HomeMy WebLinkAboutDrainage Reports - 10/06/1989' D 114Cu
COLORADO REGISYFRED PROFESSIONAL
' ENGINEERS & LAND SURVEYORS
11
I 1
DRAINAGE REPORT
for
MOUNTAIN PARK HOMES
CITY OF FORT COLLINS Colorado
by
D & W Inc.
P.O. Box 1391
Fort Collins, CO 80522
484-0533
Proje.c-t #-68-7N-16-83
Aug. 31,)1989
D & W INC.
' COLOR" REGISTERED PROfESSIONAI
ENGINEERS M LANO SURV"S
' 1913 CORRIEDALE DR., FORT COLLINS* CO 80526
484-0533
Aug. 31, 1989
Fort Collins Housing Authority
c/o James Kline
Project Manager
' 1715 W. Mountain
Fort Collins, CO 80521
' RE: Drainage Report for Mountain Park Homes Housing Project.
Dear Jim,
' Submitted herein is the drainage report you requested for
the Mountain Park Homes Housing Project. The hydrology data and
the hydraulics analysis presented here are in compliance with the
' City of Fort Collins " Storm Drainage Design Criteria ", dated
May 1984.
t It is determined based on the previous and new constructed
conditions that there is no need for a detention pond, since the
runoff.%coefficient for the new constructed homes is less than the
' runoff coefficient for the previous conditions, where the new
constructed site uses less impervious area and more grass and
gravel spaces.
' If you have any further questions or need more information
please feel free to call me at 484-0533.
' Sinc rely
AD R E GI
R0
' Mo amed S. Worayeth _
23019 `"•
Colorado Reg. P.E. 23019 s9 _;�_
TABLE OF CONTENTS
Title -- --- - -
INTRODUCTION
SITE LOCATION AND CONDITIONS
PROPOSED CONSTRUCTION
LANDSCAPING
HYDROLOGY AND HYDRAULICS ANALYSIS
SUMMARY
DISCUSSION
Pie
1
2
3
3
3
5
5
INTRODUCTION
' This drainage report provides the hydrology analysis using
The City of Fort Collins rainfall data, and hydraulic
investigation to determine the method of draining the storm water
' from the property to storm drainage facilities, according to
drainage system capacity, and the City of Fort Collins Storm
' Drainage Regulations.
This drainage report is prepared and compiled from the
' following references;
1. Storm Drainage Criteria, City of Fort collins,.May
' 1984.
2. Federal Emergency Management Agency ( FIMA ) Maps.
' 3. Topographic Maps, previous, as built contours and
previous conditions plot plan by D & W Inc.,May 1988,
' and Jan. 1989.
' SITE LOCATION AND CONDITIONS
The site is located on the Southeast corner of Mountain and
Bryan Avenues, also known as Lots 11, 12, 13 and 14, Block 5,
Scott -Sherwood Addition to the City of Fort Collins, Colorado.
' There is an old four plex building apartment on the Southwest
side of the site, that will remain in place. Nineteen single wide
' mobile homes were removed, as well as the asphalt driveway and
parking lot and the concrete sidewalks, which are replaced by
grass, gravel concrete sidewalks, and asphalt parking lots._
A total of 23 trees out of 24 had been saved on the site,
' with 16 trees are inside the property lines and 7 trees are
located outside the property.
1
2
PROPOSED CONSTRUCTION
Four 6-Plexes, a total of 24 units are constructed on the
site, to be known as Mountain Park Homes. The new construction
included two parking lots, a large one was built on the Northwest
side of the complexes, a smaller parking lot was built on the
Southwest side of the site. Gravel, grass and sidewalks are built
surrounding the complexes and the old existing building.
LANDSCAPING
It was proposed that gravel and grass would be planted around the
new housing units. I had recommended that the finished grades
around these units should be sloped away from the structure on
all sides to provide positive drainage. A minimum of 112 foot.
fall in the first ten feet was recommended.
HYDROLOGY AND HYDRAULICS ANALYSIS
The total area involved in this drainage study is 38,980
square feet or 0.89 acres. Since the area is far less than 200
acres, the Rational Method to calculate the storm runoff quantity
can be used.
I. Estimated runoff quantity "Q" in cfs. under historical
conditions would be;
A.- Using the rational Method to determine runoff storm
drainage criteria for 2 year initial storm, based on
design storm frequencies for medium density mobile home (MM)
residential district with runoff coefficient equal to 0.65.
1. The determined composite runoff coefficient for the
total area of 38,980 square feet is 0.70.
2. The length of basin (D) is equal to 290 feet.
3. The average slope with 3.18 feet drop within 290
feet long is 0.012 (S = 1.2%)
3
4. To determine time of concentration in minutes
Tc 1 . 87 ,� 1=_ CxCf _Z D1 12
S113
Where
Tc = Time of Concentration, minutes
S = Slope of basin %
C = Rational Method Runoff Coefficient
D. = Length of Basin, feet
Cf = Frequency adjustment factor
S = 1.2%
D = 290
C = 0.70
Cf = 1.0 for 2 year storm.
Then
Tc = 11.99 minutes
5. Determine precipitation in inches per hour from
figure (3-1) Storm Drainage Design Manual
I2 = 2.32 inches/hour
6. Determine runoff quantity
Q = Cf CIA
Where
Then
Q = Flow quantity, cfs
A = Total area of basin, acres
Cf = Frequency adjustment factor
C = Runoff coefficient
I = Rainfall intensity, inches / hour
Q2 = 1.0 x 0.70 x 2.32 x 0.89 = 1.45 cfs
4
II. Estimated Runoff Quantity "Q" in cfs for the developed
conditions;
A. Determine runoff quantity for 100 year major design
storm return period.
1. Calculated composite runoff coefficient is equal to
C =.0.54 and frequency adjustment faction Cf = 1.25
for 100 year major storm.
2. Time of concentration: T = 13.53 minutes.
3. Precipitation in inches/hour from fig. (3-1) SDDM.
I = 6.40 inches/hour.
4. Runoff quantity for 100 year major storm
Qtoo = 1.25 x 0.54 x 6.4 x 0.89 = 3.84 cfs.
SUMMARY
The difference in runoff quantity between 2 year storm for
historical conditions and the 100 year major storm for the
Developed conditions is 2.39 cfs. However the runoff coefficient
' value, for the developed conditions (0.54) is less than the one
for the historical conditions (0.70).
DISCUSSION
' According to the City of Fort Collins Drainage Design
Criteria, detention storage is not needed, since the runoff
' coefficient for the new constructed conditions was found to be
less than the historical ones. Nineteen single wide mobile homes
were located on the site of the Mountain Park Homes. An asphalt
parking lot and two driveways were existed at the site. The
' historical drainage pattern had been to drain via the driveways.
into Mountain Ave., then through street Gutters on the South side
' to the storm drainage inlet located 350 feet east on the South
side of Mountain Ave.
5
A small portion of the drainage, which covers about 2,000
square feet had been draining to the alley, South of the
property, causing some standing and puddling of water at the
alley, which eventually drained into South Bryan Ave., then to
Mountain Ave.
Since the impervious area and runoff coefficient are less
for the new constructed development, than the historical values.
Due to the fact that the drainage patterns will not change from
the historical conditions (except that portion, which had been
draining into the alley, which will be eliminated in the new
developed process).
Most of the storm water will drain into Mountain Ave., via
the large parking lot or through the 6" drain pipe.•A small
portion may drain from the small parking lot into Bryan Ave., in
case of over flow. Both driveways will be used as a spillway (see
the drainage plan), if the drainage pipes become plugged.
The west side of the existing 2-story old building located
at the south west corner of the lot is protected partially from
' the rain by a covered porch in the front of the main door. There
is a retaining wall between the side walk at the west side of the
tbuilding and the small parking lot, to prevent surface water flow
from entering the low area. The extended roof will have gutters
draining into the west parking lot. Also, a rise in the concrete
floor will be added, of about 1/4" thick, to help drain the side
walk from the door side to the west side, then to the south, and
into a 4" pipe connected to a sump, as shown on the drainage
' plan.
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