HomeMy WebLinkAboutELEMENTARY SCHOOL AT RIDGEWOOD HILLS ( COYOTE RIDGE) - SITE PLAN ADVISORY REVIEW - 28-06 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTIf, at the -time of construction, groundwater is encountered, a Colorado Department of
Health Construction De watering Permit will be required.
7. REFERENCES
1. City of Fort Collins, "Storm Drainage Criteria Manual", (SDCM), dated March,
1986.
2. Urban Drainage and Flood Control District, "Urban Storm Drainage Criteria
Manual", Volumes 1 and 2, dated June 2001 and Volume 3, dated September
2001.
3. City of Fort Collins, "Stormwater Basins Map", dated June 1, 2004.
4. Final Drainage Report for Ridgewood Hills P.U.D. Third Filing by Nolte
Engineering dated June 16, 2000.
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5. EROSION CONTROL
5.1 General Concept
The potential exists for silt movement from the site and into the existing drainage areas
on the east side of the site. Potential also exists for tracking of mud onto existing streets
which could then wash into existing storm systems. The required performance standard
for the site is 81%. All reasonable erosion control measures are proposed. Due to the site
configuration and offsite location of the detention, maximum onsite performance will be
reached with implementation of soil roughening, silt fence, straw barriers and inlet
protection.
The erosion control escrow amount is $8,069.
5.2 Specific Details
To limit the amount of silt leaving the site several erosion control measures shall be
implemented during construction. A vehicle tracking pad shall be installed at the location
shown on the plan to control mud from being tracked onto the existing pavement. Inlet
protection will be used around all inlets throughout construction. During overlot grading,
disturbed areas are to be kept in a roughened condition and watered to reduce wind
erosion. Silt fence will be used to prevent non -point erosion where possible. Wattles will
be used within drainage swales to prevent erosion along the concentrated flow path.
6. CONCLUSIONS
6.1. Compliance with Standards
All computations that have been completed within this report are in compliance with the
Storm Drainage Design Criteria Manual. No variances are requested at this time.
6.2. Drainage Concept
All runoff from the site will be directed to existing drainage facilities in Avondale Road.
The proposed drainage concepts presented in this report and on the construction plans
adequately provide protection from flooding. Conveyance elements have been designed
to pass required flows and to minimize future maintenance.
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side of the parking lot were it is directed to the Avondale Road. The calculated 100-yr
flow rate from this basin is 13.0-cfs.
Sub -basin 0-1 and 0-2 are small offsite basins, both within basin 925 of the Nolte
report, draining onto the site from the west and the south. These basins are 0.78 and 0.94
acres respectively containing parts of the surrounding residential area and shared
community landscaping.. The existing runoff coefficients were calculated to be 0.24 and
0.36 respectively. Runoff from the basins sheet flows through basin 2 into the drainage
swale, which was sized to accommodate this runoff. The calculated 100-yr flow rate
from these combined basins is 6.6-cfs.
4.3. Water Quality Considerations
The Ridgewood Hills P.U.D., Third Filing design provides detention ponds with water
quality structures for the development. The site is located in basin 925 of that design and
was included in water quality volumes calculations for the development using a percent
imperviousness of 50%. The storm sewer on Avondale Road is the collection point for
this site. That storm sewer directs runoff to detention pond 1 from Ridgewood Hills
P.U.D Third Filing. Pond 1 provides 10.67 ac-ft of detention storage and 0.75 ac-ft of
storage for water quality. The proposed site was calculated to have a smaller percent
imperviousness than was used in the Ridgewood Hills P.U.D., Third Filing design and
will conform the water quality constraints of that design. No onsite water quality
detention is proposed with this project.
4.4. -Drainage Summary
Drainage patterns for this project will meet the requirements of the City of Fort Collins
Drainage Criteria. Drainage has been designed to adequately convey the 100-year storm
event to existing drainage facilities. Emergency overflow from offsite basins has been
provided for in the design of the onsite drainage facilities without inundating the
proposed school building. The City of Fort Collins will be responsible for maintenance of
the existing and proposed storm drainage facilities located within the right-of-way. These
facilities will be Class III RCP to conform to the City of Fort Collins criteria. The
drainage facilities located outside of the right of way (including all private storm sewer
systems, and the landscape and roof drain system and inlets) will be maintained by the
property owner.
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4. DRAINAGE FACILITY DESIGN
4.1. General Concept
Proposed flow patterns will match existing patterns and those required by adjacent
developments as closely as possible. Runoff will be directed to drainage facilities on
Avondale Road. Emergency overflow from offsite has been accounted for in the drainage
design and will be routed to Avondale Road with onsite flow.
The swale from the Nolte Engineering design was originally designed to convey the full
runoff flow rate from all offsite drainage basins simultaneously. The re-routed swale,
directing offsite overflow to Avondale Road was sized to accommodate runoff from the
site and flow from each offsite concentration point assuming one overflow event at a
time.
4.2. Specific Flow Routing
There are 5 basins within this project including 2 offsite basins. The following is a
summary of the 100-year flow routing from the site:
Sub -basin 1 contains the northeast half of the proposed school building, kindergarten
play areas and the bus loop. The basin area is 1.64-acres with a calculated developed
runoff coefficient 0.46. Runoff sheet flows to the bus loop where it is conveyed east to
Avondale Road. The calculated 100-yr flow rate from this basin is 9.0-cfs.
Sub -basin 2 includes the west portion of the building, proposed future modular
classrooms, grass sports fields and the play ground. The basin area is 3.55-acres with a
developed runoff coefficient calculated to be 0.28. Runoff sheet flows to the rerouted
drainage swale near the south property boundary and is conveyed to Avondale Road. The
swale was designed to accommodate flow from this basin and the offsite basins including
emergency overflow from basin 904, 905, 906, 907, 911 and 913 from the Ridgewood
Hills P.U.D Third Filing drainage report. The calculated 100-yr flow rate from this basin
is 13.1-cfs. The maximum cumulative flow assumed for the design from this basin, basin
0-1, basin 0-2 and emergency overflow is 47.5-cfs.
Sub -basin 3 includes the east portion of the building and the parking lot. The basin area
is 2.01-acres with a developed runoff coefficient of 0.59. Runoff sheet flows to the east
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3.3. Offsite Flows
Swales were designed to route emergency overflow from offsite basins through the site in
the Ridgewood Hills P.U.D., Third Filing drainage report. Swale section C-C was
designed for emergency overflow from basins 904 and 905 (Agate Court) with a 100-year
overflow rate of 10.96-cfs.
Swale section D-D was designed for flow from swale C-C and additional emergency
overflow from basins 906 and 907 (Prichett Court) with a cumulative 100-year flow rate
of 31.63-cfs of this, basins 906 and 907 were expected to contribute 20.67-cfs of
emergency overflow to the site. Swale section H-H was designed for emergency overflow
from basins 911 and 913 (Jansen Drive) with a cumulative 100-year flow rate of 27.35-
cfs.
Drainage facilities were designed to accommodate the cumulative runoff from individual
emergency overflow from each of these basins and onsite runoff at the designed
confluence of the overflow and onsite runoff. The drainage Swales were designed for
failure of one drainage facility at a time. It was assumed that there is negligible
probability of simultaneous failure of multiple drainage facilities.
3.4. Hydrologic Criteria
Runoff computations were prepared for the 2-year minor and 100-year major storm
events utilizing the Rational Method. All hydrologic calculations associated .with the
basins are included in Appendix B of this report. Standard Form 8 (SF-8) provides time
of concentration calculations for all sub -basins. Standard Form 9 (SF-9) provides a
summary of the design flows for all sub -basins and design points associated with this site.
3.5. Hydraulic Criteria
All hydraulic calculations, including pipe and swale sizing, for this site are based on the
100-year storm in accordance with the City of Fort Collins Drainage Criteria. Hydraulic
elements have been designed to convey onsite 100-year flows and emergency overflows
from the adjacent basins to Avondale Road. Existing hydraulic elements are in place to
convey the 100-year runoff from Avondale Road to Detention Pond 1.
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2.2. Sub -basin Description
The property is located within the basin described in the Ridgewood Hills P.U.D., Third
Filing design as basin 925. The drainage report for Ridgewood Hills P.U.D., Third Filing
states that the expected developed runoff from this site during the 100-year storm event is
43.93-cfs with an expected overall runoff coefficient of 0.70 and 50% imperviousness.
After development the proposed imperviousness for the site will be 45%, corresponding
to a 100-year runoff coefficient of 0.59. The overall proposed 100-year runoff is 33.9-cfs
resulting in a 10-cfs reduction in expected 100-year runoff for the site. The site was
divided into 5-individual basins detailed in section 4.2. All basins drain to Avondale road.
3. DRAINAGE DESIGN CRITERIA
3.1. Regulations
This report was prepared to meet or exceed the "City of Fort Collins Storm Drainage
Design Criteria Manual' specifications. Where applicable, the criteria established in the
"Urban Storm Drainage Criteria Manual" (UDFCD), 2001, developed by the Denver
Regional Council of Governments, has been implemented.
3.2. Development Criteria Reference and Constraints
The runoff from this project will be routed to conform to existing drainage patterns.
Offsite emergency overflow from basins 904, 905, 906, 907, 911 and 913 from.
Ridgewood Hills P.U.D., Third Filing were accounted for in the drainage design. These
basins are directly adjacent to the site.
Basins 911 and 913 are located to the south and runoff from these basins concentrates at
an inlet by the southwest corner of the site. Basins 906 and 907 are located to the west of
the site and runoff from these basins concentrates west of the site at the end of Prichett
Court. Emergency overflow from these basins will be collected in the re-routed swale.
Basins 904 and 905 are located to the west of the site and runoff from these basins
concentrates northwest of the site at the end of Agate Court. Emergency overflow from
these basins will sheet flow to the bus loop where it will be directed to Avondale Road.
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1. GENERAL LOCATION AND DESCRIPTION
1.1. Location
The proposed Coyote Ridge Elementary School site is located in Ridgewood Hills
P.U.D., Third Filing, Tract U between Jansen Dive and Strasburg Drive west of and
adjacent to Avondale Road. The property is located in the SE quarter of Section 14,
Township 6 North, Range 69 West of the Sixth Principal Meridian, in the City of Fort
Collins, Larimer County, Colorado. See vicinity map located in Appendix A. The project
site is bounded on the north by a city park, on the east by Avondale Road and on the
south and west by single family residential housing.
1.2. Description of Project
This site is located on 7.2-acres of land. The land is naturally vegetated and slopes at
approximately 2.5 %, toward Avondale Road. The property is currently undeveloped,
containing emergency overflow drainage facilities for the surrounding development.
Existing runoff sheet flows to Avondale Road where it is conveyed via curb and gutter, to
an existing inlet and then to an existing detention pond. Drainage facilities for offsite
flows include a drainage swale to convey emergency overflow from Agate Court, Prichett
Court and Jansen Drive south and east to Avondale Road.
The project is proposed to include a school building, drives, parking lot, play ground and
sports fields. It is proposed to reroute the drainage swale through the site to accommodate
emergency overflows from the existing development west of the site. Drainage patterns
will remain similar to existing conditions. Refer to section 4 of this report for more
detailed flow routing.
2. DRAINAGE BASINS AND SUB -BASINS
2.1. Major Basin Descriptions
Tract U of Ridgewood Hills P.U.D., Third Filing is located in the Fossil Creek Drainage
Basin as delineated by the City of Fort Collins. Runoff from the site was included in the
drainage design of the Ridgewood Hills P.U.D., Third Filing by Nolte Engineering, dated
June 2000. Both storm water and water quality detention are provided east of the site in
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TABLE OF CONTENTS
TABLEOF CONTENTS............................................................................................................... iii
1. GENERAL LOCATION AND DESCRIPTION
1.1 Location...................................................................................................................1
1.2 Description of Project..............................................................................................1
2.
DRAINAGE BASINS AND SUB -BASINS
2.1 Master Basin Description.........................................................................................1
2.2 Major and Sub -Basin Description............................................................................2
3.
DRAINAGE DESIGN CRITERIA
3.1 Regulations..............................................................................................................2
3.2 Offsite Flow.............................................................................................................2
3.3 Development Criteria Reference and Constraints....................................................3
3.4 Hydrologic Criteria..................................................................................................3
3.5 Hydraulic Criteria....................................................................................................3
4.
DRAINAGE FACILITY DESIGN
4.1 General Concept.......................................................................................................4
4.2 Specific Flow Routing.............................................................................................4
4.3 Water Quality Considerations..................................................................................5
4.4 Drainage Summary ...................................................................................................5
5.
EROSION CONTROL
5.1 General Concept.......................................................................................................6
5.2 Specific Details........................................................................................................6
6. CONCLUSIONS
6.1 Compliance with Standards.............................................:......................................6
6.2 Drainage Concept.....................................................................................................6
7. REFERENCES....................................................................................................................7
APPENDICES
A Vicinity Map
B Hydrologic Computations
C Hydraulic Computations
D Erosion Control Calculations
E Excerpts from Previous Reports
F Tables and Figures
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North Star
o.design, inc,
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January 23, 2006
Mr. Basil Hamdan
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80522-0580
RE: Final Drainage and Erosion Control Report for Coyote Ridge Elementary School at
Ridgewood Hills P.U.D. Third Filing, Tract U
Dear Basil,
I am pleased to submit for your review and approval, this Final Drainage and Erosion Control
Report for the proposed Coyote Ridge Elementary School located at the northwest comer of
Jansen Road and Avondale Drive. Hydraulic and hydrologic calculations have been completed
in compliance with the City of Fort Collins Storm Drainage Manual.
I appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
Sincerely,
Patricia Kroetch, P.E.
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700 Automation Drive, Unit I Windsor, Colorado 80550
970-686-6939 Phone 0 970-686-1188 Fax
FINAL
DRAINAGE AND EROSION CONTROL REPORT
FOR
COYOTE RIDGE ELEMENTARY SCHOOL
RIDGEWOOD HILLS P.U.D. THIRD FILING
TRACT U
Prepared for:
Thompson School District
800 S. Taft.,Avenue
Loveland, CO 80537
Prepared by:
North Star Design
700 Automation Drive, Unit I
Windsor, Colorado 80550
(970)686-6939
January 23, 2006
Job Number 210-10