HomeMy WebLinkAboutPROSPECT STATION II - FDP - FDP160014 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE REPORT
Prospect Station II
Prepared for:
Prospect Station LLC
605 S. College Ave., Suite A
Fort Collins, CO 80524
(970) 219-3300
Prepared by:
Interwest Consulting Group
1218 West Ash, Suite A
Windsor, Colorado 80550
(970) 674-3300
March 23, 2016
Job Number 1240-140-00
iii
TABLE OF CONTENTS
TABLE OF CONTENTS ............................................................................................................ iii
1. GENERAL LOCATION AND DESCRIPTION ................................................................ 1
1.1 Location ........................................................................................................................... 1
1.2 Description of Property ................................................................................................. 1
1.3 Floodplain Submittal Requirements ............................................................................. 1
2. DRAINAGE BASINS AND SUB-BASINS .......................................................................... 2
2.1 Major Basin Description ................................................................................................ 2
2.2 Sub-basin Description .................................................................................................... 2
3. DRAINAGE DESIGN CRITERIA ...................................................................................... 2
3.1 Regulations ...................................................................................................................... 2
3.2 Directly Connected Impervious Area (DCIA) Discussion .......................................... 3
3.3 Development Criteria Reference and Constraints ...................................................... 4
3.4 Hydrological Criteria ..................................................................................................... 4
3.5 Hydraulic Criteria .......................................................................................................... 5
3.6 Floodplain Regulations Compliance ............................................................................. 5
3.7 Modifications of Criteria ............................................................................................... 5
4. DRAINAGE FACILITY DESIGN ....................................................................................... 6
4.1 General Concept ............................................................................................................. 6
4.2 Specific Details ................................................................................................................ 6
5. CONCLUSIONS .................................................................................................................... 7
5.1 Compliance with Standards .......................................................................................... 7
5.2 Drainage Concept ........................................................................................................... 7
6. STANDARD OPERATING PROCEDURES ..................................................................... 8
6.1 Purpose ............................................................................................................................ 8
6.2 Site Specific SOPs ........................................................................................................... 8
7. REFERENCES .................................................................................................................... 10
APPENDIX
VICINITY MAP AND DRAINAGE PLAN .............................................................................. A
HYDROLOGIC COMPUTATIONS .......................................................................................... B
HYDRAULIC COMPUTATIONS .............................................................................................. C
WATER QUALITY/LID AND SNOUT® INFORMATION .................................................. D
EXCERPTS FROM REFERENCE REPORTS......................................................................... E
1
1. GENERAL LOCATION AND DESCRIPTION
1.1 Location
The Prospect Station II development is located in Fort Collins. It is located in the
Northeast Quarter of Section 23, Township 7 North, Range 69 West of the Sixth Principal
Meridian, in the City of Fort Collins, Larimer County, Colorado. Please refer to the
vicinity map in Appendix A.
The project site is located at the southwest corner of West Prospect Road and the vacated
Tamasag Drive right-of-way. The vacated Tamasag Drive bounds the property on the
east, West Prospect Road on the north, Lot 2 of the Hause Subdivision on the west and
Lots 3 and 11 of Griffin Plaza Subdivision on the south. The legal description of the site
is Lot 1 Prospect Station Subdivision Second Filing being a replat of Lots 1 and 2, Griffin
Plaza Subdivision and a portion of vacated Tamasag Drive.
1.2 Description of Property
The property consists of 1.04 acres of land with 0.08 acres being dedicated to Prospect.
The project consists of a new building replacing the existing building and a new parking
and drive configuration. The northerly 0.2 acres drains northeast to Prospect with the
remainder sheeting east and south at a range of approximately 0.5% to 1.5%. The land is
currently occupied by an existing building and parking areas. There is no offsite flow
contributing to the site.
According to FEMA Panel 08069C0979H there are no mapped FEMA Floodways on this
property.
1.3 Floodplain Submittal Requirements
Because the project is not within any FEMA or City of Fort Collins mapped floodway, a
Floodplain Submittal is not required and a “City of Fort Collins Floodplain Review
Checklist for 100% Submittals” has not been included with this report.
2
2. DRAINAGE BASINS AND SUB-BASINS
2.1 Major Basin Description
The proposed development lies within the Old Town (a small part of the northern portion
of the site) and Spring Creek (the remainder of the site) Master Drainage Basins. Today,
the entire site locally drains to Spring Creek via sheet flow or existing inlets and pipe in
Prospect and BNSF ROW and not to the Old Town Basin. The development has also
been accounted for in the design of the Mason Street Outfall (MSO) pond (showing the
entire site in Spring Creek Basin) and is accounted for in the detention provided behind
the RR embankment (BNRR Pond).
The site is considered to be basin 801 of the Griffin Plaza in the Mason Street Outfall
report and a part of Spring Creek Basin 126 in the Spring Creek Master Plan. Outfall for
this site is Spring Creek.
Please refer to Appendix F for an explanation of the division of Spring Creek and Old
Town basins.
2.2 Sub-basin Description
The northern portion of the site that is included in the Old Town Master Drainage Basin
drains to the north where it is intercepted by West Prospect Road and then piped back to
Spring Creek. The remainder of the site (included in the Spring Creek Master Drainage
Basin) drains south through adjacent Lots 3 and 11 of the Griffin Plaza Subdivision.
There are no offsite flows associated with this site.
3. DRAINAGE DESIGN CRITERIA
3.1 Regulations
This report was prepared to meet or exceed the “City of Fort Collins Storm Drainage
Design Criteria Manual” specifications. Where applicable, the criteria established in the
“Urban Storm Drainage Criteria Manual” (UDFCD), developed by the Denver Regional
Council of Governments, has been used.
3
3.2 Directly Connected Impervious Area (DCIA) Discussion
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).
Runoff for the northern and eastern portions of the site will be routed through vegetated
areas through sheet flow thereby reducing runoff from impervious surfaces over
permeable areas to slow runoff and increase the time of concentration and promote
infiltration. Runoff from the parking lot and building roof shall drain directly to a Type C
inlet with sump that incorporates a SNOUT® water quality system from Best
Management Products, Inc. device before draining into a CDOT #4 Water Quality
Chamber that promotes further infiltration and sedimentation (similar to the bottom of a
pervious pavement section).
Step 2: Implement BMPs that Provide a Water Quality Capture Volume with Slow
Release
Once runoff has been minimized, the remaining runoff shall be treated through the CDOT
#4 Water Quality Chamber and a sump with a SNOUT® water quality system from Best
Management Products, Inc. device. Both allow for settlement of sediments prior to
entering the rock chamber.
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 water quality pond, bank stabilization is unnecessary with this
project.
4
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.
3.3 Development Criteria Reference and Constraints
The runoff from this site has been routed to conform to the requirements of the City
Stormwater Department. Water quality facilities are required for the new construction
proposed on the site. Water quality will be met through the use of the CDOT #4 Water
Quality Chamber that includes 1,290 cf of storage in the voids below the pavement and a
Type C inlet with sump and SNOUT® water quality system from Best Management
Products, Inc. device to prevent sands and silt from clogging the rock treatment chamber.
Impervious area for the site has already been accounted for in the hydrology for Spring
Creek (the BNRR pond); therefore, detention is not required for this development. Please
refer to excerpts from the Mason Street Outfall report in Appendix E.
3.4 Hydrologic Criteria
Runoff computations were prepared for the 10-year minor and 100-year major storm
frequency utilizing the rational method.
All hydrologic calculations associated with the basins are included in Appendix B of this
report. Standard Form 8 (SF-8) provides time of concentration calculations for all sub-
basins. Standard Form 9 (SF-9) provides a summary of the design flows for all Sub-
basins and Design Points associated with this site.
Water quality capture volume was determined using the method recommended in the
“Urban Storm Drainage Criteria Manual”. This volume is achieved within the storage in
the voids of the CDOT #4 Water Quality Chamber. All related information is located in
Appendix D.
5
3.5 Hydraulic Criteria
All hydraulic calculations will be presented in the final drainage report and prepared in
accordance with the City of Fort Collins Drainage Criteria. All calculations will be
included in Appendix C of this report.
Hydraulic calculations will be presented in the final drainage report.
3.6 Floodplain Regulations Compliance
The project is not within any FEMA or City of Fort Collins mapped floodway; therefore,
Floodplain Regulations Compliance is not required.
3.7 Modifications of Criteria
The site will meet the full water quality volume requirement. Basins C and D will not be
captured for treatment but both basins continue to follow existing conditions. The entire
site’s required water quality capture volume is 1,288 cf and will be treated by the CDOT
#4 Water Quality Chamber. The treated water and flow from basins C and D will
eventually reach the MSO water quality pond via the proposed storm system or overland
where it will be treated again. The MSO pond has ample volume for the site. Please
refer to Appendix D for supporting information regarding water quality and the MSO
pond.
If the CDOT #4 Water Quality Chamber is completely saturated or overwhelmed, water
will overtop into the 15” RCP bypass pipe in the Type C inlet and then be conveyed south
in the proposed system that conveys water to the MSO pond (which is within the
boundaries of the large BNRR detention pond). Note that the entire site today drains to
the MSO pond.
The 2016 LID Criteria of No less than seventy five percent (75%) of any newly developed
or redeveloped area, and any modification on a previously developed area for which a
construction permit is required under City codes and regulations, must be treated using
one or a combination of LID techniques is met. There is 33,984 sf of new impervious
area. The new impervious area of Basins A and B treated in the LID method of CDOT #4
Water Quality Chamber is 27,248 sf, which is 80% of new impervious treated by LID. In
6
addition, a SNOUT® water quality system from Best Management Products, Inc. is
proposed to provide additional water quality and pretreatment ahead of the rock chamber.
Also, as mentioned in Section 3.7, the BNRR pond has ample volume for water quality
where this water will eventually be routed to and additionally treated.
4. DRAINAGE FACILITY DESIGN
4.1 General Concept
The majority of the proposed development will be collected and conveyed to the
proposed storm drain system where it will be treated for water quality via a the CDOT #4
Water Quality Chamber and a sump and SNOUT® water quality system from Best
Management Products, Inc. before being released into the proposed system that conveys
water south to the BNRR pond.
4.2 Specific Details
A summary of the drainage patterns within each basin is provided in the following
paragraphs. Please refer to Appendix A for the drainage plan.
Basin A is 0.59 acres and contains half of the roof (south portion) and the entire parking
area. This basin is calculated to have a 10-year discharge of 2.3 cfs and a 100-year
discharge of 5.8 cfs. Flows from Basin A are captured by the Type C sump inlet and the
CDOT #4 Water Quality Chamber. A new storm system is proposed to release this flow
into the BNRR pond. Currently, this area sheets to the pond.
Basin B is 0.17 acres, contains half of the roof (north portion) and is calculated to have a
10-year discharge of 0.7 cfs and a 100-year discharge of 1.7 cfs. Flows from Basin B are
captured by the proposed roof drains that direct flow to the Type C sump inlet and the
CDOT #4 Water Quality Chamber before being released into the proposed storm system.
This system then releases flow into the BNRR pond. Currently, this area sheets to the
pond.
Basin C is 0.19 acres and has a 10-year discharge of 0.5 cfs and 1.2 cfs. Flows from this
basin will continue current conditions and sheet north to West Prospect Road where it
7
will be conveyed east via curb and gutter to the existing storm inlet in West Prospect
Road. This inlet is part of the existing storm system that discharges to the BNRR pond.
Basin D is 0.09 acres and is calculated to have a 10-year discharge of 0.4 cfs and a 100-
year discharge of 0.9 cfs. This basin is the west half of the concrete drive built with
Prospect Station I in 2013. Flows from this basin will continue current conditions and
flow south through a curb cut and through Lot 11 of Griffin Plaza Subdivision to the
BNRR pond as they do today
The percent impervious weighted average of the entire site is 72% which is below the
Mason Street Outfall and the BNRR model assumption of 80%; therefore, detention is
not required. The voids in the rock water quality chamber will provide some detention
simply by slowing the flow to the outlet. Please refer to Appendix E for excerpts from
the Mason Street Outfall drainage report.
5. CONCLUSIONS
5.1 Compliance with Standards
All computations that have been completed within this report are in compliance with the
City of Fort Collins Storm Drainage Design Criteria Manual.
5.2 Drainage Concept
The proposed drainage concepts presented in this report and on the construction plans
adequately provides 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.
8
6. STANDARD OPERATING PROCEDURES
6.1. Purpose
In order for physical stormwater Best Management Practices (BMPs) to be effective,
proper maintenance is essential. Maintenance includes both routinely scheduled activities,
as well as non-routine repairs that may be required after large storms, or as a result of
other unforeseen problems. Standard Operating Procedures (SOPs) should clearly
identify BMP maintenance responsibility. BMP maintenance is typically the
responsibility of the entity owning the BMP.
Identifying who is responsible for maintenance of BMPs and ensuring that an adequate
budget is allocated for maintenance is critical to the long-term success of BMPs.
Maintenance responsibility may be assigned either publicly or privately. For this project,
the privately owned BMPs shown in Section B below are to be maintained by the
property owner or property manager.
6.2. Site Specific SOPs
The following stormwater facilities contained within the Propsect Station II development
are subject to SOP requirements:
- CDOT #4 Water Quality Chamber
- Storm Drains
The location of said facilities can be found on the Utility Plans for Prospect Station II.
Inspection and maintenance procedures and frequencies, specific maintenance
requirements and activities, as well as BMP-specific constraints and considerations shall
follow the guidelines outlined below.
SOP Maintenance Summary:
Stormwater Facility/BMP Ownership/Responsibility
CDOT #4 Water Quality Chamber Private
Storm Drains Private
9
CDOT #4 Water Quality Chamber Maintenance Plan
Routine Maintenance Table
Required Action Maintenance Objective Frequency of Action
Debris Removal from CDOT
Type C inlet with Sump and
SNOUT®
Remove floatable debris and oils
on the surface of the captured
water, and grit and sediment on
the bottom of the structure.
Maintenance is best done with a
vacuum truck.
Routine – The structure should be
cleaned twice a year. An annual
flushing of the vent or a gentle
rodding with a flexible wire
should be performed once a year
on the SNOUT® hood.
Non-routine – The structure
should be cleaned when the sump
is half full. Structures should also
be cleaned if a spill or other
incident causes a larger than
normal accumulation of pollutants
in a structure.
Debris Removal from CDOT #4
Aggregate Chamber
Ensure that the facility continues
to function as initially intended.
Routine – Jet stream through the
cleanouts into the Type C inlet
and the manhole twice a year to
flush the system.
Inspection of CDOT Type C inlet
with Sump and SNOUT®
Schedule maintenance based on
the solids collected in the sump.
New Installation – Monthly
monitoring for the first year of a
new installation after the site has
been stabilized. Measurements
should be taken after each rain
event of 0.5 inches or more, or
monthly, as determined by local
weather. Checking sediment
depths and noting the surface
pollutants in the structure will be
helpful in planning maintenance.
Routine – Measurements should
be taken after each rain event of
0.5 inches or more, or monthly, as
determined by local weather.
An annual inspection of the anti-
siphon vent and access hatch of
the SNOUT® hood should be
performed.
10
Inspection of the CDOT #4
Aggregate Chamber
Inspect to ensure that the facility
continues to function as initially
intended.
Routine – Visually Inspect pipes
and cleanouts at least annually or
after major storm events. Every
2-5 years the pipes should be
inspected with a video camera.
Storm Drain Lines Maintenance Plan
Routine Maintenance Table
Required Action Maintenance Objective Frequency of Action
Debris Removal from Inlets and
Catch Basins
Remove debris and trash from
inlets to prevent them from
continuing downstream or
clogging and reducing the flow
capacity of the system.
Non-routine – Remove debris as
needed after storm events or
seasonally such as during the Fall
with heavy amounts of leaves and
twigs entering the system.
Debris Removal from Storm
Pipes
Ensure the pipe systems function
as intended. Reduced capacities
in the pipes will cause the system
to back up and increase the
frequency of surface flooding that
could damage property.
Non-routine – Pipe cleaning is
recommended as needed based on
the results of inspections or when
the system is no longer able to
regularly convey routine storm
flows from the site.
Inspection Use a video camera to inspect the
condition of the storm drain pipes
looking for sediment buildup and
structural integrity. Clean out
pipes as needed. If the integrity
of the pipe is compromised, then
repair the damaged section(s).
Routine – Visually Inspect pipes
and inlets at least annually or after
major storm events. Every 2-5
years the pipes should be
inspected with a video camera.
7. REFERENCES
1. City of Fort Collins, “Fort Collins Stormwater Criteria Manual Amendments to
the Urban Drainage and Flood Control District Criteria Manual”, adopted
December 2011.
2. Urban Drainage and Flood Control District, “Urban Storm Drainage Criteria
Manual”, Volumes 1 and 2, dated June 2001, and Volume 3 dated November
2010.
3. Ayers Associates, “Alternative Analysis for the Design of the Mason Street
A
APPENDIX A
VICINITY MAP AND DRAINAGE PLAN
B
APPENDIX B
HYDROLOGIC COMPUTATIONS
SUMMARY
DRAINAGE SUMMARY TABLE
Design Tributary Area C (10) C (100) tc (10) tc (100) Q(10)tot Q(100)tot
Sub-basin REMARKS
Point (ac) (min) (min) (cfs) (cfs)
A A 0.59 0.82 1.00 5.0 5.0 2.3 5.8 Area Draining to Underground Treatment and Inlet
B B 0.17 0.86 1.00 5.0 5.0 0.7 1.7 Roof Area to Storm Sewer
C C 0.19 0.56 0.70 7.2 5.9 0.5 1.2 Area Draining to W. Prospect
D D 0.09 0.80 1.00 5.0 5.0 0.4 0.9 Area Draining to Curb Cut
Page 7
Interwest Consulting Group
RUNOFF COEFFICIENTS & % IMPERVIOUS
LOCATION: Prospect Station II
PROJECT NO: 1068-069-01
COMPUTATIONS BY: es
DATE: 2/16/2016
Recommended Runoff Coefficients from Table 3-3 of City of Fort Collins Design Criteria
Recommended % Impervious from Urban Storm Drainage Criteria Manual
Runoff %
coefficient Impervious
C
Streets, parking lots (asphalt): 0.95 100
Sidewalks (concrete): 0.95 96
Roofs: 0.95 90
Porous Pavers: 0.50 40
Landscape Areas: 0.25 0
SUBBASIN TOTAL TOTAL PAVED ROOF SIDEWALK POROUS LANDSCAPE RUNOFF %
DESIGNATION AREA AREA AREA AREA AREA PAVERS AREA COEFF. Impervious REMARKS
(ac.) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (C)
Proposed
LOT 1.04 45,223 16,292 12,531 5,161 0 11,240 0.78 72
Existing
LOT 1.04 45,223 16,821 4,667 3,616 0 20,118 0.64 54
Equations
- Calculated C coefficients & % Impervious are area weighted
C = Σ (Ci Ai) / At
Ci = runoff coefficient for specific area, Ai
Ai = areas of surface with runoff coefficient of Ci
n = number of different surfaces to consider
At = total area over which C is applicable; the sum of all Ai's
2-1-16 Flow.xls
Interwest Consulting Group
RUNOFF COEFFICIENTS & % IMPERVIOUS
LOCATION: Prospect Station II
PROJECT NO: 1068-069-01
COMPUTATIONS BY: es
DATE: 2/1/2016
Recommended Runoff Coefficients from Table 3-3 of City of Fort Collins Design Criteria
Recommended % Impervious from Urban Storm Drainage Criteria Manual
Runoff %
coefficient Impervious
C
Streets, parking lots (asphalt): 0.95 100
Sidewalks (concrete): 0.95 96
Roofs: 0.95 90
Porous Pavers: 0.50 40
Landscape Areas: 0.25 0
SUBBASIN TOTAL TOTAL PAVED ROOF SIDEWALK POROUS LANDSCAPE RUNOFF %
DESIGNATION AREA AREA AREA AREA AREA PAVERS AREA COEFF. Impervious REMARKS
(ac.) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (C)
A 0.59 25,543 13,085 6,022 1,534 0 4,902 0.82 78 Area Draining to Underground Treatment and Inlet
B 0.17 7,617 0 6,509 98 0 1,010 0.86 78 Roof Area to Storm Sewer
C 0.19 8,168 702 0 2,949 0 4,517 0.56 43 Area Draining to W. Prospect
D 0.09 3,895 2,505 0 580 0 811 0.80 79 Area Draining to Curb Cut
Total 1.04 45,224 16,292 12,531 5,161 0 11,240 0.78 72
Equations
- Calculated C coefficients & % Impervious are area weighted
C = Σ (Ci Ai) / At
Ci = runoff coefficient for specific area, Ai
Ai = areas of surface with runoff coefficient of Ci
n = number of different surfaces to consider
At = total area over which C is applicable; the sum of all Ai's
2-1-16 Flow.xls
Interwest Consulting Group
STANDARD FORM SF-2
TIME OF CONCENTRATION - 10 YR
LOCATION: Prospect Station II
PROJECT NO: 1068-069-01
COMPUTATIONS BY: es
DATE: 2/1/2016
10-yr storm Cf = 1.00
SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS
DATA TIME (ti) (tt) (URBANIZED BASIN) tc
DESIGN SUBBASIN(s) Area C Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10
PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)
(1) (2) (3) (4) (5) (6) (7) (8) rough. (9) (10) (11) (12) (13) (14)
A A 0.59 0.82 17 2.0 1.7 230 1.3 0.016 2.3 1.67 3.4 247 11.4 5.0
B B 0.17 0.86 0 2.0 0.0 230 0.5 0.016 1.4 2.70 2.7 230 11.3 5.0
C C 0.19 0.56 38 2.0 4.9 245 0.8 0.016 1.8 2.27 7.2 283 11.6 7.2
D D 0.09 0.80 22 2.0 2.1 96 0.6 0.016 1.6 1.03 3.1 118 10.7 5.0
EQUATIONS:
tc = ti + tt
ti = [1.87 (1.1 - CCf ) L0.5 ] / S 1/3
tt = L/Vel.
Velocity from Manning's Equation with R=0.1 (corresponds to Figure 3-3 of City of Fort Collins Design Manual)
final tc = minimum of ti + tt and urbanized basin check
min. tc = 5 min. due to limits of IDF curves
2-1-16 Flow.xls
Interwest Consulting Group
STANDARD FORM SF-2
TIME OF CONCENTRATION - 100 YR
LOCATION: Prospect Station II
PROJECT NO: 1068-069-01
COMPUTATIONS BY: es
DATE: 2/1/2016
100-yr storm Cf = 1.25
SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS
DATA TIME (ti) (tt) (URBANIZED BASIN) tc
DESIGN SUBBASIN(s) Area C C*Cf Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10
PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)
(1) (2) (3) (4) (5) (6) (7) (8) rough. (9) (10) (11) (12) (13) (14)
A A 0.59 0.82 1.00 17 2.0 0.6 230 1.3 0.016 2.3 1.67 2.3 247 11.4 5.0
B B 0.17 0.86 1.00 0 2.0 0.0 230 0.5 0.016 1.4 2.70 2.7 230 11.3 5.0
C C 0.19 0.56 0.70 38 2.0 3.6 245 0.8 0.016 1.8 2.27 5.9 283 11.6 5.9
D D 0.09 0.80 1.00 22 2.0 0.7 96 0.6 0.016 1.6 1.03 1.7 118 10.7 5.0
EQUATIONS:
tc = ti + tt
ti = [1.87 (1.1 - CCf
) L
0.5
] / S
1/3
tt = L/Vel.
Velocity from Manning's Equation with R=0.1 (corresponds to Figure 3-3 of City of Fort Collins Design Manual)
final tc = minimum of ti + tt and urbanized basin check
min. tc = 5 min. due to limits of IDF curves
2-1-16 Flow.xls
Interwest Consulting Group
RATIONAL METHOD PEAK RUNOFF
(City of Fort Collins, 10-Yr Storm)
LOCATION: Prospect Station II
PROJECT NO: 1068-069-01
COMPUTATIONS BY: es
DATE: 2/1/2016
10 yr storm, Cf = 1.00
DIRECT RUNOFF CARRY OVER TOTAL REMARKS
Design Tributary A C Cf tc i Q (10) from Q (10) Q(10)tot
Sub-basin Design
Point (ac) (min) (in/hr) (cfs) Point (cfs) (cfs)
A A 0.59 0.82 5.0 4.87 2.3 2.3
B B 0.17 0.86 5.0 4.87 0.7 0.7
C C 0.19 0.56 7.2 4.29 0.5 0.5
D D 0.09 0.80 5.0 4.87 0.4 0.4
Q = Cf
C
iA
Q = peak discharge (cfs)
C = runoff coefficient
Cf
= frequency adjustment factor
i = rainfall intensity (in/hr) from City of Fort Collins IDF curve (4/16/99)
A = drainage area (acres) i = 41.44 / (10+ tc)
0.7974
2-1-16 Flow.xls
Interwest Consulting Group
RATIONAL METHOD PEAK RUNOFF
(City of Fort Collins, 100-Yr Storm)
LOCATION: Prospect Station II
PROJECT NO: 1068-069-01
COMPUTATIONS BY: es
DATE: 2/1/2016
100 yr storm, Cf = 1.25
DIRECT RUNOFF CARRY OVER TOTAL REMARKS
Des. Area A C Cf tc i Q (100) from Q (100) Q(100)tot
Design
Point Design. (ac) (min) (in/hr) (cfs) Point (cfs) (cfs)
A A 0.59 1.00 5.0 9.95 5.8 5.8
B B 0.17 1.00 5.0 9.95 1.7 1.7
C C 0.19 0.70 5.9 9.33 1.2 1.2
D D 0.09 1.00 5.0 9.95 0.9 0.9
Q = C
iA
Q = peak discharge (cfs)
C = runoff coefficient
i = rainfall intensity (in/hr) from City of Fort Collins IDF curve (4/16/99)
A = drainage area (acres) i = 84.682 / (10+ tc)0.7975
2-1-16 Flow.xls
C
APPENDIX C
HYDRAULIC CALCULATIONS
Profile Report
Engineering Profile - Profile - 1 (3-23-16 STORM 1.stsw)
27 Siemon Company Drive Suite 200 W Watertown, CT 06795 USA Page 1 of 1
+1-203-755-1666
3/22/2016
Bentley StormCAD V8i (SELECTseries 3)
3-23-16 STORM 1.stsw Bentley Systems, Inc. Haestad Methods Solution Center [08.11.03.84]
FlexTable: Conduit Table
Hydraulic
Grade Line
(Out)
(ft)
Hydraulic
Grade
Line (In)
(ft)
Velocity
(ft/s)
Capacity
(Full
Flow)
(cfs)
Flow
(cfs)
Manning's
n
Diam
eter
(in)
Section
Type
Slope
(Calcula
ted)
(ft/ft)
Length
(Unified)
(ft)
Invert
(Stop)
(ft)
Stop
Node
Invert
(Start)
(ft)
Label Start Node
CO-1 MSO POND 4,989.00 MH-1 4,995.00 297.0 -0.020 Circle 15.0 0.013 7.50 9.18 8.34 4,996.09 4,991.27
4,999.20 20.0 -0.005 Circle 15.0 0.013 7.50 4.57 6.11 5,000.54 5,000.19
TYPE C
INLET
CO-2 MH-1 4,999.10
CO-3 TYPE C INLET 4,999.30 MH-2 5,000.75 72.0 -0.020 Circle 12.0 0.013 1.70 5.06 5.80 5,001.30 5,001.07
CO-4 MH-2 5,000.75 MH-3 5,001.37 61.5 -0.010 Circle 12.0 0.010 1.70 4.65 5.46 5,001.92 5,001.44
CO-5 MH-3 5,001.37 MH-4 5,002.50 227.0 -0.005 Circle 12.0 0.010 1.70 3.27 4.20 5,003.05 5,001.88
27 Siemon Company Drive Suite 200 W Watertown, CT 06795 USA Page 1 of 1
+1-203-755-1666
3/22/2016
Bentley StormCAD V8i (SELECTseries 3)
3-23-16 STORM 1.stsw Bentley Systems, Inc. Haestad Methods Solution Center [08.11.03.84]
FlexTable: Catch Basin Table
Energy Grade
Line (Out)
(ft)
Energy Grade
Line (In)
(ft)
Hydraulic Grade
Line (Out)
(ft)
Hydraulic Grade
Line (In)
(ft)
Flow (Additional
Carryover)
(cfs)
Elevation
(Invert)
(ft)
Elevation (Rim)
(ft)
Elevation
(Ground)
(ft)
ID Label
5,001.67 5,001.67 4,992.70 1.70 5,001.07 5,000.54 5,001.14 5,001.13
TYPE C
INLET
31
27 Siemon Company Drive Suite 200 W Watertown, CT 06795 USA Page 1 of 1
+1-203-755-1666
3/22/2016
Bentley StormCAD V8i (SELECTseries 3)
3-23-16 STORM 1.stsw Bentley Systems, Inc. Haestad Methods Solution Center [08.11.03.84]
FlexTable: Outfall Table
Energy Grade
Line
(ft)
Flow (Total Out)
(cfs)
Hydraulic Grade
(ft)
Elevation (User
Defined Tailwater)
(ft)
Elevation
(Invert)
(ft)
Set Rim to
Ground
Elevation?
Elevation
(Ground)
(ft)
Label
4,993.00 False 4,989.00 4,991.27 4,991.27 7.50 4,991.27
MSO
POND
27 Siemon Company Drive Suite 200 W Watertown, CT 06795 USA Page 1 of 1
+1-203-755-1666
3/22/2016
Bentley StormCAD V8i (SELECTseries 3)
3-23-16 STORM 1.stsw Bentley Systems, Inc. Haestad Methods Solution Center [08.11.03.84]
D
APPENDIX D
WATER QUALITY/LID
AND
SNOUT® INFORMATION
E
APPENDIX E
EXCERPTS FROM REFERENCE REPORTS
Outfall”, dated November 2010.