HomeMy WebLinkAboutDrainage Reports - 10/01/1985FINAL DRAINAGE REPORT
SUNDERING TOWNHOMES, P.U.D.
SECOND FILING
OCTOBER 1985
Prepared by:
Engineering Professionals, Inc.
2625 Redwing Road, Suite 110
Fort Collins, Colorado 80526
�j
II
II
' This Final Drainage Report prepared for Sundering Townhomes
P.U.D. - Second Filing as prepared by Engineering Professionals,
Inc., is intended to give a professional opinion as to the
' existng (historic) and proposed (developed) storm water runoff
conditions for this development and the surrounding properties
' affected by this development. The Grading and Drainage Plan
(sheet 6/7) of the Final Utility Plans for. Sundering Townhomes
P.U.D. - Second Filing is included as part of this report to
provide supplemental informtion. The plan shows both the
historic and developed site conditions as well as basin
delineation, design points, and a summary of storm water runoff
' information.
' The "City of Fort Collins Storm Drainage Design Criteria and
Construction Standards" manual was used as a guid in the
preparation of this report and the analysis of the storm water
runoff for this site.
A drainage report prepared by Taranto, Stanton, and Tagge of
'
Fort Collins entitled "Drainage Study .for Sundering Townhomes,
Fort Collins, Colorado" was prepared in 1980 for the entire
Sundering Townhomes P.U.D. as originally platted and designed.
Information from that report was reviewed and used as basis of
runoff information for Basins D-1, D-2, and D-3 as part of this
report.
LOCATION
Sundering Townhomes, P.U.D. - Second Filing is located in
the Northwest quarter of Section 23, Township 7 North, Range 69
'
West of the 6th P.M. in the City of Fort Collins, County of
Larimer, State of Colorado. More specifically, the project site
is located off of South Shields Street immediately. east and south
'
of the existing portion of Sundering Towmhomes and south of Hill
Pond Townhomes. Vacant land abuts the project on the south, east
'
and northeast. Spring Creek is located approximately 800 feet
north of Hill Pond Road.
HISTORIC CONDITIONS
The site in its present condition receives runoff only from
the existing Sundering Townhomes to the west. Shields Street
prevents runoff from entering the site from the west, and
although the property to the south generally slopes from
' southwest to northeast, the runoff from this area is intercepted
by a broad Swale just to the south of this site and directs all
runoff to the east. A visual examination of this area to the
' south as well as topographic information from recent surveys
substantiates this claim. As this area to the south develops,
' the runoff should be routed to the historic discharge area for
release. Provisions for offsite runoff from the south are not
being made as part of the improvements for this development.
Runoff from the existing development flows detained either
overland through the Second Filing or in an open channel along
' the south property line of the Second Filing. All runoff is
routed to the east side of this site where it then sheet flows
overland in. a northeasterly direction into Spring Creek.
1 At full development, all runoff from Sundering Townhomes
P.U.D. - Second Filing will be routed overland and via streets to
' the northeast corner of the site at the east 'end of Hill Pond
Road. At this point runoff will be intercepted by a grass lined
open channel and conveyed to Spring Creek through an existing
drainage easement. All areas except D-6 will be discharged
directly into this open channel. Area D-6, which consists only
' of grass open space will discharge runoff to the south property
line of the site and will then flow in an easterly direction east
in a manner similar to the historic runoff.
Street capacities for both minor (2-year) and major (100-
' year) storms were checked based on the City of Fort Collins
criteria. All streets have sufficient capacity to handle the
amount of runoff being conveyed and are summarized with the
'
calculations at
the end of
this report.
Basin D-2,
part of
the existing development, currently
' discharges into an inlet at the southeast corner of Mirrormere
Court and is conveyed via a 15" R.C.P. storm sewer to an open
channel along the south property line of the site. The inlet
will be removed as part of the second filing and replaced with a
concrete sidewalk culvert. Runoff will then be conveyed via a
concrete channel to Shire Court. The existing open channel
currently in use will be abandoned. Other drainage improvements
Ll
I
1
1
will be the construction of a concrete pan in the rear of the
units along the north side of Shire Court. This will help to
prevent ponding and swampy areas behind those units. As
mentioned above, a grass line open channel will convey the
majority of on -site runoff to Spring Creek. The entrance to the
channel at the east end of Hill Pond Road will be protected from
severe erosion by lining it with bedded rip -rap as indicated on
the Grading and Drainage Plan.
All calculations used for the analysis of both the historic
and developed conditions of this site are presented in the.
section following this report and are also indicated on the
Grading and Drainage Plan submitted as part of this report.
KLR:psm
ENGINEERING PROFESSIONALS, INC.
Kenneth L. Rabbers
Michael N. Schmid, P.E.
14533
,1
' FORMULAE
Time of Concentration:
' T__ 1.870.1 - Ccf)6'5
c S.33
1
Velocity and Capacity:
' V = 1.487 X R.67 X S.5
n
Q= 1.n86 X A X R.67 X S.5
' Runoff Quantities:
Q = CIAcf
1
�I
Runoff Volume:
V=Q..XTcX60
Orifice Plate:
Q = 0.65A 2gh
1
Where: C = Runoff Coefficient
D = Distance in feet
S = Slope in percent
cf = Antecedent precipitation factor
1.0 for 2-year and 10-year
1.25 for 100-year
Where: n = Manning's roughness coefficient
A = Cross -sectional area in square feet
R = Hydraulic radius
S = Slope in feet per foot
Where: C = Runoff Coefficient
I = Rainfall intensity, inches per hour
A = Area in acres
cf = Antecedent precipitation factor
1.0 for 2-year and 10-year
1.25 for 100-year
Where: Q = Runoff in cubic feet per second
Tc = Time of concentration
Where: A = Cross-section area in square feet
g = Acceleration due to gravity,
32 feet/sec .2
h = Height of water above center
of opening
Detention: Volume is computed by means of a program, using the Modified
' Rational Method which varies the rate of flow in, while dis-
charging at a constant rate.
1
1
1
1
1
1
1
SUNDERING TOWNHOMES DRAINAGE CALCULATIONS
Historic
A = 13.36 acres Tc2 = 61.6-IDins 12 = 0.90 Q2 = 2.4 cfs
c = 0.20
L = 1400' Tc100 = 5-O&I-min, I100 = 2.65 Q100 = 8.9 cfs
H = 15'
S = 1.07%
Developed c = 0.50 for all areas
Basin Area L H S Tc2 Tc100 12 I100 Q2 Q100
D-1
5.38
Ac
1600'
11'
0.7%
50.5
40.0
1.0
3.5
2.7
cfs
11.8
cf,
D-2
2.08
Ac
650'
7'
1.1%
27.7
21.9
1.55
5.0
1.6
cfs
6.5
cf,
D-3
0.94
Ac
450'
6'
1.3%
21.8
17.3
1.8
5.5
0.'8
cfs
3.2
cf;
D-4
0.96
Ac
680'
6.1'
0.9%
30.3
24.0
1.5
4.7
0.7
cfs
2.8
cf;
D-5
1.61
Ac
1180'
11'
0.9%
39.9
31.6
1.2
4.0
1.0
cfs
4.0
cf,
D-6
0.83
Ac
880'
8'
0.9%
34.5
27.3
1.35
4.4
0.6
cfs
2.3
cf,
D-7
1.03
Ac
320'
2.3'
0.7%
22.6
17.9
1.75
5.4
0.9
cfs
3.5
cf!
D-8
0.64
Ac
390'
5'
1.3%
20.3
16.1
1.8
5.5
0.6
cfs
2.2
cfe
Point
Basins
Area
Tc2
Tc100
1
D-2, D-3
3.02 Ac
27.7
21.9
2
D-2, D-3, D-4
3.98 Ac
43.2
34.0
3
D-5, D-7
2.64 Ac
39.9
31.6
4 D-2
thru D-5, D-7
12.00 Ac
50.5
40.0
5
D-1 thru D-5,
12.74 Ac
50.0
40.0
D-7, D-8
Street Capacity Summary
Point Q2
Street Slope
12 I100 Q2 Q100
1.55
5.0
2.3
cfs
9.54
cf;
1.15
3.9
2.3
cfs
9.7
cf;
1.2
4.0
1.6
cfs
6.6
cf;
1.0
3.5
6.0
cfs
26.3
cf;
1.0
3.5
6.3
cf s
27.7
cf;
Capacity
1 2.3
cfs
0.45%
2.8 cfs
2 2.3
cfs
0.7 - 1.1%
4.9 - 6.2 cfs
3 1.6
cfs
0.7 - 1.1%
4.9 - 6.2 cfs
4 6.0
cfs
1.05%
6.0 cfs
5 6.3
cfs
Open Channel
36.0 cfs
d EN/ST/N610'ORd/Nd6E EASEMENT
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