HomeMy WebLinkAboutFORT COLLINS SECOND AND HARMONY PUD AT THE VILLAGES AT HARMONY WEST LOT ONE PRELIMINARY AND FINAL - 3 90E, F - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT1
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FINAL DRAINAGE REPORT
for
THE CHURCH OF JESUS CHRIST
OF LATTER-DAY SAINTS
t
PREPARED BY
TEC, THE ENGINEERING CO.
JA_NUARY 1992
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TABLE OF CONTENTS
I. INTRODUCTION
Scope of Work
Executive Summary
II. HYDROLOGY AND HYDRAULICS
A. Introduction
B. Design Objectives and Approach
C. Hydraulic Analysis
III. DRAINAGE DESIGN
A. Scope of Design
B. Concrete Channel Sizing, Location
IV. TECHNICAL APPENDIX
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INTRODUCTION
The Latter -Day Saint (LDS) church site consists of 3.02 acres that is proposed for a new church
building. The property is bordered by Harmony Road to the south, Regency Drive to the west,
the City of Fort Collins regional storm water detention pond to the north, and Pineview PUD,
Phase II, to the east. The site includes 0.43 acres of Harmony Road right-of-way that is not
included in the buildable acres.
A. Scope of Work
The areas of emphasis, included as part of this investigation, are:
1. A hydrologic analysis
2. Analysis of detention considerations
B. Executive Summary
This report was prepared for the LDS church site in Fort Collins, Colorado to evaluate
drainage improvements required as a result of the work proposed to develop the site.
Drainage improvements to the site will include the use of parking lots to direct runoff to
the existing regional detention pond to the north of the property. Due to the proximity
of the site, no on -site detention will be required. Some minor runoff will be directed to
Harmony Road according to the grading plan.
A grass -lined ditch has been built in the outlot to the west of the LDS site. This ditch
is a continuation of a swale along the north right -of --way of Harmony Road which has
been built to convey stormwater runoff from developments to the west. It is the
responsibility of the property owner of this outlot to allow this runoff to continue to pass.
Plans are being developed to carry the minor storm flows through a pipeline to the
existing storm inlet at the intersection of Regency Drive and Hilburn Drive. The major
storm would pass through a curb chase at this intersection to be channeled via an earthen
ditch to the regional detention pond.
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1 II. HYDROLOGY AND HYDRAULICS
1 A. Introduction
The hydrologic techniques and analytic tools utilized in the design flow hydrology for the LDS
1 site are described in this chapter. The facilities constructed as a result of this analysis will
convey the runoff resulting from storm events with the design frequencies of 2-year and 100-year
1 recurrence intervals. Because there will be no detention, the facilities constructed will be sized
to carry the major storm.
1 B. Design objectives and Approach
1 The objective of the hydrologic analysis for the LDS property concentrates on two principal
issues:
1 1. To investigate the impact of the proposed development upon the changes in the
magnitude of storm runoff.
1 2. Designing for the conveyance of storm runoff by means of appropriate strategies
as specified by the applicable drainage guidelines of the City of Fort Collins.
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The Rational Method, in widespread use in the Colorado area, will be utilized for the
1 determination of the runoff magnitude from the site in the developed condition and to size the
appropriate means of conveying this runoff.
The limit of application of the Rational Method is approximately 160 acres. Because the site is
3.0 acres, more or less, the Rational Method will be used for this analysis.
1 Accomplishing the modeling objectives has been attained through a sequence of model simulation
runs for each of the two contributing basins: basin "A" and basin "B" (see Exhibit "A"). The
100-year storm output in the developed condition has been used for the design of curb and gutter
sections as well as the rectangular concrete channel. We have not figured the minor storm as it
1 will be easily conveyed in the facilities proposed to handle the major storm (100-year developed).
C. Hydraulic Analysis.
Historic Conditions
The site historically drains from the earthen channel to the east. Due to temporary
improvements to Harmony Road, the earthen channel, the regional detention pond, and
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the irrigation ditch to the east the site generally sits in a hole. The Pleasant Valley and
Lake Canal runs along the east property line from north to south_. The existing layout
of this ditch dictated the position of our parking lot to the east of the building site. Given
the constraints of the site, positive sloping away from the building, the building running
from north to south; and the storm runoff required to flow to the regional "detention pond,
the grading scheme was designed to allow the building to be placed on the high point of
the site and the adjacent parking lots (with curb and gutter) to carry flows to the north.
Due to the proximity of the site to this detention pond, no on -site detention was required.
Flows, after being collected by the parking lots, drained to the north exiting the site
through a concrete channel and dumping into the existing pond. The present use of the
site is a vacant lot that is maintained only to keep the weeds down.
III. DRAINAGE DESIGN
A. Scope of Design
' The site is proposed for a church and accompanying parking lot use. Because we will
be changing the site from a relatively gentle sloping vacant lot to a concentrated use of
rooftops and asphalt parking lots, the permeability of the site is drastically altered.
' Therefore, we have considered a composite "C' factor when calculating the developed
major storm runoff. The developed condition will include downspouts to collect runoff
from the roof of the building and direct this to the parking lots. Parking lots would then
collect and convey runoff to concrete curb and gutter. Concrete channels will convey
runoff from the parking lots to the existing regional detention pond. Riprap will provide
' protection against erosion at the entrance to the pond.
B. Gutter. Channel Sizing. and Location
' We have calculated the major storm developed runoff 'for the site.. This runoff was then
used to size the triangular channel section required to carry this amount of flow without
topping the section. A 6-inch vertical curb and gutter section, with a cross -slope of two
percent, is adequate for this use. In addition, the off -site concrete channels were also
sized to carry this magnitude of runoff (see calculation sheets in the Appendix of this
1 report).
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1 SUMMARY
By elevating the proposed church building on compacted fill, thus directing runoff towards the parking
lots, the overall scheme of grading and drainage has been accomplished. The combined use of parking
lots, curb and gutter, concrete channels, and stone rigrap insures a safe, economical and sensible means
to direct storm runoff in both the minor and major storm events.
In the event clogging may occur in the channels, this would not pose a serious problem as runoff would
top the gutters and flow towards the detention pond, therefore, not endangering the safety of the property.
If the recommended construction, as illustrated on Exhibit A and outlined in this report, are implemented,
we feel the site will adequately handle the runoff for the minor as well as the major storm.
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