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NORTHERNENGINEERING.COM | 970.221.4158 PRELIMINARY DRAINAGE REPORT: THE CROWNE AT SUNIGA
FORT COLLINS | GREELEY 6 | 11
Three separate design storms have been utilized to address distinct drainage scenarios. The
first event analyzed is the "Minor" or "Initial" Storm, with a 2-year recurrence interval. The
second event considered is the "Major Storm," which has a 100-year recurrence interval. The
final event analyzed was the 10-year recurrence interval for comparative analysis only.
E. HYDRAULIC CRITERIA
The drainage facilities proposed with the Crowne at Suniga project are designed in accordance
with criteria outlined in the NECCO Backbone Design Report, FCSCM and/or the Mile High Flood
District's (UDFCD) Urban Storm Drainage Criteria Manual.
As stated in Section I. C. 1. above, the subject property is not located within a FEMA 100-year or
a City of Fort Collins designated floodplain.
F. FLOODPLAIN REGULATIONS COMPLIANCE
As stated in Section I. C. 1. above, the subject property is not located within a FEMA 100-year
or a City of Fort Collins designated floodplain.
G. MODIFICATIONS OF CRITERIA
No formal modifications are requested at this time.
H. CONFORMANCE WITH LOW IMPACT DEVELOPMENT (LID)
The project site will conform with the requirement to treat a minimum of 75% of newly or
modified impervious area using an LID technique. Please see Appendix C for LID design
information, table, and exhibit(s). As shown in the LID table provided in the appendix, 98%
of the proposed site will receive LID Treatment, which exceeds the minimum required.
I. SIZING OF LID FACILITIES
The Stormtech isolator chambers were sized by determining the required water quality capture
volume (WQCV) for Major Basin SC. A 12-hour drain time was used in this calculation. Once the
WQCV was identified, the minimum number of vaults needed to achieve this volume was
calculated. The required WQCV for Major Basin SC is 13,691 cf . A minimum of 60, MC-7200
chambers will be required to meet the storage needs and will supply 16,038 cf of WQCV. Each
isolator row will have an inspection port and a Nyloplast basin at the end for easy maintenance
and cleanout.
A volume calculation utilizing the WQ flow rate into the chamber and the calculated release
rate through the fabric was completed. The number of chambers has been increased as needed
to confirm the resulting volume is provided within the empty volume of the
uderground chambers. This is intended to ensure the chambers do not become overwhelmed
in the water quality storm event before "discharging" flows into the surrounding aggregates.
For additional clarification, please refer to Appendix C.
NORTHERNENGINEERING.COM | 970.221.4158 PRELIMINARY DRAINAGE REPORT: THE CROWNE AT SUNIGA
FORT COLLINS | GREELEY 7 | 11
DRAINAGE FACILITY DESIGN
A. GENERAL CONCEPT
The main objective of the Crowne at Suniga drainage design is to maintain existing drainage
patterns and to not adversely impact downstream infrastructure.
No notable off-site runoff passes directly through the project site.
A list of tables and figures used within this report can be found in the Table of Contents at the
front of this document. The tables and figures are located within the sections to which the
content best applies.
Drainage for the project site has been analyzed using two (2) Major Drainage Basins, designated
as Basins SC, & OSC. Both basins have associated sub-basins. The drainage patterns
anticipated for the basins are further described below.
Major Basin SC
Major Basin SC (Stormtech Combined) has 23 sub-basins A-H & R1-R15. Sub-basins A-H
consist of asphalt & concrete paving, and landscaping. Sub-basins R1-R15 consist of
building roofs only. Major Basin SC has a total area of 9.28 acres and an impervious value of
84%. All runoff generated within Major Basin SC is routed via a combination of overland
flow, storm line conveyance, and curb and gutter routing to the Stormtech system. Major
Basin SC will receive LID treatment and detention within the Stormtech system. After being
treated and detained by the Stormtech system runoff from Major Basin SC will be routed to
the NECCO Backbone via an HDPE pipe that is connected to a proposed manhole, which will
replace the existing area inlet located in the south-east portion of the site.
Major Basin OSC
Major Basin OSC (off-Site Combined) has four (4) sub-basins (OS1-OS4) and is associated
with the outer permitter of the Crowne at Suniga project site. Major Basin OSC has a total
area of 1.79 acres and an impervious value of 6%. Major Basin OSC consists of primarily
landscaping and some concrete and asphalt paving. All runoff generated within Major Basin
OSC is routed via a combination of overland flow, storm line conveyance, and curb and
gutter routing to existing inlets located on 9th street, East Suniga Road, & North Lemay
Avenue. These existing inlets outfall into the NECCO Backbone. Runoff generated in Major
Basin OSC is negligible and will not have an adverse impact on downstream infrastructure.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of this report.
In addition, excerpts from earlier drainage reports referenced in this Section can be found in
Appendix E.
NORTHERNENGINEERING.COM | 970.221.4158 PRELIMINARY DRAINAGE REPORT: THE CROWNE AT SUNIGA
FORT COLLINS | GREELEY 8 | 11
B. SPECIFIC DETAILS
As mentioned in Section III.A. the historical 2-year release rate, as perscribed by the NECCO
Design Report, will be used as the allowable release rate for the project site. City staff agreed
that the Major Basin OSC is mostly pervious and therefore will be allowed to free release into
adjacent curb & gutter. However, Major Basin OSC’s area of 1.79 acres will be subtracted from
the the project sites total area of 11.07 acres and the remaining area of 9.28 acres (Major Basin
SC) will be multiplied by the perscirbed 0.2 cfs/acre to obtain the release rate from the
Stormtech system. See Table 1. below.
Max Release Rate Calculation by Area
Project Site Area (acres) 11.07
Major Basin OSC Area (acres) 1.79
Major Basin SC Area (acres) 9.28
Max Release Rate (cfs) (9.28 ac x 0.2 cfs/ac) 1.86
Table 1 - Maximum release rate calculated by area.
LID treatment will be provided for Major Basin SC within the Stormtech System.
LID Summary Table
Area (ac) % of Area
Total Area Treated 9.28 84%
Total Area Not Being Treated by LID 1.79 16%
Table 2 - Summary of new impervious areas being treated by LID
The area that is not getting treated by LID is unable to be captured and routed to the Stormtech
system for a few reasons.
A. Existing sanitary lines in this area are very shallow and it makes it impossible to
have storm lines that are capable of bucking grade all the way back to the Stormtech
system.
B. The site is bordered by existing easements and Crowne at Suniga is unable to
modify the grading in these areas that allow for drainage to flow back into the site.
It should be noted that the areas that are not getting LID treatment are mostly landscapinG
and thus will have negligible impact on downstream water quality.
CHARACTER OF SURFACE1:
Percentage
Impervious
2-yr Runoff
Coefficient
10-yr Runoff
Coefficient
100-yr Runoff
Coefficient
Developed
Asphalt .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………100%0.95 0.95 1.00
Concrete .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………100%0.95 0.95 1.00
Rooftop .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………90%0.95 0.95 1.00
Gravel .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………40%0.50 0.50 0.63
Pavers .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………40%0.50 0.50 0.63
Landscape or Pervious Surface
Playgrounds .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………25%0.35 0.35 0.44
Lawns Clayey Soil .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………2%0.25 0.25 0.31
Lawns Sandy Soil .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………2%0.15 0.15 0.19
Notes:
Basin ID Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Rooftop
(ac)
Area of Lawns
(ac)
Composite
% Imperv.
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
A 0.48 0.37 0.05 0.00 0.06 88%0.86 0.86 0.91
B 0.37 0.27 0.04 0.00 0.05 86%0.85 0.85 0.90
C 0.83 0.66 0.05 0.00 0.12 86%0.85 0.85 0.90
D 1.23 0.84 0.11 0.00 0.27 78%0.79 0.79 0.85
E 0.34 0.00 0.34 0.00 0.00 100%0.95 0.95 1.00
F 0.75 0.35 0.15 0.00 0.25 68%0.72 0.72 0.77
G 0.44 0.31 0.08 0.00 0.06 87%0.86 0.86 0.91
H 1.83 1.31 0.21 0.00 0.31 83%0.83 0.83 0.88
R1 0.16 0.00 0.00 0.16 0.00 90%0.95 0.95 1.00
R2 0.12 0.00 0.00 0.12 0.00 90%0.95 0.95 1.00
R3 0.24 0.00 0.00 0.24 0.00 90%0.95 0.95 1.00
R4 0.17 0.00 0.00 0.17 0.00 90%0.95 0.95 1.00
R5 0.14 0.00 0.00 0.14 0.00 90%0.95 0.95 1.00
R6 0.22 0.00 0.00 0.22 0.00 90%0.95 0.95 1.00
R7 0.15 0.00 0.00 0.15 0.00 90%0.95 0.95 1.00
R8 0.15 0.00 0.00 0.15 0.00 90%0.95 0.95 1.00
R9 0.20 0.00 0.00 0.20 0.00 90%0.95 0.95 1.00
R10 0.26 0.00 0.00 0.26 0.00 90%0.95 0.95 1.00
R11 0.14 0.00 0.00 0.14 0.00 90%0.95 0.95 1.00
R12 0.34 0.00 0.00 0.34 0.00 90%0.95 0.95 1.00
R13 0.24 0.00 0.00 0.24 0.00 90%0.95 0.95 1.00
R14 0.31 0.00 0.00 0.18 0.13 53%0.66 0.66 0.71
R15 0.18 0.00 0.00 0.18 0.00 90%0.95 0.95 1.00
OS1 0.48 0.00 0.02 0.00 0.46 6%0.28 0.28 0.34
OS2 0.56 0.02 0.02 0.00 0.52 9%0.30 0.30 0.36
OS3 0.34 0.00 0.00 0.00 0.34 2%0.25 0.25 0.31
OS4 0.41 0.00 0.01 0.00 0.40 5%0.27 0.27 0.33
MAJOR BASIN SC (STORMTECH, COMBINED)9.28 4.11 1.04 2.88 1.25
84% 0.86 0.86 0.91
MAJOR BASIN OSC (OFF-SITE, COMBINED)1.79 0.02 0.05 0.00 1.72
6% 0.28 0.28 0.34
DEVELOPED BASIN % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
2) Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Chapter 3. Table 3.2-1 and 3.2-2
1) Percentage impervious taken from the Fort Collins Stormwater Criteria Manual, Chapter 5, Table 4.1-2 and Table 4.1-3
Combined Basins
Overland Flow, Time of Concentration:
Channelized Flow, Time of Concentration:
Total Time of Concentration :
T c is the lesser of the values of Tc calculated using T c = T i + T t
C2 C100
Length,
L
(ft)
Slope,
S
(%)
Ti2 Ti100
Length,
L
(ft)
Slope,
S
(%)
Roughness
Coefficient
Assumed
Hydraulic
Radius
Velocity,
V
(ft/s)
Tt
(min)Tc (Eq. 3.3-5) Tc2 = Ti +Tt Tc100 = Ti +Tt Tc2 Tc100
a1 A 0.86 0.91 59 2.24%2.6 2.1 160 0.87%0.013 0.08 2.03 1.3 11.2 3.9 3.4 5.0 5.0
b1 B 0.85 0.90 44 1.66%2.6 2.1 117 0.61%0.013 0.08 1.69 1.2 10.9 3.8 3.3 5.0 5.0
c1 C 0.85 0.90 130 1.82%4.4 3.5 194 1.07%0.013 0.08 2.25 1.4 11.8 5.8 4.9 5.8 5.0
d1 D 0.79 0.85 161 4.08%4.6 3.7 158 0.60%0.013 0.08 1.68 1.6 11.8 6.2 5.3 6.2 5.3
e1 E 0.95 1.00 210 1.67%3.4 2.3 0 N/A 0.013 0.08 N/A N/A 11.2 3.4 2.3 5.0 5.0
f1 F 0.72 0.77 39 6.17%2.4 2.1 175 0.60%0.013 0.08 1.68 1.7 11.2 4.1 3.8 5.0 5.0
g1 G 0.86 0.91 32 4.84%1.5 1.2 196 0.83%0.013 0.08 1.98 1.6 11.3 3.1 2.8 5.0 5.0
h1 H 0.83 0.88 89 2.18%3.7 3.0 156 1.00%0.013 0.08 2.17 1.2 11.4 4.9 4.2 5.0 5.0
R1 0.95 1.00 46 2.19%1.5 1.0 0 N/A N/A N/A N/A N/A 10.3 1.5 1.0 5.0 5.0
R2 0.95 1.00 46 2.19%1.5 1.0 0 N/A N/A N/A N/A N/A 10.3 1.5 1.0 5.0 5.0
R3 0.95 1.00 46 2.19%1.5 1.0 0 N/A N/A N/A N/A N/A 10.3 1.5 1.0 5.0 5.0
R4 0.95 1.00 46 2.19%1.5 1.0 0 N/A N/A N/A N/A N/A 10.3 1.5 1.0 5.0 5.0
R5 0.95 1.00 46 2.19%1.5 1.0 0 N/A N/A N/A N/A N/A 10.3 1.5 1.0 5.0 5.0
R6 0.95 1.00 46 2.19%1.5 1.0 0 N/A N/A N/A N/A N/A 10.3 1.5 1.0 5.0 5.0
R7 0.95 1.00 46 2.19%1.5 1.0 0 N/A N/A N/A N/A N/A 10.3 1.5 1.0 5.0 5.0
R8 0.95 1.00 46 2.19%1.5 1.0 0 N/A N/A N/A N/A N/A 10.3 1.5 1.0 5.0 5.0
R9 0.95 1.00 46 2.19%1.5 1.0 0 N/A N/A N/A N/A N/A 10.3 1.5 1.0 5.0 5.0
R10 0.95 1.00 46 2.19%1.5 1.0 0 N/A N/A N/A N/A N/A 10.3 1.5 1.0 5.0 5.0
R11 0.95 1.00 46 2.19%1.5 1.0 0 N/A N/A N/A N/A N/A 10.3 1.5 1.0 5.0 5.0
R12 0.95 1.00 46 2.19%1.5 1.0 0 N/A N/A N/A N/A N/A 10.3 1.5 1.0 5.0 5.0
R13 0.95 1.00 46 2.19%1.5 1.0 0 N/A N/A N/A N/A N/A 10.3 1.5 1.0 5.0 5.0
R14 0.66 0.71 46 2.19%4.3 3.8 0 N/A N/A N/A N/A N/A 10.3 4.3 3.8 5.0 5.0
R15 0.95 1.00 46 2.19%1.5 1.0 0 N/A N/A N/A N/A N/A 10.3 1.5 1.0 5.0 5.0
os1 OS1 0.28 0.34 71 10.95%5.8 5.4 557 1.01%0.013 0.08 2.19 4.2 13.5 10.1 9.6 10.1 9.6
os2 OS2 0.30 0.36 42 2.29%7.3 6.8 592 0.60%0.013 0.08 1.68 5.9 13.5 13.2 12.6 13.2 12.6
os3 OS3 0.25 0.31 70 6.91%7.0 6.5 379 0.58%0.013 0.08 1.66 3.8 12.5 10.8 10.3 10.8 10.3
os4 OS4 0.27 0.33 42 2.29% 7.6 7.0 592 0.60% 0.013 0.08 1.68 5.9 13.5 13.5 12.9 13.5 12.9
a1 MAJOR BASIN SC
(STORMTECH, COMBINED)0.86 0.91 59 2.24% 2.6 2.1 160 0.87% 0.013 0.083 0.20 13.1 10.3 1.5 1.0 5.0 5.0
c1 MAJOR BASIN OSC (OFF-
SITE, COMBINED)0.28 0.34 71 10.95% 5.8 5.4 59 9.49% 0.013 0.083 0.67 1.5 12.5 10.1 9.6 10.1 9.6
Combined Basins
DEVELOPED DIRECT TIME OF CONCENTRATION
Channelized Flow
Design
Point Basin
Overland Flow Time of Concentration
Frequency Adjustment Factor:
(Equation 3.3-2 FCSCM)
(Equation 5-5 FCSCM)
(Equation 5-4 FCSCM)
(Equation 3.3-5 FCSCM)
Table 3.2-3 FCSCM
Therefore Tc2=Tc10
Rational Method Equation:
Rainfall Intensity:
a1 A 0.48 5.0 5.0 0.86 0.91 2.85 4.87 9.95 1.19 2.03 4.39
b1 B 0.83 5.0 5.0 0.85 0.90 2.85 2.85 9.95 2.00 2.00 7.41
c1 C 0.83 5.0 5.0 0.85 0.90 2.85 4.87 9.95 2.00 3.42 7.41
d1 D 0.34 5.3 5.3 0.95 1.00 2.85 2.85 9.95 0.92 0.92 3.39
e1 E 0.34 5.0 5.0 0.95 1.00 2.85 4.87 9.95 0.92 1.58 3.39
f1 F 0.44 5.0 5.0 0.86 0.91 2.85 2.85 9.95 1.08 1.08 3.98
g1 G 0.44 5.0 5.0 0.86 0.91 2.85 4.87 9.95 1.08 1.84 3.98
h1 H 0.16 5.0 5.0 0.95 1.00 2.85 2.85 9.95 0.45 0.45 1.64
R1 0.16 5.0 5.0 0.95 1.00 2.85 4.87 9.95 0.45 0.76 1.64
R2 0.24 5.0 5.0 0.95 1.00 2.85 2.85 9.95 0.64 0.64 2.35
R3 0.24 5.0 5.0 0.95 1.00 2.85 4.87 9.95 0.64 1.09 2.35
R4 0.14 5.0 5.0 0.95 1.00 2.85 2.85 9.95 0.37 0.37 1.37
R5 0.14 5.0 5.0 0.95 1.00 2.85 4.87 9.95 0.37 0.64 1.37
R6 0.15 5.0 5.0 0.95 1.00 2.85 2.85 9.95 0.41 0.41 1.49
R7 0.15 5.0 5.0 0.95 1.00 2.85 4.87 9.95 0.41 0.69 1.49
R8 0.20 5.0 5.0 0.95 1.00 2.85 2.85 9.95 0.53 0.53 1.95
R9 0.20 5.0 5.0 0.95 1.00 2.85 4.87 9.95 0.53 0.91 1.95
R10 0.14 5.0 5.0 0.95 1.00 2.85 2.85 9.95 0.38 0.38 1.40
R11 0.14 5.0 5.0 0.95 1.00 2.85 4.87 9.95 0.38 0.65 1.40
R12 0.24 5.0 5.0 0.95 1.00 2.85 2.85 9.95 0.64 0.64 2.36
R13 0.24 5.0 5.0 0.95 1.00 2.85 4.87 9.95 0.64 1.10 2.36
R14 0.18 5.0 5.0 0.95 1.00 2.85 2.85 9.95 0.49 0.49 1.79
R15 0.18 5.0 5.0 0.95 1.00 2.85 4.87 9.95 0.49 0.83 1.79
os1 OS1 0.56 9.6 9.6 0.30 0.36 2.26 2.26 7.88 0.38 0.38 1.58
os2 OS2 0.56 12.6 12.6 0.30 0.36 2.02 3.45 7.04 0.34 0.58 1.41
os3 OS3 0.41 10.3 10.3 0.27 0.33 2.21 2.21 7.72 0.24 0.24 1.04
os4 OS4 0.41 12.9 12.9 0.27 0.33 2.02 3.45 7.04 0.22 0.38 0.95
MAJOR BASIN SC
(STORMTECH,
COMBINED)
9.28 5.0 5.0 0.86 0.91 2.85 2.85 9.95 22.74 24.06 84.01
MAJOR BASIN OSC (OFF-
SITE, COMBINED)1.79 9.6 9.6 0.28 0.34 2.26 2.26 7.88 1.13 1.38 4.80
DEVELOPED RUNOFF COMPUTATIONS
Design
Point Basin(s)Area, A
(acres)
Tc2
(min)
Flow,
Q2
(cfs)
Flow,
Q100
(cfs)
C2 C100
IDF Table for Rational Method - Table 3.4-1 FCSCM
Intensity,
i10
(in/hr)
Flow,
Q10
(cfs)
Combined Basins
Tc100
(min)
Intensity,
i2
(in/hr)
Intensity,
i100
(in/hr)
()()()AiCCQf=
B2
100-yr
0.92
5.00 min Storage 121531 ft3
11.07 acres
Max Release Rate =1.86 cfs 2.79 ac-ft
Time (min)
Ft Collins
100-yr
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustment
Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage
Volume
(ft3)
5 9.950 30400 1.00 1.86 558 29842
10 7.720 47174 1.00 1.86 1116 46058
15 6.520 59762 1.00 1.86 1674 58088
20 5.600 68439 1.00 1.86 2232 66207
25 4.980 76077 1.00 1.86 2790 73287
30 4.520 82860 1.00 1.86 3348 79512
35 4.080 87260 1.00 1.86 3906 83354
40 3.740 91415 1.00 1.86 4464 86951
45 3.460 95143 1.00 1.86 5022 90121
50 3.230 98687 1.00 1.86 5580 93107
55 3.030 101834 1.00 1.86 6138 95696
60 2.860 104859 1.00 1.86 6696 98163
65 2.720 108036 1.00 1.86 7254 100782
70 2.590 110786 1.00 1.86 7812 102974
75 2.480 113658 1.00 1.86 8370 105288
80 2.380 116347 1.00 1.86 8928 107419
85 2.290 118944 1.00 1.86 9486 109458
90 2.210 121541 1.00 1.86 10044 111497
95 2.130 123649 1.00 1.86 10602 113047
100 2.060 125879 1.00 1.86 11160 114719
105 2.000 128323 1.00 1.86 11718 116605
110 1.940 130401 1.00 1.86 12276 118125
115 1.890 132815 1.00 1.86 12834 119981
120 1.840 134923 1.00 1.86 13392 121531
*Note: Using the method described in Urban Storm Drainage Criteria Manual Volume 2.
DETENTION VOLUME CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1893-001
The Crowne at Suniga
Project Number :
Project Name :
Stormtech System - Detention
A =
Tc =
Project Location :
Design Point
C =
Design Storm
Storage System :
Page 1 of 1
1893-001_Pond_FAA_Fort Collins_Detention Volume.xls
User Inputs
Chamber Model: MC-7200
Outlet Control Structure: Yes
Project Name: Crowne at Suniga
Engineer: S. King KING
Project Location: Colorado
Measurement Type: Imperial
Required Storage Volume: 121531 cubic ft.
Stone Porosity: 40%
Stone Foundation Depth: 9 in.
Stone Above Chambers: 12 in.
Average Cover Over Chambers: 24 in.
Design Constraint Dimensions:(110 ft. x 292 ft.)
Results
System Volume and Bed Size
Installed Storage Volume: 123008.69 cubic ft.
Storage Volume Per Chamber: 175.90 cubic ft.
Number Of Chambers Required: 441
Number Of End Caps Required: 22
Chamber Rows: 11
Maximum Length:282.21 ft.
Maximum Width: 101.77 ft.
Approx. Bed Size Required: 28127.46 square ft.
System Components
Amount Of Stone Required: 4127 cubic yards
Volume Of Excavation (Not Including
Fill):
7032 cubic yards
Total Non-woven Geotextile Required:8200 square yards
Woven Geotextile Required (excluding
Isolator Row):
192 square yards
Woven Geotextile Required (Isolator
Row):
644 square yards
Total Woven Geotextile Required:835 square yards
Impervious Liner Required:0 square yards
Project Title Date:
Project Number Calcs By:
City
Basins
0.8
WQCV = Watershed inches of Runoff (inches)84%
a = Runoff Volume Reduction (constant)
i = Total imperviousness Ratio (i = Iwq/100)0.284 in
A =11.07 ac
V = 0.3143 ac-ft
V = Water Quality Design Volume (ac-ft)
WQCV = Water Quality Capture Volume (inches)
A = Watershed Area (acres)
13691 cu. ft.
Drain Time
a =
i =
WQCV =
Figure EDB-2 - Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
The Crowne at Suniga February 13, 2023
1893-001 S. King
Fort Collins
Stormtech LID Pond
0.231
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
00.10.20.30.40.50.60.70.80.91WQCV (watershed inches)Total Imperviousness Ratio (i = Iwq/100)
Water Quality Capture Volume
6 hr
12 hr
24 hr
40 hr
()iii78.019.10.91aWQCV 23 +-=
()iii78.019.10.91aWQCV 23 +-=
12 hr
1.20
WQCV
12 ∗
Pond No :
Stormtech Pond
WQ
0.92
5.00 min 10453 ft3
11.07 acres 0.24 ac-ft
Max Release Rate =2.35 cfs
Time (min)
Ft Collins
WQ
Intensity
(in/hr)
Inflow
Volume
(ft3)
Outflow
Adjustmen
t Factor
Qav
(cfs)
Outflow Volume
(ft3)
Storage Volume
(ft3)
5 1.425 4354 1.00 2.35 705 3649
10 1.105 6752 1.00 2.35 1409 5343
15 0.935 8570 0.67 1.57 1409 7161
20 0.805 9838 0.63 1.47 1761 8077
25 0.715 10923 0.60 1.41 2114 8809
30 0.650 11916 0.58 1.37 2466 9450
35 0.585 12512 0.57 1.34 2818 9693
40 0.535 13077 0.56 1.32 3170 9906
45 0.495 13611 0.56 1.30 3523 10089
50 0.460 14054 0.55 1.29 3875 10179
55 0.435 14620 0.55 1.28 4227 10392
60 0.410 15032 0.54 1.27 4580 10453
65 0.385 15292 0.54 1.26 4932 10360
70 0.365 15613 0.54 1.26 5284 10329
75 0.345 15811 0.53 1.25 5636 10175
80 0.330 16132 0.53 1.25 5989 10143
85 0.315 16361 0.53 1.24 6341 10020
90 0.305 16774 0.53 1.24 6693 10080
95 0.290 16835 0.53 1.24 7046 9789
100 0.280 17110 0.53 1.23 7398 9712
105 0.270 17324 0.52 1.23 7750 9574
110 0.260 17476 0.52 1.23 8102 9374
115 0.255 17919 0.52 1.23 8455 9465
120 0.245 17965 0.52 1.22 8807 9158
*Note: Using the method described in FCSCM Chapter 6 Section 2.3
A =
Tc =
Project Location :
Design Point
C =
Design Storm
DETENTION POND CALCULATION; MODIFIED FAA METHOD w/ Ft Collins IDF
Input Variables Results
Required Detention Volume
Fort Collins, Colorado
1893-001
The Crowne at Suniga
Project Number :
Project Name :
Stormtech LID Pond
Page 1 of 1
1893-001 LID Chamber Summary.xlsx
Vault ID
Total
Required
WQ Volume
(cf)
Flow,
WQ
(cfs)
Chamber
Type
Chamber Release
Ratea
(cfs)
Chamber
Volumeb
(cf)
Installed Camber
w/ Aggregatec
(cf)
Mimimum No.
of Chambersd
Total Release
Ratee
(cfs)
Required
Storage
Volume by
FAA Method
(cf)
Mimimum
No. of
Chambersf
Storage
Provided
within the
Chambersg
(cf)
Minimum
Total
Installed
System
Volumeh
(cf)
Stormtech LID Pond 13691 11.37 MC-7200 0.045 175.90 267.30 52 2.35 10453 60 10554 16038
a. Release rate per chamber, limited by flow through geotextile with accumulated sediment.
b. Volume within chamber only, not accounting for void spaces in surrounding aggregate.
c. Volume includes chamber and void spaces (40%) in surrounding aggregate, per chamber unit.
d. Number of chambers required to provide full WQCV within total installed system, including aggregate.
e. Release rate per chamber times number of chambers.
f. Number of chambers required to provide required FAA storage volume stored within the chamber only (no aggregate storage).
g. Volume provided in chambers only (no aggregate storage). This number must meet or exceed the required FAA storage volume.
h. System volume includes total number of chambers, plus surrounding aggregate. This number must meet or exceed the required WQCV.
Chamber Configuration Summary
P:\1893-001\Drainage\LID\1893-001 LID Chamber Summary.xlsx