HomeMy WebLinkAboutSPANJER OFFICE BUILDING - PDP - 25-01 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTI
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APPENDIX
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All construction activities must also comply with the State of Colorado permitting process for
Stormwater Discharges associated with construction activities. A Colorado Department of
Health NPDES discharge permit will be required before any construction grading can begin.
VI CONCLUSIONS
Compliance with Standards
All computations within this report have been completed in compliance with the City of Fort
Collins Storm Drainage Design Criteria.
Drainage Concept
The proposed drainage concepts presented in this study and shown on the grading and
drainage plans adequately provide for the conveyance of developed runoff from the proposed
development.
If groundwater is encountered during construction, and dewatering is used to install utilities, a
State of Colorado Construction Dewatering Wastewater Discharge Permit will be required.
Stormwater Quality
Because water quality is important to this developer, water quality mechanisms will be
incorporated into all aspects of construction and final design of drainage systems.
Erosion Control Concepts
Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites, at the time
of Final Design, the erosion control performance standard will need to be calculated and
appropriate measures taken to control rain and wind -erosion from the site.
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Lot 7 (basins H-1. and H-2) can be approximated to be 0.36 cfs in the 10 year storm event and
0.76% cfs in the 100 year storm event. The release from basin D-6, which will sheet flow from
our site, can be approximated to be 0.0396 cfs for the 10 year storm event and 0.0792 cfs in the
100 year storm event, thereby reducing the existing by a factor of 10.
As mentioned above, the master plans drainage plans for this area do not require detention.
Therefore, the entire site will be released un-detained to the existing creek north of Fossil Creek.
A 60' wide drainage easement has been obtained to provide access to this existing drainage -
way. Also, the impacts of this development do not significantly increase the flows downstream.
IV WATER QUALITY
In compliance with City of Fort Collins criteria, the Water Quality Capture Volume Ponds have
been designed. Sub -basins D-1, D-2 and D-3 are routed to WQCV Pond A, located in the
southeast area of sub -basin D-3.
Sub -basin D-5 is routed to the southwest area of the sub -basin to WQCV Pond B.
Based on criteria for a 40-hour dry extended detention basin outlined in the Urban Storm
Drainage Criteria Manual, Volume 3 — Best Management Practices by the Urban Drainage and
Flood Control District (September 1999), the reuired volume of Pond A is 247.0 cubic feet,
obtained at the elevation of 5056.89; the required volume of Pond B is 313.6 cubic feet, obtained
at the elevation of 5057.37.
V EROSION CONTROL
General Concept
This site lies within the Moderate Rainfall Erodibility Zone, and the Moderate Wind Erodibility
Zone, per the City of Fort Collins zone maps. The desired effectiveness goal for this site was
estimated to be approximately 83%.
The intent of the erosion control plan for the site includes the following guidelines. As these
measures can vary depending on the time of year construction activities take place, as well as
the construction window involved, we would look to the contractor to work closely with the City to
insure the intent of the plan is generally complied with.
It is the intent of the owner to move quickly ahead with development once over -lot grading takes
place. It is anticipated that over -lot grading would start sometime around March, 1999, or
sooner if possible. Therefore, once over -lot grading and utilities have been completed, the
owner would like to re -stabilize all disturbed areas, either with vegetative means, or by hard
surfaces. In no cases shall re -stabilization occur more than 30 days after disturbance.
In addition, silt fence will be provided around most of the exterior of the disturbed areas, in
particular around the north, east and south property lines. In addition, a gravel inlet filter will be
installed at the curb opening located within sub -basin D-5. It is our intent to restrict construction
vehicular traffic to Cameron Drive, and to install a vehicle truck -wash pad at the entrance to the
site.
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III DEVELOPED DRAINAGE
Design Criteria and Reference
Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design Criteria Manual,
and Storm Drainage Criteria Manual by the Urban Drainage and Flood Control District have
been used for this Drainage Study.
Hydrologic Criteria
The Rational Method was used to estimate peak stormwater runoff from the proposed site. The
10 year storm event and the 100 year storm event was used to evaluate the proposed drainage
system. Rainfall intensity data for the Rational Method was taken from the City of Fort Collins
Stormwater Utility Intensity curves (Figure 3-1).
Hydraulic Criteria
City of Fort Collins Storm Drainage Criteria has been used for all hydraulic calculations.
Drainage Concepts
The site has been broken down into 6 smaller sub -basins. A copy of the sub -basin layout has
been included in the appendix of this report. Sub -basins D-1,2 and 3 generally drain from north
to south, and to the existing curb and gutter in the Frontage Road. Sub -basins D-4 and 5
generally drain from the north to the south and to the existing curb and gutter in Cameron Drive.
Sub -basin D-6 represents a small area of the site which will sheet flow to the existing Day Care
center.
Sub -basin D-1 represents a very small portion of the site (approximately 0.01 acres) between
our proposed curb and gutter, and the northerly property line. This site will release
approximately 0.0198 cfs in the 10 year storm event and approximately 0.0396 cfs in the 100
year storm event to the existing curb and gutter north of our site, which in turn will be conveyed
to sub -basin D-3 via a 3' cross pan. No impervious surfaces are being included within this basin.
Sub -basin D-2 will surface drain developed runoff via curb and gutter to a cross pan which
empties through a 2'wide curb opening into a grass -lined swale contained in sub -basin D-3.
Sub -basin D-3 will convey developed runoff around the new building to water quality capture
volume Pond A, then released to the south to the existing creek north of Fossil Creek.
D4 represents the westerly part of the site, which will sheet flow to existing Cameron Drive.
Sub -basin D-5 will be conveyed to a 2'wide curb opening to water quality capture volume Pond
B, then released through the outlet structure to a 2'wide sidewalk culvert, and on to Cameron
Drive. Developed flows will be conveyed to the southeast via existing curb and gutter, to the
Frontage Road and combined with the developed flows described above, will be conveyed to an
existing creek just north of Fossil Creek.
D-6, approximately 0.02 acres, represents the area between our proposed south curb and
gutter, and the southerly property line. Historically, the sheet flows to the Day Care center from
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Final Drainage Report for Cameron Park Lot 7
I GENERAL LOCATION AND SITE DESCRIPTION
The Cameron Park Lot 7 project is located between Cameron Drive and the Frontage Road
within the Cameron Park development. The site can also be described as a portion of Section 2,
Township 6 North, Range 69 West of the a PM, City of Fort Collins, Larimer County, Colorado.
A vicinity map of the site is included in the appendix of this report. This site is also located within
the Fossil Creek Major Drainage Basin.
Lot 7 includes approximately 0.45 acres. The site is presently undeveloped, and consists mainly
of native grasses. The site generally slopes from the north to the south at approximately 6%.
Plans for this site include a commercial building, with associated parking.
II HISTORIC DRAINAGE
As mentioned above, the site is presently undeveloped, and consists mainly of native grasses
and vegetation. Cameron Drive along the westerly side of the project has been built, as well as
the Frontage Road along the easterly boundary of the project. A Day Care center has been built
on Lot 6, south of this project, and a small office building and parking lot has been built on Lot 8,
north of this project.
The site was broken into 2 historic basins, designated as H-1 and H-2. H-1 represented the
westerly end of the site which presently sheet flows generally towards the Day Care center and
Cameron Drive. H-2 represents the easterly end of the site, which also generally sheet flows
from the northwest to the southeast across the existing Day Care center and to the Frontage
Road. Both the Frontage Road and Cameron Drive have existing 24" culvert under College Ave.
The developer of the Fossil Creek Office Park has obtained a 60' drainage easement from the
termination point of the Frontage Road to Fossil Creek for the purposes of conveying stormwater
runoff thereby eliminating the need for onsite detention. It is also our understanding that this
existing 60' wide drainage easement is for all of the lots in Cameron Park.
The existing topography is such that Lots 9 & 15 generally sheet flow across this site (Shown in
the appendix as historic basins H-3 and 1-14). The owner is concerned about not blocking their
historic runoff, and will provide an interception swale along the northwesterly boundary of his
site, and will allow runoff around his storage structures and through his parking lot to the existing
Frontage Road. He would be willing to grant a drainage easement to the owners of these lots
should that need ever arise.
Lot 8 was developed into a small office complex with an attached parking lot south of the
building. Drainage from this site is directed to the southeast across this parking lot, and directed
by curb and gutter to a small concrete drainage pan which allows flows to enter the existing curb
and gutter of the Frontage Road.
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SERVICES INC
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July 10, 2001
Mr. Glen Schlueter
City of Fort Collins
Stormwater utility
700 Wood Street
Fort Collins, Colorado 80522
RE: Cameron Park Lot 7
Fort Collins, Colorado
Project Number: 9858.00
Dear Glen:
Northern Engineering is elated to submit this revised Final Drainage Report for Cameron Park
Lot 7 for your review. It represents a study of existing and proposed stormwater characteristics
of the project site.
This report was prepared in compliance with technical criteria set forth in the City of Fort Collins,
Storm Drainage Design Criteria and Construction Standards manual.
If you should have any questions or comments as you review this report, please fell free to
contact me at your convenience.
Sincerely,
HERN ENGINEERING SERVICES,
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Roger A. Curtiss, P. E. ; 4 27362 N
cc: Steve Spanjer — Spanjer
420 SOUTH HOWES, SUITE 202, FORT COLLINS, COLORADO 80521, (970) 221.4158, FAX (970) 221-4159
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Final Drainage Report
For
Cameron Park, Lot 7
Fort Collins, Colorado
July 10, 2001
Prepared For:
Spanjer Construction Corp.
PO Box 9644
Office 5731 Bueno Drive, #C
Fort Collins, Colorado 80525
Prepared By:
Northern Engineering Services, Inc.
420 South Howes St., Suite 202
Fort Collins, Colorado 80521
(970) 221-4158
Fax (970) 221-4159
Project Number: 9856.00
Initial Submittal