HomeMy WebLinkAboutDrainage Reports - 12/20/2013 (3)City of Ft. Collin ov Plans
Approved By
Date D- O:
FINAL DRAINAGE AND EROSION
CONTROLSTUDY
218 WEST LAUREL STREET
C peck )Irk)
Prepared for:
Dana Lockwood
Lockwood Architects
415 East Pitkin
Fort Collins, CO 80524
Prepared by:
North Star Design, Inc.
700 Automation Drive, Unit I
Windsor, Colorado 80550
(970)686-6939
September 11, 2013
Job Number 34M]
t' i.
North Star
design
700 Automation Drive, Unit I
Windsor, CO 80550
Phone:970-686-6939
Fax: 970-686-1188
September 11, 2013
Glen Schlueter
City of Fort Collins Stormwater
700 Wood Street
Fort Collins, CO 80522-0580
RE: Final Drainage and Erosion Control Study for
218 West Laurel Street
Dear Glen,
1 am pleased to submit for your review and approval, this Final Drainage and Erosion Control
Study for 2118 West Laurel Street. I certify that this report for the drainage design was prepared
in accordance with the Old Town Master Plan and the criteria in the City of Fort Collins Storm
Drainage Manual.
1 appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
Patricia Kroetch, P.E.
m
TABLE OF CONTENTS
TABLEOF CONTENTS............................................................................................................... iii
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..........................................................................................1
2.2 Sub -Basin Description.............................................................................................I
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....................................................................................................2
4. DRAINAGE FACILITY DESIGN
4.1
General Concept......................................................................................................3
4.2
Specific Flow Routing.............................................................................................3
4.3
Drainage Summary..................................................................................................4
4.4
Variances Requested................................................................................................4
5. STORMWATER MANAGEMENT CONTROLS
5.1
Written Analysis.....................................................................!..............................4
5.2
SWMP Contact Information...................................................................................5
5.3
Identification and location of all potential pollution sources..................................6
5.4
Best Management Practices (BMP's) for Stormwater Pollution Prevention ...........
6
5.5
BMP Implementation...............................................................................................8
6. CONCLUSIONS
6.1
Compliance with Standards..................................................................................12
6.2
Drainage Concept..................................................................................................12
7. REFERENCES..................................................................................................................13
APPENDICES
A Vicinity Map
B Hydrologic Computations
C Detention Pond Calculations
ff
1. GENERAL LOCATION AND DESCRIPTION
1.1 Location
The site is located on the East %: of the East % of Lots 12 and 13, Block 106 Harrison's
Addition in Section 5, Township 6 North, Range 69 West of the Sixth Principal Meridian,
in the City of Fort Collins, Larimer County, Colorado. The address of the existing site is
218 West Laurel Street. See the location map in Appendix A.
The project is located on the north side of West Laurel Street between South Mason
Street and South Howes Street. The project is bounded on the north and west by existing
residential, on the east by Rainbow Cafe and the alley and on the south by Laurel Street
and CSU campus.
1.2 Description of Property
The entire site consists of approximately 0.15 acres of land. The land is currently
developed with an existing house and concrete walks and drives. The site currently drains
to the alley on the east and then to the north and south. Slopes on site range from
approximately 0.5% to I%.
This project will include the development of a six-plex residential building, driveways
and landscape area. The site will be reconfigured so that a majority of the runoff will be
directed to the west property line and south into a water quality swale and into Laurel
Street.
2. DRAINAGE BASINS AND SUB -BASINS
2.1 Major Basin Description
The proposed development lies within the Old Town Drainage Basin.
2.2 Sub -basin Description
This site has not been included in any known previous drainage study.
a
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 Development Criteria Reference and Constraints
The runoff from this site has been routed to conform to the Old Town Master Drainage
plan and the existing conditions on site. The Old Town Basin is normally restricted to a 2
year historic release rate with redevelopment. Because of the existing development on all
four sides to this site, the east portion of the development (the driveways) will release
directly onto the alley without detention. The runoff from the remainder of the site,
including the entire proposed building, will be directed to a swale on the west property
line that conveys the runoff to the water quality swale and into Laurel Street. It is
proposed to not provide detention for this basin because of the minor increase in
imperviousness. In the Old Town Basin, 1000 square feet of additional imperviousness is
allowed without detention and this site is proposing an increase of 1383 square feet of
imperviousness. Also, the proposed increase in runoff from this site is 0.07 cfs in the 2
year storm event, 0.09 cfs in the 10 year event and 0.14 cfs in the 100 year event. This
increase will have a negligible impact on the existing downstream conveyances.
3.3 Hydrologic Criteria
Runoff coefficients calculations were prepared for the 2 and 10-year minor and 100-year
major storm frequency utilizing the rational method. No detention is proposed on site.
3.4 Hydraulic Criteria
No subsurface drainage conveyances are proposed with this development; therefore no
hydraulic calculations were completed with this design.
K
2
4. DRAINAGE FACILITY DESIGN
4.1 General Concept
The runoff from this site will be collected in a grassed swale along the west property line
and be conveyed to the water quality swale on the south portion of the site. A small
amount of runoff will be allowed to discharge directly to the existing alley on the east
property line.
A small amount of flow from the property on the west is anticipated to enter the site and
will be conveyed to Laurel Street through the proposed swale and sidewalk culvert. The
offsite flows will not be detained.
4.2 Specific Flow Routing
A summary of the drainage patterns within each basin is provided in the following
paragraphs.
Basin 1 encompasses the majority of the proposed development including the building,
front porch, front walk and the landscaping on the north, west and south sides of the site.
A majority of the runoff flows to the grassed swale on the west property line which will
convey the flows south to a sidewalk culvert and Laurel Street. In the south most
portion of the swale, an LID swale is being incorporated into the conveyance.
Basins 2 includes the proposed driveways on the east side of the site. The runoff from
this basin will flow east directly into the alley and be conveyed to the south and into
West Laurel Street or north eventually reaching West Myrtle Street. This flow path is the
historic flow path for the runoff from this site.
We are requesting a variance from the criteria that requires that 25% of the site
pavements be impervious. This site has approximately 1200 square feet of concrete
proposed on site which is entirely within Basin 1, a majority of which is in the driveways
with a small portion being the sidewalk and the trash enclosure. Of the 1200 square feet,
approximately 900 square feet can be driven on and 25% of this area would equate to 225
square feet of pervious pavement. We believe this amount of pervious pavement would
have little to no impact on the quality of the runoff from this site.
3
4.3 Drainage Summary
All runoff from this site and the adjacent sites will be safely conveyed via surface flow to
Laurel Street. The site is included in the Old Town Drainage plan and will generally
conform to this plan.
The City of Fort Collins will be responsible for maintenance of the existing storm
drainage facilities located within the right-of-way. The drainage facilities located outside
of the right of way (including the LID swale) will be maintained by the property owner.
4.4 Variances Requested
Two variances are being requested for this site. It is being requested that the site not
provide detention and that the site not be required to provide 25% pervious pavement.
The variance to the detention is being requested because the increase in runoff from this
site will be minimal (refer to Section 3.2 of this report) and the impact to the downstream
drainage system will be negligible. The site is proposing an increase of approximately
1380 square feet of imperviousness and 1000 square feet of additional imperviousness is
allowed in the Old Town basin before the detention requirement is applied.
The variance to the pervious pavement is being requested because the amount of pervious
pavement that would amount to is 225 square feet which has little or no impact to the
water quality on site (refer to Section 4.2 of this report). A small area (30 square feet) is
being proposed to be pavers and is located under the bicycle parking.
5. STORMWATER MANAGEMENT CONTROLS
5.1 Written Analysis
The soils on this site are classified by the USGS Soil Survey as Fort Collins Loam and
are classified in the hydrologic group B. The rainfall and wind erodibility is deemed to be
moderate. The Group B soils are Soils having a moderate infiltration rate when
thoroughly wet. These consist chiefly of moderately deep or deep, moderately well
4
a
drained or well drained soils that have moderately fine texture to moderately coarse
texture. These soils have a moderate rate of water transmission.
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 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 the
existing curb and the proposed sidewalk culverts.
The site may 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.
Permanent 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 section 5.5 for the timing of the construction phases and the sequential
installation of all BMP phasing for this site.
Refer to the end of Section 5.4 for the Erosion Control Surety calculations.
5
5.2 SWMP contact information
Permit holder:
Name:
Address:
Phone Number:
Email Address:
Appointed agent:
Name:
Address:
Phone Number:
Email Address:
5.3 Identification and location of all potential pollution sources
Potential Pollutant Source Activitv
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
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
X
Concrete washout
Concrete, sediment
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
m
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.
All BMP's shall be installed per the details shown on the construction plan set.
Temporary & Permanent Structural BMP's:
Structural BMP
Approximatelocation on site
bApplicable to this ,
Project
Silt Fence
Site perimeter, refer to site map
X
Straw bale dams
Rock Socks
At proposed sidewalk culverts, refer to site
map
x
Earthen diversion dams
Vegetated swales
Sediment trap/pond
Pipe slope drains
Geogrid
Inlet/outlet protection
Culverts
Riprap
Erosion control mats
Inlet protection
7
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.
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 boundary 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
West boundary of site
X
existing vegetation & trees
Good site housekeeping (routine
Entire Site
X
cleanup of trash & constr debris)
Heavy equip staged on site,
properly maintained & inspected
Staging area
X
daily (no onsite maintenance)
8
5.5 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. 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.
The following phase depictions and erosion controls are suggestions to the contractor on/y
and are in no way intended to dictate construction phasing or control of the work on site.
The contractor shall be responsible to control construction phasing and provide adequate
erosion control associated with each phase in order to comply with the SWM Plan and
Permit that is obtained by the contractor (or owner) for the site.
Phase I — Mobilization
Install silt fence, Install rock socks, set dumpster.
Phase 2 — Clear site, Overlot Grading
Clear existing house, concrete and treess. Cut and fill on site to achieve subgrade
elevations
Phase 3 - Utilities
Excavate and install for water service, fire line and sewer service modification, excavate
and install dry utilities
Phase 4 — Install Concrete Foundation
Establish temporary concrete washout area, cut for building foundation, place
concrete foundation.
Phase 5 — Concrete Site Paving
Remove silt fence in pavement area, Install sub base, install Concrete pavement. Remove
concrete wash out.
Phase 6 — Building construction
Complete vertical building construction
Phase 7 — Landscape installation
Final shaping of detention pond, install LID Swale, final shape planting areas, Install
irrigation system, Install soil amendments, Landscape plant installation, Install mulch
ground cover
Phase 8 — Final Stabilization
Final stabilization is complete when constructed improvements are in place, Inspect
completed construction for possible sources of erosion and amend the plan as required to
trap sediments.
SEDIMENT/EROSION CONTROL
BEST MANAGEMENT PRACTICES (BMPs)
COST OPINION SPREADSHEET
218 West Laurel Street
Item
No.
BMP
ID
Unit
Installation
Unit Cost
Quantity
Cost
1
Check Dam
CDR
LF
$0.00
2
Check Dam (Reinforced)
CDR
LF
$0.00
3
Concrete Washout Area
CWA
EA
$1,200.00
1
$1,200.00
4
Construction Fence
CF
LF
$0.00
5
Construction Markers
CM
LF
$0.00
6
Culvert Inlet Filter
CIF
LF
$0.00
7
Dewatering
DW
EA
$0.00
8
Diversion Ditch (Unlined)
DD
LF
$0.00
9
Diversion Ditch (ECM or plastic)
DD
LF
$0.00
10
Sediment/Erosion Control Matting
ECM
SY
$0.00
11
Inlet Protection
IP
LF
$0.00
12
Reinforced Rock Berm
RRB
LF
$0.00
13
Sediment Basin
SB
LF
$0.00
14
Sediment Control Log (Wattle)
SCL
LF
$4.60
0
$0.00
15
Seeding and Mulching
SM
AC
$0.00
16
Silt Fence
SF
LF
$3.00
370
$1,110.00
17
Rock Sock
RS
LF
$10.00
30
$300.00
18
Stabilized Staging Area
SSA
SY
$0.00
19
Surface Roughening
SR
AC
$0.00
20
Temporary Stream Crossing
MSSCL
EA
$0.00
21
Topsoil (6-inch Lift)
AC
$2,500.00
0.06
$150.00
22
IVehicle Tracking Control
VTC
EA
$1,500.00
1
$0.00
Contractor Added BMP(s)
23
$0.00
24
$0.00
25
$0.00
26
$0.00
SUBTOTAL COST
CONTINGENCY 50%
TOTAL COST
$2,760.00
$1,380.00
$4,140.00
2) Materials Handling and Spill Prevention:
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 [o 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 tracked 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 or by the State of Colorado.
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 will be determined by the contractor. 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 encountered during soils exploration
therefore 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
12
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 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.
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 Storm Drainage Design Criteria Manual and the Old Town Master
Drainage Plan.
6.2 Drainage Concept
The proposed drainage concepts presented in this report and on the construction plans
adequately provide for conveyance of runoff to Laurel Street. 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 would be required.
13
7. REFERENCES
City of Fort Collins, "Storm Drainage Criteria Manual", (SDCM), dated March,
1986.
2. Urban Drainage and Flood Control District, "Urban Storm Drainage Criteria
Manual", Volumes I and 2, dated March, 1969, and Volume 3 dated September,
1992.
14
APPENDIX A
VICINITY MAP
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DRAINAGE & EROSION CONTROL PLAN
City o[ Fort Cdlina. COIaroDo
OPLITY PLAN APPROVAL
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APPENDIX B
HYDROLOGIC COMPUTATIONS
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