient values stated above. The pond outlet structure has been designed
info@bulldogeng.com 970-460-0089PO Box 114 - 1540 Main Street - Suite 218, Windsor, CO 80550
BULLDOG
ENGINEERING
Grading/Stormwater Plan Accepted
(Building Permit Released)
Accepted by:
Date:
SW - DEREK LUTZ
10/21/2025
to treat and release the calculated water quality capture volume for the development within 40
hours to the existing storm system as detailed in the Storm Water Run-off & Water Quality
Calculations for the Spirt of Joy Church, prepared by Forbes Engineering, Civil & Structural
Engineering, revised June 1, 2011. Reference Exhibit E for the water quality capture volume
design completed in 2011, which further demonstrates that the existing water quality pond
provides more than the adequate volume for the proposed improvements. A new water quality
capture volume calculation is not required or provided since the original design assumes a
greater percent impervious area and higher composite runoff coefficient than what is being
proposed.
To demonstrate the details of the drainage design, the following exhibits have been provided.
• Exhibit A - Vicinity Map
• Exhibit B – Existing Drainage Plan & Original Design Runoff Coefficient from the
Storm Drainage Report for Lot 1, Spirit of Joy Lutheran Subdivision
• Exhibit C – Updated Design Runoff Coefficient from Storm Water Run-off & Water
Quality Calculations for the Spirt of Joy Church
• Exhibit D – Proposed Composite Runoff Coefficients (Using same coefficients from
the original reports)
• Exhibit E – Existing Water Quality Capture Volume Calculation from Storm Water Run-
off & Water Quality Calculations for the Spirt of Joy Church
• Exhibit F – Proposed Drainage Plan
If you have any questions or need additional information, please contact me.
Sincerely,
Bulldog Engineering, LLC
Mark Harris, PE
Principal/Owner
Enclosures
BULLDOG
ENGINEERING
MARK EDWARD HARRIS
PROFESSIONAL ENGINEER
COLORADO LICENSED
56775
10/17/2025
Spirit of Joy Lutheran
Church Landscape
Improvements
Exhibit A: Vicinity Map
970-502-6444
BULLDOG
ENGINEERING
N
S
W E
Site
COMPUTATIONS*
Stewart & Associates, Inc. 214 N. Howes St. Ft. Collins, CO 80521 (303) 482-9331
BY: P) K Date z 9 Client,:2icli Q4 --Seel vf6errn Civ-CA Sheet No: 3 of 17
Chkd By: —Date cof'_ Le?mov4 1'or&Ar
Subject S70rrn Drainage Si -Le rv/v 5AC2
0' is
J
101 7
dk r:
two; rd z k 0. 10, F
S.
II i
A l..i i
0
Exhibit B (Sheet 1 of 2)
n/o SCALE)
13LVEFIN COURTT-
3
tij
rp
Exis-r 4' cr3
OTC
S. LEMAY
EXIsT 4' cQ U
EX I STl N G- —1 rIDriFIIN171TGy
O N F
GIfVFZG-J 517E
FULL - = 4-.6 cis II ao
DEVELOPED GA c 6.0
cfstooIY
18.6
Ex15T
x
F
i Q
c I ROLE
a
2
I LL
o
Ia
Ia
Y
r
Q
2
O
SHEET I ( of )Z
Exhibit B (Sheet 2 of 2)
SPIRIT OF JOY CHURCH
FORT COLLINS, COLORADO
DEVELOPED RUN-OFF CALCULATIONS
CHECK OF PREVIOUS RUN—OFF CALC'S — FULLY DEVELOPED
3/28/1991 REPORT BY STEWART & ASSOC)
17 = 1.9 Q2 = 4.6 CFS THIS WAS DEVELOPED W/ TC = 18 MIN
1 t0= 3.3 Q10 = 8.0 CFS (14 MIN FOR TC100 ). COMPOSITE C = .57
1100 = 6.2 Q100 = 18.8 CFS & A 1.25 FACTOR FOR FOR THE 100 YEAR
USING CURRENT FEQUENCY CURVE DATA, RUNOFF COEFFICIENTS & TC = 14 MIN
COMPOSITE RUNOFF COEFFICIENT CALCULATIONS
RUNOFF COEFFICIENTS PER TABLE 3-3
LAND USE RUN—OFF COEFFICIENT
LAWNS, SANDY SOIL 0.10
LAWNS, HEAVY SOIL 0.20
CONCRETE 0.95
ROOFS 0.95
ASPHALT 0.95
PACKED GRAVEL 0.50
COMPOSITE RUNOFF COEFFICIENT WAS CALCULATED
USING THE FOLLOWING FORMULA; n
C= IE CI AI /At
WHERE C = COMPOSITE RUNOFF COEFFICIENT
C1= RUNOFF COEFFICIENT FOR SPECIFIC AREA Al
A, = AREA OF SURFACE WITH RUNOFF COEFFICIENT OF C,
n = NUMBER OF DIFFERENT SURFACES TO BE CONSIDERED
At= TOTAL AREA OVER WHICH C IS APPLICABLE;
THE SUM OF ALL A1's IS EQUAL TO At
DEVELOPED SITE AREAS
AL(LANDSCAPE) AC(CONC) AR(ROOFS) AG(GRAVEL) AG(PAVEMENT) At(TOTAL) SQ FT SQ FT SQ FT SQ FT SQ FT SQ FT
124,664
2.862 AC)
11,972 12,306 0
0.275 AC) (0.283 AC)
36,384
0.835 AC)
185,326
4.25 AC)
COMPOSITE RUNOFF COEFFICIENT C = 0.45
Page 3
Exhibit C (Sheet 1 of 1)
Exhibit D: Proposed Composite
Runoff Coefficient
970-502-6444
BULLDOG
ENGINEERING
Spirit of Joy Lutheran
Church Landscape
Improvements
Basin Roofs/Deck
(C=0.95)
Packed Gravel
(C=0.5)
Rubber Playground
(C=0.95)
Concrete
(C=0.95)
Asphalt
(C=0.95)
Landscape
(C=0.20)
Total
Area
Composite Runoff
Coefficient
Existing Lot (Per 2011
Drainage Report)12,306 0 0 11,972 36,384 124,664 185,326 0.45
Proposed Lot (With
Landscape Improvements)12,616 1,160 2,150 12,609 31,714 126,237 185,326 0.44
Composite Runoff Coefficient Calculation
11 Design Procedure Form: Extended Detention Basin (EDB) - Sedimentation Facility 11
11
Designer. Kevin Forbes
1 of 3
Company: Forbes Engineering
Date: REVISED MAYS. 2011
Project: Spirit of Joy Church
Location: Ft Collins, CO
1. Basin Storage Volume
A) TriblgaryArea's Imperviousness Ratio (i = I,/ 1D0 ) B)
Contributing Watershed Area (Area) C)
Water Quality Capture Volume (WQCV) WQCV =
t0•(0.91 •0-1.19-P+0.78-D) D)
Design Volume: Vol = (WQCV / 12) - Area' 1.2 2.
Outlet Works A)
Outlet Type (Check One) B)
Depth at Outlet Above Lowest Perforation (H) C)
Recommended Mapmum Outlet Area per Row, (AJ D)
Perforation Dimensions: i)
Cinwlar Perforation Diameter or ii)
Width of 2" High Rectangular Perforations E)
Number of Columns (nc, See Table 6a-1 For Ma)dmum) F)
Actual Design Outlet Area per Row (Ao) G)
Number of Rows (m) H)
Total Outlet Area (A,) 3.
Trash Rack A)
Needed Open Area: Ah = 0.5 • (Figure 7 Value)' Ad B)
Type of Outlet Opening (Check One) C)
For 2", or Smaller, Round Opening (Ref.: Figure 6a): i)
Width of Trash Rack and Concrete Opening (W.) from
Table 6a-1 ii)
Height of Trash Rack Screen (Hm) 1, =
12.00 % i=
1 0.12 I Area =
4.250 acres WOCV =
0.08 watershed inches Vol =
0.0332 acre-feet X
Orifice Plate Perforated
Riser Pipe Other.
H =
1.83 feet Q
Ao=
squam Inches D=
r o-jirhca, Of33 ke W =
1 l inc hes nc=
F --- l---1 number Ao=
0.1 square inches nr =
number Aa =
0.6 square inches A, =
square inches 2"
Diameter Round I --
IT High Rectangular Other
W. =
inches Hm =
52 inches
Exhibit E (Sheet 1 of 1)
ST
ST
ST
ST
ST
ST
ST
ST
ST ST ST
ST SS
SS
SS
SS
SS
SS
SS
SS
W W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
EE
E
E
E
E
TELE
TELE
TELE
TELE
E
E
E
ST
ST
ST
ST
SOUTHEAST CORNER SECTION 36,
T.7N, R.69W, FOUND #6 REBAR WITH
2.5" ALUMINUM CAP LS 38318
COLORADO STATE HIGHWAY 68
(HARMONY ROAD)
N0
0
°
0
8
'
5
9
"
W
6
3
9
.
9
8
'
LE
M
A
Y
A
V
E
N
U
E
(1
0
0
'
R
O
W
)
PE
R
G
O
L
D
E
N
M
E
A
D
O
W
S
S
E
C
O
N
D
F
I
L
I
N
G
N89°52'29"E 2652.13'
(BASIS OF BEARINGS)
LOT 2
64,815 sq. ft.
1.488 acres
LOT 1
120,026 sq. ft.
2.755 acres
S0
0
°
0
8
'
5
9
"
E
4
8
5
.
3
3
'
N89°52'31"E 357.55'
N0
0
°
0
8
'
5
9
"
W
5
2
0
.
0
0
'
S89°52'31"W 323.00'S44°45'46"W
48.94'
N89°52'31"E 66.29'
S0
0
°
0
7
'
2
9
"
E
44
.
7
3
'
S0
0
°
0
8
'
5
9
"
E
1
4
5
.
3
8
'
S0
0
°
0
8
'
5
9
"
E
3
4
0
.
9
6
'
ROW
DEDICATED
BY THIS PLAT
486 sq. ft.
0.011 acres
S89°52'31"W 290.24'
SPIRIT OF JOY LUTHERAN SUBDIVISION 2ND FILING
Existing Building
Existing Building
Existing Trash
Enclosure
Existing
Sidewalk
Existing
Telephone
Service
Existing
Light Pole
(2) Proposed 2'
Sidewalk Chases
Existing 24"
Storm Pipe
Existing 24"
Storm Pipe
2,660 SF of Proposed Lawn Area
(PBSI Low Grow Mix per Separate
Document provided by Owner)
2,150 SF of Proposed Tatonka
Poured-In-Place Rubber Surface
(Contractor to Coordinate with Owner)
Proposed Ornamental Fence
1,160 SF of
Crusher Fines
Existing Low
Point of
Parking Lot
Contractor to Grade
Flowline from Edge of
Existing Parking to
Existing Outlet
Structure @ 1%
Minimum Slope
Existing Outlet
Structure
Existing Detention &
Water Quality Area
Contractor to Grade
Flowline from Edge of
Existing Parking to
Existing Outlet
Structure @ 1%
Minimum Slope
Contractor to Grade Proposed
Improvements to Slope to
Proposed Flowline @ 1%
Minimum Slope
Existing 12"
Storm Pipe
Existing
Concrete Pan
Existing
Concrete Pan
Existing Storm
Culvert
Existing Storm
Culvert
Proposed Flowline
Proposed Flowline
Property Line
Easement
Major Contour
Minor Contour
4800
4801
4800
4801
Legend
Flowline
Curb and Gutter
Pavement
Concrete
Swale Flowline
LODLimits of Disturbance
Grade Break
Spot Elevation4800 4800
ProposedExisting
0
Scale:1" = 40'
8040
N
S
W E
NU
M
B
E
R
RE
V
.
DA
T
E
RE
V
I
S
I
O
N
D
E
S
C
R
I
P
T
I
O
N
SHEET NUMBER
ma
r
k
@
b
u
l
l
d
o
g
e
n
g
.
c
o
m
97
0
-
5
0
2
-
6
4
4
4
BULLDOG ENGINEERING, LLC
ASSUMES NO RESPONSIBILITY FOR
EXISTING UTILITY LOCATIONS
(HORIZONTAL OR VERTICAL). THE
EXISTING UTILITIES SHOWN ON
THIS DRAWING HAVE BEEN
PLOTTED FROM THE BEST
AVAILABLE INFORMATION. IT IS
HOWEVER THE RESPONSIBILITY OF
THE CONTRACTOR TO VERIFY THE
LOCATION OF ALL THE UTILITIES
PRIOR TO THE COMMENCEMENT OF
ANY CONSTRUCTION ACTIVITIES.
JOB NUMBER
DATE
Sp
i
r
i
t
o
f
J
o
y
C
h
u
r
c
h
25-005
10-17-2025
10
-
1
7
-
2
0
2
5
Re
l
e
a
s
e
d
F
o
r
C
o
n
s
t
r
u
c
t
i
o
n
45
0
1
S
.
L
e
m
a
y
A
v
e
n
u
e
Wo
r
s
h
i
p
S
p
a
c
e
&
P
l
a
y
g
r
o
u
n
d
Fo
r
t
C
o
l
l
i
n
s
,
C
O
0
C4
Pr
o
p
o
s
e
d
D
r
a
i
n
a
g
e
P
l
a
n
B:\Bulldog Engineering\25-005 Church Improvements\CADD\Sheets\25-005 Drainage Plan.dwg, 10/17/2025 4:00:28 AM, Mark, Bulldog Engineering
NU
M
B
E
R
RE
V
.
DA
T
E
RE
V
I
S
I
O
N
D
E
S
C
R
I
P
T
I
O
N
SHEET NUMBER
ma
r
k
@
b
u
l
l
d
o
g
e
n
g
.
c
o
m
97
0
-
5
0
2
-
6
4
4
4
BULLDOG ENGINEERING, LLC
ASSUMES NO RESPONSIBILITY FOR
EXISTING UTILITY LOCATIONS
(HORIZONTAL OR VERTICAL). THE
EXISTING UTILITIES SHOWN ON
THIS DRAWING HAVE BEEN
PLOTTED FROM THE BEST
AVAILABLE INFORMATION. IT IS
HOWEVER THE RESPONSIBILITY OF
THE CONTRACTOR TO VERIFY THE
LOCATION OF ALL THE UTILITIES
PRIOR TO THE COMMENCEMENT OF
ANY CONSTRUCTION ACTIVITIES.
JOB NUMBER
DATE
NU
M
B
E
R
RE
V
.
DA
T
E
RE
V
I
S
I
O
N
D
E
S
C
R
I
P
T
I
O
N
SHEET NUMBER
ma
r
k
@
b
u
l
l
d
o
g
e
n
g
.
c
o
m
97
0
-
5
0
2
-
6
4
4
4
BULLDOG ENGINEERING, LLC
ASSUMES NO RESPONSIBILITY FOR
EXISTING UTILITY LOCATIONS
(HORIZONTAL OR VERTICAL). THE
EXISTING UTILITIES SHOWN ON
THIS DRAWING HAVE BEEN
PLOTTED FROM THE BEST
AVAILABLE INFORMATION. IT IS
HOWEVER THE RESPONSIBILITY OF
THE CONTRACTOR TO VERIFY THE
LOCATION OF ALL THE UTILITIES
PRIOR TO THE COMMENCEMENT OF
ANY CONSTRUCTION ACTIVITIES.
JOB NUMBER
DATE
Exhibit F (Sheet 1 of 1)
Basin Roofs/Deck
(C=0.95)
Packed Gravel
(C=0.5)
Rubber Playground
(C=0.95)
Concrete
(C=0.95)
Asphalt
(C=0.95)
Landscape
(C=0.20)
Total Area
(SF)
Composite Runoff
Coefficient
Existing Lot (Per 2011
Drainage Report)12,306 0 0 11,972 36,384 124,664 185,326 0.45
Proposed Lot (With
Landscape Improvements)12,616 1,160 2,150 12,609 31,714 126,237 185,326 0.44
Net Change in Area from the
Original Design to the
Proposed Design
310 1,160 2,150 637 -4,670 1,573 0 NA
Composite Runoff Coefficient Calculation
Based on the Existing Conditions, less asphalt has been constructed than designed for in the original design of the Water Quality Pond, resulting in a net loss in
asphalt area as shown above. There will not be any demolition of pavement or other existing elements for the proposed improvements.