HomeMy WebLinkAboutLEVON'S 2ND PHASE, WAREHOUSE & OFFICE BUILDING - PDP/FDP - 19-96C - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTAll soils exposed during land disturbing activity (stripping, grading, utility
installations, stockpiling, filling, etc.) shall be kept in a roughened condition by
ripping or discing along land contours until mulch, vegetation, or other
permanent erosion control is installed. No soils in areas outside project street
rights -of -way 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, unless otherwise approved by the
Stormwater Utility.
The property shall be watered and maintained at all times during construction
activities so as .to prevent wind -caused erosion. All land disturbing activities
shall be immediately discontinued when fugitive dust impacts adjacent
properties, as determined by the City of Fort Collins Engineering Department.
All temporary (structural) erosion control measures shall be inspected and
repaired or reconstructed as necessary after each runoff event in order to
assure continued performance of their intended function. All retained
sediments, particularly those on paved roadway surfaces, shall be removed and
disposed of in a manner and location so as to not cause their release into any
drainageway.
No soil stockpile shall exceed ten (10) feet in height. All soil stockpiles shall be
protected from sediment transport by surface roughening, watering, and
perimeter silt fencing. Any stockpile remaining after 30 days shall be seeded
and mulched.
City Ordinance prohibits the tracking, dropping or depositing of soils or any
other material onto City streets by or from any vehicle. Any inadvertently
deposited material shall be cleaned immediately by the contractor.
Attached is the cost estimate for the erosion control escrow required by the
proposed construction of a warehouse -office building in the 300 block of West Hickory
Street (Levons 2nd Warehouse and Office Building).
Seeding - 2.33 ac @ $655/ac
Escrow required = $1526.15 x 1.5 =
$1526.15
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In the southeast corner of the site, regrading reults in a smaller subbasin
discharging south along the Union Pacific RR. Because the runoff coefficient "c"
does not change in this basin, developed runoff is less than the historical runoff
rate.
The SDDC outlines the causes and results of soil erosion due to wind and
rain. Along with the requirements of this report and the erosion control plans,
the SDDC shall be considered in it's entirety for guidelines to aid in preventing
rainfall and wind soil erosion. The SDDC will govern requirements and
specifications for earth moving and other construction at the site.
' Until permanent seeding is established, straw bale dikes will be constructed
to cause any loose, fine grained soils transported by surface runoff to settle out.
Along the south property line and a portion of the west property line, temporay silt
fences will be constructed to prevent sediment from being deposited upon the
public right of way in the event of heavy rains. The fence also will act somewhat
as a wind barrier, keeping low blowing fugitive dust from leaving the site. As field
operations continue, disturbed areas will have hay mulch disced into the ground to
provide cohesiveness to the soils. Where disturbed areas are to be of very short
term, discing ridges perpindicular to the prevailing winds may be substituted.
Below are general erosion control requirements which the contractor will be
required to follow.
As required, a cost estimate for an erosion control security escrow is
included with this report.
1 A. Summary of Erosion Control Requirements
The following is a summary of the storm drainage improvements and erosion
control measures that will be adhered to during construction.
GENERAL EROSION CONTROL REQUIREMENTS
The City of Fort Collins Stormwater Utility erosion control inspector must be
notified at least 24 hours prior to any construction on this site.
All required perimeter fencing shall be installed prior to any land disturbing
activity (stockpiling, stripping, grading, etc.). All other required erosion control
measures shall be installed at the appropriate time in the construction sequence
t as indicated in the approved project schedule, construction plans, and erosion
control report.
Pre -disturbance vegetation shall be protected and retained wherever possible.
Removal or disturbance of existing vegetation shall be limited to the area
required for immediate construction operations, and for the shortest practical
' period of time.
utility drawings, and are also included in this report
building site is not affected.
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In summary, the proposed
Because the site is located in the Poudre River Drainage Basin, the
StormWater Utility does not require on -site detention to maintain historical release
rates.
D. Proposed Drainage Improvements
Site grading will generally allow storm run-off to maintain existing sheet
flow patterns. Concentrations of run-off will be avoided to keep run-off velocities
' very low, assisting in percolation and infiltration into the on -site clay loams.
Existing conditions are flat and do not allow the customary 2% min. slope for
earthen drainage, and there may be areas of standing water for brief periods of
' time after severe storms. The Owner is willing to accept this condition, and is
asking the Stormwater Utility to grant a variance for a minimum .40 % grade due
to existing conditions. The Owner is also requesting that fill areas be allowed to
be constructed with 3:1 side slopes in lieu of the recommended 4:1 slope to
diminish the amount of fill required to raise the building pad.
Proposed drainage improvements consist primarily of filling and grading the
site to direct runoff to the southwest corner of the site. RCP pipes, structural
class IV, will be installed on -site to transport runoff from the north and east
portions of the site beneath the entry drive and parking areas to the southwest
corner of the site.
The Stormwater Utility requires that accomodations be provided to ensure
that runoff water is not polluted with nitrates, oils, sediment and other deleterious
materials that could harm receiving waters. The general concept is to retain the
initial flush of runoff to allow such matter to settle out or percolate into the
ground, rather than discharging the matter into downstream waterways. One
method recommended is to provide orifice plates at a headwall to detain a certain
volume of runoff, ( a -water quality capture Volume, or WOCIA, discharging it
slowly over 40 hours. A problem arises when the release rate is very small,
(slow),- resulting in quite small orifice perforations that are susceptible to clogging.
Structured Engineering has chosen to utilize a rectangular weir of comparable
discharge rate lieu of individual circular orifices. It is expected that such a weir
will will perform the same function as the orifice plate with less likliehood of
clogging completely. Therefore, prior to leaving the site, runoff quality will be
improved with temporary detention behind a WQCV weir. The clarified runoff will
be released over a 40hr time period through the calibrated weir.
A 9.98 cfs 100yr release rate will pass over the WQCV weir and cross
Hemlock Street in the drain pan designed and constructed during Phase 1 to pass
9.98 cfs. Runoff then will sheet flow to the Poudre River across the Salyer Open
Space in an existing 150' wide drainage easement. The difference between the
9.98 cfs originally expected and the 13.51 cfs now anticipated due to the
proposed development will be detained on site. A total of 4872 cubic feet of
runoff will be detained, with a high water surface elevation of 4973.83.
The new building is to be located in a presently undeveloped portion of the
' site. There are about a half dozen mature trees on this portion of the site... large
diameter poplars. The remainding vegetation consists of local, native grasses or
bare ground.
tA public concrete bike/pedestrian trail borders the site along the west side
(offsite), and the Union Pacific railroad tracks are along the east side. Hemlock
' Street forms the south boundary, and Hickory Street the north.
The proposed building, (approximately 80' x 250'), will be about 20' north
of the south PL and about 78' from the west property line. Existing lot grading is
at approximately .4% slope, generally from the north to the south.
Hickory Street is paved and has vertical curb and gutter. Hemlock Street
along the south property line is gravel now and will remain so. No street access is
going to be provided to or from Hemlock Street as part of these improvements.
There is a concrete cross pan across Hemlock Street near the southwest corner of
the building site. This pan was designed and constructed as part of Phase 1 to
pass 9.98 cfs, anticipating Levons 2nd development.
There are no pronounced natural drainage features on or adjacent to the site
except for an existing swale that parallels the UP railroad tracks.
The soils group making up the site is primarily clay loam according to the
Larimer County Soils Survey by the Soil Conservation Service. A soils report
prepared by Earth Engineering Consultants April 5, 1996 (EEC Project No.
1962025) for the first building more specifically defines the on -site material as a
sand and gravel granular material.
A. Design Criteria
The City of Fort Collins has prepared a Storm Drainage Design Criteria and
' Construction Standards (SDDC) which provides the basis for the analysis used in
predicting storm runoff and the recommended drainage improvements. The latest
precipitation rates have been used.
B. Hydrology
' The Rational Method is used to predict the amount of peak runoff. The
100-year return frequency was used in this report to predict major peak
' discharges, and the 10-year storm is analyzed as the minor storm.
C. Conformance With Existing Master Drainage Plans
rThe FIRM Flood Insurance Rate Map prepared by FEMA ( Community Panel
Number 08012-004-C, revised March 18, 1996) was consulted to determine flood
' plain boundaries in the area. The flood plains are indicated on sheet 3 of the
I
FINAL STORM DRAINAGE
and
EROSION CONTROL REPORT
for
Levon's 2nd
Warehouse and Office Building
May 7, 2001
INTRODUCTION
A second warehouse - office building is proposed for construction on a 3.36
acre (gross, 3.29 acres net after street R.O.W. dedications), parcel zoned CN,
Commercial - North College, in the 300 block of West Hickory Street. The parcel
' is just west of Union Pacific railroad tracks, south of Hickory Street and north of
Hemlock Street. There is an existing 14,700sf warehouse on the property.
This report sums up the analysis that was undertaken to determine what
impacts the construction of a proposed new 20,000sf speculative warehouse will
have on current drainage patterns in the area.
This report addresses the following:
1 .Site Descriptions
2.Storm Drainage
A. Design Criteria
B. Hydrology
C. Conformance With Existing Master Drainage Plans
D. Proposed Drainage Improvements
3.Erosion Control
A. Erosion Control Measures
It is intended that the recommendations found in this report become an
integral part of the design documents and construction of the project.
The property is described as "a parcel of land being a portion of Block 15,
the vacated alley therein, vacated Fourth Street and vacated Fourth Avenue, in
Riverside Park of the City of Fort Collins, and other property in the SE 1 /4 of
Section 2, Township 7 North, Range 69 West of the 6th Principal Meridian, in
Larimer County, Colorado". The parcel is being re -platted as "First Replat of
Levon's Minor Subdivision".
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May 7, 2001
Structured Engineering
318 East Oak Street
Fort Collins, CO 80524
Phone (970)-495-0810
Fax (970)-224-1314
May 7, 2001
Mr. Basil Hamden
Stormwater Utility
City of Fort Collins
PO Box 580
Fort Collins, Colorado 80522
Dear Basil,
Attached is the final Final Storm Drainage Report that accompanies the construction
of a second warehouse and office building to be located in the Poudre River drainage basin
in the 300 block of West Hickory Street in north Fort Collins. The project is titled Lemon's
2nd Warehouse and Office Building.
The report is in essence a continuation of , or, a modification to, the previous Final
Storm Drainage and Erosion Control Report for Levon's Warehouse and Office Building,
dated March 16, 1996, revised December 11, 1996, and approved by the City of Fort
' Collins January 3, 1997. The development now proposed is on the same site analyzed in
the earlier report.
The earlier report anticipated this second building would be built at some time, and
anticipated all site drainage would leave at the southwest corner of the site and sheetflow
across a Salyer Open Space drainage easement obtained then from the City of Fort Collins.
Proposed drainage improvements as part of this 2nd development closely follow the
intent and assumptions of the drainage plan prepared for the first development.. As part of
water discharge quality requirements imposed on new developments since the time the
first development was approved, detention will be provided on -site with appropriate
grading and a Water Quality Capture Volume (WGCV) weir structure and in the southwest
corner of the site. The WQCV has been provided only for the portion of the site proposed
to be developed now, after WQCV requirements were enacted.
All design is in conformance with the latest edition of the City of Fort Collins' Storm
Drainage Design Criteria and Construction. Standards and.uses the -latest precipitation -- --
rates. All Stormwater Utility comments from earlier submittals have been addressed
herein.,
Josepb(P. Man
Structured Eng
FINAL
STORM DRAINAGE
and
EROSION CONTROL REPORT
LEVON'S 2nd
WAREHOUSE AND OFFICE BUILDING
300 BLOCK OF WEST HICKORY STREET
CITY OF FORT COLLINS, CO
May 7, 2001
Prepared For:
Charles Meserlian
North College Avenue
Fort Collins, CO 80521
(970) 221-0700
Prepared By:
Structured Engineering
318 East Oak Street
Fort Collins, Colorado, 80524
Phone (970) 495-0810
Fax (970) 224-1314