HomeMy WebLinkAboutDrainage Reports - 07/16/1979No Text
I.. PROJECT LOCATION AND DESCRIPTION
This study was performed on Brown Farm 6th and 7th filing in the
City of Fort Collins. Its location is shown on the inset of a portion of
a U.S.G.S. map shown on the Master Drainage Plan (Sheet 0, included in the
back of this report." The site is located in one historic drainage basin
which drains to the Pleasant Valley and Lake Canal.
The proposed subdivision plan calls for the 89.23-acre project to be
subdivided into 298 single-family lots and a recreation center. Average
lot size will be approximately 8,000 square feet upon which single-family
detached units of approximately 1,200 square feet are proposed to be built.
II. DESIGN CRITERIA AND REQUIREMENTS
The estimated peak 100-year runoff.rates have been calculated based
upon the assumed development and runoff pattern. This report is intended
to meet the City of Fort Collins -drainage design criteria as well as the
criteria of the Department of Housing and Urban Development - Federal
Housing Administration as set forth In their directive, "Land Planning
Guidelines for HUD/FHA Projects."
III. METHOD OF ANALYSIS
Peak runoff rates were calculated based upon the rational method.
The City of Fort Collins Rainfall Intensity - Duration Curve was used for
determining intensities." The Master Drainage Plan presented in the back of
this report identifies drainage sub -basins and indicates the contributing
basin area as well as the peak 100-year runoff rate estimated at the point
of concentration as indicated. All calculations are included in the letter
part of this report.
IV. OFFSITE DRAINAGE CONTRIBUTION
All contributory offsite drainage comes from west of the site. Most
of Sub -basin C is offsite and a small portion of Sub -basins B and D are
offsite. Offsite drainage is included in all calculations of peak runoff
rates. Offsite drainage is not included in the calculations for sizing.
the detention pond.. Only that runoff which is generated from the site is
considered in the detention calculations.
V. SITE DRAINAGE
A. Sub -basins A and L.
Due to the lot grading required in these two areas for adequate
drainage, a small amount or runoff will drain to Drake Road. It will then
be picked up by the proposed gutter along the North side of Drake Road
and flow East.
B. Sub -basins B, C, D, and E
A sag point in Yorkshire Street will pick up flow coming in from
the North and South. Sub -basins B. C. and D all drain to this sag point.
The channel in Basin C is passed under Yorkshire Street at this point in
a 36-inch 0 R•C•P. culvert. Sub -basins B and D drain to_curb inlets at
this sag point in Yorkshire. These curb inlets drain into a 27-inch 0
R.C.P. culvert which crosses the street. Excess flow, which these inlets
cannot accommodate, will flow East on Montmorency Street. Both of these
culverts empty into the box at the curb inlet on the East side of Yorkshire.
^r A 60-inch x 38-inch R.C.P.`Oval Culvert comes out of the East side of the
box and empties into the 18-foot wide grass -lined channel. This channel
-2-
flows East through Sub -basin E.and drains into the detention pond. The
channel accommodates all the runoff.from Sub -basins B, C, D, and E.
C. Sub -basin F
Sub -basin F will drain along Clydesdale Drive to the sag point
in Clydesdale and then into the detention pond via curb inlets and .
a 24-inch 0 R.C.P.`culvert.
D. Sub -basins G, H, I, J, and K
Sub -basins G,_H, and I will drain East to Montmorency Street and
then North along Montmorency to the sag point at the detention pond. Some
of the runoff from Sub -basin G will overflow the centerline of Montmorency.
at the intersection with Blue Grass Drive. This excess will flow North to
Quince Court and then East to the low point at the end.of Quince. Sub -
basin J will drain North.on Yorkshire.Street to Montmorency. Sub -basins
J and K will drain East on Montmorency to the sag point at the detention
pond. At this point the.. runoff from Sub -basins G, H, 1, J, and K will
empty into the detention pond via curb inlets and `a 33-inch R.C.-P'. culvert.
E. Sub -basins M, N, and 0
Sub -basin M drains to a curb inlet at the low point at the end
of Lodi Court. From this point the water is carried by a 15-inch 0 R.C.P.
culvert to the 14-foot wide grass -lined channel along the East property
line. Sub -basin N drains to a curb inlet at the low point at the end of
Quince Court where it is picked up by a similar 15-inch culvert which
empties into the.same channel.. This channel accommodates all of the run-
off from Sub -basins M, N, and 0. It drains North to a 36-inch 0 R.C.P.
- 3-
culvert which passes the water under Wyandotte.Drive and Into the
detention pond.
F. Sub -basins P and Q
Sub -basin P drains East on Stuart Street to an existing catch
basin. Sub -basin Q drains North on White Rock Court and then Southeast to
an existing catch basin -in Langshire Drive.in the 5th Filing.of Brown
Farm.
VI. DETENTION
The detention pond is sized to accommodate the runoff from a 100-
n year storm while releasing the historic runoff from a 2-year storm. .This
requires a pond size of;'" 9.73�acre-feet, viith an areaof3.05 acres and
an average depth of 3.19 feet.""The release structure is a 21-inch 0
R.C.P. culvert which releases 19.3 CFS.
VII. SUMMATION
: The proposed Brown Farm 6th and 7th filing has been designed to
accommodate an initial storm with a return period of two years and a major
storm with a return period of 100-years. Runoff will be conveyed in
street curb and gutter sections, channels, and storm drains. It is anti-
cipated that no damage to proposed structures will occur within this
subdivision in a 100-year flood and that no damage to upstream or down-
stream properties will occur..
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