HomeMy WebLinkAboutFORT COLLINS DISCOVERY MUSEUM - FDP - 6-10/A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTN� NORTHERN
ENGINEERING Fort Collins Discovery Science Museum
References
1) Storm Drainage Design Criteria and Construction Standards, City of Fort Collins,
Colorado, Updated April 1999.
2) Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control
District, Wright -McLaughlin Engineers, Denver, Colorado, Updated June 2001.
3) Old Town Master Plan for Howes, Udall, and Magnolia Basins, Icon Engineering, Inc.,
November 2006.
Final Drainage and Erosion Control Report
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ENGINEERING Fort Collins Discovery Science Museum
' 12.0 Conclusions
' The proposed development conforms to current City Standards and floodplain regulations found
in Chapter 10 of City Code 10 . Proposed storm drainage facilities will adequately convey up to
the 100-year stone event and provide adequate treatment of storm runoff prior to discharge into
' the Cache La Poudre River. No adverse stormwater impacts are expected as a result of this
project. Final improvements will be designed in accordance with City of Fort Collins criteria.
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' Final Drainage and Erosion Control Report 5
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of 13.3 cfs (see developed runoff calculations, appendix B) will be conveyed via the pond outlet
structure and pipe to the existing sump area north of the pond, as shown on the Drainage Exhibit.
Pond information is summarized in Table 1, below.
TABLE 1— Preliminary Pond Volume Estimate
Onsite Water
Required Volume
Quality
Pond
Water Quality
0.045 ac-ft
Volume
Water Surface
4960.3
Elevation
100- ear Overflow
13.3 cfs
Water quality capture volume (WQCV) is proposed within the onsite water quality pond to
remove sediment and other pollutants from the developed runoff. Criteria for a 40-hour dry
extended detention basin outlined in the Urban Storm Drainage Criteria Manual, Volume 3 —
Best Management Practices (Reference 5) by the Urban Drainage and Flood Control District will
be used to verify adequate water quality capture volume at final design.
10.0 Additional Water Quality Measures
A Porous Landscape Detention (PLD) area has been provided along the southern perimeter of the
project site. The intent of this PLD is to provide enhancement of water quality through
infiltration of frequent storm flows. In general PLD's provide filtering, adsorption, and
biological uptake of constituents in stormwater. Lower frequency storm flows are designed to
bypass the PLD.
A landscaped island has been provided within the south parking lot. This landscaped island has
been graded to encourage infiltration and thereby enhance water quality. The area inlet within
the island has been designed with an open bottom, further encouraging infiltration.
11.0 Erosion and Sediment Control
An Erosion and Sediment Control Plan has been provided in the final construction set. The plan
addresses both temporary measures to be implemented during construction, as well as permanent
erosion control protection. Best Management Practices (BMPs) from the UDFCD and the City
of Fort Collins Erosion Control Reference Manual for Construction Sites have been utilized.
The following erosion control devices have been implemented for the project site: silt fencing
has been placed along the disturbed perimeter, wattle inlet protection has been provided at storm
inlets as well as around the water quality pond's outlet structure, and a vehicle tracking control
pad has been placed at the site's construction entrance. Riprap outlet protection has been placed
at all storm sewer outlets.
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The development will be in compliance with all applicable floodplain regulations per Chapter 10
of City Code.
7.0 Proposed Development
The proposed development will include construction of a museum structure and associated
parking and utilities. A water quality pond will be constructed at the north end of the site. A
Porous Landscape Detention (PLD) will be constructed along the south perimeter of the site. The
majority of drainage will be directed into either of these features. A portion of the site,
consisting mostly of vegetated landscape area, will drain into the existing Howes Street Outfall
Water Quality Pond.
8.0 Proposed Drainage Plan
The developed site has been broken into 10 developed drainage basins. In general, developed
stormwater from the site will be conveyed primarily via gutter flow and through on onsite storm
line system into either the onsite Extended Detention Water Quality Pond or the onside Porous
Landscape Detention (PLD), or the existing Howes Street Outfall Water Quality Pond.
Basins 1 through 6 will be conveyed via overland flow, roof drain system, gutter, storm line, and
swale flow north to the Water Quality Pond. The Water Quality Pond outlet structure has been
designed with an area inlet component, which will convey up to a 100-year event.
Frequent storm events will be treated in this pond, which will outfall to an existing sump area.
The sump area drains north to the Poudre River via an existing 12-inch culvert. The capacity of
this culvert has been estimated at 4.6 cfs (Please see Appendix D). In a 100-year event, this
culvert is expected to overtop, with a total 100-year flow of 13.3 cfs from the project site being
routed to the culvert. The existing concrete trail will serve as an overflow weir causing flow to
spread, and the existing area is very well vegetated. Therefore, we believe that the potential
overflow of approximately 8.7 cfs in a 100-year storm event will not damage the existing trail.
Basin 7 will be conveyed via sheet flow, and gutter flow, south into the Porous Landscape
Detention (PLD) area. The PLD will outfall via storm sewer west into the existing Howes Street
Water Quality Pond. The storm sewer has been designed to convey up to a 100-year event.
Additionally, there will be some conveyance of storm flows via an intermediate storm inlet and
storm sewer placed within the landscaped island within the south parking lot. The intent of this
landscaped island is to provide an additional water quality feature. Primary storm conveyance,
however, will be through the storm line draining the PLD. This storm line has been modeled
with full 100-year flows from the entirety of Basin 7.
Basins 8, 9, and 10 will be directed into the existing Howes Street Outfall Water Quality Pond.
' 9.0 Extended Detention Water Quality Pond
A Required water quality volume for the onsite water quality pond has been calculated in
Appendix E. All calculations conform to Volume 3 of the Urban Storm Drainage Criteria
Manual (Reference 2) for extended (40-hour) detention basins. The estimated 100-year overflow
Final Drainage and Erosion Control Report 3
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E N G I N E E R I N G Fort Collins Discovery Science Museum
' 5.0 Howes Street Outfall Water Quality Area
The Howes Street Outfall Water Quality Area and Outfall Channel are located just west of the
proposed development. Significant discussion has occurred with City staff regarding this area.
The area has been studied in detail by Icon Engineering, Inc. and Icon's report entitled "Old
' Town Master Plan for Howes, Udall, and Magnolia Basins", dated November 2006 is referenced
in the current study. Portions of this study are provided in Appendix G.
' The Icon study summarizes the area draining to the Howes Street Outfall and provides
recommendations for future improvements to the Howes Street Outfall Water Quality Area.
Currently, the water quality area is significantly undersized, providing 0.20 acre-feet of water
' quality volume for the Howes Basin. Improvement of the water quality area would involve the
construction of two new water quality ponds as well as the expansion of the existing water
quality area. These improvements would result in an addition of 4.1 acre-feet of water quality
' volume to the existing system.
The currently proposed extended detention water quality pond is located near the area to be used
' for one of the additional ponds proposed by Icon. It is anticipated that when the ultimate
improvements are made to the water quality area, the current proposed water quality pond will be
merged with Icon's design pond.
' 6.0 Cache La Poudre Floodplain
' The Cache La Poudre 100-year and 500-year floodplain encroaches the project site and is
delineated on the Drainage Exhibit (see back map pocket). FEMA FIRM Panel Numbers 977
and 979 for Larimer County, Dated June 17, 2008 are referenced in this study, and delineation of
' floodplain and floodway boundaries shown on the Drainage Exhibit are consistent with the
FIRM. A copy of portions of these FIRM Panels are provided in Appendix F.
The base (100-year) flood elevation in the vicinity of the proposed structure is 4966.0 which is
referenced to the City of Fort Collins NGVD 29. The finished floor of the proposed structure is
at elevation 4973.0, allowing the regulatory flood protection elevation (minimum 2-feet above
base flood elevation) to be met. All HVAC will also exceed the regulatory flood protection
elevation.
' The proposed structure is located outside of the 100-year and 500-year floodplain boundaries.
Proposed use of the structure is a children's museum. Based on discussion with the City
Floodplain Administrator, the proposed structure is considered a critical facility.
The Cache La Poudre half -foot floodway also encroaches the site and is delineated on the
' Drainage Exhibit. No fill is proposed within the half -foot floodway.
It is noted that the vertical datum utilized for site survey work is the City of Fort Collins
Benchmark #V 401 (Elevation=4974.64, NGVD 29).
A floodplain use permit will be required for each structure and each site construction element
' (water quality pond, bike path, parking lots, utilities, etc.) in the floodplain. Additionally, FEMA
elevation certificates must be completed and approved for any structures in the floodplain prior
to issuance of Certificate of Occupancy.
Final Drainage and Erosion Control Report 2
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ENGINEERING Fort Collins Discovery Science Museum
' 1.0 Scope
' This Final Drainage Report has been prepared for the proposed the Fort Collins Discovery
Museum development project, and is intended to document the associated stormwater impacts.
Existing storm drainage features are discussed in this report. Analysis of proposed storm
' drainage facilities have been conducted and are summarized in this report.
2.0 Design Criteria and References
' Drainage criteria outlined in the City of Fort Collins Storm Drainage Design Criteria and
Construction Standards (SDDCCS) has been referenced in this study.
The Rational Method has been used to estimate the peak discharge rates for the minor and major
storm events. The minor and major rainfall events are considered to be the 2-year and 100-year
' storms, respectively. Runoff coefficients and rainfall values utilized in the Rational Method
computations are consistent with the SDDCCS.
' The Urban Drainage and Flood Control District's (UDFCD) Urban Storm Drainage Criteria
Manual ,Volume III has been used for water quality design.
3.0 Site Location
The project site is located in a portion of the northeast quarter of section 11, Township 7 North,
' Range 69 West of the 6`h Principal Meridian in the City of Fort Collins, Larimer County,
Colorado. The site is bounded on the south by Cherry Street, on the east by College Avenue, and
on the north by the Cache La Poudre River.
4.0 Historic Drainage and Major Drainage Basin
' The area to be developed is roughly 5.4 acres in size and currently cosists of undeveloped land.
The site slopes generally from south to north at slopes ranging from 0.5% to 3.0%. Ground
' cover consists of native grasses. Three historic onsite basins have been defined in the Historic
Drainage Exhibit (please see back map pocket). No offsite basins contribute to the project site.
' The site lies entirely within the Old Town Major Drainage Basin. Due to the site's proximity to
the Cache La Poudre River, detention is not required for this development.
It is noted that there are no major irrigation facilities located on the project site.
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TABLE OF CONTENTS
1.0 Scope...................................................................................................................................1
2.0 Design Criteria and References...........................................................................................1
3.0 Site Location........................................................................................................................1
4.0 Historic Drainage and Major Drainage Basin.....................................................................1
5.0 Howes Street Outfall Water Quality Area...........................................................................2
6.0 Cache La Poudre Floodplain...............................................................................................2
7.0 Proposed Development........................................................................................................3
8.0 Proposed Drainage Plan.......................................................................................................3
9.0 Water Quality Pond.............................................................................................................3
10.0 Additional Water Quality Measures....................................................................................4
11.0 Erosion and Sediment Control.............................................................................................4
12.0 Conclusions............................................................................................5
References.......................................................................................................................................6
APPENDICES:
APPENDIX A— Historic Drainage Calculations
APPENDIX B — Proposed Drainage Calculations
APPENDIX C — Inlet, Storm Line, and Culvert Calculations
APPENDIX D - Riprap Calculations
APPENDIX E — Water Quality Calculations
APPENDIX F — FEMA FIRM Panel Excerpts
APPENDIX G— Excerpts from Previous Reports
BACK MAP POCKET:
Historic Drainage Exhibit
Developed Drainage Exhibit
Preliminary Drainage and Erosion Control Report
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' May 4, 2010
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ENGINEERING
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
ADDRESS: PHONE:970.221.4158 WEBSITE:
200 S. College Ave. Suite 100
Fort Collins, CO 80524 FAX: 970.221.4159 www.northernengineering.com
RE: Final Drainage and Erosion Control Report
Fort Collins Discovery Museum
Dear Staff:
Northern Engineering is pleased to submit this Final Drainage and Erosion Control Report for
your review. This report accompanies a Project Development Plan (PDP) application submittal.
The FDP submittal is typically considered to have 100% of the final engineering details.
This report has been prepared in accordance to City of Fort Collins Storm Drainage Design
Criteria and Construction Standards (SDDCCS), and serves to document the stormwater impacts
associated with the proposed development. We understand that review by the City is to assure
general compliance with standardized criteria contained in the SDDCCS.
If you should have any questions as you review this report, please feel free to contact us.
Sincerely,
' a"""r EERINSERVICES, INC.
' Aaron Cvar, PE
Final Drainage and Erosion Control Report
for
Fort Collins Discovery Museum
Fort Collins, Colorado
May 4, 2010
Prepared for
Oz Architecture
1805 29' St.
Suite 2054
Boulder, CO 80301
Prepared by:
NORTHERN
ENGINEERING
200 South College Avenue, Suite I(X)
Fort Collins. Colorado 80524
Phone: 970.221.4158 Fax: 970.221 A159
www.nonhernengineering.cont
Project Number: 532-002