HomeMy WebLinkAboutLEVON'S 2ND PHASE, WAREHOUSE & OFFICE BUILDING - MAJOR AMENDMENT - 19-96D - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT`g
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All 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
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.
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.
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 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.
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. The recommended method is to provide orifice
plates at a headwall to detain a certain volume of runoff, ( a -water quality
capture Volume, or WQCV), 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 plate of comparable discharge rate
lieu of individual circular orifices. It is expected that such a weir 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.
The historical 9.98 cfs 100yr release rate will overtop the WQCV
detention weir and cross Hemlock Street in a new cross pan designed to
pass 133% of the flow (13.33 cfs) that will be constructed as part of these
improvements. 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 historical flow and the 16.40 cfs now
anticipated due to the proposed development will be detained on site. A
total of 10312 cubic feet of runoff will be detained, which includes aWQCV
of 3117 cubic feet. With the full 10312 cf in storage, ie; assuming the
WQCV storage is already full when the 100yr storm occurs, the 100yr WSL
in the detention pond will be at elevation 4974.36, resulting in a freeboard
of about 7". Raising the finish grade of the pond berm to increase or
maintain existing freeboard would reduce the volume in the pond presently
available for detention storage by a like amount. Owner is therefore
requesting a variance from the typical requirement that a full 1 ft. of
freeboard be provided in the detention area. Even with only 7" of freeboard
in lieu of 12", the pond has 1 67% of the total combined WQCV and 100yr
storage volume required.
Elsewhere, in the southeast corner of the site, re -grading results in
less runoff discharging south along the Union Pacific RR than historically.
Hence, no further discussion is warranted here.
2. STORM DRAINAGE
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 for the minor. storm.
C. Conformance With Existing Master Drainage Plans
The 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 utility drawings, and are also included in this report. In
summary, the proposed building site is not impacted by any existing
floodplain.
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 sand and gravel materials. 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.
s Proposed drainage improvements will consist primarily of filling and
grading the site to direct runoff to the southwest corner of the site. RCP
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 has been re -
platted as "First Replat of Levon's Minor Subdivision".
The new building will 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.
A 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 an approximate .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 constructed as
part of Phase 1 to pass 9.98 cfs.
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.
Major Amendment
to the
FINAL STORM DRAINAGE
and
EROSION CONTROL REPORT
for
Levon's 2nd
Warehouse and Office Building
November 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, for '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 construction of a new 20,000sf speculative warehouse will
have on current drainage patterns in the area.
The 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
The recommendations found in this report are an integral part of the
design documents. .
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of the historical release without overtopping the pan. Accordingly, it is now
proposed to replace the pan with a new one that has the capacity to pass 133% of
Q 100.
This report utilizes a portion of the calculations included in the previous
report. Copies of those calculations with appropriate revisions are attached herein
as part of this report.
All design, except where variances are requested herein, 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.
November 7, 2001
Structured Engineering
318 East Oak Street
Fort Collins, CO 80524
Phone (970)-495-0810
Fax (970)-224-1314
Mr. Basil Hamden
Stormwater Utility
City of Fort Collins
PO Box 580
Fort Collins, Colorado 80522
Dear Basil,
Attached is a Major Amendment to the storm drainage report for Levon's .
2nd Warehouse and Office Building P.D.P. This report revises the earlier report,
dated May 7, revised June 18, and approved by the Fort Collins Stormwater Utility
July 26, 2001.
Because of the strong potential for a school being at least a partial tenant in
the speculative building, the Poudre Fire Authority, the Fort Collins transportation
staff and others have requested that moderate revisions to the interior drives and
parking be performed to facilitate smoother traffic and pedestrian circulation. This
report addresses the impact the associated increase in paving area will have on
runoff.
In brief, new and revised runoff calculations contained in this report indicate
an increase in site runoff from approximately 13.5 cfs to 16.4 cfs will occur. Two
alternatives were studied to determine how to best handle the increase in runoff.
The two alternatives considered were:
A. Increase the release rate from the site above the historical 10
(9.98) cfs to a number maintaining the present storage capacity and the already
sub -standard freeboard in the pond (presently 9" instead of the standard 12").
B. Maintain the historical 10 cfs release rate and accept the additional
runoff volume in the pond, further reducing further the available freeboard (from 9"
to 7"). (Because of site constraints, additional fill that would be required to
increase the freeboard also subtracts from the volume available to store runoff).
It was decided to maintain the pond grading as already proposed and further
decrease the remaining freeboard. This will allow the new developed runoff to
release at the historical rate of 10 cfs.
Additionally, inspection of the existing cross pan in Hemlock Street at the
southwest corner of the site indicates there is insufficient capacity to pass 133%
I
I
Major Amendment
to the
O
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
November 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