HomeMy WebLinkAboutDrainage Reports - 09/10/2015City of Fort Collins Approve Plans
Approved by:
Date: o L2b (s
FINAL DRAINAGE AND EROSION
CONTROL REPORT
FOR
FIRST REPLAY OF PROSPECT
RIVERSIDE SUBDIVISION
(RIVERSIDE STORAGE)
q
FINAL DRAINAGE AND EROSION,
CONTROL REPORT
FOR
FIRST REPLAT OF PROSPECT
RIVERSIDE SUBDIVISION
(RIVERSIDE STORAGE)
Prepared for:
Wickham Gustafson E� rchitects
1449 Riverside Avenue
Fort Collins, CO 80524
Prepared by:
North Star Design
700 Automation Drive, Unit I
Windsor, Colorado 80550
(970)686-6939
July 29, 2015
Job Number 264-10
1
1
1 North Star
1Aft., design
700 Automation Drive. Unit I
Windsor, CO 80550
Phone:970-686-6939
Fax:970-686-1188
July 29, 2015
Shane Boyle
City of Fort Collins Stormwater
700 Wood Street '
Fort Collins, CO 80522-0580
RE: Final Drainage and Erosion Control Report for First Replat of Prospect Riverside
Subdivision (Riverside Storage)
Dear Shane,.
I am pleased to submit for your review and approval, this Final Drainage and Erosion Control
Report for First Replat of Prospect Riverside Subdivision. I certify that this report for the
drainage design was prepared in accordance with the criteria in the City of Fort Collins Storm
Drainage Manual.
I appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
Si erely. ..wOJKAG/`_S�.:_
Patricia Kroetch, P.E. -"'I'w1iIIIIII "
It
'
TABLE OF CONTENTS
TABLE OF CONTENTS...............................................................................................................
iii
' 1.
GENERAL LOCATION AND DESCRIPTION
1.1 Location...................................................................................................................1
1.2 Description of Property ............................................................................................I
' 2.
DRAINAGE BASINS AND SUB -BASINS
2.1 Major Basin Description..........................................................................................I
'
2.2 Sub -Basin Description.............................................................................................1
3.
DRAINAGE DESIGN CRITERIA
3.1 Regulations..............................................................................................................2
'
3.2 Development Criteria Reference and Constraints...................................................2
3.3 Hydrologic Criteria..................................................................................................2
3.4 Hydraulic Criteria....................................................................................................3
'
3.5 Modifications to Criteria..........................................................................................3
4.
DRAINAGE FACILITY DESIGN
'
4.1 General Concept......................................................................................................4
4.2 Specific Flow Routing.............................................................................................4
4.3 Drainage Summary..................................................................................................6
' 5.
STORMWATER MANAGEMENT CONTROLS
5.1 Written Analysis.....................................................................................................7
5.2 SWMP Contact Information ................. :.................................................................
8
'
5.3 Identification and location of all potential pollution sources..................................9
5.4 Best Management Practices (BMP's) for Stormwater Pollution Prevention ...........
9
5.5 BMP Implementation.............................................................................................11
'
6.
CONCLUSIONS
6.1 Compliance with Standards..................................................................................14
'
6.2 Drainage Concept..................................................................................................14
7.
REFERENCES..................................................................................................................15
' APPENDICES
A Vicinity Map
B Hydrologic & Hydraulic Computations
'
C Detention Pond Sizing Calculations
D BMP Schedule and Cost Estimate
E Variance Request
'
F Figures and Tables
iii
1. GENERAL LOCATION AND DESCRIPTION
1.1 Location
■ This site is located on the east side of Riverside Drive north of East Prospect Road in the
Southeast Quarter of Section 18, Township 7 North, Range 68 West of the Sixth
Principal Meridian, in the City of Fort Collins, Larimer County, Colorado. See the
Vicinity Map in Appendix A of this report.
' This project is bounded on the north by existing storage units, on the east by existing
Union Pacific Railroad tracks, on the west by Riverside Drive, and on the south by
' existing Rivendell School.
' 1.2 Description of Property
The entire project consists of approximately 2.2 acres. The site is currently developed,
' with areas of existing asphalt and gravel. Existing slope is to the northeast with slopes
ranging from approximately 1.5% to 3%. The site currently drains into an existing swale
' located at the northeast corner of the site.
Proposed development on -site will include one office building, five self -storage
' buildings, and associated drives, parking, and walks. Existing drainage patterns will not
be significantly altered with this development.
' 2. DRAINAGE BASINS AND SUB -BASINS
2.1 Major Basin Description
The proposed development lies within the Spring Creek Drainage Basin. Both
' stormwater detention and extended water quality detention are required in this basin. The
City requirement for stormwater detention in the Spring Creek basin is a single -stage
' detention with a 100-year release rate equal to the existing 2-year runoff.
2.2 Sub -basin Description
Runoff from this site currently flows to an existing swale located in the northeast comer
' of the site. From there, the runoff is conveyed in the existing swale to the north along the
rear of the adjacent properties to an existing pipe under the railroad tracks. The existing
1
' swale across the adjacent properties was determined to be a historic conveyance for this
site. With the proposed drainage concept for this site, the detained runoff will continue
to be released into the existing swale via an orifice plate mounted on the back wall of the
' outlet structure.
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 except where variances are requested as noted in
Section 4.2 of this report. Where applicable, the criteria established in the "Urban Storm
Drainage Criteria Manual' (UDFCD), 2001, developed by the Denver Regional Council
' of Governments, has been used.
3.2 Development Criteria Reference and Constraints
The runoff from this site has been routed to conform to the requirements of the City of
' Fort Collins Stormwater Department. Both stormwater runoff detention and extended
water quality detention are required for this site and are being provided by the proposed
' on -site detention pond. The release rate from the site will be equal to the existing 2-year
runoff.
3.3 Hydrologic Criteria
Runoff computations were prepared for the 2-year minor and 100-year major storm
' frequencies 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.
Detention volume was calculated using the runoff rate for the 2-year rainfall event with
' existing site conditions, which includes existing sections of asphalt paving and gravel.
The FAA method for detention pond sizing was utilized to determine the required
' volume. Water quality volume was calculated using the method recommended in the
"Urban Storm Drainage Criteria Manual". Refer to the detention calculations included in
Appendix C of this report.
2
3.4 Hydraulic Criteria
Hydraulic elements have been designed per City of Fort Collins standards to adequately
' convey the 100-year storm runoff from this site to the proposed detention pond. An
existing drainage swale will convey the detained runoff from the site to the downstream
railroad crossing.
3.5 Modifications of Criteria
Three modifications to Criteria are being requested for this project. They are 1) A
reduction in the freeboard for the detention pond, 2) A reduction in the required
interlocking permeable pavers on site and 3) an alternative compliance for the LID
requirement.
Refer to Appendix E for the Variance application and supporting justifications for the
variance requests.
4. DRAINAGE FACILITY DESIGN
1 4.1 General Concept
The runoff from this site will flow into the parking lot and drive aisles which will be
constructed using conventional materials (asphalt or concrete) and permeable
interlocking pavers. The runoff from the site will either flow on the surface or enter a
storm pipe via the permeable interlocking pavers or inlets. In a situation where the
permeable interlocking pavements are clogged, the runoff will flow on the surface and
enter the detention pond on the east side of the site. On -site runoff will also be conveyed
to the detention pond via flows in LID swales along the north and south property
boundaries. The detained runoff will discharge into the existing swale located at the
northeast comer of the site. From there, runoff will be conveyed in the existing swale
downstream to an existing railroad crossing. This existing swale may need to be cleaned
out (with percussion of the downstream property owner) to ensure adequate conveyance
and removal of any obstructions.
3
4.2 Specific Flow Routing
With this design, the site has been broken into 8 basins which correspond with the LID
feature that the basin flows to. The porous pavements areas have each been assigned a
letter designation (A, B or Q and the remaining areas have been assigned a number
designation (1-5). The runoff from the site will follow the historic runoff path and will
flow from the west (Riverside Avenue) to the east and into the detention area. The basin
are described in the following paragraphs.
Basin 1-1 is located in the very northwest most portion of the site and contains only
landscape area. The runoff from this basin is directed to area inlet #3.
Basin 1 is located in the northmost portion of the site and contains the north most storage
building and LID feature #1 which is an LID swale with an underdrain. The roof of the
storage building is sloped to drain to the north and the swale is sloped to drain east and
into the detention pond.
Basin 2 is located in the southmost portion of the site and contains the south most storage
building and LID feature #2 which is an LID swale without an underdrain. The roof of
the storage building is sloped to drain to the south and the swale is sloped to drain east
and into the detention pond.
Basin 3 is located in the west portion of the site and contains the north half of the office
building and LID feature #3 which is an LID swale without an underdrain. The roof of
the office building is sloped to drain to the west and the swale is sloped to drain north and
into Inlet #2. The water enters the storm system via Inlet #2 and is conveyed north and
east into the detention pond.
Basin 4 is located in the southwest portion of the site and contains sidewalks, landscape
areas and Inlet #1. The runoff will flow to the inlet and enters the storm system which
will convey the runoff north and east and into the detention pond.
Basin 5 is the largest basin on site and is located in the east central portion of the site.
This basin contains the remaining storage buildings and drive aisles. This basin will drain
to the east and directly into the detention pond.
4
Basin A is located in the northwest portion of the site and contains only 6 parking stalls
that contain porous pavers. Runoff from this basin will either enter the storm system via
the porous pavers or be collected in a concrete pan and conveyed east into Basin 5.
Basin B is located in the southwest portion of the site and contains the south half of the
office building, sidewalks and 9 parking stalls. The parking stalls are surfaced in porous
pavement. Runoff from the roof is directed east into a gutter and this gutter will convey
the runoff north to a drain basin and storm pipe. This storm pipe will discharge the roof
runoff into a concrete channel and directed onto the porous pavement. The underdrain in
the porous pavement will collect runoff from the entire basin and convey it north and east
to the detention pond.
Basin C is located in the northwest portion of the site and contains 8 parking stalls that
contain porous pavers. Runoff from this basin will either enter the storm system via the
porous pavers or be collected in a concrete pan and conveyed east into Basin 5.
' There is no offsite flow entering the site from the north, west or east. The flow from the
west is intercepted by Riverside Avenue and the flow from the east (railroad) is captured
' in a swale in the railroad right of way. Runoff from the north is contained on that site
and routed away from this site. Runoff from the site to the south flow in two directions.
The west half of the site is captured in an existing curb and appears to pond on site. The
' east half of the site drains to the east and north. This flow will enter the Riverside Storage
site in the grassed swale along the shared property line and will enter the detention pond.
' This runoff will not be detained but will flow over the spillway and enter the railroad
right of way as it has historically done. The spillway was sized with a 0.25' flow depth
but the spillway will be constructed 0.74' deep therefore sufficient overflow capacity is
provided in the spillway.
' Drainage design for this site has been designed to convey on -site runoff to the proposed
detention pond and incorporate the required water quality enhancement features. On -site
runoff will be conveyed to the detention pond via surface flow in the drive aisles, in the
' LID swales and subsurface in the perforated pipes. The detention pond will release the
detained runoff from the site at the existing (historic) 2-year runoff rate of 2 cfs. The
' developed 2-year runoff rate for this Site is 3.8 cfs and the developed 100-year runoff
rate is 19.3 cfs.
5
I
' 4.3 Drainage Summary
This site has been designed to meet or exceed the "City of Fort Collins Storm Drainage
' Design Criteria Manual" specifications with exceptions noted in Appendix E. The
proposed drainage design for this site has been designed to convey on -site runoff to the
' detention pond while minimizing future maintenance. The site incorporates LID (Low
Impact Development) treatment areas including an LID swale with underdrain along the
north property line, and an LID swale without underdrain along the south property line
and permeable interlocking pavers in the parking stalls and in the entry drive aisles. Refer
to the end of Appendix D for a table indicating the size of the LID treatment area and the
area of the site that drains to that LID treatment area.
All drainage facilities proposed with this project, including the detention pond and outlet
structure are private and will be owned and maintained by the property owner or Owner's
Association.
6
I
5. STORMWATER MANAGEMENT CONTROLS
5.1 Written Analysis
The soils on this site are classified by the USGS Soil Survey as Kim Loam with a small
area of Santana Loam and are classified in the hydrologic group B. The soils are
described as having a slow runoff rate and the hazard of water erosion is slight and the
hazard of wind erosion is moderate.
The site is surrounded by developed sites including streets and paved areas. The
construction shall utilize silt fence around the perimeter to control sediment transport
from rainfall and from wind. The silt fence that is located in the proposed pavement areas
will be removed prior to placing new pavement. Rock socks will be utilized in the
existing curb and the newly constructed swales to capture sediments that are not fully
contained by the silt fence placement. The locations of the rock socks will be in the areas
' of concentrated flow such as in the existing curb, at the new swales and on the existing
concrete sidewalks as needed.
' The site will also utilize a vehicle tracking control pad to minimize sediment from being
tracked onto adjacent pavements. Sediment that is tracked will be removed and placed
within the site or permanently disposed of offsite. A concrete washout will be used on
site during the concrete placement. All hardened concrete will be disposed of offsite.
These BMP's have not been located on the site map due to the fact that the site is very
small and these BMP's will need to be placed by the contractor in locations that are most
beneficial and will minimize disruption of adjacent traffic.
tPermanent erosion control consists of covering the soils with a building, concrete walks,
' concrete drives and sod. No soil will be left exposed to erosion after the construction is
complete. Refer to the landscape plan for areas of and instructions for placement of sod
and soil amendments required prior to placement of sod.
' Refer to Appendix D for the timing of the construction phases and the sequential
installation of all BMP phasing for this site.
Refer to the Appendix D for the Erosion Control Surety calculations.
7
5.2 SWMP contact information
Permit holder:
Name:
Address:
Phone Number:
Email Address:
Appointed agent:
Name:
Address:
Phone Number:
Email Address:
1
1
1
1
1
1
8
I
5.3 Identification and location of all potential pollution sources
Potential Pollutant Source Activity
Potential Pollutant Generated
Applicable to
this project
Disturbed Areas
Sediment
X
Soil stockpiles
Sediment
X
Travel to adjacent public streets
Tracked sediment
X
Contaminated soils
Sediment, chemicals
Loading and unloading chemicals
Chemicals
Unloading of building materials
Trash, debris
X
Outdoor storage of chemicals
Chemicals
On site equipment maintenance
Oil, grease
On site equipment fueling
Diesel, gasoline
X
Dust generating activities
Particulates, sediment
X
Use of fertilizer, pesticides, herbicides
Fertilizer, pesticides
Use of detergents, solvents, oils
Detergents, solvents, oil
X
Waste dumpsters, waste piles
Chemicals, trash, debris
X
Concrete washout
Concrete, sediment, wash water
X
On site equipment washing
Detergents, oil
On site asphalt batch plant
Asphaltic cement, sediment
On site concrete batch plant
Cement, sediment
Portable toilets
Domestic sewage
X
' 5.4 Best Management Practices (BMP's) for Stormwater Pollution Prevention
' Structural Practices for Erosion and Sediment Control
Structural practices for the site will consist mainly of silt fence and rock sock filters and are
described in detail in the following paragraphs. These BMP's are expected to change as the
construction progresses and it is the responsibility of the contractor to ensure appropriate BMP's
are in place and/or removed at the appropriate time in the construction sequence. 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 rock sock filters shall be in place prior to commencement of construction
activities. During clearing and grubbing necessary for silt fence installation, all cleared material
shall be placed on the uphill side so that if erosion occurs from the cleared material, the sediment
will be trapped and not transported downstream. Rock socks shall be implemented in the existing
curb line as shown on the Drainage & Erosion Control Plan.
9
All BMP's shall be installed per the details shown on the construction plan set.
Temporary & Permanent Structural BMP's:
Structural BMP
Approximate location on site
Applicable to this
Project.
Silt Fence
Site perimeter, refer to site map
X
Straw bale dams
Rock Socks
At existing sidewalk culverts, in existing
gutters, refer to site map
X
Earthen diversion dams
Vegetated swales
Sediment trap/pond
East boundary of site, in proposed det pond
X
Pipe slope drains
Geogrid
Inlet/outlet protection
In the detention Pond
X
Culverts
Riprap
Erosion control mats
Inlet protection
Vehicle Tracking Control Pad
At site entrance, refer to site map
X
Concrete Washout
To be located by Contractor, near site entry
X
Non -Structural Practices for Erosion and Sediment Control:
Soils exposed during the earthwork phase and landscape prep phase shall be kept in a roughened
condition by ripping or disking along land contours until mulch, vegetation, or other permanent
erosion control is installed. No large amount of soils (in excess of 15 yards) will be allowed to be
stock piled on site. Overburden from the utility pipe trenching will be piled adjacent to trenches
upstream of sediment controls and will be replaced in the trenches within 72 hours.
Excess excavated materials from the demolition and grading phases of the project that cannot be
reused on site will be exported as it is excavated. This includes any asphalt pavement from the
existing site that is to be removed.
A vehicle tracking pad will be installed at a location most beneficial to the site construction as
determined by the contractor. Vehicles will not be permitted in the excavated area if soil is
muddy. Gravel sub base will be placed and compacted in the areas indicated for pavement
following excavation. In the current pre construction state the site enables tracking of silt onto
the adjacent streets during wet conditions. During construction activities the street will be
monitored for foreign debris tracked out of the site and mechanical sweeping and clean up will
be performed as needed.
10
No area shall remain exposed by land disturbing activity for more than thirty (30) days before
required temporary or permanent erosion control (e.g. seed/mulch, landscaping, etc.) is installed.
Temporary & Permanent non-structural BMP's:
Non -Structural BMP
Approximate location on site
Applicable to this
Project
Surface roughening
Entire site
X
Soil stockpile height limit (less than
10')
Perimeter vegetative buffer
West and north boundaries of site
X
Minimization of site disturbance
Mulch
Seed & mulch stockpiles after 30 days
Stockpile toe protection (silt fence,
wattles or ditch)
Preservation & protection of existing
West and north boundaries of site
X
vegetation & trees
Good site housekeeping (routine
Entire Site
X
cleanup of trash & constr debris)
Sweeping & scraping ofhardscape
On and off site pavements
X
areas
Heavy equip staged on site, properly
maintained & inspected daily (no
Staging area
X
onsite maintenance)
I5.5 BMP Implementation
' 1) Phased BMP Implementation
BMP's are expected to change as the construction progresses and it is the responsibility of
the contractor to ensure appropriate BMP's are in place and/or removed at the appropriate
time in the construction sequence. A construction sequence schedule has been included on
the Drainage & Erosion Control Plan and included in the construction plans for this site.
' All BMP's shall be inspected and repaired or replaced as required to satisfy the conditions of
the Stormwater Discharge Permit. All BMP's must be maintained and repaired as needed to
assure continued performance of their intended function. Refer to Appendix D for the BMP
schedule and estimated costs.
11
71 Materials Nnnrllino nnrl Cnill PrevPntinn-
Materials Handling & Spill
Approximate location on site
Applicable to this
Prevention BMP
Project
Portable toilets, anchored &
Contractor to determine
X
located away from drainages
Fuel storage located in bulk tanks
with secondary containment &
spill kit
Mobile fueling performed at least
200 feet away from drainages &
Contractor to determine
X
fully attended
Fertilizers, form oil, solvents,
cleaners, detergent stored in 55 gal
Contractor to determine
X
or smaller containers, kept in
storage units
Dumpsters containing used
chemicals containers & liquid
Contractor to determine
X
wastes kept covered
Equipment cleaning (on site) uses
no detergents & flows to onsite
retention basin
In case of a release of fuel or other
chemicals, absorbent booms or
earthen berms will be immediately
Location of spill
X
constructed to contain the spill &
prevent runoff to adjacent surface
waters
MSDS sheets for onsite chemicals
will be kept at the construction.
Contractor to determine
X
trailer to facilitate spill response &
cleanup
' 3) Dedicated Asphalt or Concrete Batch Plant:
Not proposed with this development
4) Vehicle Tracking Pad:
' Vehicle tracking control pad shall be installed wherever construction vehicle access routes
intersect paved public roads. Vehicle tracking control pads shall be installed to minimize the
transport of sediment (mud) by runoff or vehicles tracking onto the paved surface. Any mud
Itracked to public roads shall be removed on a daily basis and after any significant storm that
causes sediment to be transported. It is unlawful to track sediment/mud onto public streets
' and may be enforced by the City of Fort Collins, by the State of Colorado or by the EPA.
12
5) Waste Management and Disposal:
Portable toilets will be anchored & periodically maintained by waste management company.
Dumpsters on site will be covered & periodically emptied by waste management company.
Concrete waste will be allowed to harden and then will be removed from site.
No washing activities will occur on site.
Location of the concrete washout is shown on the site map. The washout will be sufficiently
deep to accommodate all anticipated concrete truck wash water. Waste concrete will be
allowed to harden and be removed from site periodically as the washout reaches 50% of its
capacity. Truck wash water will not be allowed to reach the curb & gutter or any other water
course.
6) Groundwater and Stormwater Dewatering:
No groundwater was encountered during soils exploration therefore ground water is not
anticipated to be an issue. If groundwater is encountered a groundwater discharge permit
shall be obtained and a detailed report shall be completed describing the location and the
route of where pumped groundwater will be conveyed and the measures taken to prevent the
transport of any pollutants to downstream waters.
7) Inspection & Maintenance:
It is required that routine site inspections are performed to effectively address maintenance
and repair of Best Management Practices (BMP's). The site inspections are to be performed
by the contractor or an inspector designated by the administrator at a minimum of once every
fourteen (14) calendar days on active construction sites and after any significant storm event
(an event causing runoff). As part of the site inspections the inspector is required to keep
documentation of
all inspections and BMP maintenance, including an updated Site Map indicating new BMP's
or the removal of BMP's since the previous inspection.
Any maintenance, repair, or necessary installation of BMP's that are noted during the
inspection must be completed within seven (7) calendar days from the date of the inspection.
13
6. CONCLUSIONS
6.1 Compliance with Standards
All computations that have been completed within this report are in compliance with the
"City of Fort Collins Erosion Control Reference Manual for Construction Sites", the
"City of Fort Collins Storm Drainage Design Criteria Manual", and the "Urban Storm
Drainage Criteria Manual" except where variances are requested as noted in Appendix E
of this report.
6.2 Drainage Concept
The proposed drainage concepts presented in this report and on the construction plans
adequately provide for the collection and conveyance of on -site runoff to the detention
area. Conveyance elements exist to adequately convey detained runoff downstream.
If, at the time of construction, groundwater is encountered, a Colorado Department of
Health Construction Dewatering Permit would be required.
14
7. REFERENCES
1. Urban Drainage and Flood Control District, "Urban Storm Drainage Criteria
Manual", 2001 Edition Volume 1 updated June 2001, January 2004 and April
2008; Volume 2 updated June 2001 and April 2008; and Volume 3 updated
November and December 2010.
2. The Fort Collins Amendments to the Urban Drainage and Flood Control District
Criteria Manual, adopted by the City Council of the City of Fort Collins, as
referenced in Section 26-500 (c) of the Code of the City of Fort Collins.
3. ORDINANCE NO. 152, 2012 of the Council of the City of Fort Collins amending
Chapter 26 of the Code of the City of Fort Collins and the Fort Collins
Stormwater Criterial Manual to incorporate provisions implementing Low Impact
Development (LID) Principles.
15
' APPENDIX A
' VICINITY MAP
A
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SHEET 1 OF 1
DATE: 10/10/14
1640 RIVERSIDE DRIVE
North Star
SCALE: 1•=1000'
(RIVERSIDE STORAGE)
VICINITY MAP
'�� design, inc.
700 Automation Drive, Unit
Windsor, Colorado 80550
Phone: 970-686-6939
DESIGNED BY: PPK
JOB NO.: 264-03
Fax: 970-686-1188
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IAPPENDIX B
tHYDROLOGIC & HYDRAULIC COMPUTATIONS
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II 11 II
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O
AREA INLET IN A TRAPEZOIDAL GRASS -LINED CHANNEL
Riverside Storage
Inlet 1
Ti, i Grass Type Unsling Mannin 's n
_ A 0.06
e 0.04
a C 0.033
D 0.03
�. _.._._... .._....... .�/ t E 0.024
F(— B
Analysis of Tra emidat Grass -Lined Channel U.mn SCS Method
RCS Vegetal Relardance (A, B. C, D. or E)
A. B. C, D or E
-
Manning's n (Leave cell D16 blank to manually ender an n value)
n
Channel Invent Slope
So =
0.0270
Wit
Bottom Width
B=
1.W
It
Left Side Slope
Z1 =
10.00
Wit
Right Side Slope
Z2=
500
6/ft
Check one of the following wit types
Sod�T ae'. Max. Velocity, W....1 Max F.W. No. IF,...1
Q senty
Sandy 5.0 fps 0.50
® Non -sandy
Nan 7.0 0.80
Minor sbm
Major Stone
Max. AAmvebb Top KrHN at Charnel for Mron 8 Major Storm
Teu =
10.00
10.00
feet
Max. ADowable Water Depth in Chwrel for Miry 6 Major Stem
dear =
6.00
6.00
feet
towable ChannelCapacity Based On Channel Geometry
Minor Storm
Major Storm
MINOR STORM Allowable Capacity is bawd on Top Width Criterion
O, =
1.26
1.28
Ns
MAJOR STORM Allowable Capacity is based on Top Width Criterion
d. =
0.60
0.68
ft
Baastl On Deai nPaak Flow
O,=
0.10
0.30
c7s
rW�n.nnell
it
0.20
O.Sf
fast
llowable capacity GOOD - greater than flow given on sheet'O-Peak'
Maiorstormma,. allowable aaoacftv GOOD- greater than flow given on sheet'O-Peak'
Hat 1.1dsm, Area Inlet 7/3012015, 3:39 PM
AREA INLET IN A TRAPEZOIDAL GRASS -LINED CHANNEL
Riverside Storage
Inlet t
Dasian hdormztlon flop A
,
Of Inlet
Inlet Type =
CDOTTWeC
P of lndined Grow (in" be <=
30 degrees)
0=
ow
degrees
i or Grate
W=
3.00
feet
'.h of Grate
_
.�"� ���-
L=
3.00
feel
Area Ratio
„.^
".` •.._
Awro=
0.70
a of Inclined Grate
W,r'
He=
0.00
feel
limit Factor
„✓ ,..':—(
-•,•..
C,=
0.50
Oisrliarge coefficient
l`-( 'f-•w .•` -
�°
Cu=
0.90
e coaffidera
a ,,..
G-_t
C.
Dee
MINOR
MAJOR
r Depth at Inlet (for depressed
Wells. t foot is added for depression) it =
II Inlet Interception Capacity (assumes clogged condition) o, =
cfs
Capacity IS GOOD for Minor
and Major Stones(>O PEAK) Bypassed Flow, O.=
cfs
Capture Percentage= OJO, = C
%
0.20
0.33
1.W
l.d]
0.00
O.Oe
100
100
Warning 02: Depth (d) exceeds USDCM Volume I recommendation.
INlel 1.xism, Area Intel 7/30/2015, 3:39 PM
AREA INLET IN A TRAPEZOIDAL GRASS -LINED CHANNEL
Riverside Storage
Inlet 2
T1_ Grass Type Limitln Mannin 's n
`( A 0.06
�.... i T o �.✓_�_,--. B 0.04
/ C 0.033
`�� O f/fr drnnx D 0.03
� .... ... - _C
t E 0.024
F--(— B
nor sis of Trapezoidal Grwxs lnal Channel Using SCS Method
NRCS Vagetal Reterdaree (A, B. C. D, or E)
A. B. C, D or E
Manrdng's n (Leave call Of 6 blank to manually enter an n value)
n =
0.300
Charmel Invent Slope
So =
0.0350
ft/ft
Bodom WloN
B=
- 1.W
0
Left Side Slope
zl =
4 00
ft/ft
Right Side Slope
Z2=
1 .W
ft/ft
Check one of the followi spilt
Soil Max. Velocity (V....1 Max FroW a No, (F.-,
a S-rdy
Sandy &0 fps 0,50
® Nnn Sxidy
Nor-Serxt 7.0f s 0,80
Mirror Storm Ma'or Slonn
Movable Top WMN of Channel(or Miror 8 Major Storm
Taex =
10.00
10.00
test
Max. AAowable Water Depth in Channel for Minx 6 Major Storm
da,u =
6.00
6.00
Ifeet
STORM Movable Capacity Is based on Top Wldm Criterion
STORM Moveable Capacity Is based on Top Width Criterion
peak Flow
storm max. allowable capacity GOOD - greater than flow given on shoet'O-Peak'
storm max. allowable capacity GOOD - greater than flow given on shoot'O-Peak'
1.63
C, -1 0.20 1 1.00 oh
dzl 0.26 1 0.52 1heet
Inlet 2.xlsm, Area Inlet 7130/2015, 3:39 PM
AREA INLET IN A TRAPEZOIDAL GRASS -LINED CHANNEL
Riverside Storage
Inlet 2
rlet Design Infonnrtion INputl
ype of Inlet
Inlet TypeCDOTTypeC
Asia of Indirwd Grace(must De<=30
degrees)
0=
am
degrees
YMthgf Grde
W=
3,00
feet
mglhof Gme
"I , _
L=
3.00
feet
Ipen Area Ratio
Aexrp =
0.70
Ieight of lridirietl Grate
logging Faoor
,,-<.__,. —... ....�_�"'.•�_ Ne=
„.---- "_' /� G=
0.00
050
feel
{rele D'adwge Coefficient-,
^..�"" �-'
_.•../~ NA Ca
0.00
Idfce Coelfidenl
""� .._
-__'^. "Y" n ._d Ce
O13s
ye'v Coefficient
""t-.._ "'-,--�.
1'" C.
2.05
�^_'
MINOR
MAJOR
View Depth rt Inlet (for depressed
inlets, 1 foot is added for depression)
d =
0.28
0.52
'Dial Inlet Interception Capacity (assumes clogged condition)
�. =
zs7
aoz
cis
filet Capacity IS GOOD for Minor
and Major Storms(>O PEAK)
Bypassed Flow, De=
0.00
0.00
ofe
Capture Percentage = QIO. = C%1
100
100
%
Warning 02: Depth (d) exceeds USDCM Volume I recommendation.
Inlet 2.KISm, Area Inlet 7/30/2015, 3:39 PM
LL
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APPENDIX C
DETENTION POND SIZING CALCULATIONS
C
MINIMUM DETENTION VOLUME REQUIRED
FAA METHOD
(100-YEAR)
LOCATION: First Replat of Prospect Riverside Subdivision
PROJECT NO: 264-10
COMPUTATIONS BY: PPK
SUBMITTED BY: North Star Design, Inc.
DATE: 7/30/2015
Equations: A trib. To pond = 2.16
QD = CiA C100 = 0.98
V; = T*CiA = T*QD Developed C*A = 2.1
V. =K*QPo*T QPo = 2.0
S=V; -Vo K= 1
Rainfall intensity from City of Fort Collins IDF Curve
acre
acre
cfs
(from fig 2.1)
Storm
Duration, T
(min)
Rainfall
Intensity, i
(in/hr)
QD
(cfs)
Vol. In
V;
W)
Vol. Out
Vo
(ft)
Storage
S
(ft)
Storage
S
(ac-ft)
5
9.95
21.1
6319
600
5719
0.131
10
7.72
16.3
9805
1200
8605
0.198
20
5.60
11.9
14225
2400
11825
0.271
30
4.52
9.6
17222
3600
13622
0.313
40
3.74
7.9
19000
4800
14200
0.326
50
3.23
6.8
20512
6000
14512
0.333
60
2.86
6.1
21795
7200
14595
0.335
70
2.62
5.5
23293
8400
14893
0.342
80
2.38
5.0
1 24t82
9600
14582
1 0.335
90
2.22
4.7
25376
10800
14576
0.335
100
2.05
4.3
26037
12000
14037
0.322
110
1.93
4.1
26964
13200
13764
0.316
120
1.80
3.8
27434
14400
13034
0.299
130
1.60
3.4
26418
15600
10818
0.248
140
1.40
3.0
24894
16800
8094
0.186
150
1.20
2.5
22861
18000
4861
0.112
160
1.15
2.4
23369
19200
4169
0.096
170
1.10
2.3
23750
20400
3350
0.077
180
1.05
2.2
24005
21600
2405
0.055
Required Storage Volume: 14893 It
0.342 acre-ft
�0000 ooao°
a000 oaoa
I
LOCATION:
PROJECT NO:
COMPUTATIONS BY:
SUBMITTED BY:
DATE:
WQCY
100 WSEL
STAGE - STORAGE TABLE
(100-YEAR)
First Replat of Prospect Riverside Subdivision
264-10
PPK
North Star Design, Inc.
7/8/2015
100 yr Detention Volume Required = 0.342
Water Quality Volume Required= 0.076
Total Volume Required= 0.418
Stage
(ft)
Surface
Area
(ft)
Incremental
Storage
(ac-ft)
Total
Storage
(ac-ft)
4934.30
0
4935.0
7,850
0.042
0.04
4935.30
9,528
0.060
0.102
4936.0 1
13,442
0.242
0.284
4936.36
19,395
0.134
0.418
4937.0
30,070
0.487
0.770
Detention Pond Outlet Sizing
(100 yr event)
LOCATION:
First Replat of Prospect Riverside Subdivision
PROJECT NO:
264-10
COMPUTATIONS BY:
PPK
SUBMITTED BY:
North Star Design, Inc.
DATE:
7/30/2015
Submerged Orifice Outlet:
release rate is described by the orifice equation,
Qo = Copt sqrt( 2g(h-E.))
where Qo =
orifice outflow (cfs)
Co =
orifice discharge coefficient
g =
gravitational acceleration = 32.2 ft/s
k =
effective area of the orifice (ft)
Eo =
greater of geometric center elevation of the orifice or d/s HGL (ft)
h =
water surface elevation (ft)
Qo =
2.0 cfs
outlet pipe dia = D =
12.0 in
Invert elev. =
4934.30 It
Eo =
4934.61 ft
h =
4936.36 ft - 100 yr WSEL
Co =
0.62
solve for effective area of orifice using the orifice equation
Ao =
0.304 ftz
=
43.8 in
orifice dia. = d =
7.47 in
Check orifice discharge coefficient using Figure 5-21 (Hydraulic Engineering)
d/D= 0.62
kinematic viscosity, u = 1.22E-05 ftz/s
Reynolds no. = Red = 4Q/(pdu) = 3.35E+05
Co = (K in figure) = 0.62 check
Use d = 7.50 in
A0 = 0.307 .it? = 44.18 in
/�z
Emergency Overflow Spillway Sizing
LOCATION: First Replat of Prospect Riverside Subdivision
PROJECT NO: 264-10
COMPUTATIONS BY: PPK
SUBMITTED BY: North Star Design, Inc.
DATE: 5/24/2005
Equation for flow over a broad crested weir Adbffm
Q = CLH" � spill �IsdN�4i®n
where C = weir coefficient = 2.8 L
H = overflow height
L = length of the weir 900 yr WSEL
The pond has a spill elevation 0 ft above the maximum water surface elevation in the pond
Spillways will be designed with 0.25 ft flow depth, thus H = 0.25 It
Size the spillway assuming that the pond outlet is completely clogged.
Q (100) =
19.0
cfs
Spill elev =
4936.36
It 100 yr WSEL = 4936.36 ft
Top of berm elev.=
4937.10
Weir length required:
L =
54
ft
Use L =
55
ft
v =
1.21
f /S
l
Stormwater Detention and Infiltration Design Data Sheet
Workbook Protected Worksheet Protected
stormwater Facility Name: Riverside Storage
Facility Location &Jurisdiction: Riverside Avenue, Fort Collins
User (Input) Watershed Characteristics
Watershed Slope=
0.007
ft/ft
Watershed Length -to -Width Ratio=
1.68
L:W
Watershed Area =
2.16
acres
Watershed Imperviousness=
74.0%
percent
Percentage Hydrologic Soil Group A =
0.0%
percent
Percentage Hydrologic Soil Group B =
0.0%
percent
Percentage Hydrologic Soil Groups C/D =
100.0%
percent
Location for 1-hr Rainfall Depths (use dropdown):
Use, Input
User Input: Detention Basin Characteristics
WQCV Design Drain Time= 40.00 hours
After completing and printing this worksheet to a pdf, go to:
httas://manerture.digitaidatasemices.com/evh/?viewer--awdif
create a new stormwater facility, and
attach the pdf of this worksheet to that record.
Routed Hydrograph Results
Design Storm Return Period =
One -Hour Rainfall Depth =
Calculated Runoff Volume =
OPTIONAL Override Runoff Volume =
Inflow Hydrograph Volume =
Time to Drain 97% of Inflow Volume =
Time to Drain 99%of Inflow Volume =
Maximum Ponding Depth =
Maximum Ponded Area =
Maximum Volume Stored =
User Defined
Stage [ftl
User Defined
Area [ft-2]
User Defined
Stage [ft]
User Defined
Discharge [cfs]
0.00
0
0.00
0.00
0.70
7,850
0.70
0.03
1.00
9,528
1.00
0.03
1.70
13,442
1.20
1.44.
2.06
19,395
1.70
1.80
2.70
30,070
2.06
2.02
2.10
38.96
2.30
71.57
2.50
110.19
2.70
154.00
FEE]
WQCV
2Year
5Year
10 Year
25 Year
50 Year
100 Year
0.53
0.98
1.36
1.71
2.31
2.91
3.67
0.052
0.128
0.193
0.255
0.367
0.475
0.619
0.051
0.128
0.193
0.255
0.366
0.474
0.619
37
63
61
59
56
54
51
41
68
68
66
65
64
63
0.61
1.00
1.11
1.22
1.49
1.76
2.05
0.156
0.218
0.233
1 0.246
0.281
0.329
0.440
0.047
0.122
0.148 1
0.173
0.244
0.325
0.438
n
cre-ft
cre-ft
cre-ft
lours
lours
t
cres
cre-ft
SDI_Design_Data_FC_Rainfall.xlsm, Design Data 8/21/2015, 4:53 PM
Stormwater Detention and Infiltration Design Data Sheet
14
1 1 1
—100YR IN
I
1
I
I
I
— — 100YR OUT
1
12
—50YR IN
I I
I
I
I
— — 50YR OUT
i
I
—25YR IN
I
I
I !
I
I
I
10
--- 25YR OUT
I I
R
—10YR IN
--- 10YR OUT
I
_
I
I
I
�SYR IN
0
•••••• SYR OUT
1
LL 6
-2YR IN
I
_
I
— I
.!
I
I
--- 2YR OUT
I
4
—WQCV IN
!
!
...... WQCV OUT
2
_
04' .�' — _ .
- � • I I ' I `
o -- —
0.1 1 10
TIME [hr]
2.5
—100YR
—50YR
2
—25YR
I
—10YR
1.5
—2YR
z
—WQCV
O
I
I I
I
0-5
I
0
0.1 1 10 100
DRAIN TIME [hr]
SDI_Design_Data_FC_Rainfall.xlsm, Design Data 8/21/2015, 4:53 PM
' APPENDIX D
BMP SCHEDULE & COST ESTIMATE
Erosion and Sediment Control Escrow/Security Calculation
' for The City of Fort Collins
' Project: Riverside Storage
Disturbed Acres: 2.18
l3MP Amount
Estimated Unit
Total
'
EROSION CONTROL BMPs
Units
Quantity Price
Price
Silt Fence
L.F.
1300 $3.00
$3,900.00
Rock Sock
each
15 $85.00
$1,275.00
'
Vehicle Tracking Control Pad
each
1 $1,500.00
$1,500.00
Concrete Washout
each
1 $1,200.00
$1,200.00
Rock Berm
each
1 $65.00
$65.00
(add all other BMPs for the site in this list)
Sub -Total:
$7,940.00
1.5 x Sub -Total:
$11,910.00
'
Amount of security:
$11,910.00
Reseeding Amount
'
Total Acres x Price/acre:
$2,616.00
Unit Price of Seeding per acre:
$1,200.00
Sub -Total:
$2,616.00
1.5 x Sub -Total:
$3,924.00
'
Amount to Re -seed:
$3,924.00
Minium_um_ Escrow Amount
Minimum escrow amount:
$3,000.00
Erosion Control Escrow: $11,910.00
' "The amount of the security must be based on one and acre -half times the estivate of the cost to install the approved measures, or one and one-ha/jtimes
Use cost to re -vegetate the disturbed land to dry land grasses based upon unit cost determined by the City's Annual Revegetation and Stabilization Bid,
whichever is greater. /n no instance, will the amount ofrecurity be less than one thousand five hundred dollars (51,500) jor residential development or three
thousand dollars (53,000) jor commercial development"
1
7/30/2015 2:33 PM
N:Q2 10 RwmWe SWmgeWmmge%E mple Ewc ,xk
CONSTRUCTION SEQUENCE
PROJECT: RIVERSIDE STORAGE DATE: 7/30/15
CONSTRUCTION PHASE
eeeeeeeeee®®
GRADING (INCLUDES OVERLOT)
mmmmmmmmmmm
DETENTION / WO PONDS
PIPELINE INSTALLATION (INCLUDES OFFSITE)
SAINITARY SEWER
STORM SEWER
-r-INCRETE INSTALLA-MON (INCLUDES OFFSITE)
CURB AND CUTTER
PAVEMENT INSTALLTA-ILON
BESTMANAGEMENT PRACTICES
STRUCTURAL
SILT FENCE IARRiEiRS
CONTOUR FURROWS (RIPPING/DISKING)
SEDIMENT TRAP / FILTER
VEHICLE TRACKING PADS
FL#W 8ARRIERS (WATTLES, ETC)
CONCRETE WASHOUT
TEMPORARY SEED PLANTING
MULCHING / SEALANT
PERMANENT SEE# PLANTING
S#Il INSTALLATION
Riverside Storage LID Table
New Impervious Area
72757 sq. ft.
Required Minimum Impervious Area to be Treated (50%)
36379 sq. ft.
Impervious Area Treated by LID Treatment Method #1 (LID
swale with underdrain)
4850 sq. ft.
Impervious Area Treated by LID Treatment Method #2 (LID
swale without underdrain)
4800 sq. ft.
Impervious Area Treated by LID Treatment Method #3 (LID
swale without underdrain)
3373 sq. ft.
Impervious Area Treated by Porous Pavement
17430 sq. ft.
Total Impervious Area Treated
30453 sq. ft.
New Pavement Area
38365 sq. ft.
Required Minimum Area of Porous Pavement (25%)
9591 sq. ft.
Area of Paver Section A
918 sq. ft.
Run-on area for Paver Section A
108 sq. ft.
Area of Paver Section B
1460 sq. ft.
Run-on area for Paver Section B
6303 sq. ft.
Area of Paver Section C
4644 sq. ft.
Run-on area for Paver Section C
3997 sq. ft.
Total Porous Pavement Area
7022 sq. ft.
APPENDIX E
VARIANCE REQUEST L,
E
' Stormwater
Alternative ComplianceNariance Application
' City of Fort Collins Water Utilities Engineering
Engineer/OwnerSection A:
Engineer Name North Star Design Inc. Phone 970-686-6939
' Street Address 700 Automation, Unit I
City. Windsor State CO Zip 80550
Owner Name Corey Seitz Phone 970-567-7549
Street Address 1019 Club View Road
' City Fort Collins State CO Zip 80524
' Project Name Riverside Storage
Project/Application Number from Development Review (i.e. FDP123456)
' Legal description and/or address of property Prospect -Riverside Subdivision Second Replat
Description of Project Storage units and office uses
' Existing Use (check one): Cj residential C non-residential 0 mixed -use (E) vacant ground
Proposed Use (check one): 0 residential Q non-residential 0 mixed -use C) other
If non-residential or mixed use, describe in detail Storage units and office uses.
Section C: Alternative ComplianceNariance Information
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?
See attached sheet
Attach separate sheet if necessary
What alternative is proposed for the site?
See attached sheet
Attach separate sheet if necessary
' Modifications of Criteria
Three modifications to Criteria are being requested for this project. They are 1) A reduction
in the freeboard for the detention pond, 2) A reduction in the required interlocking
permeable pavers on site and 3) an alternative compliance for the LID requirement.
' The reduction in freeboard is being requested from the 1' requirement to 0.54'. The
spillway is set at elevation 36.36 and the lowest building floor elevation adjacent to the
' pond is set at elevation 36.9. The buildings are used ONLY for storage purposes and the,
reduction in the freeboard will not pose any risk to public health or safety.
' The reduction in the required interlocking permeable pavers is being requested from the
25% (9590 'so of the new pavement on site to 18.3% (7022 so. Originally it was intended
' to place the permeable pavers in the eastern portion of the site but due to slope constraints,
this did not allow for the inclusion of a perforated underdrain which is desired. Therefore,
the permeable pavers were moved to the west portion of the site into the areas that allow
' for the inclusion of an underdrain. The permeable paver area has been maximized but is
still under the 25% requirement therefore a variance is being requested.
' The current requirement for LID (low impact development) is that 50% of the site
imperviousness must drain through a filtering device (36,380 sf on this site). Currently,
' 13,023 sf drain to an LID swale and 17,430 sf drain to permeable pavers totaling 30,453 sf
01.8% of the site imperviousness). Other options to reach the required 50% have been
considering including a bioretention area in the west portion of the site but this would be
redundant to the LID swale that is proposed. The remaining option is to place an LID swale
in the bottom of the detention pond but, because the elevations do not allow for inclusion
of an underdrain, this is not a desirable option.
page 2
The owner agrees to comply with the provisions of the zoning ordinance, building code and all other
applicable sections of the City Code; Land Use Code, City Plan and all other laws and ordinances
' ....--.-.-----.-affecting_the-construction-and-occupancy-of-the-proposed-building-that-are-not-directly-approved-by--
this variance. The owner understands that if this variance is approved, the structure and its occupants
maybe more susceptible to flood or runoff damage as well as other adverse drainage issues.
1640 erside, LLC Corey Seitz, Manager 9/8/2015
' Signature of owner: Date:
' The engineer hereby certifies that the above information, along with the reference plans and project
descriptions is correct. �1 i , /
' Signature of engi
, /29/15/ g/tS
PE STAMP
Date complete application submitted: Q 8/ /s
-------- - ----- ----- _. __...-.._...._....._......:...
Date of approval/denial: 4 �O//S Variance:
_.._......._............._...._......--_
Staff justification/notes/conditions:
approved enied e n
e Twt G e(ii
r
u[[ -�-t! Gh n, I vGs t' a fW
/
A a / G /��
7 i I o �.
ro
•
Approved by:
Entered in Utility.File Database❑no.
S
APPENDIX F
FIGURES AND TABLES
F
I
(11) Section 4.0 is amended to read as follows:
4.0 Intensity -Duration -Frequency Curves for Rational Method:
The one -hour rainfall Intensity -Duration -Frequency tables for use the Rational Method
of runoff analysis are provided in Table RA-7 and in Table RA-8.
Table RA-7 -- City of Fort Collins
Rainfall Intensity -Duration -Frequency Table
for Use with the Rational Method
(5 minutes to 30 minutes)
Duration
(min)
5
2-Year
Intensity
(in/hr)
2.85
10-Year
Intensity
(in/hr)
4.87
100-Year
Intensity
(in/hr).
9.95
6
2.67
4.56
9.31
7
2.52
4.31
8.8
8
2.4
4.1
8.38
9
2.3
3.93
8.03
10
2.21
3.78
7.72
11
2.13
3.63
7.42
12
2.05
3.5
7.16
13
1.98
3.39
6.92
14
1_92
3.29
6.71
15
1.87
3.19
6.52
16
1.81
3.08
6.3
17
1.75
2.99
6.1
18
1.7
2.9
5.92
19
1.65
2.82
5.75
20
1.61
2.74
5.6
21
1.56
2.67
5.46
22
1.53
2.61
5.32
23
1.49
2.55
5.2
24
1.46
2.49
5.09
25
1.43
2.44
4.98
26
1.4
2.39
4.87
27
1.37
2.34
4.78
28
1.34
2.29
4.69
29
1.32
2.25
4.6
30
1.3
2.21
4.52
33
Table RA-8 -- City of Fort Collins
Rainfall Intensity -Duration -Frequency Table
for Use with the Rational Method
(31 minutes to 60 minutes)
Duration
(min)
31
2-Year
Intensity
(in/hr)
1.27
10-Year
Intensity
(in/hr)
2.16
100-Year
Intensity
(in/hr)
4.42
32
1.24
2.12
4.33
33
1.22
2.08
4.24
34
1.19
2.04
4.16
35
1.17
2.0
4.08
36
1_15
1.96
4.01
37
1.16
1.93
3.93
38
1.11
1.89
3.87
39
1.09
1.86
3.8
40
1.07
1.83
3.74
41
1.05
1.8
3.68
42
1.04
1.77
3.62
43
1.02
1.74
3.56
44
1.01
1.72
3.51
45
0.99
1.69
3.46
46
0.98
1.67
3.41
47
0.96
1.64
3.36
48
0.95
1.62
3.31
49
0.94
1.6
3.27
50
0.92
1.58
3.23
51
0.91
1.56
3.18
52
0.9
1.54
3.14
53
0.89
1.52
3.1
54
0.88
1.5
3.07
55
0.87
1.48
3.03
56
0.86
1.47
2.99
57
0.85
1.45
2.96
58
0.84
1.43
2.92
59
0.83
1.42
2.89
60 1
0.82
1.4
2.86
34
I
1
1
1
1
10.00
9.00
6.00
t 7.00
N
0
L
)_ 6.00
F_
H 5.00
2
W
z
4.00
J
J
Q
z 3.00
9
RAINFALL INTENSITY -DURATION -FREQUENCY CURVE
2.00
1.00
0.00
0.00 10.00 20.00 30.00 40.00 50.00
STORM DURATION (minutes)
- 2-Year Storrs - - - 10-Year Storm -100-Year Storm
Figure RA-16 City of Fort Collins Rainfall Intensity -Duration -Frequency Curves
(13) Section 5.0 is deleted in its entirety.
(14) Section 6.0 is deleted in its entirety.
(15) Section 7.0 is deleted in its entirety.
(16) Section 7.1 is deleted in its entirety.
(17) Section 7.2 is deleted in its entirety.
(18) Section 7.3 is deleted in its entirety.,
(19) Section 8.0 is deleted in its entirety.
(20) Table RA-1 is deleted in its entirety.
36
60.00
I
Table RO-10
Rational Method Minor Storm Runoff Coefficients for Zoning Classifications
Description of Area or Zoning
Coefficient
R-F
0.3
U-E
0.3
L-M-In
0.55
R-L, N-C-L
0.6
M-M-N, N-C-M
0.65
N-C-13
0.7
Business:
C-C-N, C-C-R, C-N, N-C, C-S
0.95
R-D-R, C-C, C-L
0.95
D, C
0.95
H-C
0.95
C-S
0.95
Industrial:
E
0.85
1
0.95
Undeveloped:
R-C, T
0.2
P-0-1-
0.25
For guidance regarding zoning districts and classifications of such districts please refer to
Article Four of the City Land Use Code, as amended,
40
Table RO-11
Rational Method Runoff Coefficients for Composite Analysis
Character of Surface
Runoff Coefficient
Streets, Parking Lots,
Drives:
Asphalt
0.95
Concrete
0.95
Gravel
0.5
Roofs
0.95
Recycled Asphalt
0.8
Lawns, Sandy Soil:
Flat <2%
0.1
Average 2 to 7%
0.15
Steep >7%
0.2
Lawns, Heavy Soil:
Flat <2%
0.2
Average 2 to 7%
0.25
Steep >7%
0.35
(4) A new Section 2.9 is added, to read as follows:
2.9 Composite Runoff Coefficient
Drainage sub -basins are frequently composed of land that has multiple surfaces or zoning.
classifications. In such cases a composite runoff coefficient must be calculated for any
given drainage sub -basin.
The composite runoff coefficient is obtained using the following formula:
E(Ci *A,)
C = ;=1 A (RO-8)
Where: C = Composite Runoff Coefficient
C; = Runoff Coefficient for Specific Area (A)
A; = Area of Surface with Runoff Coefficient of C;, acres or feet
n = Number of different surfaces to be considered
A,= Total Area over which C is applicable, acres or feet
(5) Anew Section 2.10 is added, to read as follows:
41
2.10 Runoff Coefficient Adjustment for Infrequent Storms
- The runoff coefficients provided in tables RO-10 and RO-1 1 are appropriate for use with
the 2-year storm event. For storms with higher intensities, an adjustment of the runoff
coefficient is required due to the lessening amount of infiltration, depression retention,
evapo-transpiration and other losses that have a proportionally smaller effect on storm
runoff. This adjustment is applied to the composite runoff coefficient.
Table RO-12
Rational Method Runoff Coefficients for Composite Analysis
Storm Return Period
Frequency Factor
ears
Cr
2 to 10
1.00
I l to 25
1.10
26 to 50
1.20
51 to 100
1.25
Note: The product of C times Cf cannot exceed the value of 1, in the cases where it does a value of
1 must be used
(6) Section 3.1 is deleted in its entirety.
(7) Section 3.2 is deleted in its entirety.
(8) Section 3.3 is deleted in its entirety.
(9) A new Section 4.3 is added, to read as follows:
4.3 Computer Modeling Practices
(a) For circumstances requiring computer modeling, the design storm hydrographs must
be determined using the Stormwater Management Model (SWMM). Basin and
conveyance element parameters must be computed based on the physical characteristics
of the site.
(b) Refer to the SWMM Users' Manual for appropriate modeling methodology, practices
and development. The Users' Manual can be found on the Environmental Protection
Agency (EPA) website (http://www.epa.gov/ednnnnrl/models/swmm/index.htm).
(c) It is the responsibility of the design engineer to verify that all of the models used in
the design meet all current City criteria and regulations.
' 4.3.1 Surface Storage, Resistance Factors, and Infiltration
Table RO-13 provides values for surface storage for pervious and impervious surfaces
and the infiltration rates to be used with SWMM. Table RO-13 also lists the appropriate
' infiltration decay rate, zero detention depth and resistance .factors, or Manning's "n"
values, for pervious and impervious surfaces to be used for SWMM modeling in the city
of Fort Collins.
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