HomeMy WebLinkAboutVALUE PLASTICS PUD, TIMBERLINE PLAZA (LOTS 3 - 5) - PRELIMINARY / FINAL - 26-94 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT7. James H.Stewart & Associates, Drainage Report Value Plastics P.U.D., Part Lot 3,
New Hampshire Subdivision, December 1983.
8. James H. Stewart & Associates, Sheet 1 Value Plastics P.U.D. Grading, Drainage &
Drives, December 1983, Revised February 1984.
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INSTALLATION SCHEDULE
Construction of the new Value Plastics property is proposed to start in June, 1994 and
continue during the summer with the floors, grading and paving completed by August
of 1994. The approximate date of implementation of the erosion control measure
during construction are shown on Standard Form C in Appendix II. As shown on Form
C the gravel inlet filters, silt fence, the eastern and northern drainage channels and the
hay bale dikes will be constructed prior to overlot grading. Soils grading and topsoil
stockpile areas, which will not be disturbed during construction until final grading and
landscaping, will be roughened. Paving of the parking and walk areas is scheduled to
begin in mid -July and be complete by mid -August. Permanent vegetation will be
seeded and mulched after the completion of the project during the fall, cool season
planting beginning in August prior to the next wind erosion season. The hay bale dike
at point B will be left in place through the end of the rainfall erosion season in October
or until establishment of the permanent grass cover. All other feature may be removed
upon seeding and mulching.
EROSION CONTROL SECURITY
IThe erosion control security requirement for the new Value Plastics site was estimated
based on the specification of Section 2.0 of the Manual. The cost of the erosion
i control measures at the site as detailed above were estimated to cost $1,130 with a
security requirement of $1,700. The estimated cost to revegetate the disturbed areas
with a dryland grass mix according to the city's 1993 mulch and revegetation bid was
$2,600 with a security requirement of $3,900. The larger amount is required prior to
construction. Both cost estimates are detailed in Appendix II.
REFERENCES
1 . Resource Consultants, Inc., Foothills Basin (Basin G) Drainage Master Plan. February,
1981.
2. City of Fort Collins, Colorado, Storm Drainage Design Criteria and Construction
Standards, May 1984, Revised January 1991.
3. Denver Regional Council of Governments, Urban Storm Drainage Criteria Manual,
' Volumes I and II, March, 1969, 6th Printing Vol I September 1978.
4. RBD Inc., Final Drainage and Erosion Control Study for Fire Station No. 10 Fort
' Collins Colorado, January 1993.
5. RBD Inc. Letter to G. D. Schlueter, City of Fort Collins Stormwater Utility, February 22,
1993, Maximum Off Site Flow Allowed Into The Proposed Swale, Along The South
Prooerty Line of Fire Station No 10 To Limit Vermont Drive Overtopping to 0.5 Feet.
6. RBD Inc., Sheet No 2 Fire Station No 10 Utility Grading. Drainage and Erosion
Control Plan, November 1992.
D
Standard value of 93.5 percent. The Net Effectiveness was calculated using basin
effectiveness values of 97.1 and 94.8 percent for the Basin 2 and Basin 3,
respectively. Calculations of the basin effectiveness value and the Net Effectiveness
for the site are presented on Standard Form B in Appendix II.
WIND EROSION ANALYSIS
The surface soils at the new Value Plastics site are rated as moderately wind erodible.
Construction at the site will not occur during the wind season of November to May and
the site does not fall under any of the exclusions available in the Manual.
Construction disturbance at the site as detailed above will occur across the entire site
except for the future expansion area in the southern third of lot 3. The limited size of
the construction area and the necessary access in this area will restrict the available
area for placement of a wind barrier. For this reason the wind erosion features to be
constructed at the site will consist primarily of natural features at the site, water
erosion controls and the features to be constructed.
The wind erosion control measures which will be implemented during construction will
include the items listed below and are detailed on the Grading and Drainage Plan.
• The east drainage channel along the east margin of the development.
• The silt fence along the southeast margin of the property.
• The topsoil stockpile area located to the south of the proposed building in the
future expansion area.
• The natural grass cover over the remainder of the future expansion area.
• The stormwater detention pond berm to the north of the proposed building.
• The walls and structural fill of the building.
• The paved parking and walk areas.
• The garage and existing landscaping along the eastern margin of the existing
Value Plastics property.
• The existing office building and landscaping to the northwest of the property.
Wind erosion control measures which will be implemented after construction will
consist of mulching and seeding the disturbed areas. Hay or straw mulch will be
applied and crimped into the soil surface at a rate of 2 tons per acre after seeding of
the site. The silt fence and topsoil stockpile will be removed when the mulch is
applied. The remainder of the wind erosion control features will remain intact to
counter soil loss during vegetative establishment.
Practice Factor Measures
Sediment control practice measures for the Value.Plastics development will consist of
the construction of a silt fence, two hay bale dikes, two gravel filters and the
roughening of the upper surface of the topsoil stock pile. The location and details of
these practice measures are shown on the Grading and Drainage Plan and the Grading
and Erosion Control Details Sheet appended at the end of this report.
Practice factor measures for the site after construction will be dismantled and thus a
weighted P - Factor of 1.0 was used to calculate the effectiveness. The calculations
for the weighted P - Factor for areas contributing to the east pond and west pond for
both during and after construction cases are presented on Standard Form B in
Appendix II.
Cover Factor Measures
Cover factor measures for the site during construction will consist of the building and
the parking areas and the undisturbed areas. The building and paved areas were
assigned a C - Factor value of 0.01. The undisturbed areas were estimated to have
approximately 50 percent grass cover and were assigned a C - Factor value of 0.07
from Figure 5.1 of the Manual. Undisturbed grassed areas cover the future expansion
area across the southern portion of lot 3. The topsoil stockpile area will be placed in
this area.
Cover factor measures for the site after construction is completed will consist of
implementation of the landscaping plan which calls for establishment of the grass
cover of at least 60 percent cover over the disturbed areas of the site. Grass will be
established with the use of hay or straw mulch applied and secured at a rate of 2 tons
per acre. The mulched and revegetated areas were assigned C - Factor values of 0.06
as selected from Table 5.2 and Figure 5.1. Cover factor values for the paved areas
and the undisturbed grassed areas were not changed from during construction
conditions. The calculations for the weighted C - Factor for areas contributing to the
east pond and west pond for both during and after construction are presented on
Standard Form B in Appendix 11.
"Durino Construction" Effectiveness Evaluation
The Net Effectiveness for the erosion control measures at the site during construction
was calculated as 80.7 percent and exceeds the "During Construction" Performance
Standard value of 79.5 percent. The Net Effectiveness was calculated using basin
effectiveness values of 80.6 and 80.7 percent for the Basin 2 and Basin 3,
respectively. Calculations of the basin effectiveness value and the Net Effectiveness
for the site are presented on Standard Form B in Appendix II.
"After Construction" Effectiveness Evaluation
The Net Effectiveness for the erosion control measures at the site after construction
was calculated as 96.0 percent and exceeds the "After Construction" Performance
RAINFALL EROSION ANALYSIS
Site Soils
The Larimer County, Soil Conservation Service Soils Report identifies the soils as
belonging to two similar soil units, the Nunn Clay Loam and the Fort Collins Loam,
both of which are described as having moderate rainfall erodibility characteristics. The
rainfall erosion season as detailed in the City of Fort Collins, Erosion Control Reference
Manual (21 (the Manual) is between May 1 and October 31. The natural drainage of
the site is from the south and west to the northeast corner where any runoff is
discharged to an open ditch flowing north along the west margin of Timberline Drive
to a storm drain in the northeast corner of proposed Fire Station 10. A mixture of
dryland grass and weed cover currently provides an estimated 50 percent cover over
the entire site.
The Manual details the site as having moderate wind erodibility characteristics. The
Manual states the predominant wind direction is from the west-northwest in this area.
The wind erosion season as detailed in the manual is between November 1 st and May
31 st.
Construction at the site is estimated to begin in June 1994 and continue through
October of 1994, with the majority of the structural and grading work completed by
August of 1994. This schedule places the project out of the wind erosion season and
during the rainfall season for this area.
Performance Standard
The estimated "During Construction" and "After Construction" Performance Standard
for the new Value Plastics site are 79.5 and 93.5, respectively. For the purpose of
estimating the site's Performance Standard the entire site was broken into 2 separate
basin areas based on the final development contours. The basins, as shown on the
Grading and Drainage Plan appended at the end of this report, consist of:
• 2.40 acre Basin 2, located north and west of the building and draining generally
northeast to the detention pond, and
• 2.21 acre Basin 3, located south and east of the building draining to the east
drainage channel.
The Performance Standard for the site was estimated using the methods detailed in the
Manual and the estimated, average slope length and slope for each basin. Flow
lengths and slopes developed for calculation of the "During Construction" Performance
Standard is presented on Standard Form A in Appendix II. The Performance Standard
was taken from Table 5.1 of the Manual. The "After Construction" Performance
Standard is calculated by dividing the "During Construction" Performance Standard by
0.85.
detention pond plus the peak flow from expanded basin 3 of 18.6 cfs equals the
allowable addition of off -site flow at design point B of 40.45 cfs.
An analysis of inflow to the detention pond over time, (i.e. runoff from basins 1 and
2 less a constant discharge of 4.4 cfs at design point A during the storm) determined
the required detention pond volume was less than 3,000 cubic feet. The detention
pond as designed with a spillway elevation of 4,941 feet provides over 4,500 cubic
feet of stormwater runoff storage.
The peak flow of 18.6 cfs from expanded basin 3, which contains both the existing
Value Plastics facility and the southeast portion of the new Value Plastics
development, will be conveyed to design point B via a trapezoidal, drainage channel
with a concrete invert on a slope of 0.5% and 4:1, horizontal to vertical, side slopes.
The depth in the channel at design point B, during the peak flow from a 100-year
storm of 18.6 cfs, is less than 1.0 foot. The channel provides adequate freeboard.
An 18" concrete pipe was selected to drain the detention pond at the design release
rate. The pipe was designed with the pond water surface at 4,941 feet and tailwater
at elevation 4,939 and 4,940 feet. This will prove academic if runoff ponds in
Vermont Drive to elevation 4,941.5 feet during a 100-year event [4][5][6]. Under this
condition, water would pond in the northeast portion of the site, the extent of which
would be determined by the shape of the runoff hydrograph. However, it would not
affect the building floors in the garage and the main building of the new Value Plastics
development, set at 4,941.5 and 4,946 feet, respectively.
The swale located along the south boundary of Fire Station 10 will collect runoff from
part of the Fire Station roof and a small portion of the developed site. WWL-
redesigned this channel allowing for the reconfigured flow patterns from the new Value
Plastics development which routes all off -site (non -Fire Station) flows through the
detention pond rather than the swale as detailed in the RBD report 141. The new
design consists of a triangular, grass -lined channel with a slope of 1.0 percent graded
from west to east to design point B. The channel will have 4:1, horizontal to vertical,
side slopes and will be contained with in a 10 foot easement which will merge with
the drainage easement for the detention pond. Estimated peak flows for the 100-year,
storm event vary from 0.3 to 1.3 cfs from the start of the swale to design point B
where the channel merges with the east channel and the outfall from the detention
pond. The channel at these flows will be stable for both pre -vegetative and vegetated
conditions. The maximum depth of flow under an uncut grass condition would be less
than 0.5 feet and adequate freeboard will be provided.
For a cross section of the channel and swale see the drawing entitled Grading and
Drainage Details appended at the end of this report.
James H. Stewart and Associates [7][8]. Runoff from this existing facility will now
be directed to the east and north to the Fire Station swale as will the runoff from 1 /3
of the roof area of the new building and the remaining area to the south and east of
the new building. This flow will be conveyed to the Fire Station swale via an open
channel along Timberline Road.
Details
Three drainage basins were utilized in analyzing and routing runoff to two design points
and a detention pond as shown on the Grading and Drainage Plan appended at the end
of this report. Basins 1 consists of the existing office building at the southeast corner
of Vermont and Eastbrook Drive. Basin 2 consists of the west parking lot, 2/3 of the
roof area of the new Value Plastics development and the area to the north of the
proposed building. Basins 1 and 2 were analyzed at the storm drain inlet, design point
A, (RBD design point 1 for the proposed Fire Station [4][51) before being routed to the
new detention pond in the northeast corner of the site. Basin 3 initially consisted of
the remaining area of the new Value Plastics development. Basin 3 was expanded to
include all runoff from the existing Value Plastics facility when the proposed access
to the new Value Plastics visitors parking lot, located on to the south of the proposed
building, eliminated existing detention capabilities on this property. The discharge from
this combined basin was analyzed at design point B where it combines with flows from
Basins 1 and 2. In all cases, future development shown on this Plan was accounted
for in determining the runoff that might be expected from a 100-year storm.
It was determined that the three basins generate a peak flow of 52.2 cfs, 7.65 cfs
more than the 44.85 cfs allowed by the constraints established by RBD [4][5]. The
peak flow will be attenuated in the new pond and released to design point B at the
appropriate rate. Expanded basin 3 runoff will be routed to design point B via sheet
and channelized flow without detention.
During a 100-year storm, basins 1 and 2 generate a peak flow at design point A of
33.9 cfs. A portion of this peak, 4.4 cfs [51, flows through the inlet at A and the
existing 18" storm drain to the north leaving 29.5 cfs to overflow to the detention
pond. The Final Drainage and Erosion Control Study for Fire Station 10 planned to
route this overflow via a swale in a 20' drainage easement flowing east along the
south side of the Fire Station property and then north to a system carrying flow to the
main drainageway of Foothills Basin G [6]. The drainage plan proposed for the new
Value Plastics development modifies this routing and the required easements. The
Value Plastics driveway paving between the main building and a garage will now be
the route that carries the overflow to the detention pond. This route and the pond will
be located within easements and the Swale along the south side of Fire Station 10 will
be narrowed as it will now only carry runoff from a portion of the Fire Station
development. This redesigned Swale will fit within a 10' easement at its western end.
A print of the Plat for the new Value Plastics development delineating the proposed
easements is appended to the end of this report.
The allowable release rate from the pond was determined to be 21.85 cfs or 9,807
gpm (i.e. the overflow from basins 1 and 2 at design point A of .29.5 cfs minus 7.65
cfs, the difference between the total peak runoff from the site of 52.2 cfs and the
maximum allowable peak flow of 44.85 cfs). The release rate of 21.85 cfs from the
DRAINAGE DESIGN CRITERIA
Regulations
The City of Fort Collins Storm Drainage Design Criteria [21 is being used as the basis
for this report.
Development Criteria Constraints
The constraints are established by RBD, Inc., in their study [4][51 for Fire Station 10.
The existing inlet near the southwest corner of Fire Station 10 and the storm drain
carrying stormwater flows to the north can only handle 4.4 cfs during the 100-year
storm. Overflow from this inlet, in the RBD design, will be collected and conveyed in
the proposed swale along the east side of the Fire Station 10 property. This swale is
designed to accept an additional 40.45 cfs from off -site sources not generated by Fire
Station 10. Based on these constraints the maximum discharge rate from the
remaining properties in the Timberline Plaza P.U.D. bounded by Danfield Court,
Eastbrook Drive, Vermont Drive and Timberline Road is 44.85 cfs. The water surface
during a 100-year storm is predicted to be a maximum of 4041.5 in Vermont Drive
near Timberline Road. This flood stage includes the 44.85 cfs from the remaining
areas of Timberline Plaza P.U.D..
' Hydrologic Criteria
The Rational Method and the runoff from a 100-year storm were used to design the
drainage system for the Value Plastic development. Calculations are included in
Appendix 1.
Calculations
All calculations for this report have been made in accordance with criteria established
by the City of Fort Collins.
Variances
No variances are requested.
DRAINAGE DESIGN
Concept
Referring to the print of the Value Plastics Grading and Drainage Plan appended at the
end of this report, runoff from the west parking area accessed from Eastbrook Drive,
the area on the north side of the new building, about 2/3 of the roof area and excess
runoff from the existing office building will flow to a detention pond in the northeast
corner of the site discharging to the Fire Station swale. The detention pond may
eventually be paved for parking.
The existing Value Plastics facility paved area will be used to access the visitors
parking area for the new building. This will eliminate the detention pond designed by
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SCALE IN FEET
0 1000 2000
Date:
WATER MAR 1994
WASTE VALUE PLASTICS SITE MAP
Project:
& LAND 94406100
INC.
FINAL DRAINAGE AND EROSION CONTROL REPORT
FOR
A NEW BUILDING FOR VALUE PLASTICS
FORT COLLINS, COLORADO
DEVELOPMENT LOCATION AND DESCRIPTION
Location
A new, one-story building is planned for Value Plastics on a site along Timberline Road
as shown on the enclosed Site Map. A site layout at a larger scale is shown on a print
of the Grading and Drainage Plan appended at the end of this report. The site,
containing approximately 4.65 acres, is within the block bounded by Danfield Court
on the south, Eastbrook Drive on the West, Vermont Drive on the North and Timberline
Road on the east. Existing development within this block consists of Value Plastics'
present facilities in the southwest corner and an office building in the northwest
corner. The northeast corner is the proposed location for Fire Station 10, to be erected
in the near future. The site lies in the Southeast Quarter of Section 30, Township 7
North, Range 68 West, City of Fort Collins, County of Larimer, State of Colorado.
Property Description
The property Value Plastics' new building will occupy is undeveloped. It is presently
covered with native grasses and slopes from the southwest to the northeast at a
gradient of approximately 1 %. There are existing utilities on site consisting of an 8"
ductile iron water line, cross -connecting to lines in Danfield Court and Vermont Drive,
aligned with a private drive on the north half of the site, an 8" sanitary sewer and a
18"in storm drain, also located within this private drive right-of-way. The water line
and the sanitary sewer will be modified and utilized by the new development. The
storm drain will be abandoned upstream of an existing area inlet draining the existing
office building parking lot. This was design point 1 in the Fire Station Drainage Study
(4] and is labeled design point A in this study. This storm drain and the proposed
swale along the east side of the Fire Station site will be utilized for draining this new
Value Plastics development within the limitations set out in earlier work [4][5].
DRAINAGE BASIN IDENTIFICATION
Description
The proposed Value Plastics development lies in the Foothills Drainage Basin (Basin G).
The Foothills Basin Drainage Master Plan indicates that this area is served by Reach
2 of the major drainageway located north of Vermont Drive flowing generally from the
southwest towards the northeast [11. Runoff from the Value Plastics development will
be directed to this major drainageway via an existing storm drain system and new
drainage work proposed in conjunction with the new Fire Station 10.
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WATER
WASTE
& LAND
�G
April 4, 1994
2629 Redwing Rd. Suite 200, Fort Collins, Colorado 80526-2879
(303) 226-3535
fax (303) 226-6475
Mr.Glen D. Schlueter
City of Fort Collins
Utility Services Stormwater
235 Mathews
Fort Collins, Colorado 80522
RE: VALUE PLASTICS - DRAINAGE AND EROSION CONTROL REPORT
Dear Mr. Schlueter:
Transmitted herewith is the subject report for your review and approval.
If you have any questions or require any modifications please call me. I will be pleased
to meet with any of your people at their convenience.
Thank you.
Sincerely,
WATER,^ WASTE & LAND, I
JriceMa
cz
H. Lutkin, P.r, Civil Engin ering Division
Consulting Engineers and Scientists
DRAINAGE AND EROSION CONTROL REPORT
FOR
VALUE PLASTICS
FORT COLLINS, COLORADO
Prepared for:
The Neenan Company
2290 East Prospect
t<<<.`G
,t • ..�;
61
P.O. Box 2127
Fort Collins, CO 80522
';
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Prepared by:
''�1•-„.„°"'
Water, Waste & Land, Inc.
2629 Redwing Road, Suite 200
Fort Collins, Colorado 80526
April 4, 1994