HomeMy WebLinkAboutHORSETOOTH EAST BUSINESS PARK, 2ND FILING - FINAL PUD - 43-94F - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFinal Drainage Report Northern Engineering Services, Inc.
Horsetooth East Business Park, Pad G Center P.U.D.
May 15, 1998
Page 6
TABLE OF CONTENTS
PAGE
Section A:
Excerpts from Reference 1.............................................................. Al -All
Section B:
B1-
B7
Developed Hydrology ........................................ ...........................
Section C:
C 1-
CS
I Design of Inlets
Section D:
D l -
D4
Design of Storm Sewers..................................................................
Section E:
E1-
E2
I Designof Swales.....................................................................
Section F:
F1-
F3
I Design of Culverts..................................................................
I Section G:
G 1-
G5
Detention Pond Calcuations.............................................................
Section H:
Hl- H4
Designof Orifaces..................................................................
Section I:
Riprap Calculations I1- I2
......................................................................
ISection j:
Erosion Control Calculations J 1- J
...........................................................
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Final Drainage Report Northern Engineering Services, Inc.
Horsetooth East Business Park, Pad G Center P.U.D.
May 14, 1998
Page 5
REFERENCES
1). Final Drainage and Erosion Control Study for Carriage Wash P.U.D., RBD, Inc.
Engineering Consultants, October, 1995.
2.) Storm Drainage Report of Horsetooth Business Park, First Filing, Stewart and
Associates, Inc., February 1991.
3.) Storm Drainage Design Criteria and Construction Standards, City of Fort
Collins, Colorado, May, 1984.
4.) Drainage Criteria Maunal, Urban Drainage and Flood Control District, Wright -
McLaughlin Engineers, Denver, Colorado, March, 1969.
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Final Drainage Report
Horsetooth East Business
May 15, 1998
Page 4
Park, Pad G Center P.U.D.
Northern Engineering Services, Inc.
Timberline and Big Horn Drive.
Basin 5 flows east to a low point in Elk Road (Design Point 5). The flow will then
continue south in a swale along Timberline Drive to the existing detention ponds on the
Carriage Wash Site.
An existing orifice on the outlet of Pond B restricts the flow to 0.46 cfs, which is the
designed release rate from the Carriage Wash P.U.D. The orifice will be replaced to allow
flows up to 0.757 cfs (See Section H).
V. EROSION CONTROL and WATER QUALITY
5.1 Erosion Control Plan
The erosion control plan presented here is intended to control both wind and rainfall
erosion. Evaluation of the rainfall erosion control plan will be completed first, with the wind
erosion control plan to follow. The Erosion Control Reference Manual for Construction Sites
(ECRM), City of Fort Collins, has been referenced for this erosion control plan.
The proposed rainfall erosion control plan during construction will consist of temporary
structural erosion control measures. Gravel inlet filters will be placed at all area inlets and
sidewalk chases. Temporary sediment control consisting of straw bale dikes will be used in
swales until permanent vegetation is established. Riprap outlet protection provided at the
outlet of the swale will be buried with a minimum of six inches of native topsoil.
Performance standards for the City of Fort Collins to be used for "During
Construction" activities are given in Table 5.1. Computation of the "Performance Standard"
and "Effectiveness" of the Erosion and Sediment Control Plan are presented in Section ] of
this report.
The proposed wind erosion control plan during construction will consist of silt fencing.
From the Wind Erodibility Map for Fort Collins, Colorado, the site is located in a moderate
erodibility zone. From Table 4.1 (page 19 of the ECRM) the maximum barrier spacing is 200
feet. Silt fencing will be placed along the south and east property lines to act as a wind
barrier.
See the Grading and Erosion Control Plan for locations of proposed erosion control
measures.
VI. CONCLUSIONS
6.1 Compliance with Standards
All drainage analyses have been performed according to the City of Fort Collins Storm
Drainage Design Criteria Manual (SDDCM) and the Urban Drainage and Flood Control
District's Drainage Criteria Manual. The only variance requested has to do with the depth of
Pond 1. Pond 1 is parking lot detention that was required as part of the Horsetooth East
Business Park Master Drainage Plan. In order to get the required volume, the ponding depth
will need to be 23.16 inches which is greater than the standard ponding depth maximum of 18
inches.
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Final Drainage Report Northern Engineering Services, Inc.
Horsetooth East Business Park, Pad G Center P.U.D.
May 15, 1998
Page 3
• The computer program "Storm Sewer" by Eagle Point has been used to analyze
the capacity of storm sewers..
4.5 Previous Studies
Per the Final Drainage and Erosion Control Study for the Carriage Wash P.U.D.
(Reference 1), about 8.11 acres of the entire Horsetooth East Business Park, Second Filing is
to be detained onsite, requiring 1.64 ac-ft of storage with a maximum release rate of 0.17
cfs/ac. That study also determined that upstream four parking lots could provide a total of
0.34 ac-ft of storage. The use of the parking lots was then found to create a need for only
1.30 ac-ft of storage to be contained in Ponds A, B, and C on the Carriage Wash site. Using
the coefficients and release rates from the Final Drainage and Erosion Control Study for the
Carriage Wash P.U.D. , the existing ponds could accommodate 0.363 ac-ft of storage from the
Pad G site (see Section G). Using the actual coefficients from the new site plan and the FAA
Method for Pad G, 0.404 ac-ft of storage will be required (See Section G). This leaves a
deficit of 0.041 ac-ft which will be detained in the Pad G parking area.
As stated previously, the Drainage and Erosion Control Study for the Carriage Wash
P. U. D. had anticipated 0.34 ac-ft of storage in upstream parking lots. The plan seemed to
indicate detention in each of the four major parking lots for Pad A, Pad B/C, Pad D, and Pad
G. Using this basis we calculated 0.34/4 = 0.085 ac-ft of storage in the Pad G parking area.
This in combination with the storage required by the new site layout will give a parking lot
storage requirement of 0.085 + 0.041 = 0.126 ac-ft.
4.6 Drainage Concept
Basin 1 will drain overland to the southeast to a proposed area inlet (Design Point 1)
and proposed Storm Sewer Line A. This line then drains south to an existing 24"x38" HERCP
and then to existing Pond B.
Basin 2 drains overland to the south to a proposed area inlet (Design Point 2). This
basin will have detention in the parking area (Pond 1). Using the FAA Method it was
determined that the required detention in the parking lot was 0.186 ac-ft, which is more than
the 0.126 ac-ft that was previously calculated (See Section G). An orifice plate will restrict
the flow to 0.15 cfs (See Section H). This line then drains to Storm Sewer Line A and again,
south to Pond B.
Basin 3 drains overland to Automation Way as proposed in previous drainage studies
(Design Point 3).
Basin 4 flows north along Automation Way, east along Horsetooth Road, and south
along Timberline. This basin historically continued to run south along Timberline into a Type
R curb inlet at the comer of Timberline and Big Horn Drive. Due to the proposed of a turn
lane off of Timberline as part of this project, this basin will now drain to a low point in
Timberline Road (Design Point 4). The flow will enter a Type "R" curb inlet then continue
south in Storm Sewer Line C along Timberline Road to the existing curb inlet at the corner of
Final Drainage Report Northern Engineering Services, Inc.
Horsetooth East Business Park, Pad G Center P.U.D.
May 15, 1998
Page 2
3.1 Maior Basin Identification
The site is located in the Foothills Drainage Basin. Runoff from the project area will
be routed by onsite storm pipes and then to an existing storm drain system which exits the
Carriage Wash site along the south property line. These storm pipes eventually outlet to the
downstream Collindale Regional Detention Pond.
3.2 Historic Drainage Patterns
The site historically drains from northwest to southeast at slopes ranging from 0.90 to
2.70%. The majority of the site has historically drained to the south through the Carriage
Wash site and into the existing Carriage Wash detention ponds. The Storm Drainage Report
of Horsetooth Business Park (Reference 2), and the Final Drainage and Erosion Control Study
for the Carriage Wash P.U.D. (Reference 1), were used as basis' for drainage planning for the
Pad G site.
IV. DEVELOPED DRAINAGE
4.1 Developed Conditions
Planned development for Horsetooth East Business Park, Pad G includes:
• a commercial office building
• utilities including storm and sanitary sewers and water.
Off -site easements for drainage and grading will be required for this development.
4.2 Design Criteria and References
Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design
Criteria Manual (SDDCM) and Storm Drainage Criteria Manual by the Urban Drainage and
Flood Control District have been referenced for this Final Drainage Study.
4.3 Hydrologic Criteria
The Rational Method has been used to estimate peak stormwater runoff within the
developed site with a minimum time of concentration of 5.0 minutes. The initial 10-year and
major 100-year design storms have been used in the design of the proposed drainage system
which include swales, inlets and storm sewers. Rainfall intensity data for the Rational Method
has been taken from IDF curves (Figure 3-1) obtained from the "Larimer County Storm -Water
Management Manual."
4.4 Hydraulic Criteria
The City of Fort Collins Storm Drainage Design Criteria has been referenced for all
hydraulic analyses. In addition, the following computer programs have been utilized:
• The computer program "UDINLET" has been used to analyze inlet capacities;
• The computer program "Flowmaster" has been used to analyze the capacity of
proposed swales.
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Final Drainage Report
for
Horsetooth East, Pad G
Fort Collins, Colorado
May 15, 1998
I. INTRODUCTION
I 1.1 Objective
To provide a final drainage scheme for the proposed Pad G in Horsetooth East
Business Park. Specific objectives as part of this study are:
1. To adopt the hydrology and hydraulics contained in the Final Drainage
and Erosion Control Study for Carriage Wash P.U.D. (Reference 1) and
I the Storm Drainage Report of Horsetooth Business Park, First Filing
(Reference 2),
2. To consider all off -site storm water runoff from adjacent properties and
' the design intent of future adjacent developments,
3. To consider any possible adverse effects downstream of the development
due to developed stormwater.
1.2 Mapping and Surveying
Topography of the site was provided to Northern Engineering Services by Landstar
Surveying with a contour interval of one (1) foot.
1.3 Site Reconnaissance
IA site visit was conducted on April 3, 1998 by the project engineer. Based on the
topographic mapping, existing drainage basins and land use were confirmed as well as existing
structures. The location and dimensions of existing culverts were verified as well as their
condition and flow direction.
II. SITE LOCATION AND DESCRIPTION
2.1 Site Location
The site is located within Section 31, Township 7 North, Range 68 West of the 6th
Principal Meridian in Fort Collins, Colorado. The project is bounded by Timberline Road on
the east, the Carriage Wash on the south, and Automation Way on the west, (See Vicinity
Map).
2.2 Site Description
Horsetooth East Business Park, Pad G is approximately 1.918 acres and has historically
been open space. There are no existing structures on the site.
2.3 Reservoirs and Irrigation Ditches
There are no irrigation ditches or laterals located on the site.
iIII. HISTORIC DRAINAGE BASIN
PROJECT
LOCATION
HORSETOOTH ROAD
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May 14, 1998
City of Fort Collins
Stormwater Utility
235 Mathews
Fort Collins, Colorado 80522
RE: Pad G, Horsetooth East Business Park
Fort Collins, Colorado
Project Number: 9805.00
Dear Staff:
Northern Engineering Services, Inc. is pleased to submit this Final Drainage Report for
Pad G Horsetooth East Business Park for your review.
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 feel
free to contact me at your convenience.
Sincerely,
NORTHERN ENGINEERING SERVICES, INC.
Zqlissa
L.
Mary B. Wohnrade, P.E.
420 SOUTH HOWES, SUITE 202, FORT COLLINS, COLORADO 80521, (970) 221-4158, FAX (970) 221-4159
Final Drainage Report
for
Pad G
Horsetooth East Business Park
Fort Collins, Colorado
May 15, 1998
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Prepared For:
W.W. Reynolds Companies
1600 Specht Point Road
Fort Collins, Colorado 80525
Prepared By:
-NORTHERN
Northern Engineering Services, Inc
420 S. Howes, Suite 202
Fort Collins, Colorado 80521
Phone: (970)221-4158
Project Number: 9905.00