HomeMy WebLinkAboutAVONDALE COTTAGES - FDP - FDP140018 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL 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
August 6, 2014
Job Number 1192-117-00
August 6, 2014
Mr. Wes Lamarque
Fort Collins Utilities – Stormwater
700 Wood Street
Fort Collins, CO 80522
RE: Final Drainage Report for Avondale Cottages
Dear Wes,
I am pleased to submit for your review and approval, this Final Drainage Report for the
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
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.
Sincerely,
Jason T. Claeys, P.E., LEED AP
Interwest Consulting Group
TABLE OF CONTENTS
1. INTRODUCTION ................................................................................................................................................. 1
2. EXISTING CONDITIONS .................................................................................................................................... 1
3. DEVELOPED CONDITIONS ............................................................................................................................... 1
4. LOW IMPACT DEVELOPMENT TECHNIQUES .............................................................................................. 3
5. CONCLUSION ...................................................................................................................................................... 3
6. REFERENCES ...................................................................................................................................................... 3
APPENDIX A — SITE DESCRIPTIONS, CHARACTERISTICS & REFERENCES ........................................ A
APPENDIX B — DEVELOPED RATIONAL CALCULATIONS ........................................................................ B
APPENDIX C — STORM DRAIN SIZING & RIPRAP CALCULATIONS ....................................................... C
APPENDIX D — BIORETENTION POND ............................................................................................................ D
1
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 55.8%.
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
2
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 45,775 cu-ft of runoff to Pond 28.
This is an ultimate reduction of 5,639 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.
3
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 80% of the site’s improved runoff. 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.
6. REFERENCES
1. Urban Storm Drainage Criteria Manual (Volumes 1, 2, and 3), Urban Drainage
4
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.nrcs.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
APPENDIX A — SITE DESCRIPTIONS, CHARACTERISTICS & REFERENCES
vicinity map
Scale: 1" = 1000'
Hydrologic Soil Group—Larimer County Area, Colorado
(Avondale Cottages)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
3/28/2014
Page 1 of 4
4482580 4482590 4482600 4482610 4482620 4482630 4482640 4482650 4482660
4482580 4482590 4482600 4482610 4482620 4482630 4482640 4482650 4482660
492860 492870 492880 492890 492900 492910 492920 492930 492940 492950 492960 492970 492980
492860 492870 492880 492890 492900 492910 492920 492930 492940 492950 492960 492970 492980
40° 29' 40'' N
105° 5' 3'' W
40° 29' 40'' N
105° 4' 58'' W
40° 29' 37'' N
105° 5' 3'' W
40° 29' 37'' N
105° 4' 58'' W
N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 25 50 100 150
Feet
0 5 10 20 30
Meters
Map Scale: 1:592 if printed on A landscape (11" x 8.5") sheet.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at 1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil line
placement. The maps do not show the small areas of contrasting
soils that could have been shown at a more detailed scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more accurate
calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as of
the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
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 C/D), 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.
Hydrologic Soil Group—Larimer County Area, Colorado Avondale Cottages
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
3/28/2014
Page 3 of 4
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil Group—Larimer County Area, Colorado Avondale Cottages
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
3/28/2014
Page 4 of 4
Ridgewood Hills - First Filing
References
Ridgewood Hills PUD - First Filing - Utility Plans
Dated March 1995
Drainage & Erosion Control Plan, Sheet 7 of 54
Final Drainage & Erosion Control Study for Ridgewood Hills PUD - First Filing
Dated March 3, 1995
Appendix - Composite "C" Values (page 16 of pdf version)
Avondale Cottages
RUNOFF VOLUME COMPARISON
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
Old Rainfall w/ Original Runoff Coefficient versus New Rainfall w/ Proposed Runoff Coefficient
Area
(acres)
%
Impervious*
Runoff
Coefficient (C2 )**
Runoff
Coefficient (C100)
Area
(acres)
%
Impervious*
Runoff
Coefficient (C2 )**
Runoff
Coefficient (C100)
0.11 60.00% 0.70 0.88 0.11 60.00% 0.70 0.88
0.67 90.00% 0.85 1.00 0.67 90.00% 0.85 1.00
1.62 10.00% 0.25 0.31 1.62 10.00% 0.25 0.31
1.51 90.84% 0.95 1.00 1.51 55.81% 0.66 0.82
3.91 56.27% 0.64 0.79 3.91 42.76% 0.52 0.65
Time
(min)
Intensity
(in/hr)
Incremental
Runoff Volume
(cu-ft)
Cumulative
Runoff Volume
(cu-ft)
Time
(min)
Intensity
(in/hr)
Incremental
Runoff Volume
(cu-ft)
Cumulative
Runoff Volume
(cu-ft)
5 9.00 8,383 8,383 5 9.95 7,630 7,630
10 7.30 6,799 15,182 10 7.72 5,920 13,551
15 6.00 5,588 20,770 15 6.52 5,000 18,551
20 5.20 4,843 25,614 20 5.60 4,295 22,845
25 4.60 4,284 29,898 25 4.98 3,819 26,665
30 4.15 3,865 33,764 30 4.52 3,466 30,131
35 3.80 3,539 37,303 35 4.08 3,129 33,260
40 3.50 3,260 40,563 40 3.74 2,868 36,128
45 3.25 3,027 43,590 45 3.46 2,653 38,781
50 3.00 2,794 46,384 50 3.23 2,477 41,258
55 2.80 2,608 48,992 55 3.03 2,324 43,582
5 10 15 20 25 35 40 45 50 55
6.0
5.2
4.6
4.15
3.8
3.5
3.25
3.0
2.6
2.8
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
Intensity (in/hr)
City of Fort Collins
Rainfall Intensity-Duration-Frequency Curve
2-yr (FTC)
10-yr (FTC)
100-yr (FTC)
2-yr (UD)
10-yr (UD)
100-yr (UD)
100-yr
10-yr
0.0
1.0
2.0
3.0
4.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0
Duration (min)
2-yr
10-yr
Duration
(minutes)
2-yr
Intensity
(in/hr)
10-yr
Intensity
(in/hr)
100-yr
Intensity
(in/hr)
Duration
(minutes)
2-yr
Intensity
(in/hr)
10-yr
Intensity
(in/hr)
100-yr
Intensity
(in/hr)
5 2.85 4.87 9.95 33 1.22 2.08 4.24
6 2.67 4.56 9.31 34 1.19 2.04 4.16
7 2.52 4.31 8.80 35 1.17 2.00 4.08
8 2.40 4.10 8.38 36 1.15 1.96 4.01
9 2.30 3.93 8.03 37 1.13 1.93 3.93
10 2.21 3.78 7.72 38 1.11 1.89 3.87
11 2.13 3.63 7.42 39 1.09 1.86 3.80
12 2.05 3.50 7.16 40 1.07 1.83 3.74
13 1.98 3.39 6.92 41 1.05 1.80 3.68
14 1.92 3.29 6.71 42 1.04 1.77 3.62
15 1.87 3.19 6.52 43 1.02 1.74 3.56
16 1.81 3.08 6.30 44 1.01 1.72 3.51
17 1.75 2.99 6.10 45 0.99 1.69 3.46
18 1.70 2.90 5.92 46 0.98 1.67 3.41
19 1.65 2.82 5.75 47 0.96 1.64 3.36
20 1.61 2.74 5.60 48 0.95 1.62 3.31
21 1.56 2.67 5.46 49 0.94 1.60 3.27
22 1.53 2.61 5.32 50 0.92 1.58 3.23
23 1.49 2.55 5.20 51 0.91 1.56 3.18
24 1.46 2.49 5.09 52 0.90 1.54 3.14
25 1.43 2.44 4.98 53 0.89 1.52 3.10
26 1.40 2.39 4.87 54 0.88 1.50 3.07
27 1.37 2.34 4.78 55 0.87 1.48 3.03
28 1.34 2.29 4.69 56 0.86 1.47 2.99
29 1.32 2.25 4.60 57 0.85 1.45 2.96
30 1.30 2.21 4.52 58 0.84 1.43 2.92
31 1.27 2.16 4.42 59 0.83 1.42 2.89
32 1.24 2.12 4.33 60 0.82 1.40 2.86
Figure 3-1a
City of Fort Collins
Rainfall Intensity-Duration-Frequency Table
for using the Rational Method
Duration 2-yr 10-yr 100-yr 2-yr ∆∆∆∆ 10-yr ∆∆∆∆ 100-yr ∆∆∆∆
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 8.04 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 2-yr 0.82
12 2.05 3.50 7.16 2.05 0.00 3.51 0.01 7.16 0.00 10-yr 1.40
13 1.98 3.39 6.92 1.98 0.00 3.39 0.00 6.92 0.00 100-yr 2.86
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 C 1 28.5
17 1.75 2.99 6.10 1.75 0.00 2.99 0.00 6.10 0.00 C 2 10
18 1.70 2.90 5.92 1.70 0.00 2.90 0.00 5.93 0.01 C 3 0.786651
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
Coefficients
Intensity (in/hr)
Urban Drainage
Intensity (in/hr)
City of Fort Collins
Urban Drainage
Inputs
Urban Drainage Intensity Equation
1-hr Rainfall Depths (P 1 )
City of Fort Collins
Rainfall Intensity-Duration-Frequency Table
Use of Urban Drainage Intensity Equation for CoFC IDF Values
This cell was determined
using Solver to best match
intensities given from the
Fort Collins IDF values.
C 3
2
1 1
( c )
C t
C P
I
+
=
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
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
City of Fort Collins
Design Storms
for using SWMM
Figure 3-1c
Time
(min)
Intensity (in/hr)
These are the 1-hour storm
2-year 5-yr 10-yr 25-yr 50-yr 100-yr
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
Storm
Duration
Rainfall Depth (in)
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
depths that are used in the
Urban Drainage intensity
equation, derived from the CoFC
Hyetograph.
B
APPENDIX B — DEVELOPED RATIONAL CALCULATIONS
TRACT K
WEST TRILBY ROAD
AVONDALE ROAD
LOT 2
LOT 1
LOT 5
LOT 4
LOT 3
LOT 6
LOT 7
LOT 8
LOT 9
LOT 10
PREPARED FOR
PROJ. NO.
DATE:
SCALE (H):
SCALE (V):
CHECKED BY:
DESIGNED BY:
PROJECT NAME
Avondale Cottages
Drainage Exhibit
08/06/2014
1"=X'
N/A
JTC
RA
1192-117-00
X of XX
LEGEND
SILT FENCE
INLET PROTECTION
DRAINAGE ARROW
BASIN DESIGNATION
BASIN AREA
BASIN COEFFICIENT (5-YR)
DESIGN POINT
0
40'
40 20 40 80
SCALE: 1" =
Avondale Cottages
DEVELOPED IMPERVIOUS AREA CALCULATION
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised August 2006)
BASINS:
C2 C5 C10 C100 C2 C5 C10 C100
0.89 0.90 0.92 0.96 0.89 0.90 0.92 0.96
0.71 0.73 0.75 0.81 0.73 0.75 0.77 0.83
0.71 0.73 0.75 0.81 0.73 0.75 0.77 0.83
0.23 0.30 0.36 0.50 0.28 0.35 0.42 0.58
0.02 0.08 0.15 0.35 0.04 0.15 0.25 0.50
C2 C5 C10 C100
D1 C 41,801 0.960 13,749 9,529 1,202 0 17,322 56.0% 0.38 0.43 0.49 0.62
D2 C 6,392 0.147 0 1,856 1,134 0 3,402 42.1% 0.29 0.36 0.42 0.59
D3 C 4,809 0.110 3,104 0 422 0 1,220 72.4% 0.51 0.55 0.59 0.69
OF1 C 20,502 0.471 10,605 3,225 1,222 0 5,450 71.3% 0.50 0.54 0.58 0.68
OF2 C 17,063 0.392 0 5,789 2,278 0 8,997 30.5% 0.23 0.31 0.38 0.57
OF1 + D1 C 62,303 1.430 24,354 12,755 2,423 0 22,771 57.5% 0.39 0.44 0.49 0.62
Total C 90,567 2.079 27,458 20,399 6,257 0 36,453 50.6% 0.34 0.40 0.46 0.60
Roof 90%
COMPOSITE
Weighted %
Impervious
Alawn
(sq feet)
Apavers
(sq feet)
Lawns, clayey soil
Awalk
(sq feet)
Aroof
(sq feet)
0%
Pavers 40%
Walk 90%
Land Use % Impervious
Hydrologic Soil
Classification B
Runoff Coefficient
Hydrologic Soil
Classification C
Runoff Coefficient
Paved 100%
Sub-basin
Designation
Apaved
(sq feet)
Atotal
(acres)
Atotal
(sq feet)
Soil
Type
J.Claeys
Interwest Consulting Group
1192-117-00
Avondale Cottages
DEVELOPED TIME OF CONCENTRATION
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised August 2006)
EQUATIONS:
-Equation RO-3 -Equation RO-4 -Urbanized Check Equation RO-5
-Equation RO-3
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition
500 ft - Overland flow shall not exceed for undeveloped condition
Final t c = minimum of t i + t t and urbanized basin check
recommended minimum t c = 5 min for urbanized basins
BASINS:
Type of Travel
Surface
Cv
D1 D1 0.43 0.960 79 0.0677 5.77 241 0.0162 Paved Areas 20 2.54 1.58 7.35 11.78 7.35
D2 D2 0.36 0.147 70 0.0392 7.20 40 0.0714 Paved Areas 20 5.34 0.13 7.33 10.61 7.33
D3 D3 0.55 0.110 16 0.0463 2.42 109 0.0112 Paved Areas 20 2.12 0.85 5.00 10.69 5.00
OF1 OF1 0.54 0.471 134 0.0198 9.45 161 0.0197 Paved Areas 20 2.81 0.96 10.40 11.64 10.40
OF2 OF2 0.31 0.392 57 0.0526 6.31 142 0.0250 Grassed Waterway 15 2.37 1.00 7.31 11.10 7.31
REMARKS
tc
Urban
Check
Final tc
(min)
tc
=ti
+tt
SLOPE (min)
(ft/ft)
VEL.
(ft/s)
tt
ti (min)
(min)
LENGTH Table RO-2
(ft)
SUB-BASIN DATA
INITIAL/OVERLAND
TIME (ti)
DESIGN
POINT
Sub-basin C5
AREA
(acres)
LENGTH
(ft)
TRAVEL TIME (tt)
J.Claeys
Interwest Consulting Group
1192-117-00
August 6, 2014
SLOPE
(ft/ft)
Avondale Cottages
DEVELOPED PEAK RUNOFF
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
City of Fort Lupton - Standards and Specifications, June 1994 (Rainfall Depths)
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised August 2006)
EQUATIONS: I = rainfall intensity (in/hr)
Q n = n-yr peak discharge (cfs) P 1 = one-hour point rainfall depth (in)
C n = n -yr runoff coefficient t c = time of concentration (min)
I n = n -yr rainfall intensity (in/hr) P 1-2yr = 0.82 in
A n = Basin drainage area (ac) P 1-5yr = 1.42 in
P 1-10yr = 1.68 in
P 1-100yr = 2.71 in
BASINS:
Runoff Coeff.
(C5
)
C(A)
(acres)
Intensity
(in/hr)
Q (ft
3
/s)
Runoff Coeff.
(C5
)
C(A)
(acres)
Intensity
(in/hr)
Q (ft
3
/s)
Runoff Coeff.
(C10
)
C(A)
(acres)
Intensity
(in/hr)
Q (ft
3
/s)
Runoff Coeff.
(C100
)
C(A)
(acres)
Intensity
(in/hr)
Q (ft
3
/s)
D1 D1 0.960 7.35 0.38 0.36 4.29 1.55 0.43 0.41 4.29 1.78 0.49 0.47 5.07 2.37 0.62 0.59 8.18 4.86
D2 D2 0.147 7.33 0.29 0.04 4.29 0.18 0.36 0.05 4.29 0.23 0.42 0.06 5.08 0.32 0.59 0.09 8.19 0.70
D3 D3 0.110 5.00 0.51 0.06 4.81 0.27 0.55 0.06 4.81 0.29 0.59 0.07 5.69 0.37 0.69 0.08 9.18 0.70
Maple Hill - Fourth Replat
Attenuated Flows for Pipe Sizing
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001
EQUATIONS:
-Equation RO-3 -Equation RO-4
-CoFC Tov Equation
CONSTRAINTS:
300 ft - Overland flow shall not exceed for developed condition Final t c = minimum of t i + t t and urbanized basin check
500 ft - Overland flow shall not exceed for undeveloped condition recommended minimum t c = 5 min for urbanized basins
Qn
= n -yr peak discharge (cfs) I = rainfall intensity (in/hr)
Cn
= n -yr runoff coefficient P1
= one-hour point rainfall depth (in)
In = n -yr rainfall intensity (in/hr) tc
= time of concentration (min)
A = drainage area (ac) P1-2yr
= 0.82 in. P1-10yr
= 1.40
P1-5yr
= 1.14 in. P1-100yr
= 2.86
BASINS:
UD-Sewer - DP/Manhole D1
Contributing Basins D1+OF1
Contributing Area (acres) 1.43
C2
C5
C10
C100
Runoff Coefficients 0.39 0.44 0.49 0.62
Overland Flow Time
Length (ft) 137
Slope (%) 0.02
2-yr 5-yr 10-yr 100-yr
ti
(min) 11.30 11.30 11.30 11.30
Travel Time
Length (ft) Slope (%) Type of Travel Surface Cv
Velocity (ft/s) tt
(min)
246 1.29% Paved Areas 20 2.27 1.81
Total Time 1.81
Final Time of Concentration - tc (min)
2-yr 5-yr 10-yr 100-yr
13.11 13.11 13.11 13.11
Intensities (in/hr)
2-yr 5-yr 10-yr 100-yr
1.98 2.75 3.37 6.89
Discharge (cfs)
2-yr 5-yr 10-yr 100-yr
1.10 1.73 2.39 6.15
J. Claeys, PE
Interwest Consulting Group
1192-117-00
C
APPENDIX C — STORM DRAIN SIZING & RIPRAP CALCULATIONS
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Gilcrest Bus Facility
Riprap Protection Downstream of Culverts-Circular Conduits
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA:
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, Revised April 2008
PIPE/FLOW PROPERTIES:
7.98
1.25
2.98
*Pipe Flow and Tailwater Depth from HY-8
PROTECTION DESIGN:
Step 1: Is Method Applicable, Q/D c
2.5 O6 Q/D
c
2.5
= 4.57
Step 2: Apply Diameter Adjustments if Pipe Flow is Supercritical (Values from HY-8)
Flow Velocity (ft/s) 6.50
Flow Depth (ft) 1.25
Froude No. 1.02
Pipe Flow is: Supercritical
D c
or D a = 1.25
Step 3: Determine Q/D c
1.5
or Q/D a
1.5
= 5.71
Step 4: Determine Y t
/D c
or Y t
/D a
= 1.00
Step 5: Determine Required Riprap Size, d 50
(Figure MD-21)
Riprap Type
d 50 - Median Rock Size
(inches)
L 9
M 12
H 18
VH 24
Step 5: Determine Extent of Riprap Protection, L p (Equation MD-23)
Expansion Factor, from Fig MD-23
5.95
1.45 *using V=5.5ft/s for erosive soils
L p not to be less than 3D = 3.75 ft
-0.53 ft L p not to be greater than 10D = 12.50 ft
Use L p of 3.75 ft
Step 6: Determine Width of Riprap Protection W p = 3D = 3.75 ft
Step 7: Determine Riprap Proection Thickness T p
= 2*d 50 = 18 inches
Step 8: Determine Cutoff Wall Depth (B) B = D c /2+T p = 2.13 ft
PROTECTION SUMMARY:
L
3.75 ft
3.75 ft
Project Description
Flow Element: Generic Weir
Solve For: Crest Length
Input Data
Discharge: 6.06 ft³/s
Headwater Elevation: 100.50 ft
Crest Elevation: 100.00 ft
Weir Coefficient: 2.60 US
Results
Crest Length: 6.59 ft
Headwater Height Above Crest: 0.50 ft
Flow Area: 3.30 ft²
Velocity: 1.84 ft/s
Wetted Perimeter: 7.59 ft
Top Width: 6.59 ft
Worksheet for Outlet Structure Weir Capacity
D
APPENDIX D — BIORETENTION POND
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia = 56.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.560
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.18 watershed inches
(WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i)
D) Contributing Watershed Area (including rain garden area) Area = 41,801 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = 0.43 in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER = 622.6 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 = 12 in
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin = 415 sq ft
D) Actual Flat Surface Area AActual = 423 sq ft
E) Area at Design Depth (Top Surface Area) ATop = 788 sq ft
F) Rain Garden Total Volume VT= 606 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 = 3.3 ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 = 623 cu ft
iii) Orifice Diameter, 3/8" Minimum DO = 0.52 in
Design Procedure Form: Rain Garden (RG)
J.Claeys
Interwest Consulting Group
August 6, 2014
Avondale Cottages
Avondale Road & Trilby Road, Fort Collins
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
Avondale UD-BMP_v3.03.xlsm, RG 8/6/2014, 8:13 AM
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)
J.Claeys
Interwest Consulting Group
August 6, 2014
Avondale Cottages
Avondale Road & Trilby Road, Fort Collins
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
Avondale UD-BMP_v3.03.xlsm, RG 8/6/2014, 8:13 AM
18 inches
2.13 ft
East Access Culvert
East Access Culvert
J.Claeys
Interwest Consulting Group
1192-117-00
August 6, 2014
Design Flow, Q (cfs)
Pipe Dia., Dc (ft)
Tailwater depth, Yt (ft) - if known
Concrete Cutoff Wall Depth (ft)
Use Type L Riprap
Length of Basin (ft)
Method Applicable
Width of Basin (ft)
Riprap Type
Riprap Layer Thickness (in)
= =
V
Q
At
=
2 tan θ
1
=
−
= c
t
t
p D
Y
A
L 2 tan θ
1
August 6, 2014
City of Fort Collins - Storm Water Criteria Manual (1997)
( ) 0 .786
1
10
28 . 5
t c
P
I
+
Q n = C n I n A =
t c = t i + t t 0 . 5
V = C v S w
V
L
tt
60
( ) =
0 .33
5
0 . 395 1 . 1
S
C L
ti
−
=
OF1 OF1 0.471 10.40 0.50 0.24 3.77 0.89 0.54 0.25 3.77 0.96 0.58 0.28 4.47 1.23 0.68 0.32 7.20 2.32
OF2 OF2 0.392 7.31 0.23 0.09 4.30 0.38 0.31 0.12 4.30 0.52 0.38 0.15 5.08 0.76 0.57 0.22 8.20 1.83
Total 2.079 1.55 1.78 2.37 4.86
Design
Point
Sub-basin Area (acres) tc
(min)
2-yr Peak Runoff 5-yr Peak Runoff 100-yr Peak Runoff
J.Claeys
Interwest Consulting Group
1192-117-00
August 6, 2014
10-yr Peak Runoff
Q n = C n I n A n
0.786
1
(10 )
28 . 5
t c
P
I
+
0.786 =
1
(10 )
28 . 5
t c
P
I
+
=
( )
0 .33
5
0 . 395 1 . 1
S
C L
t
i
−
=
c i t
t = t + t 0 . 5
v w
V = C S 10
180
= L +
t
c
V
L
t
t
60
=
August 6, 2014
% Impervious values from Table RO-3 in the Urban Storm Drainage Criteria Manual for Hydrologic Soil Classifications
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 0.82 1.40 2.86 0.83 0.01 1.41 0.01 2.88 0.02
0.00 -0.02 0.00
C 3
2
1 1
( c )
C t
C P
I
+
=
60 2.60 2,422 51,414 60 2.86 2,193 45,775
cu-ft
100-yr Runoff Volumes 100-yr Runoff Volumes
5,639
Under the proposed conditions with the Avondale Cottages project, and comparing the old rainfall data to the new
rain fall data, there is a reduction in runoff volume of:
Basin 300 Basin 300
Current Rainfall and Proposed Surface Characteristics
Site
Condos
Daycare
Pond 28
J.Claeys
Interwest Consulting Group
1192-117-00
August 6, 2014
Tract L (Avondale)
Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised April 2008)
Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, May 1984
*Table 3-7 Referenced for % Impervious
**Table 3-2 Referenced for Runoff Coefficients
"Final Drainage and Erosion Control Study for Ridgewood Hills P.U.D. First Filing", prepared by RBD, Dated March 3, 1995
Tract L (Avondale)
Original Rainfall and Surface Characteristics
Site
Condos
Daycare
Pond 28
Survey Area Data: Version 8, Dec 23, 2013
Soil map units are labeled (as space allows) for map scales 1:50,000
or larger.
Date(s) aerial images were photographed: Apr 22, 2011—Nov 18,
2011
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor shifting
of map unit boundaries may be evident.
Hydrologic Soil Group—Larimer County Area, Colorado
(Avondale Cottages)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
3/28/2014
Page 2 of 4