HomeMy WebLinkAboutBOARDWALK OFFICE BUILDING - PDP - PDP170032 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTPRELIMINARY DRAINAGE REPORT
Boardwalk Office Building
Prepared for:
r4 Architects
226 Remington Street, Unit #3
Fort Collins, CO 80528
(970) 224-0630
Prepared by:
Interwest Consulting Group
1218 West Ash, Suite A
Windsor, Colorado 80550
(970) 674-3300
October 17, 2017
Job Number 1326-069-00
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 .......................................... 2
3.3 Development Criteria Reference and Constraints ...................................................... 4
3.4 Hydrological Criteria ..................................................................................................... 4
3.5 Hydraulic Criteria .......................................................................................................... 4
3.6 Floodplain Regulations Compliance ............................................................................. 4
3.7 Modifications of Criteria ............................................................................................... 5
4. DRAINAGE FACILITY DESIGN ....................................................................................... 5
4.1 General Concept ............................................................................................................. 5
4.2 Specific Details ................................................................................................................ 6
5. CONCLUSIONS .................................................................................................................... 7
5.1 Compliance with Standards .......................................................................................... 7
5.2 Drainage Concept ........................................................................................................... 7
6. REFERENCES ...................................................................................................................... 8
APPENDIX
VICINITY MAP AND DRAINAGE PLAN .............................................................................. A
HYDROLOGIC COMPUTATIONS .......................................................................................... B
HYDRAULIC COMPUTATIONS (PROVIDED AT FINAL) ................................................. C
WATER QUALITY AND LID INFORMATION .................................................................... D
SOILS INFO, FEMA INFO, AND REFERENCE MATERIAL .............................................. E
STORMWATER ALTERNATIVE COMPLICANCE/VARIANCE APPLICATION ......... F
1
1. GENERAL LOCATION AND DESCRIPTION
1.1 Location
The Boardwalk Office Building development is located in Fort Collins. It is located in
the Northwest Quarter of Section 36, 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 northeast corner of JFK Parkway and Boardwalk Drive.
JFK Parkway bounds the property on the west, Boardwalk Drive on the south, Tract 9,
Block 1 of Landings Office Park PUD on the east and Landings Bay FDP on the north.
The development consists of Tracts 8 and 10, Block 2 of Landings Office Park PUD.
1.2 Description of Property
The property consists of 0.55 acres of land. The project will include construction of a
new building, sidewalks and new parking with drive aisles. The proposed development
is very similar to the original approved 1995 design of the property.
The site generally slopes in a southerly direction at approximately 5% to 7%. The land is
currently vacant. There is no offsite flow contributing to the site. Soils on site consist of
Tassel sandy loam, 3 to 25 percent slopes classified as Type D hydrologic soil group.
According to FEMA Panel 08069C0987G (effective 05/02/2012) there are no mapped
FEMA Floodways on this property.
Please refer to Appendix E for hydrologic soil and FEMA information.
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 50% 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 Mail Creek Master Drainage Plan. Outfall for
this site is the Larimer County Canal No. 2.
The site was previously studied in the “Final Drainage Report for Landings Office Park
P.U.D.” by Northern Engineering Services, Inc., dated October 27, 1995. Please refer to
Appendix E for reference material.
2.2 Sub-basin Description
Today, the entire site sheet flows onto JFK Parkway and Boardwalk Drive where the curb
and gutter conveys the flow to either the East Detention Pond of ShopKo or Detention
Pond D1 of the Landings PUD located at the northwest corner of Boardwalk Drive and
Landings Drive.
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.
3.2 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.
3
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 eastern portion 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 the eastern portion of the building shall drain directly into a porous
pavement system thereby slowing runoff and also promoting infiltration. Runoff from the
western portion of the building roof shall drain directly to a storm system that will release
to a swale that will slow runoff and increase the time of concentration and promote
infiltration.
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 porous
pavement system that allows for settlement of sediments.
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 detention pond, bank stabilization is unnecessary with this
project.
Step 4: Implement Site Specific and Other Source Control BMPs
The proposed development will provide the porous pavement system feature which will
eliminate pollution that had previously been exposed during weathering and runoff
processes. The proposed project will proactively control pollutants at their source by
preventing pollution rather than removing contaminants once they have entered the
stormwater system as compared to historic conditions.
4
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. Because water quality capture volume from this site is not
included in the development’s detention pond, water quality facilities are required for the
new construction proposed on the site. The site’s water quality will be met through the
use of a porous pavement system that includes 12” of storage in the voids below the
pavers. A variance is requested for the portion of the site that does not reach the porous
pavers for treatment.
3.4 Hydrologic Criteria
Runoff computations were prepared for the 2-year and 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.
A variance to use the porous pavement system for the water quality capture volume is
included in Appendix D.
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.
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.
5
3.7 Modifications of Criteria
The site has been designed to maximize water quality treatment but the handicap ramp
area to Boardwalk and the west and south side of the site cannot drain to the porous
pavement system. The entire site’s required water quality capture volume is 0.01 ac-ft
and will be contained in the 12” of storage in the voids below the pavers. Please refer to
Appendix D for supporting information regarding water quality.
If the porous pavement system is completely saturated or overwhelmed, water will
overtop into the Type R inlet then be conveyed east to the existing Detention Pond D1 of
the Landings PUD.
Runoff reduction practices (LID techniques) are also required. No less than fifty percent
of any newly added impervious area must be treated using one or a combination of LID
techniques. New impervious area is 16,449 sf. Basins A and B contain the porous paver
system. Using this LID technique, 15,560 sf of new impervious area (95%) will be
treated which exceeds the 50% requirement.
No less than twenty five percent of any newly added pavement areas must be treated
using a permeable pavement technology. The project adds 10,434 sf of new pavement
area. This project will incorporate 3,790sf of porous pavers which is 36% of the newly
added pavement which exceeds the required 25%.
The porous pavement system is oversized and provides full water quality volume for the
site.
Please refer to Appendix D for LID calculations and information.
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 porous
pavement system before being released into the proposed system that conveys water east
to the existing Pond D1 of the Landings PUD.
6
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 0.09 acres and contains the north drive aisle and parking. This basin is
calculated to have a 10-year discharge of 0.4 cfs and a 100-year discharge of 0.9 cfs.
Flows from Basin A are captured by the porous paver system and will discharge to the 8-
inch storm pipe around the north and east sides of the site. This system releases the
treated water into the 5’ Type R inlet and 12-inch storm pipe located at design point B.
Basin B is 0.26 acres, contains about 60 percent the roof (east portion) and the east drive
aisle and parking. This basin is calculated to have a 10-year discharge of 1.0 cfs and a
100-year discharge of 2.5 cfs. Flows from Basin B are captured by the porous paver
system. The treated water is released into the 5’ Type R inlet and 12-inch storm pipe
located at design point B.
Basin C is 0.04 acres and contains the remainder of the roof (about 40%). The basin is
calculated to have a 10-year discharge of 0.2 cfs and a 100-year discharge of 0.4 cfs.
Flows from this basin will be conveyed to the 6-inch perimeter drain that wraps around
the west and south of the building. This drain will release flow to the sidewalk chase
located on the southeast side of the building. This chase will direct the flow to Basin B’s
porous paver system for treatment.
The treated water is released into the same 5’ Type R inlet located at design point B and
is then released to an outfall swale that conveys flow to the existing pond.
100 percent of the roof is treated in the porous paver system.
Basin D is 0.13 acres and is calculated to have a 10-year discharge of 0.2 cfs and a 100-
year discharge of 0.4 cfs. This basin consists of the west and south landscape area
adjacent to the building. Flows from this basin will continue current conditions and sheet
flow onto JFK Parkway and remains untreated.
7
Basin E is 0.03 acres and is calculated to have a 10-year discharge of 0.1 cfs and a 100-
year discharge of 0.2 cfs. This basin consists of the handicap ramp adjacent to the north
side of the building. Flows from this basin will drain to a sump inlet and the 8-inch storm
pipe around the north and east sides of the site. This system releases the untreated water
into the 5’ Type R inlet and 12-inch storm pipe located at design point B.
The percent impervious weighted average of the entire site is 58% which is below the
70% imperviousness that was assumed in the previous Landings PUD study by Northern
Engineering; therefore, detention is not required. Please refer to Appendix E for excerpts
from this 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.
A waiver to the Low Impact Development Criteria of the total WQCV treated has been
requested.
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. 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. Northern Engineering Services, Inc., “Final Drainage Report for Landings Office
Park P.U.D.”, dated October 27, 1995.
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(2)tot Q(10)tot Q(100)tot
Sub-basin REMARKS
Point (ac) (min) (min) (cfs) (cfs) (cfs)
A A 0.09 0.81 1.00 5.0 5.0 0.2 0.4 0.9 PERVIOUS PAVER SYSTEM
B B 0.26 0.77 0.96 5.0 5.0 0.6 1.0 2.5 PERVIOUS PAVER SYSTEM
C C 0.04 0.83 1.00 5.0 5.0 0.1 0.2 0.4 TO 6" ROOF DRAIN SYSTEM TO PERVIOUS PAVER SYSTEM
D D 0.13 0.26 0.32 5.0 5.0 0.1 0.2 0.4 FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
E E 0.03 0.50 0.93 5.7 5.0 0.3 0.4 1.1 FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
E A+E 0.12 0.74 0.93 5.0 5.0 0.3 0.4 1.1 TO 8" PERIMETER DRAIN
B B+C 0.30 0.77 0.97 5.0 5.0 0.7 1.1 2.9 TO 18" PIPE AND TO POND
Page 7
Interwest Consulting Group
RUNOFF COEFFICIENTS & % IMPERVIOUS
LOCATION: Boardwalk and JFK
PROJECT NO: 1326-069-00
COMPUTATIONS BY: MO
DATE: 10/17/2017
Recommended Runoff Coefficients from Table RO-11 of City of Fort Collins Stormwater Code, Volume I
Recommended % Impervious from Table RO-3 Urban Storm Drainage Criteria Manual, Volume I
Type B Soils Runoff %
coefficient Impervious
C
Streets, parking lots (asphalt): 0.95 100
Sidewalks (concrete): 0.95 96
Roofs: 0.95 90
Gravel or Pavers: 0.50 40
Landscape Areas (Flat, heavy) : 0.20 0
Landscape Areas (Steep, heavy) : 0.35 0
SUBBASIN TOTAL TOTAL ROOF PAVED PAVERS SIDEWALK LANDSCAPE RUNOFF %
DESIGNATION AREA AREA AREA AREA AREA AREA AREA COEFF. Impervious REMARKS
(ac.) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (C)
LANDINGS D5 0.45 19,602 7,492 7,013 0 0 5,097 0.76 70
LANDINGS D7 0.19 8,059 0 5,706 0 0 2,352 0.73 71
A 0.09 4,071 0 2,642 989 297 143 0.81 82 PERVIOUS PAVER SYSTEM
B 0.26 11,369 2,375 4,003 2,801 1,094 1,097 0.77 73 PERVIOUS PAVER SYSTEM
C 0.04 1,625 1,360 0 0 0 265 0.83 75 TO 6" ROOF DRAIN SYSTEM TO PERVIOUS PAVER SYSTEM
D 0.13 5,556 0 0 0 408 5,148 0.26 7 FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
E 0.03 1,198 0 0 0 481 717 0.50 39 FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
A+E 0.12 5,269 0 2,642 989 778 861 0.74 72 TO 8" PERIMETER DRAIN
B+C 0.30 12,994 3,734 4,003 2,801 1,094 1,363 0.77 73 TO 18" PIPE AND TO POND
D+E 0.16 6,754 0 0 0 889 5,865 0.30 13 FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
A+B+C+D+E 0.55 23,820 3,734 6,645 3,790 2,280 7,371 0.65 58 FOR ON SITE LID CALCULATIONS
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
10-18-17 Final FC Flow.xls
Interwest Consulting Group
STANDARD FORM SF-2
TIME OF CONCENTRATION - 2 and 10 YR
LOCATION: Boardwalk and JFK
PROJECT NO: 1326-069-00
COMPUTATIONS BY: MO
DATE: 10/17/2017
2 and 10-yr storm Cf = 1.00 from Table RO-12 of City of Fort Collins Stormwater Code, Volume I
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 0.09 0.81 40 3.6 2.2 48 5.0 0.016 4.5 0.2 2.4 88 10.5 5.0 PERVIOUS PAVER SYSTEM
B B 0.26 0.77 45 5.0 2.4 140 2.5 0.016 3.2 0.7 3.2 185 11.0 5.0 PERVIOUS PAVER SYSTEM
C C 0.04 0.83 14 2.0 1.5 1 2.0 0.016 2.8 0.0 1.5 15 10.1 5.0 TO 6" ROOF DRAIN SYSTEM TO PERVIOUS PAVER SYSTEM
D D 0.13 0.26 17 25.0 2.2 1 2.0 0.016 2.8 0.0 2.2 18 10.1 5.0 FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
E E 0.03 0.50 36 2.0 5.3 1 2.0 1.016 0.0 0.4 5.7 37 10.2 5.7 FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
E A+E 0.12 0.74 40 3.6 2.8 48 5.0 0.016 4.5 0.2 2.9 88 10.5 5.0 TO 8" PERIMETER DRAIN
B B+C 0.30 0.77 45 5.0 2.4 140 2.5 0.016 3.2 0.7 3.1 185 11.0 5.0 TO 18" PIPE AND TO POND
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
10-18-17 Final FC Flow.xls
Interwest Consulting Group
STANDARD FORM SF-2
TIME OF CONCENTRATION - 100 YR
LOCATION: Boardwalk and JFK
PROJECT NO: 1326-069-00
COMPUTATIONS BY: MO
DATE: 10/17/2017
100-yr storm Cf = 1.25 from Table RO-12 of City of Fort Collins Stormwater Code, Volume I
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 0.09 0.81 1.00 40 3.6 0.8 48 5.0 0.016 4.5 0.2 1.0 88 10.5 5.0 PERVIOUS PAVER SYSTEM
B B 0.26 0.77 0.96 45 5.0 1.0 140 2.5 0.016 3.2 0.7 1.8 185 11.0 5.0 PERVIOUS PAVER SYSTEM
C C 0.04 0.83 1.00 14 2.0 0.6 1 2.0 0.016 2.8 0.0 0.6 15 10.1 5.0 TO 6" ROOF DRAIN SYSTEM TO PERVIOUS PAVER SYSTEM
D D 0.13 0.26 0.32 17 25.0 2.1 1 2.0 0.016 2.8 0.0 2.1 18 10.1 5.0 FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
E E 0.03 0.50 0.63 36 2.0 4.2 1 2.0 1.016 0.0 0.4 4.6 37 10.2 5.0 FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
E A+E 0.12 0.74 0.93 40 3.6 1.3 48 5.0 0.016 4.5 0.2 1.5 88 10.5 5.0 TO 8" PERIMETER DRAIN
B B+C 0.30 0.77 0.97 45 5.0 1.0 140 2.5 0.016 3.2 0.7 1.7 185 11.0 5.0 TO 18" PIPE AND TO POND
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
10-18-17 Final FC Flow.xls
Interwest Consulting Group
RATIONAL METHOD PEAK RUNOFF
(City of Fort Collins, 2-Yr Storm)
LOCATION: Boardwalk and JFK
PROJECT NO: 1326-069-00
COMPUTATIONS BY: MO
DATE: 10/17/2017
2 yr storm, Cf = 1.00
DIRECT RUNOFF CARRY OVER TOTAL REMARKS
Design Tributary A C Cf tc i Q (2) from Q (2) Q(2)tot
Sub-basin Design
Point (ac) (min) (in/hr) (cfs) Point (cfs) (cfs)
A A 0.09 0.81 5.0 2.85 0.2 0.2 PERVIOUS PAVER SYSTEM
B B 0.26 0.77 5.0 2.85 0.6 0.6 PERVIOUS PAVER SYSTEM
C C 0.04 0.83 5.0 2.85 0.1 0.1 TO 6" ROOF DRAIN SYSTEM TO PERVIOUS PAVER SYSTEM
D D 0.13 0.26 5.0 2.85 0.1 0.1 FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
E A+E 0.12 0.74 5.0 2.85 0.3 0.3 TO 8" PERIMETER DRAIN
B B+C 0.30 0.77 5.0 2.85 0.7 0.7 TO 18" PIPE AND TO POND
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 = 24.221 / (10+ tc)0.7968
10-18-17 Final FC Flow.xls
Interwest Consulting Group
RATIONAL METHOD PEAK RUNOFF
(City of Fort Collins, 10-Yr Storm)
LOCATION: Boardwalk and JFK
PROJECT NO: 1326-069-00
COMPUTATIONS BY: MO
DATE: 10/17/2017
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 0.09 0.81 5.0 4.87 0.4 0.4 PERVIOUS PAVER SYSTEM
B B 0.26 0.77 5.0 4.87 1.0 1.0 PERVIOUS PAVER SYSTEM
C C 0.04 0.83 5.0 4.87 0.2 0.2 TO 6" ROOF DRAIN SYSTEM TO PERVIOUS PAVER SYSTEM
D D 0.13 0.26 5.0 4.87 0.2 0.2 FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
E A+E 0.12 0.74 5.0 4.87 0.4 0.4 TO 8" PERIMETER DRAIN
B B+C 0.30 0.77 5.0 4.87 1.1 1.1 TO 18" PIPE AND TO POND
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
10-18-17 Final FC Flow.xls
Interwest Consulting Group
RATIONAL METHOD PEAK RUNOFF
(City of Fort Collins, 100-Yr Storm)
LOCATION: Boardwalk and JFK
PROJECT NO: 1326-069-00
COMPUTATIONS BY: MO
DATE: 10/17/2017
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 0.09 1.00 5.0 9.95 0.9 0.9 PERVIOUS PAVER SYSTEM
B B 0.26 0.96 5.0 9.95 2.5 2.5 PERVIOUS PAVER SYSTEM
C C 0.04 1.00 5.0 9.95 0.4 0.4 TO 6" ROOF DRAIN SYSTEM TO PERVIOUS PAVER SYSTEM
D D 0.13 0.32 5.0 9.95 0.4 0.4 FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
FLOWS TO JFK AND BOARDWALK - PART OF LANDINGS D3
E A+E 0.12 0.93 5.0 9.95 1.1 1.1 TO 8" PERIMETER DRAIN
B B+C 0.30 0.97 5.0 9.95 2.9 2.9 TO 18" PIPE AND TO POND
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
10-18-17 Final FC Flow.xls
C
APPENDIX C
HYDRAULIC CALCULATIONS
(PROVIDED AT FINAL)
D
APPENDIX D
WATER QUALITY
AND
LID INFORMATION
Design Procedure Form: Extended Detention Basin (EDB) - Sedimentation Facility
Project Name: Boardwalk Office Building
Project Number: 1326-069-00
Company: INTERWEST CONSULTING GROUP
Designer: ES
Date: 10/17/2017
1. Basin Storage Volume
A) Tributary Area's Imperviousness Ratio (i=Ia/100) Ia = 58 %
i = 0.58
B) Contributing Watershed Area (Area) A = 0.55 acres
C) Water Quality Capture Volume (WQCV) WQCV = 0.229636 watershed inches
(WQCV = 1.0 * (0.91 * i3 - 1.19 * i2 + 0.78i) )
D) Design Volume: Vol = WQCV/12 * Area * 1.2 Vol. = 0.013 ac-ft
New Impervious Area 16,449 sf
Required Minimum Impervious Area to be Treated 8,225 sf
Treatment #1 - Pervious Pavers (Basin A) 989 sf
Treatment #1 - Impervious Area Treated (Basin A) 3,928 sf
Treatment #1 - Run-on Ratio (3:1 Max) 3.0
Treatment #2 - Pervious Pavers (Basin B) 2,801 sf
Treatment #2 - Impervious Area Treated (Basin B & C) 11,632 sf
Treatment #2 - Run-on Ratio (3:1 Max) 3.2
Total Area Treated 15,560 sf
Actual % of Impervious Area On-Site Treated by LID 95 %
New Pavement Area 10,434 sf
Required Minimum Area of Pervious Pavement 2,609 sf
Area of Pervious Pavers Provided 3,790 sf
Actual % of Pervious Pavement Provided 36 %
50% On-Site Treatment by LID Requirement
LID Table
25% Porous Pavement Requirement
E
APPENDIX E
EXCERPTS FROM REFERENCE REPORTS
Page 1 of 1
https://utility.arcgisonline.com/arcgis/rest/directories/arcgisoutput/Utilities/PrintingTools_... 8/17/2017
This unofficial copy was downloaded on Jul-18-2017 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com
For additional information or an official copy, please contact Engineering Office 281 North College Fort Collins, CO 80521 USA
F
APPENDIX F
STORMWATER ALTERNATIVE
COMPLIANCE/VARIANCE APPLICATION
Stormwater
Alternative Compliance/Variance Application
City of Fort Collins Water Utilities Engineering
Section A: Engineer/Owner Information
Engineer Name____________________________________________Phone___________________________
Street Address_____________________________________________________________________________
City__________________________________________State________________________Zip_____________
Owner Name______________________________________________Phone___________________________
Street Address_____________________________________________________________________________
City__________________________________________State________________________Zip_____________
Section C: Alternative Compliance/Variance Information
Section B: Proposed Project Information
Legal description and/or address of property____________________________________________________
Project Name______________________________________________________________________________
Project/Application Number from Development Review (i.e. FDP123456)__________________________
Description of Project_______________________________________________________________________
__________________________________________________________________________________________
Existing Use (check one): ☐ residential ☐ non-residential ☐ mixed-use ☐ vacant ground
Proposed Use (check one): ☐ residential ☐ non-residential ☐ mixed-use ☐ other____________________
If non-residential or mixed use, describe in detail_______________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
State the requirement from which alternative compliance/variance is sought. (Please include
applicable Drainage Criteria Manual volume, chapter and section.)
__________________________________________________________________________________________
What hardship prevents this site from meeting the requirement?
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
What alternative is proposed for the site?
Attach separate sheet if necessary
Attach separate sheet if necessary
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✬ ✧ ☎ ✢ ✢ ✄ ✍ ✣ ✦ ✡ ✯ ✙ ✜ ✆ ✤ ✡ ✧ ✠ ✆ ✫ ✖ ✡ ✩ ✆ ✥ ✏ ✣ ✪ ✒ ✤ ✛ ✣ ✢ ✢ ✱ ✦ ✲ ✦ ✥ ✢ ✣ ✪ ✤ ✧ ✥ ✤ ✩ ✜ ✥ ✤ ✰ ✜ ✪ ✤ ✥ ✩ ✜ ✥ ✳
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