HomeMy WebLinkAboutDrainage Reports - 10/07/2014City of Ft. Collin ro Plans
Approved By
FINAL DRAINAGE REPORT
FOR
AVONDALE COTTAGES
RIDGEWOOD HILLS PUD
Prepared by:
Interwest Consulting Group
1218 West Ash, Suite C
Windsor, Colorado 80550
Phone: 970.674.3300
Fax: 970.674.3303
Prepared for:
Habitat For Humanity
4001 S. Taft Hill Road
Fort Collins, Colorado 80525
Phone: 970.223.4522
Fax: 970.223.4524
September 12, 2014
Job Number 1192-117-00
INTCRWCBT CON S U LTI N G G R O UP
I
1
1
1
1 September 12, 2014
' Mr. Wes Lamarque
Fort Collins Utilities — Stormwater
' 700 Wood Street
Fort Collins, CO 80522
1 RE: Final Drainage Report for Avondale Cottages
Dear Wes,
INTBRWHBT C O N S U LT I N G G R O U V
I am pleased to submit for your review and approval, this Final Drainage Report for the
1 Avondale Cottages affordable housing development. I certify that this report for the drainage
design was prepared in accordance with the criteria in the City of Fort Collins Storm Drainage
Manual and is in compliance with the previously approved Final Drainage and Erosion Control
1 Study for Ridgewood Hills PUD — First Filing, prepared by RBD Engineering Consultants, dated
March 3, 1995.
' I appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
1
1 SincerensAA,%
,
Jason T.
�,�
TABLE OF CONTENTS
1. INTRODUCTION............................................................................................................
2. EXISTING CONDITIONS...............................................................................................
3. DEVELOPED CONDITIONS..........................................................................................
4. LOW IMPACT DEVELOPMENT TECHNIQUES.........................................................
5. CONCLUSION.................................................................................................................
6. REFERENCES.................................................................................................................
APPENDIX A - SITE DESCRIPTIONS, CHARACTERISTICS & REFERENCES....
APPENDIX B-DEVELOPED RATIONAL CALCULATIONS ....................................
APPENDIX C - STORM DRAIN SIZING & RIPRAP CALCULATIONS ...................
APPENDIX D - BIORETENTION POND........................................................................
1. INTRODUCTION
This site is legally known as Tract L of Ridgewood Hills PUD — First Filing. It contains
1.51 acres and is bounded by W. Trilby Road to the north, Avondale Road to the west, a
' daycare and condos to the south, and a regional detention pond to the east. The regional
detention pond is labeled as Pond 28 with the drainage study mentioned above. The pond
was designed for the complete build out of contributing drainage basins. The site was
originally anticipated to be commercial use with a convenience store and office/retail
buildings. The proposed use is residential with six single family homes and two shared
single family units.
' 2. EXISTING CONDITIONS
The site is currently vacant with what appears to be native vegetation. The property line
to the south splits the existing private drive with the daycare. A portion of this drive is
' located on the Avondale Cottage site. The majority of the daycare site drains onto the
Avondale Cottage site, and a limited area at the rear of the condos drains to this site.
Currently runoff is conveyed via overland flow and a small drainage swale/depression,
' and as intended, ultimately drains to Pond 28.
' The site was originally intended to be commercial with a convenience store and
office/retail buildings.
3. DEVELOPED CONDITIONS
' The proposed development will consists of 8 single family units and 2 duplex units,
averaging a 1,100 sqft footprint, including the single car garages. Private drives are
' proposed for access to the units with additional parking off of the drives to meet land use
code requirements. The remaining site is either utilized as water quality
enhancement/low impact development, landscape areas, and pedestrian access. The
percent impervious associated with the proposed improvements is 47.5%.
The site is located within Basin 300 of the original drainage report. A detailed
breakdown of the basin percent impervious determination was not available, though the
report anticipated a 56.27% basin imperviousness upon site build -out. Basin 300 consists
' of majority of the daycare site, a small portion of the condominiums, Tract L (proposed
I
Id
Avondale Cottages) and regional detention Pond 28. Pond 28 is designed to detain the
100-yr runoff rate to the 2-yr historic runoff rate. There are a total of 10 basins (totaling
17.73 acres) within Ridgewood that drain to Pond 28 including Basin 300. Basin 300 is a
total of 3.91 acres with the Avondale project being responsible for 1.51 acres _of this
basin. Rather than only looking at the area responsible for the Avondale Cottages
project, we looked at all of Basin 300 (which consists of the regional detention pond,
existing multifamily, and the daycare outside of our site) to determine the runoff volumes
in reference to the rainfall criteria current at the time Ridgewood was designed and the
current rainfall criteria and proposed impervious area. In reference to the previous
rainfall criteria and the Fort Collins Storm Drainage Criteria and Construction Standards
(FCSDCCS) and the percent impervious associated with different land uses, we worked
backwards to determine the originally assumed percent imperviousness of Tract L.
In reference to the original drainage report, Basin 300 is 56.27% impervious and has a
runoff coefficient of 0.64. The detailed calculations supporting these values are not
included in the report. Therefore we needed to back calculate, based on the proposed
uses and the City's criteria manual, to determine the % impervious and runoff
coefficients originally assumed. The outcomes match the proposed uses at the time, with
the Avondale Cottages site proposed to be a convenience store/gas station and
commercial building.
From this information, the runoff volume was calculated from the entire Basin 300, with
the pre-1997 rainfall data, that would have contributed to Pond 28. During a 100-yr
storm, under the old rainfall data, Basin 300 would have contributed 51,414 cu-ft of
runoff volume to Pond 28.
The runoff volume was then calculated from the entire Basin 300 under the proposed
developed conditions, with the current rainfall data and the proposed percent impervious.
During a 100-yr storm, Basin 300 would contribute 44,733 cu-ft of runoff to Pond 28.
This is an ultimate reduction of 6,681 cu-ft of runoff draining from Basin 300 to Pond 28
comparing to the original runoff volume. If there would have been an increase in runoff
volume from the proposed improvements associated with Avondale Cottages, the project
would be responsible to account for the difference in runoff volumes. Since a reduction
in runoff volume is proposed, this project ultimately allows more storage from basins
outside of the responsibility of the Avondale site.
2
Please reference the attached calculations and exhibits.
4. LOW IMPACT DEVELOPMENT TECHNIQUES
In reference to the code requirements for implementation of Low Impact Development
' (LID) techniques, we have looked at many options, along with the site constraints, to
satisfy these requirements. In reference to the geotechnical engineering's soils study, the
soils on this site have a high potential of swell, with a potential change in soil volume of
' 11%. This expansive clay is sitting on impervious sandstone bed rock, approximately 6'
below the surface. With the introduction of ground moisture, there is the potential swell
of 8". With this soil information, we needed to determine means to enhance the water
quality by implementing LID techniques that would minimize ground water infiltration.
' We met with City Stormwater Staff to review the scenario and determined that it would
satisfy the code intent for LID by utilizing a lined bioretention pond/rain garden, and
' would waive the permeable paving requirement if we were able treat majority of the site
with the bioretention pond. With the proposed grading, the bioretention pond/rain garden
' will treat approximately 70% of the site's improved runoff, while also treating 0.47 acres
of the adjacent day care facility. The bioretention pond depth is limited to 12" for water
quality enhancement and is design to have an additional 6" depth to convey the 100-yr
' storm runoff.
5. CONCLUSION
' All computations that have been completed within this report are in compliance with the
CoFC Stormwater Criteria Manual, and Urban Drainage and Flood Control District
requirements and standards. The proposed drainage concepts presented in this report and
' on the construction plans adequately provide for stormwater quantity and quality
treatment of proposed impervious areas. Conveyance elements have been designed to
pass required flows and to minimize future maintenance.
If, at the time of construction, groundwater is encountered, a Colorado Department of
' Health Construction Dewatering Permit will be required.
1 3
6. REFERENCES
a
1. Urban Storm Drainage Criteria Manual (Volumes 1, 2, and 3), Urban Drainage
and Flood Control District, June 2001, Revised April 2008.
2. Storm Drainage Criteria Manual and Construction Standards, City of Fort Collins
Storm Water Utility, City of Fort Collins, Colorado, Updated January, 1997 with
2012 amendments.
3. "Hydrologic Group Rating for Larimer County Area, Colorado", USDA -Natural
Resources Conservation Service, National Cooperative Soil Survey. Web Soil
Survey URL: http://websoilsurvey.nres.usda.gov. [03/28/2014]
4. "Final Drainage and Erosion Control Study for Ridgewood Hills P.U.D. First
Filing", prepared by RBD Inc., Dated March 3, 1995
4
' APPENDIX A - SITE DESCRIPTIONS, CHARACTERISTICS & REFERENCES
VICINITY MAP
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' Hydrologic Soil Group—Ladmer County Area, Colorado
Avondale Cottages
Hydrologic Soil Group
Hydrologic Soil Group— Summary by Map Unit — Larimer County Area, Colorado (CO644)
Map unit symbol
Map unit name
Rating
Acres in AOI
Percent of AOI
26
Cushman fine sandy
loam, 0 to 3 percent
slopes
C
0.6
37.2%
108
Thedalund loam, 3 to 9
percent slopes
C
0.9
62.8%
Totals for Area of Interest
1.5
100.0%
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive precipitation
from long -duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (A/D, B/D, and C/D). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly
wet. These consist mainly of deep, well drained to excessively drained sands or
gravelly sands. These soils have a high rate of water transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well drained
soils that have moderately fine texture to moderately coarse texture. These soils
have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of water
transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink -swell
potential, soils that have a high water table, soils that have a claypan or clay layer
at or near the surface, and soils that are shallow over nearly impervious material.
These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (A/D, B/D, or VD), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in their
natural condition are in group D are assigned to dual classes.
lbl� Natural Resources Web Soil Survey 3/28/2014
i Conservation Service National Cooperative Soil Survey Page 3 of 4
Hydrologic Soil Group—Larimer County Area, Colorado
Avondale Cottages
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff. None Specified
Tie -break Rule: Higher
USDA Natural Resources Web Soil Survey 3/28/2014
2" Conservation Service National Cooperative Soil Survey Page 4 of 4
Ridgewood Hills - First Filin
References
Ridgewood Hills PUD - First Filing - Utility Plans
Dated March 1995
Drainage & Erosion Control Plan, Sheet 7 of 54
doj', 1
4* RCP•, FuTuR f tbMM_VA�
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2
2.14Ar - -
F�
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POND 28
DRAINED AREA 17.3 ACRES
100 YR. WSEL 73.00
VOL. REQUIRED = 3.2 AC —FT
VOL. PROVIDED — 3.2 AC —FT
TOP OF BERM 74.00
2 YR. HISTORICAL RELEASE RATE = 4.33 cfs
ACTUAL RELEASE RATE — 4.3 cfs
SURFACE AREA = 0.57 AC
Final Drainage & Erosion Control Study for Ridgewood Hills PUD - First Filinq
Dated March 3, 1995
Appendix - Composite "C" Values (page 16 of pdf version)
Design
Impervious
Pervious
A,total
i A,imp
Percent
Percent
Composite
Area
"C"
"C.,
(ac.)
(ac.)
Impervious
Pervious
"C.
1l IU.yS I U.zo U.03 1 U.0.3 1 04.-115 1 7J.0/ I U.04
0.95 1 0.25 3.91 1 2.20 56.27 0.64
301 1 0.95 1 0.25 1 2.14 1 1.52 1 71.03 1 28.97 1 0.75
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3.1.6 Runoff Coefficients
The runoff coefficients to be used with the Rational Method referred to in
Section 3.2 "Analysis Methodology" can be determined based on zoning
classifications if the character of the surface is unknown. However, the final
drainage study must calculate a composite coefficient using Table 3-3. Table 3-2
lists the runoff coefficients for the various types of zoning along with the
zoning definitions. Table 3-3 lists coefficients for the different kinds of
surfaces. Since the Land Development Guidance System for Fort Collins allows
land development to occur which may vary the zoning requirements and produce
' runoff coefficients different from those specified in Table 3-2, the runoff
coefficients should not be based solely on the zoning classifications. The
runoff coefficient used for design should be based on the actual conditions of
the proposed development.
The Composite Runoff Coefficient shall be calculated using the following formula:
n
C = (CiAt) / At
i=t
Where C - Composite Runoff Coefficient
C1= Runoff Coefficient for specific area Al
A1= Areas 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
Table-3-2
RATIONAL METHOD MINOR STORM RUNOFF COEFFICIENTS FOR ZONING
Description of Area or Zoning Coefficient
Business: BP,BL..................................... 0.85
Business: BG,HB,C................................... 0.95
Industrial: IL,IP................................... 0.85
Industrial: IG...................................... 0.95
Residential: RE,RLP................................. 0.45
Residential: RL,ML,RP................................ 0.50
Residential: RLM,RMP................................ 0.60
Residential: RM,MM.................................. 0.65
Residential: RH..................................... 0.70
Parks, Cemeteries .................................. 0.25
Playgrounds .................. 0.35
Railroad Yard Areas .......... ....................... 0.40
Unimproved Areas....................................0.20
Zoning Definitions
R-E Estate Residential District - a low density residential area primarily in
outlying areas with a minimum lot area of 9,000 square feet.
R-L Low Density Residential District - low density residential areas located
throughout the City with a minimum lot area of 6,000 square feet.
R-M Medium Density Residential District - both low and medium density
residential areas with a minimum lot area of 6,000 square feet for one -
family or two-family dwellings and 9,000 square feet for a multiple
family dwelling.
R-H High Density Residential District - high density residential areas with a
minimum lot area of 6,000 square feet for one -family or two-family
dwellings, 9,000 square feet for a multiple family dwelling, and 12,000
square feet for other specified uses.
R-P Planned Residential District - designation of areas planned as a unit
(PUD) to provide a variation in use and building placements with a
minimum lot area of 6,000 square feet.
May 1984
Revised January 1997
Design Criteria
3-3
R-L-P Low Density Planned Residential District - areas planned as a unit (PUD)
to permit variations in use, density and building placements, with a
minimum lot area of 6,000 square feet.
R-M-P Medium Density Planned Residential District - designation for medium
' density areas planned as a unit (PUD) to provide a variation in use and
building placements with a minimum lot area of 6,000 square feet.
R-L-M Low Density Multiple Family District - areas containing low density
multiple family units or any other use in the R-L District with a minimum
lot area of 6,000 square feet for one -family or two-family dwellings and
9,000 square feet for multiple -family dwellings.
' M-L Low Density Mobile Home District - designation for areas of mobile home
parks containing independent mobile homes not exceeding 6 units per acre.
M-M Medium Density Mobile Home District - designation for areas of mobile
' home parks containing independent mobile homes not exceeding 12 units per
acre.
B-G General Business District - district designation for downtown business
' areas, including a variety of permitted uses, with minimum lot areas
equal to 1/2 of the total floor area of the building.
B-P Planned Business District - designates areas planned is unit developments
' to provide business services while protecting the surrounding residential
areas with minimum lot areas the same as R-M.
H-B Highway Business District - designates an area of automobile -orientated
' businesses with a minimum lot area equal to 1/2 of the total floor area
of the building.
B-L Limited Business District - designates areas for neighborhood convenience
centers, including a variety of community uses with minimum lot areas
equal to two times the total floor area of the building.
C Commercial District - designates areas of commercial, service and storage
' areas.
I-L Limited Industrial District - designates areas of light industrial uses
with a minimum area of lot equal to two times the total floor area of the
building not to be less than20,000 square feet.
-
I-P Industrial Park District designates light industrial park areas
containing controlled industrial uses with minimum lot areas equal to two
times the total floor area of the building not to be less than 20,000
square feet.
I-G General Industrial District - designates areas of major industrial
development.
T Transition District - designates areas which are in a transitional stage
with regard to ultimate development.
' For current and more explicit definitions of land uses and zoning
classifications, refer to the Code of the City of Fort Collins, Chapters 99 and
118.
' May 1984 Design Criteria
Revised January 1997
' 3-9
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City of Fort Collins
Rainfall Intensity-Duration=Frequency Table
for using the Rational Method
Figure 3-1a
Duration
(minutes)
2-yr
Intensity
(in/hr)
10-yr
Intensity
(in/hr)
100-yr
Intensity
(in/hr)
5
2.85
4.87
9.95
6
2.67
4.56
9.31
7
2.52
4.31
8.80
8
2.40
4.10
8.38
9
2.30
3.93
8.03
10
2.21
3.78
7.72
11
2.13
3.63
7.42
12
2.05
3.50
7.16
13
1.98
3.39
6.92
14
1.92
3.29
6.71
15
1.87
3.19
6.52
16
1.81
3.08
6.30
17
1.75
2.99
6.10
18
1.70
2.90
5.92
19
1.65
2.82
5.75
20
1.61
2.74
5.60
21
1.56
2.67
5.46
22
1.53
2.61
5.32
23
1.49
2.55
5.20
24
1.46
2.49
5.09
25
1.43
2.44
4.98
26
1.40
2.39
4.87
27
1.37
2.34
4.78
28
1.34
2.29
4.69
29
1.32
2.25
4.60
30
1.30
2.21
4.52
31
1.27
2.16
4.42
32
1.24
2.12
4.33
Duration
(minutes)
2-yr
Intensity
(in/hr)
10-yr
Intensity
(in/hr)
100-yr
Intensity
(in/hr)
33
1.22
2.08
4.24
34
1.19
2.04
4.16
35
1.17
2.00
4.08
36
1.15
1.96
4.01
37
1.13
1.93
3.93
38
1.11
1.89
3.87
39
1.09
1.86
3.80
40
1.07
1.83
3.74
41
1.05
1.80
3.68
42
1.04
1.77
3.62
43
1.02
1.74
3.56
44
1.01
1.72
3.51
45
0.99
1.69
3.46
46
0.98
1.67
3.41
47
0.96
1.64
3.36
48
0.95
1.62
3.31
49
0.94
1.60
3.27
50
0.92
1.58
3.23
51
0.91
1.56
3.18
52
0.90
1.54
3.14
53
0.89
1.52
3.10
54
0.88
1.50
3.07
55
0.87
1.48
3.03
56
0.86
1.47
2.99
57
0.85
1.45
2.96
58
0.84
1.43
2.92
59
0.83
1.42
2.89
60
0.82
1.40
2.86
City of Fort Collins
Rainfall Intensity -Duration -Frequency Table
Use of Urban Drainage Intensity Equation for CoFC OF Values
Duration
City of Fort Collins
Intensity (in/I
2- r to- too-
2- r
A
Urban Drainage
Intensity (In/hr)
10- r A
100- r
A
5
2.85
4.87
9.95
2.78
-0.07
4.74
-0.13
9.68
-0.27
6
2.67
4.56
9.31
2.64
-0.03
4.51
-0.05
9.20
-0.11
7
2.52
4.31
8.80
2.52
0.00
4.30
-0.01
8.78
-0.02
8
2.40
4.10
8.38
2.41
0.01
4.11
0.01
8.39
0.01
9
2.30
3.93
8.03
2.31
0.01
3.94
0.01
8.D4
0.01
10
2.21
3.78
7.72
2.21
0.00
3.78
0.00
7.72
0.00
11
2.13
3.63
7.42
2.13
0.00
3.64
0.01
7.43
0.01
12
2.05
3.50
7.16
2.05
0.00
3.51
0.01
7.16
0.00
13
1.98
3.39
6.92
1.98
0.00
3.39
0.00
6.92
0.00
14
1.92
3.29
6.71
1.92
0.00
3.28
-0.01
6.69
-0.02
15
1.87
3.19
6.52
1.86
-0.01
3.17
-0.02
6.48
-0.04
16
1.81
3.08
6.30
1.80
-0.01
3.08
0.00
6.28
-0.02
17
1.75
2.99
6.10
1.75
0.00
2.99
0.00
6.10
0.00
18
1.70
2.90
5.92
1.70
0.00
2.90
0.00
5.93
0.01
19
1.65
2.82
5.75
1.65
0.00
2.82
0.00
5.77
0.02
20
1.61
2.74
5.60
1.61
0.00
2.75
0.01
5.61
0.01
21
1.56
2.67
5.46
1.57
0.01
2.68
0.01
5.47
0.01
22
1.53
2.61
5.32
1.53
0.00
2.61
0.00
5.34
0.02
23
1.49
2.55
5.20
1.49
0.00
2.55
0.00
5.21
0.01
24
1.46
2.49
5.09
1.46
0.00
2.49
0.00
5.09
0.00
25
1.43
2.44
4.98
1.43
0.00
2.43
-0.01
4.97
-0.01
26
1.40
2.39
4.87
1.39
-0.01
2.38
-0.01
4.86
-0.01
27
1.37
2.34
4.78
1.36
-0.01
2.33
-0.01
4.76
-0.02
28
1.34
2.29
4.69
1.34
0.00
2.28
-0.01
4.66
-0.03
29
1.32
2.25
4.60
1.31
-0.01
2.24
-0.01
4.57
-0.03
30
1.30
2.21
4.52
1.28
-0.02
2.19
-0.02
4.48
-0.04
31
1.27
2.16
4.42
1.26
-0.01
2.15
-0.01
4.39
-0.03
32
1.24
2.12
4.33
1.24
0.00
2.11
-0.01
4.31
-0.02
33
1.22
2.08
4.24
1.21
-0.01
2.07
-0.01
4.23
-0.01
34
1.19
2.04
4.16
1.19
0.00
2.03
-0.01
4.15
-0.01
35
1.17
2.00
4.08
1.17
0.00
2.00
0.00
4.08
0.00
36
1.15
1.96
4.01
1.15
0.00
1.96
0.00
4.01
0.00
37
1.13
1.93
3.93
1.13
0.00
1.93
0.00
3.94
0.01
38
1.11
1.89
3.87
1.11
0.00
1.90
0.01
3.88
0.01
39
1.09
1.86
3.80
1.09
0.00
1.87
0.01
3.82
0.02
40
1.07
1.83
3.74
1.08
0.01
1.84
0.01
3.76
0.02
41
1.05
1.80
3.68
1.06
0.01
1.81
0.01
3.70
0.02
42
1.04
1.77
3.62
1.04
0.00
1.78
0.01
3.64
0.02
43
1.02
1.74
3.56
1.03
0.01
1.76
0.02
3.59
0.03
44
1.01
1.72
3.51
1.01
0.00
1.73
0.01
3.54
0.03
45
0.99
1.69
3.46
1.00
0.01
1.71
0.02
3.48
0.02
46
0.98
1.67
3.41
0.99
0.01
1.68
0.01
3.44
0.03
47
0.96
1.64
3.36
0.97
0.01
1.66
0.02
3.39
0.03
48
0.95
1.62
3.31
0.96
0.01
1.64
0.02
3.34
0.03
49
0.94
1.60
3.27
0.95
0.01
1.61
0.01
3.30
0.03
50
0.92
1.58
3.23
0.93
0.01
1.59
0.01
3.25
0.02
51
0.91
1.56
3.18
0.92
0.01
1.57
0.01
3.21
0.03
52
0.90
1.54
3.14
0.91
0.01
1.55
0.01
3.17
0.03
53
0.89
1.52
3.10
0.90
0.01
1.53
0.01
3.13
0.03
54
0.88
1.50
3.07
0.89
0.01
1.51
0.01
3.09
0.02
55
0.87
1.48
3.03
0.88
0.01
1.50
0.02
3.06
0.03
56
0.86
1.47
2.99
0.87
0.01
1.48
0.01
3.02
0.03
57
0.85
1.45
2.96
0.86
0.01
1.46
0.01
2.98
0.02
58
0.84
1.43
2.92
0.85
0.01
1.44
0.01
2.95
0.03
59
0.83
1.42
2.89
0.84
0.01
1.43
0.01
2.92
0.03
60 1
0.82
1.40
2.86 1
0.83
0.01
1.41
0.01
2.88
0.02
U.VV -U.VZ u.uu
Urban Drainage Intensity Equation
/ = C I P'
(C2+1 )C>
Urban Drainage
Inputs
1-hr Rainfall Depths (P,)
2-yr 0.82
10-yr 1.40
100-yr 2.86
Coefficients
C r 28.5
Cz 10
C, 0786651
L
as determined
er to best matchgivenfromthes IDF values.
City of Fort Collins
Design Storms
for using SWMM
Figure 3-1c
Time
(min)
Intensity (in/hr)
2-year
5-yr
10-yr
25-yr
50-yr
100-yr
5
0.29
0.40
0.49
0.63
0.79
1.00
10
0.33
0.45
0.56
0.72
0.90
1.14
15
0.38
0.53
0.65
0.84
1.05
1.33
20
0.64
0.89
1.09
1.41
1.77
2.23
25
0.81
1.13
1.39
1.80
2.25
2.84
30
1.57
2.19
2.69
3.48
4.36
5.49
35
2.85
3.97
4.87
6.30
7.90
9.95
40
1.18
1.64
2.02
2.61
3.27
4.12
45
0.71
0.99
1.21
1.57
1.97
2.48
50
0.42
0.58
0.71
0.92
1.16
1.46
55
0.35
0.49
0.60
0.77
0.97
1.22
60
0.30
0.42
0.52
0.67
0.84
1.06
65
0.20
0.28
0.39
0.62
0.79
1.00
70
0.19
0.27
0.37
0.59
0.75
0.95
75
0.18
0.25
0.35
0.56
0.72
0.91
80
0.17
0.24
0.34
0.54
0.69
0.87
85
0.17
0.23
0.32
0.52
0.66
0.84
90
0.16
0.22
0.31
0.50
0.64
0.81
95
0.15
0.21
0.30
0.48
0.62
0.78
100
0.15
0.20
0.29
0.47
0.60
0.75
105
0.14
0.19
0.28
0.45
0.58
0.73
110
0.14
0.19
0.27
0.44
0.56
0.71
115
0.'13
0.18
0.26
0.42
0.54
0.69
120
0.13
0.18
0.25
0.41
0.53
0.67
Storm
Duration
I Rainfall Depth (in)
2-year
5- r
10- r
25- r
50- r
100- r
1-hr
0.82
1.14
1.40
1.81
2.27
2.86
2-hr
0.98
1.36
1.71
2.31
2.91
3.67
Note: The City of Fort Collins SWWM input hyetopgrah is used to calculate the
1-hr and 2-hr storm rainfall depths for the different storm events.
These are the 1-hour storm
depthsthat are used in the
Urban Drainage intensity
equation, derived from the CoFC
Hyetograph.
n
' APPENDIX B - DEVELOPED RATIONAL CALCULATIONS
r:3
WEST TRILBY ROAD
9
I
I I TRACT K
DRAINAGE, ACCESS &
UTILITY EASEMENT
(EXISTING REGIONAL
DETENTION POND #28)
I I
I
I
40 I 20 0 40 80
SCALE: 1 " = 40'
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Avondale Cottages
Attenuated Flows for Pipe Sizing
Design Engineer: J.Claeys, PE
Design Finn: Interest Consulting Group
Project Number. 1192-117-00
Date: September 12. 2014
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District. June 2001
City of Fort Collins - Storm Water Criteria Manual (1997)
EQUATIONS:
1, = 1, + 1,-Equaean RO-2
0.395(1.1— C, )L .Equation RO-3
1, = Sn,1
CONSTRAINTS:
300 IT - Overland flow shall not exceed for developed condition
500 ft - Overland flow shall not exceed for undeveloped condition
V = C. s", -Equation ROi
_ L
1' 60V
Final I, = minimum of I, + I, and urbanized basin check
recommended minimum I, = 5 min for urbanized basins
On = n-yr peak discharge (cfs) 28.SI = rainfall intensity (in/hr)
P
A Cn = n-yr runoff coefficient/ _ � �.n P, =one -hour point rainfall depth (in)
n )
I„ = n-yr rainfall intensity (inPo(10+1,
r) 4 =time of concentration (min)
A = drainage area (ac) 1`1 i2 , = 0.82 in. P,.,0 , = 1.40
P,." , = 1.14 in. P,.,GDY, = 2.86
BASINS:
UD-Sewer- OP/Manhole Of
Contributing Basins D1+OF1
Contributing Area (acres) 1.52
C, Cs CIO Cim
Runoff Coefficients 0.40 0.45 0.50 0.63
Overland Flow Time
Length (ft) 137
Slope (ft/ft) 0.02
t,(min) 11.19
Travel Time
Type of travel
Length (fl) Slope (%) Surface C� Velocity (f 1s) 1, (min)
246 1.29% Paved Areas 20 2.27 1.81
i
Final Time of Concentration - tc (min)
t,(min) 13.00
Intensities (Inthr)
2-yr 5-yr 10-yr 100-yr
1.98 2.76 3.39 6.92
Discharge (cfs)
2-yr 5-yr 10-yr 100-yr
1.19 1.87 2.57 6.58
Avondale Cottages
Attenuated Flows for Pipe Sizing
Design Engineer: J.Claeys, PE
Design Firm: Interwest Consulting Group
Project Number 1192-117-00
Date: 816/20149112
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001
City of Fort Collins. Storm Water Criteria Manual (1997)
EQUATIONS.
t, = It, +/, -Equation R0.2
0.395(l.l—C,}FL -Equation RO-3
1, — Su I,
CONSTRAINTS:
300 H - Overland flow shall not exceed for developed condition
500 fl - Overland flow shall not exceed for undeveloped condition
V = C,S.0.3 -Equation RD
_ L
Al"60V
Final 1, = minimum of 1, + t, and urbanized basin check
recommended minimum I� = 5 min for urbanized basins
Q„ = n-yr peak discharge (cfs) 2R.SP,
1 = rainfall intensity (iNhr)
Q. = Cnln A
Cn = n-yr runoff coefficient! = q ���
(10+0
Pt =one -hour point rainfall depth (in)
In = n-yr rainfall intensity Im/hr)
t, = time of concentration (min)
A= drainage area(ac)
P1-2W 0.82 in. Pr_,q.,= 1.40
Pt.sr, = 1.14 in. P,_,00,' = 2.86
BASINS:
UD-Sewer- DPIManhole
D4
Contributing Basins
D4+OF2
Contributing Area (acres)
0.36
C2 Cs CIO Cleo
Runoff Coefficients
0.30 0.37 0.43 0.59
Overland Flow Time
' Length (H) 57
Slope (fUfl) 0.05
1, (min) 5.84
Trawi Time
Type of Travel
Length (ft) Slope (%) Surface Cv Velocity (ftis) 1, (min)
141 1.77% Paved Areas 20 2.66 0,88
Total Time 0.88
Final Time of ConbeMration - tc (min)
t. (min) 6.72
Intensities (in/hr)
2-yr 5-yr
10-yr
100-yr
2 55 3.54
4.35
8.89
Discharge (cfs)
2-vr 5-yr
10-yr
100-yr
0.28 0.47
0.68
1.89
APPENDIX C - STORM DRAIN SIZING & RIPRAP CALCULATIONS
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' Avondale Cottages
Riprap Protection Downstream of Culverts -Circular Conduits
Design Engineer: J.Claeys
' Design Firm: Interwest Consulting Group
Project Number: 1192-117-00
Date: September 12, 2014
' DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District
PIPE/FLOW PROPERTIES:
' East Access Culvert
Design Flow, Q (cfs) 9.29
Pipe Dia., D, (ft) 1.25
' Tailwater depth, Yx (ft) - if known 2.45
'Pipe Flow and Tallwaier Depth from Hydoilow
PROTECTION DESIGN:
' Step l: Is Method Applicable, CM, 2S'=6 Q/D," = 5.32 Method Applicable
Step 2: Apply Diameter Adjustments if Pipe Flow is Supercritical (Values from HY-5)
Flow Velocity (ftts) .
7.57
Flow Depth (ft)
1.25
Froude No.
1.19
Pipe Flow is:
Supercritical
De or De=
1.25
Step 3: Determine (M�1.5 or W. f.5=
6.65
Step 4: Determine YAM, or Y,/D,=
1.00
Step 5: Determine Required Riprap Size, dsp (Figure MD-21)
Use Type L Riprap
Riprap Type
dsp - Median Rock Size
(inches)
L
9
M
12
H
18
VH
24
Step 5: Determine Extent of Riprap Protection, L. (Equation MD-23)
Expansion Factor, from Fig MD-23
1
2 tan B s:z
A, = Q = 1.69 'using V=5.5Ns for erosive soils
v
' L I A` D`ft 0.63
°—(2tan0�Y )
Step 6: Determine Width of Riprap Protection
Step 7: Determine Riprap Proection Thickness
Step 8: Determine Cutoff Wall Depth (B)
PROTECTION SUMMARY:
L, not to be less than 3D = 3.75 ft
L. not to be greater than 10D = 12.50 it
Use L, of 3.75 ft
W, = 3D = 3.75 ft
T, = 2'dsp = 16 inches
B = D,12+T, = 2.13 ft
East Access Culvert
Riprap Type
L
Length of Basin (ft)
3.75 It
Width of Basin (it)
3.75 ft
Riprap Layer Thickness (in)
18 inches
Concrete Cutoff Wall Depth (ft)
2.13 ft
DRAINAGE CRITERIA MANUAL (V. 1)
MAJOR DRAINAGE
FE
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APIA
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0 .1 .2 .3 .4
TAILWATER DEPTH/ CONDUIT HEIGHT, Yt/D
Figure M13-23—Expansion Factor for Circular Conduits
Rev. 01/2004 MD-111
Urban Drainage and Flood Control District
Worksheet for Outlet Structure Weir Capacity
Project Description
Flow Element: Generic Weir
Solve For: Crest Length
InputData.
r
Discharge: 6.58 ft'/s
Headwater Elevation: 100.50 ft
Crest Elevation: 100.00 ft
Weir Coefficient: 2.60 us
Results
..., ,
Crest Length:
7.16
ft
Headwater Height Above Crest:
0.50
ft
Flow Area:
3.58
ft'
Velocity:
1.84
ft/s
Wetted Perimeter:
8.16
ft
Top Width:
7.16
ft
APPENDIX D - BIORETENTION POND
i7
IL
Design Procedure Form: Rain Garden (RG)
'
Sheet 1 of 2
Designer:
J.Claeys
Company:
Interv,est Consulting Group
'
Date:
Project:
September 12, 2014
Avondale Cottages
Location:
Avondale Road & Trilby Road, Fort Collins, CO
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, I,
1„ =
58.6
%
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = l,(100)
=
0.586
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time
WQCV =
0.19
watershed inches
(WQCV= 0.8' (0.91• i'- 1.19' 12+ 0.78' i)
D) Contributing Watershed Area (including min garden area)
Area =
66,034
sq ft
E) Water Quality Capture Volume (WQCV) Design Volume
VwncV =
cu ft
Vol = (WQCV / 12)' Area
F) For Watersheds Outside of the Denver Region, Depth of
dv =
0.43
in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region,
Vwocv GmFR =
11,M94
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 i( a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum)
12
in
B) Rain Garden Side Slopes (Z = 4 min., hors. dist per unit vertical)
Z =
4.00
ft / 1t
(Use "0" d min garden has vertical walls)
C) Mimimum Flat Surface Area
AM,,, =
680
sq ft
D) Actual Flat Surface Area
AAA„. =
685
sq ft
E) Area at Design Depth (Top Surface Area)
A, =
1155
sq ft
F) Rain Garden Total Volume
VT=
920
cult
(V,= ((A,.+Ar ") 12) * Depth)
3. Growing Media
nose One
Q 18" Rain Garden Growing Media
O Other (Explain):
4. Underdrain System
Chooseone
r
* YES -7
A) Are underdrains provided?
p NO
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage
y=
3.7
It
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours
Vol,; =
1.019
cu ft
iii) Orifice Diameter, 3/8" Minimum
Du =
0.65
in
Avondale UD-BMP v3.03.xlsm, RG
9/12/2014, 5:49 PM
Design Procedure Form: Rain Garden (RG)
Sheet 2 of 2
Designer: J.Claeys
Company: Imerivest Consulting Group
Date: September 12, 2014
Project: Avondale Cottages
Location: Avondale Road 8 Trilby Road, Fort Collins, CO
Choose One
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
* YES
A) Is an impermeable liner provided due to proximity
O NO
of structures or groundwater contamination?
PROVIDE A 30 MIL (MIN) PVC LINER WITH CDOT CLASS B
GEOTE%TILE ABOVE n. USE THE SAME GEOTEXTILE BELOW
THE LINER IF THE SUBGRADE IS ANGULAR
Goose One
e. Inlet / Outlet Control
p Sheet Flow- No Energy Dissipation Required
A) Inlet Control
O concentrated Row• Energy Dissipation Provided
7. Vegetation
Q Seed (Plan for frequent weed control)
0 Plantings
0 Sand Grown or Other Hlgh Inflltra0on5od
Goose one
8. Irrigation
TES
A) Will the rain garden be irrigated?
O NO
Notes:
Avondale UD-BMP v3.03.xlsm, RG
9/12/2014, 5:49 PM