HomeMy WebLinkAboutZIEGLER - CORBETT ODP - ODP210004 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORT
OVERALL DRAINAGE REPORT
FOR
Ziegler–Corbett
Prepared by:
Highland Development Services
6355 Fairgrounds Ave, Suite 100
Windsor, Colorado 80550
Phone: 970.674.7550
Prepared for:
Landmark Real Estate Holdings, LLC
6341 Fairgrounds Ave, Suite 100
Windsor, Colorado 80550
Office: 970.460.0567
November 30, 2021
Job Number 21-1044-00
6355 FAIRGROUNDS AVE, SUITE 100, WINDSOR, COLORADO 80550 | PHONE 970.674.7550
November 30, 2021
Mr. Wes Lamarque
Fort Collins Utilities
700 Wood Street
Fort Collins, CO 80522
RE: Overall Drainage Report - Ziegler-Corbett
Dear Wes,
We are pleased to submit for your review, the Overall Drainage Report for the Ziegler – Corbett
Overall Development Plan. This report describes the general drainage design intent to be
implemented with future development and in accordance with the criteria in the City of Fort
Collins Storm Drainage Manual.
I appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
Sincerely,
Highland Development Services
Andrew C. Bartel, EI Jason T. Claeys, P.E., LEED AP
Page i
TABLE OF CONTENTS
Table of Contents ............................................................................................................................. i
Engineer’s Certification Block ..........................................................................................................ii
General Description and Location .................................................................................................. 1
Site Description and Location ...................................................................................................... 1
Storm Drainage Criteria .................................................................................................................. 2
Existing Conditions ...................................................................................................................... 2
Drainage Basins ............................................................................................................................... 4
Drainage Facility Design .................................................................................................................. 5
Drainage Conveyance Design ...................................................................................................... 5
Detention/Water Quality Pond Design ....................................................................................... 5
Low Impact Development ............................................................................................................... 6
Stormwater Pollution Prevention ................................................................................................... 8
Conclusions ..................................................................................................................................... 9
References .................................................................................................................................... 10
Appendix ....................................................................................................................................... 11
Appendix A – References ............................................................................................................. A
Page ii
ENGINEER’S CERTIFICATION BLOCK
I hereby certify that this Overall Drainage Report for Ziegler-Corbett was prepared by me (or
under my direct supervision) for the owners thereof and meets or exceeds the criteria of the
City of Fort Collins Stormwater Design Standards.
________________________________________
Jason T. Claeys, PE
Registered Professional Engineer
State of Colorado No. 42122
Page 1
GENERAL DESCRIPTION AND LOCATION
SITE DESCRIPTION AND LOCATION
The Ziegler-Corbett property is located in the Southeast Quarter of Section32, Township 7
North, Range 68 West of the Sixth Principal Meridian, City of Fort Collins, County of Larimer,
State of Colorado. More specifically, the Ziegler-Corbett property is located north of the Front
Range Village commercial area, east of the Affinity residences, south of the English Ranch
residential subdivision, and west of Ziegler Road.
The project site is approximately 31.31 acres currently and is undeveloped agricultural land.
The site appears to be vegetated with grasses harvested for livestock feed. The site generally
slopes from the west to the east at about 0.7% slope. There are no existing surface
improvements currently on the property.
The intent of the Overall Development Plan (ODP) is to update the existing ODP with the
anticipated uses. No improvements are being constructed with the ODP, but rather establishing
the future expectations for development. The property is anticipated to be a high-density multi-
use development, mainly multi-family residential with retail space and supporting amenities.
The Ziegler-Corbett property is located within the City’s Fox Meadows Drainage Basin. In
addition to the City of Fort Collins Stormwater Design Standards, drainage requirements are
also described in both the “Front Range Village Final Drainage and Erosion Control Study,”
prepared by Stantec Consulting Inc., dated February 2007, and the “Final Drainage Report for
Affinity Fort Collins”, prepared by JR Engineering, LLC, dated March 2, 2016.
No City or FEMA floodplains/floodways are located within the Ziegler-Corbett property.
Page 2
STORM DRAINAGE CRITERIA
This Overall Drainage Report was prepared to establish future design expectations that meet or
exceed the City of Fort Collins storm water criteria. The City of Fort Collin’s Storm Drainage
Design Criteria and amendments to the Urban Drainage Flood Control District’s (UDFCD)
Drainage Criteria Manual (USDCM) Volumes 1, 2 and 3 were referenced as guidelines for this
design.
EXISTING CONDITIONS
The Ziegler – Corbett property overall is a part of a drainage basin that is situated north of
Harmony Road, and west of Ziegler Road, which runoff is conveyed east under Ziegler Road into
the existing drainage channel on the HP Harmony Campus property. It has been determined in
the Front Range Village Final Drainage Report that this area is allowed to contribute 76.7 cfs to
the HP Campus drainage channel during 100-year event peak discharge. More specific to this
site, 20.1 cfs release rate was allocated to the Ziegler-Corbett & the Affinity Fort Collins
properties. Per The Final Drainage Report for Affinity Fort Collins, the Affinity site has a 100-yr
peak release rate of 2.1 cfs, allowing a 100-yr peak discharge of 18.0 cfs from the Ziegler –
Corbet property.
The Harmony Village Manufactured Home Community does not provide adequate detention
facilities and during a 100-yr storm event, a portion of the site that flows to the east into both
the Front Range Village development as well as the Affinity Fort Collins site. This runoff was
evaluated in the Front Range Village Final Drainage Report and was determined to be 116 cfs
peak runoff during the 100-yr event. This runoff is to be collected in the Front Range Village
Detention Pond D, which is intended to collect, but not detain this flow. During the 100-year
event, this peak flow of 116 cfs will flow over the weir on the north side of Detention Pond D
and will be conveyed via the private drive aisles to a level spreading weir on the northeast side
of the Affinity Fort Collins site, where it is discharged into the Ziegler-Corbett property. This
flow is then assumed to sheet flow east to be inadvertently detained on the east side of the
Ziegler-Corbett property along Ziegler Road.
In reference to the Front Range Village Final Drainage Report, a future detention pond is
planned to be incorporated into the Ziegler-Corbett site, Detention Pond 298. The volume of
Detention Pond 298 will be determined by the lesser of the two following scenarios:
1. Standard detention volume required for the site, detaining the 100-yr peak developed
runoff to the 2-yr historic runoff rate, plus the existing inadvertent detention volume,
Page 3
the detention volume currently provided onsite due to existing constraints such as
grade features and outlet restrictions, or
2. The volume required to detain the combination of 100-yr peak runoff rates from the
developed onsite and existing offsite flows to the allocated release rate of 20.1 cfs.
For the purposes of this report, it is assumed that scenario 1 is the lesser of the two. Future
detention volume calculations should confirm this assumption.
Based on the topographic survey of the existing conditions, the inadvertent detention volume is
constrained for this site by the spill location along the north property line, at an approximate
elevation of 4928.0 ft. The inadvertent detention volume is estimated to be 7.5± acre-ft. The
estimated volume did not account for the 2 existing culverts along the west side of Ziegler Road
that currently provide ponding relief for the Ziegler-Corbet site.
The FAA Method was utilized to estimate the required detention for the developed conditions
in accordance with the City of Fort Collins requirements (the 100-year developed peak runoff
detained to the 2-year historical peak runoff) to be 8.5± acre-ft. Combining the inadvertent
detention and the required detention volume, a total of 16.0± acre-ft is required to
accommodate the developed site, as well as account for the displacement of the historical
inadvertent detention.
All supporting preliminary calculations are located in the Appendix.
Page 4
DRAINAGE BASINS
The Ziegler-Corbett property conceptual developed drainage basins, percent impervious, and
flow paths are to be determined with future applications. For the purposes of this study, it is
assumed the site is approximately 90% impervious for high-density mixed-use sites and the
corresponding runoff coefficient. Historical drainage analysis was completed for the Ziegler-
Corbett property to determine the allowed 2-yr historic runoff rate.
Page 5
DRAINAGE FACILITY DESIGN
DRAINAGE CONVEYANCE DESIGN
Storm infrastructure to convey runoff will potentially include overland grass-lined swales,
concrete trickle pans, inlets, storm sewer and culverts. Stormwater detention and water quality
enhancement will be achieved through the use of a series of extended detention basins and low
impact development techniques. Storm inlets, storm sewers and the roadway culverts will be
appropriately sized with the final drainage design
DETENTION/WATER QUALITY POND DESIGN
Multiple extended detention basins (EDB) with a dry bottom will be utilized as the detention
and water quality facility for the Ziegler-Corbett property. The EDBs will combine to provide an
estimated detention volume of 16.0± acre-ft, accounting for the existing inadvertent detention
on the site, as well as the additional detention required to accommodate the site in its
developed condition. Detention volume calculations are to be confirmed with future
applications. For the overall drainage study, the FAA method was used to estimate the
detention volume needed. EPA SWWM or the Rational Method may be utilized for the final
drainage design, as determined by the City. UDFCD is referenced for the water quality capture
volume (WQCV) with a 40-yr drain time. Due to the limited grades on the site, multiple ponds
are proposed throughout the site with the main detention pond being located in the northwest
corner of the site. The ultimate outfall will be the existing HP Harmony Campus storm channel
system, which ultimately flows into the Cache La Poudre River.
Reference the appendix for estimated calculations and the drainage plan.
Page 6
LOW IMPACT DEVELOPMENT
The City of Fort Collins updated the Low Impact Development ordinance in 2016 (Ordinance No.
007, 2016) to require:
· Treat at least 75% of any newly developed or redeveloped impervious area using one or
a combination of LID techniques, or
· Treat at least 50% of any newly developed or redeveloped impervious area using one or
a combination of LID techniques when 25% of private drivable surfaces are permeable.
To satisfy the required implementation of Low Impact Development (LID) techniques, the
Ziegler-Corbett property could utilize below grade infiltration galleries (such as ADS StormTech
chamber system), bioretention ponds/rain gardens, and/or permeable pavers. Other LID
techniques will be explored, but due to the limited grade available and the amount of detention
volume required, shallow infiltration galleries may assist in maintaining storm drain grades and
detention volumes. Infiltration galleries, rain gardens, and permeable pavers can promote
infiltration while capturing fine sediment that drains off the impervious areas. Isolator rows can
be implemented at the headworks to the infiltration galleries to allow larger sediment particles
to settle prior to entering the infiltration gallery. The isolator rows will be accessible to remove
sediments. Standard water quality is also provided, as needed, within the detention ponds in
addition to these LID infiltration galleries. A Standard Operations Procedure will be provided at
final design to assist in ensuring that these BMPs will adequately perform over time.
Below is a description of the 4-step process for selecting structural BMPs:
Urban Drainage and Flood Control District (UDFCD) recommends a Four Step Process for
receiving water protection that focuses on reducing runoff volumes, treating the water quality
capture volume (WQCV), stabilizing drainageways and implementing long-term source controls.
The Four Step Process applies to the management of smaller, frequently occurring events.
Step 1: Employ Runoff Reduction Practices
To reduce runoff peaks, volumes, and pollutant loads from urbanizing areas, implement Low
Impact Development (LID) strategies, including Minimizing Directly Connected Impervious
Areas (MDCIA).
Captured runoff from strategic areas are routed through below grade infiltration galleries,
bioretention pond/rain gardens, and/or permeable pavers. Infiltration galleries, rain gardens,
Page 7
and permeable pavers will slow runoff, promote infiltration, and filter runoff prior to being
released into the adjacent storm drain system.
Step 2: Implement BMPs that Provide a Water Quality Capture Volume with Slow Release
The infiltration galleries, rain gardens, and permeable pavers are designed to provide water
quality capture volume per Urban Drainage’s recommendations and calculations. The captured
runoff is design for a 12-hr drain time.
Step 3: Stabilize Drainageways
Natural Drainageways are subject to bed and bank erosion due to increases in frequency,
duration, rate, and volume of runoff during and following development. Because the site will
drain to an existing storm system, bank stabilization is unnecessary with this project.
Step 4: Implement Site Specific and Other Source Control BMPs
Proactively controlling pollutants at their source by preventing pollution rather than removing
contaminants once they have entered the stormwater system or receiving waters is important
when protecting storm systems and receiving waters. This can be accomplished through site
specific needs such as construction site runoff control, post-construction runoff control and
pollution prevention / good housekeeping. It will be the responsibility of the contractor to
develop a procedural best management practice for the site.
Page 8
STORMWATER POLLUTION PREVENTION
Erosion and sedimentation can be controlled on-site by use of sediment control logs, inlet
protection, a gravel construction entrance, seeding, mulch, and turf. The measures are
designed to limit the overall sediment yield increase due to construction as required by the City
of Fort Collins. During overlot and final grading the soil will be roughened and furrowed
perpendicular to the prevailing winds.
During the performance of the work required by these specifications or any operations
appurtenant thereto, whether on right-of-way provided by the City or elsewhere, the
contractor shall furnish all labor, equipment, materials, and means required. The Contractor
shall conduct proper efficient measures wherever and as necessary to reduce dust nuisance,
and to prevent dust nuisance that has originated from his operations from damaging crops,
orchards, cultivated fields, and dwellings, or causing naissance to persons. The Contractor will
be held liable for any damage resulting from dust originating from his operations under these
specifications on right-of-way or elsewhere.
It is unlawful to track or cause to be tracked mud or other debris onto city streets or rights-of-
way. Wherever construction vehicles access routes or intersect paved public roads, previsions
must be made to minimize the transport of sediment by runoff or vehicles tracking onto the
paved surface. Stabilized construction entrances are required with base material consisting of
6” coarse aggregate. The contractor will be responsible for clearing mud tracked onto city
streets on a daily basis.
All temporary and permanent erosion and sediment control practices must be maintained and
repaired as needed to assure continued performance of their intended function. Silt fence and
sediment control logs will require periodic replacement. Maintenance is the responsibility of
the contractor.
All disturbed areas must be seeded and mulched within 30 days of project start. Vegetation
shall not be considered established until a ground cover is achieved which is demonstrated to
be mature enough to control soil erosion to the satisfaction of the City Inspector and to survive
severe weather condition.
Page 9
CONCLUSIONS
This Overall Drainage Report for the Ziegler-Corbett property has been prepared to comply with
the stormwater criteria set by the City of Fort Collins. The proposed development’s drainage
system will be designed to convey the developed peak storm water runoff through the site to
the existing storm drain system and to the development’s detention, water quality, and LID
facilities. Storm drains will be sized to provide the required roadway relief in both the 2-yr and
100-yr storm events, and to adequately convey the released runoff from the detention ponds
disbursed throughout the site. Overland relief will be provided at all sump locations. The
calculated 100-yr peak flows released from the Ziegler-Corbett property will adhere to the
allowed rates as established in the Front Range Village & Affinity Fort Collins drainage studies.
This overall drainage report anticipates the implementation of best management practices for
erosion control, temporary and permanent, and on-site construction facilities that will be
further designed and details in future Preliminary and Final Drainage Reports.
It can therefore be concluded that future development of the Ziegler-Corbett property will
comply with the storm water jurisdictional criteria and will not adversely affect the adjacent
properties, streets, storm drain system and/or detention/water quality facilities. Controlling the
developed runoff from these improvements will improve the current situations currently
existing on the site. Therefore, this preliminary report satisfies the burden of proof needed to
proceed to a future Preliminary & Final Drainage Reports.
Page 10
REFERENCES
1. Urban Storm Drainage Criteria Manual (Volumes 1, 2, and 3), Urban Drainage and Flood
Control District, Revised August 2018.
2. Fort Collins Stormwater Criteria Manual, Fort Collins Utilities, City of Fort Collins,
Colorado, Dated November 2018
3. “Final Drainage Report for Affinity Fort Collins,” prepared by JR Engineering, LLC, Dated
March 2, 2016.
4. “Final Drainage and Erosion Control Study for Front Range Village, Fort Collins,
Colorado,” Prepared by Stantec Consulting, Inc., dated February 2007.
Page 11
APPENDIX
Appendix A – References
Appendix A
APPENDIX A – REFERENCES
Ziegler-Corbett
Inadvertent Detention Volume
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
Stage Storage
Volume (pond volume calculated using the prismoidal formula):
CONTOUR (FT)AREA
(FT2)
AREA
(ACRE)
VOLUME
(ACRE-FT)
DEPTH
(FT)
CUMULATIVE VOLUME
(ACRE-FT)
4925.00 0 0.00 0.00
0.00 0.00
4926.00 3144 0.07 0.02
1.00 0.02
4927.00 164156 3.77 1.45 2.00 1.48
4928.00 377427
8.66 6.05 3.00 7.53
*Inadvertant spill elevation = 4928.00 ft
Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, Revised August 2018
A. Bartel
Highland Development
21-1044-00
October 5, 2021
()
3
2121 DepthAAAAV++=
21-1044-00 Inadvertant Detention.xls Page 1 of 1 Highland Development Services
Design Engineer:
Design Firm:
Project Number:
Date:
%
Impervious
Runoff
Coefficient C
Return
Period
Frequency
Adjustment
Factor (Cf)
100% 0.95
2-year to
10-year 1.00
90% 0.95 100-year 1.25
90% 0.95
40% 0.50
2% 0.20
C2 to C10 C100
H1 1,363,820 31.31 0 0 0 0 1,363,820 2.0% 0.20 0.25
Lawns
(Clayey Soil)
A. Bartel
Highland Development Services
21-1044-00
October 1, 2021
Runoff Coefficients and Frequency Adjustment Factors for City of Fort Collins - Storm Water Criteria Manual
Land Use
Paved
Roof
Walks/RAP
Gravel/Pavers
Agravel/pavers
(sq feet)
Alawn
(sq feet)
Weighted %
Impervious
COMPOSITE
Ziegler-Corbett
EXISTING IMPERVIOUS AREA CALCULATION
Fort Collins Stormwater Criteria Manual, December 2018
DESIGN CRITERIA:
BASINS:
% Impervious values from Table RO-11 in the Fort Collins Amendments to the Urban Drainage and Flood Control District Criteria Manual
Sub-basin
Designation
Atotal
(sq feet)
Atotal
(acres)
Apaved
(sq feet)
Aroof
(sq feet)
Awalk/RAP
(sq feet)
21-1044-00 Rational Calcs.xlsx Page 1 of 4 Highland Development Services
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
-Equation 6-2 -Equation 6-4 -Urbanized Check Equation 6-5
- CoFC Overland Flow
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
Time of Concentration (2-yr to 10-yr)
Type of Travel
Surface Cv
H1 H1 2.0% 0.20 31.31 500 0.0074 41.61 1453 0.0074
Tilage/Field 5 0.43 56.30 97.91 0.0074 48.02 48.02
Fort Collins Stormwater Criteria Manual, December 2018
tt
(min)
OVERALL SLOPE
(ft/ft)
tc
(min)
SLOPE
(ft/ft)
ti
(min)
LENGTH
(ft)
SLOPE
(ft/ft)
Table RO-2 VELOCITY
(ft/s)
LENGTH
(ft)
DESIGN CRITERIA:
SUB-BASIN DATA INITIAL/OVERLAND TIME
(ti)TRAVEL TIME (tt)
tc=ti+tt
(min)
Urban Check Final
tc
(min)DESIGN
POINT Sub-basin %
Impervious C2-10
AREA
(acres)
October 1, 2021
Ziegler-Corbett
HISTORIC TIME OF CONCENTRATION
A. Bartel
Highland Development
21-1044-00
ticttt+=5.0
wvSCV=
V
Ltt60
=
=18 − 15 +
60 24 +12
=
1.87(1.1 − )
21-1044-00 Rational Calcs.xlsx Page 2 of 4 Highland Development Services
Design Engineer:
Design Firm:
Project Number:
Date:
EQUATIONS:
-Equation 6-2 -Equation 6-4 -Urbanized Check Equation 6-5
- CoFC Overland Flow
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
Time of Concentration (100-yr)
Type of Travel
Surface Cv
H1 H1 2.0% 0.25 31.309 500 0.0074 39.29 1453 0.0074
Tilage/Field 5 0.43 56.30 95.60 0.0074 48.02 48.02
Fort Collins Stormwater Criteria Manual, December 2018
tt
(min)
OVERALL SLOPE
(ft/ft)
tc
(min)
SLOPE
(ft/ft)
ti
(min)
LENGTH
(ft)
SLOPE
(ft/ft)
Table RO-2 VELOCITY
(ft/s)
LENGTH
(ft)
DESIGN CRITERIA:
SUB-BASIN DATA INITIAL/OVERLAND TIME
(ti)TRAVEL TIME (tt)
tc=ti+tt
(min)
Urban Check Final
tc
(min)DESIGN
POINT Sub-basin %
Impervious C100
AREA
(acres)
October 1, 2021
Ziegler-Corbett
HISTORIC TIME OF CONCENTRATION
A. Bartel
Highland Development
21-1044-00
ticttt+=5.0
wvSCV=
V
Ltt60
=
=18 − 15 +
60 24 +12
=
1.87(1.1 − )
21-1044-00 Rational Calcs.xlsx Page 3 of 4 Highland Development Services
Design Engineer:
Design Firm:
Project Number:
Date:
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 1-100yr =2.86 in
BASIN SUMMARY:
tc (min)Runoff Coeff
(C5)C(A) (acres)Intensity
(in/hr)Q (ft3/s)tc (min)Runoff Coeff.
(C100)C(A) (acres)Intensity
(in/hr)Q (ft3/s)
H1 H1 31.31 48.02 0.20 6.26 0.96 6.00 48.02 0.25 7.83 3.34 26.15
DESIGN CRITERIA:
Design
Point Sub-basin Area (acres)
2-yr Peak Runoff 100-yr Peak Runoff
Fort Collins Stormwater Criteria Manual, December 2018
October 1, 2021
Ziegler-Corbett
HISTORIC PEAK RUNOFF
A. Bartel
Highland Development Services
21-1044-00
nnnnAICQ=
(0.786651)
1
)10(
5.28
ct
PI
+
=
21-1044-00 Rational Calcs.xlsx Page 4 of 4 Highland Development Services
Design Engineer:
Design Firm:
Project Number:
Date:
DESIGN CRITERIA
0.85
1.25
1.00 ft3 acre-ft
31.310 acres 371,595 8.53
6.00 cfs
Time
(min)
100-yr
Intensity
(I , in/hr)
Q100
(cfs)
Accumulative
Runoff Volume
(ft3)
Accumulative
Release
Volume
(ft3)
Detained
Volume
(ft3)
Detained
Volume
(acre-ft)
0 0.00 0.00 0 0 0 0.00
5 9.95 311.53 93,460 1,800 91,660 2.10
10 7.72 241.71 145,028 3,600 141,428 3.25
15 6.52 204.14 183,727 5,400 178,327 4.09
20 5.60 175.34 210,403 7,200 203,203 4.66
25 4.98 155.92 233,886 9,000 224,886 5.16
30 4.52 141.52 254,738 10,800 243,938 5.60
35 4.08 127.74 268,264 12,600 255,664 5.87
40 3.74 117.10 281,039 14,400 266,639 6.12
45 3.46 108.33 292,498 16,200 276,298 6.34
50 3.23 101.13 303,394 18,000 285,394 6.55
55 3.03 94.87 313,069 19,800 293,269 6.73
60 2.86 89.55 322,368 21,600 300,768 6.90
65 2.72 85.16 332,136 23,400 308,736 7.09
70 2.59 81.09 340,590 25,200 315,390 7.24
75 2.48 77.65 349,420 27,000 322,420 7.40
80 2.38 74.52 357,685 28,800 328,885 7.55
85 2.29 71.70 365,669 30,600 335,069 7.69
90 2.21 69.20 373,654 32,400 341,254 7.83
95 2.13 66.69 380,135 34,200 345,935 7.94
100 2.06 64.50 386,992 36,000 350,992 8.06
105 2.00 62.62 394,506 37,800 356,706 8.19
110 1.94 60.74 400,893 39,600 361,293 8.29
115 1.89 59.18 408,314 41,400 366,914 8.42
120 1.84 57.61 414,795 43,200 371,595 8.53
Ziegler-Corbett
100-yr Detention Volume - FAA Method
Highland Development Services
October 1, 2021
21-1044-00
A. Bartel
Area (A )
Allowed Release Rate
Fort Collins Stormwater Criteria Manual, December 2018
Runoff Coefficient (C )
Frequency Factor (C f )Required Detention
Adjusted Runoff Coefficient (CC f )
Developed Detention Volume Calculation