HomeMy WebLinkAboutFOSSIL CREEK NURSERY PUD - FINAL - 40-95A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFossil Creek Nursery P.U.D. November 20, 1995
Final Drainage Report Page 8
APPENDIX
PAGE
Exhibits......................................................................... 1 - 2
Historic Hydrology.......................................................... 3 - 5
Developed Hydrology...................................................... 6 - 15
Developed Detention....................................................... 16 - 26
Design of Culverts.......................................................... 27 - 41
Design of Drainage Swales................................................ 42 - 48
Erosion Control Cost Estimate ................................................ 49
Fossil Creek Nursery P.U.D. November 20, 1995
Final Drainage Report Page 7
REFERENCES
1. Fossil Creek Drainage Basin Master Drainageway Planning
Study, City of Fort Collins, Larimer County, Colorado, Simons,
Li & Associates, Inc., August, 1982.
2. Overall Development Plan Drainage Report for Shenandoah,
City of Fort Collins, Colorado, Northern Engineering Services,
Inc., October 16,.1995.
3. Soil Survey of Larimer.County Area. Colorado, U.S.
Department of Agriculture, Soil Conservation Service and
Forest Service, Issued December, 1980.
4. Storm Drainage Design Criteria and Construction Standards,
City of Fort Collins, Colorado, May, 1984.
5. Drainage Criteria Maunal, Urban Drainage and Flood Control
District, Wright -McLaughlin Engineers, Denver, Colorado,
March, 1969.
6. Final Drainage and Erosion Control Study for Ridgewood Hills
P.U.D. First Filing, RBD; Inc. Engineering Consultants,
November 23, 1994.
Fossil Creek Nursery P.U.D. November 20, 1995
Final Drainage Report Page 6
During a 100-year event, stonmwater will be released to the existing downstream on -
site wetlands and from there will be conveyed to Robert Benson Lake.
Grass -Lined Swales A and B will provide initial treatment of stormwater prior to the
retention/detention pond. Table 4.1 (Pg 48 in the Appendix) specifies the criteria used in the
design of Swale A. Both Swales' A & B will be vegetated with wetland plants in the
flowline and seeded sideslopes as per specifications given on the Grading Plan. The velocity
in Swale A for the two-year design storm is less than 2 fps per the criteria established in the
Urban Drainage and Flood Control District Drainage Criteria Manual.
The majority of the chemical products used on -site are controlled release fertilizers.
Because this site is a commercial nursery rather than an agricultural field, fertilizers and
whatever pesticides may be needed will be spot applied on an as needed basis rather than in
broad surface coverage.
VI. EROSION CONTROL
6.1 Erosion Control Plan
Permanent erosion control will be provided in all swales, ponds and disturbed areas
using the seed mix specified on the Grading Plan.
Temporary sediment control consisting of straw bale dikes will be used in swales until
permanent vegetation is established. Silt fencing will also be required around the existing
wetlands.
VII. CONCLUSIONS
7.1 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.
7.2 Summary of Drainage Concept
The overall drainage concept for the Fossil Creek Nursery site has taken into
consideration all studies known to have an influence on the proposed site. The hydraulic and
hydrologic analyses conducted for this study have been performed in a manner consistent
with standard practice and principles of civil engineering.
Fossil Creek Nursery P.U.D. November 20, 1995
Final Drainage Report Page 5
f The proposed retention/detention pond will be clay lined to retain water below an
i elevation of 5013.00. The retention volume required was determined by estimating the
volume of runoff for both existing(0:68 ac-ft) and proposed(0.74 ac-ft) conditions for the
P 100-yr, 1-hr storm (See Pages 5 & 11 in the Appendix). The difference between these
P volumes 0.74 - 0.68 ac-ft = 0.06 ac-ft was doubled to determine the minimum amount of
retention required or 0.12 ac-ft.
V. WATER QUALITY
5.1 Stormwater Ouality Enhancement
Due to the nature of the proposed use of the site, constant runoff will be inherent due
to irrigation of trees and shrubs with additional runoff occurring during storm events. This
irrigation water, supplied by the North Louden Ditch Company, will be collected in the
proposed clay -lined retention/detention pond. Water that is received in the pond due to both
irrigation and stormwater runoff will be recirculated by mechanical pumping from the pond
to an irrigation system and continuously recycled for use on -site thus containing controlled
release fertilizer and pesticides which are used on -site.
The majority of the year, the retention/detention pond will contain recycled irrigation
water, which represents a permanent pool of water. This permanent pool is mixed with
stormwater during storm runoff events. _ Permanent retention and temporary detention is
provided above the permanent pool to allow additional sedimentation and capture in total a
volume of runoff from frequently occurring storms. The retention pond will require regular
maintenance to remove sediment.
Methods outlined in the Drainage Criteria Manual. Volume 3, by the Urban Drainage
and Flood Control District, for nonstructural Best Management Practices (BMP's) have been
utilized in stormwater quality enhancement and design of on -site BMP's.
The retention/detention pond has been designed according to Section A -A shown in
Figure 6-1 (Page 26a in Appendix) with the recycled irrigation water representing the
permanent pool. The proposed aquatic pond will be constructed in the same manner. Due to
a possible large influx of off -site stormwater (assuming the Louden Ditch is full), the space
for an extended detention based on water quality capture volume (WQCV) is not available.
However, the first flush of any storm, which has the most deteriorated water quality, will
pass through the onsite retention/detention pond as well as wetland fields for water quality
enhancement.
Fossil Creek Nursery P.U.D. November 20, 1995
Final Drainage Report Page 4
4.5 Drainage Concept
Developed stormwater will be -conveyed to an on -site retention/detention facility via
grasslined swales. Stormwater will be retained for all storms with a frequency up to and
including 100-years. -The 100-year event will be the only storm to, be detained and will be
released at a rate of 0.19 cfs/acre or, 14.59 acres x 0.19 cfs/acre= 2.77 cfs for on -site
developed stormwater. This allowable release rate was established by RBD, Inc.
Engineering Consultants as part of the Final Drainage and Erosion Control Study for
Ridgewood Hills P.U.D. (See Ref. 6).
i.
Off -site stormwater entering the site.from the west (31.4 cfs at Design Point 02) will
be routed through the pond undetained: It has been assumed that the Louden Irrigation Ditch
is flowing full at the time of the major event. and off -site stormwater would not be
intercepted by the ditch, this is the worst case scenario.
The total release rate from the pond, as determined by routing of the 100-year storm,
is 30.69 cfs at 33.0 minutes with a pond water surface elevation of 5019.62 (See page 18 in
the Appendix). This release is less than the total inflow from the off -site basin and well
below an allowable release of 31.4 (Off -site)+ 2.77 (On -site)= 34.2 cfs
The site has been graded in a manner that poses the least amount of disturbance to the
existing topography. The North Louden Irrigation Ditch requires only minor relocation and
the addition of three (3) culvert crossings (Culverts' C-1 thru C-4). Design hydrology (15
cfs) used to size the proposed crossings was provided by the North Louden Irrigation
Company and the computer program "HY8" was used to develop a rating curve for each
culvert (See Appendix).
The majority of the site will be routed to the proposed retention/detention facility with
only a small portion (Basin D1= 1.0 acres) draining to South College Avenue undetained
compared to the area of historic Basin H2 (1.413 acres).
The existing 10' curb inlet in the flowline of South College will require modification
due to the location of the proposed entrance and will most likely comprise of a series of
frames and grates similar to the CDOT Type 13 Inlet. Final design of the modified inlet will
be done as part of final revisions as the State Department of Transportation is currently
reviewing the location of the entrance and is subject to change.
The proposed aquatic pond will not be drainage related and is strictly for display of
aquatic plants. The pond will be clay lined to retain water supplied by the Louden Irrigation
Company through the existing pond to the west.
Fossil Creek Nursery P.U.D. November 20, 1995
Final Drainage Report Page 3
IV. DEVELOPED DRAINAGE BASIN
I 4.1 Developed Conditions
The proposed development of the site includes:
• -expansion of an'existing structure into a caretakers residence,
I • conversion of ,existing buildings into sales and information centers,
• a proposed greenhouse,
• an asphalt drive and parking,
• utilities,
• an on -site retention/detention facility,
• a fire access drive,
• tree growing areas,
• aquatic pond.
The existing Louden irrigation ditch will require relocation through a portion of the
site.
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 referencedfor this Final Drainage Study.
4.3 Hydrologic Criteria
The Rational Method has been used to estimate peak stormwater runoff from the
developed site. The initial 2-year and major 100-year design storms have been used in the
evaluation of the proposed drainage system. Rainfall intensity data for the Rational Method
has been taken from Figure 3-1 of SDDCM. A maximum irrigation flow of 15 cfs has been
confirmed with the Louden Ditch Company for sizing of proposed culvert crossings.
Routing of the detention pond .was done with the use of the computer program module
"Watershed Modeling" by Eagle Point using the Modified Puls method. This model
incorporates the combined inflow hydrograph developed at Design Point D3 (See Page 16 in
the Appendix) for both on -site and off -site basins, the pond stage -storage rating curve and the
outlet rating curve of the 24" RCP (See pages 21 -26). Results of the routing are shown on
pages 17 - 20 in the Appendix.
4.4 Hydraulic Criteria
The City of Fort Collins Storm Drainage Design Criteria has been used for all
hydraulic calculations.
Fossil Creek Nursery P.U.D. November 20, 1995
Final Drainage Report Page 2
U. SITE LOCATION AND DESCRIPTION
2.1 Site Location
The project is located in the Northeast Quarter of Section 14, Township 6
North, Range 69 West of the 6th Principal Meridian in Fort Collins, Colorado. The project
is bounded by South College Avenue.(U.S. Route 287) to the east, County Road 23 to the
south, and W. Trilby Road on the north. (See Vicinity Map).
2.2 Site Description
The Fossil Creek Nursery site covers approximately 14.59 acres, the majority of
which is pasture land with a single residence and outbuildings. The Soil Survey of Larimer
County Area. Colorado (Reference 3) was used initially to identify the soils on -site. A total
of three (3) soil classifications were found at the site ranging from Renohill Clay Loam with
slow permeability and rapid runoff to. Longmont Clay, with low permeability and slow
runoff, in the low-lying areas. (See Exhibit 1). The Geotechnical Engineering Report. Fossil
Creek Nursery. P.U.D., Fort Collins, Colorado, July 20, 1995, by Terracon Consultants
Western, Inc. was also referred to in the design of site drainage.
2.3 Irrigation Ditches and Reservoirs
The Louden irrigation ditch currently traverses the site flowing from south to north at
slopes ranging from 0.1025% to 0.1881%.
III. HISTORIC DRAINAGE BASIN
3.1 Major Basin Description
The site is located in the Fossil Creek Drainage Basin but is entirely within a non-
contributing area (See Exhibit 2) which drains to Robert Benson Lake.
3.2 Historic Drainage Patterns
The site drains generally from west to east, at slopes ranging from 6.7% to 11.1%, to
an existing wetlands adjacent to South College Avenue in the southeast comer of the site.
Stormwater from this non-contributing area is conveyed under College Avenue to Benson
Lake through an existing twenty-four (24) inch RCP. Off -site runoff enters the site along the
entire west propertyline, from land which is currently vacant, and is intercepted by the
existing Louden Irrigation Ditch.
Final Drainage Report
for
Fossil Creek Nursery P.U.D.
I. INTRODUCTION
1.1 Objective
To provide a final drainage scheme for the proposed Fossil Creek Nursery
planned unit development based on design criteria and master drainageway planning adopted
by the City of Fort Collins, Colorado. Specific objectives as part of this study are:
1. To adopt the hydrology and hydraulics contained in the Fossil Creek
Drainage Basin Master Drainageway Planning Study
(Reference 1),
2. To consider all off -site stormwater runoff from adjacent properties and
the design intent of future adjacent developments (Reference 2),
3. To consider utilizing any existing adjacent stormwater appurtenances,
4. To consider any possible adverse effects downstream of the
development due. to developed stormwater,
5. To minimize the impacts of development on the existing on -site
wetlands.
1.2 Mapping and Surveying
A field survey of the site was conducted by Landstar Surveying, Inc.
Loveland, Colorado in July, 1995. Based on this field survey information, topographic
mapping was computer generated by Northern Engineering Services, Inc. with a contour
interval of one (1) foot.
1.3 Site Reconnaissance
A site visit was conducted on Saturday October 21, 1995 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
and storm inlets were verified as well as their condition and flow direction.
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Northern Engineering Services, Inc.
November 20, 1995
City of Fort Collins
Stormwater Utility
235 Mathews
Fort Collins, Colorado 80522
RE: Fossil Creek Nursery P.U.D.
Fort Collins, Colorado
Project Number: 9539.00
Dear Staff:
Northern Engineering is pleased to submit this Final Drainage Report for Fossil Creek
Nursery P.U.D. 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 S
Mary B. Wohnrade, P.E.
420 S. Howes, Suite 202 • Fort Collins, Colorado 80521 0 (970) 221-4158 • Fax (970) 221-4159
Final Drainage Report
.for
Fossil Creek Nursery P.U.D.
City of Fort Collins, Colorado
November 20, 1995
Prepared For:
Jack Fetig
Fossil Creek Nursery
Fort Collins, Colorado 80525
Prepared By:
Northern Engineering Services, Inc.
420 South Howes, Suite 202
Fort Collins, Colorado 80521
(970)221-4158
Fax (970)221-4159
Project Number: 9539.00
First Final Submittal