HomeMy WebLinkAboutDrainage Reports - 09/18/1985FINAL DRAINAGE REPORT
FOR
SOMERVILLE P.U.D.
CITY OF FORT COLLINS
LARIMER COUNTY
COLORADO
September, 1985
Prepared By:
TEC, The Engineering Co.,
1630 So. College Ave.
Ft. Collins, Colorado 80525
STORM DRAINAGE REPORT
SOMERVILLE.P.U.D.
FORT COLLINS, COLORADO
General
The purpose of this report is to outline the methods of conveyance and
disposal of stormwater runoff for the proposed Somerville P.U.D. the project
consists of 9 duplex lots situated on 2.56 acres. This report was prepared in
combination with the "Preliminary Design Report - Diversion of Storm Water
Runoff Through Irrigation Canals From Mulberry St. To Spring Creek, Ft.
Collins, Colorado" by Resource Consultants, July 1980, and the "Final Drainage
Report for Fairbrooke S.I.D." by Parsons and Associates, Nov. 1983.
Site Description
The Somerville P.U.D. is located in Section 21, Township 7N, Range 69W of the
6th P.M., City of. Ft. Collins, Larimer Co., Colorado, consisting of 2.56
acres. In general the site is bounded on the north and east by the Pleasant
Valley and Lake Canal, on the west by Somerville Dr. and on the south by
unplatted land.
The site is presently undeveloped and is used primarily for agricultural
purposes. The existing drainage pattern is to the northeast at a slope of
approximately 1 to 3% and drains in to the Pleasant Valley and Lake Canal.
Design Criteria
The design criteria for this study was based upon the Denver Regional Council
of Governments "Urban Storm Drainage Manual". The rational method can be
used to evaluate flows for the site for the 2 year and 100 year for both the
developed and undeveloped conditions. The rational method relates runoff to
rainfall intensities by the formula Q = CiACf where:
Q = Maximum peak runoff (cfs)
C = Runoff coefficient (in./hr.)
0.45 for developed lots
0.95 for asphalt paving
0.20 for unimproved areas
0.20 for lawns with flat slopes (less than 2%)
0.25 for lawns with average slopes (2% to 7%.)
0.35 for lawns with steep slopes (greater than 7%)
L = Average rainfall intensity
Intensities are based on intensity curves shown in Exhibit A.
Cf = Frequency Factor
1.00 for a 2 to 10 year storm
1.25 for a 100 year storm
1
Proposed Storm Drainage System
The overall drainage plan for the Somerville P.U.D. is shown of Exhibit B with
the two and one hundred year flow routes. With the grading plan it is
intended to convey all storm water from the site into the Pleasant Valley and
Lake Canal. It is understood that the canal cannot handle undetained runoff
from new developed areas. The Final Design Report for Fairbrooke S.I.D. has
proposed using a 66 cfs side outlet spillway downstream from Somerville P.U.D.
It is proposed to allow the Peak flows from Somerville to flow into the canal,
then released those flows at the side outlet downstream. The location of the
outlet structure is shown on Exhibit B.
Basin A consists of 1.18 acres which include Somerville Ct. and the lots on
the west and south side of the P.U.D. Drainage is generally off of the .lots
onto Somerville Ct. and collected at a low spot in the southeast corner of the
Cul-de-sac. From there water is released through a curb cut and flows through
a concrete lined Swale into the canal.
Basin B consists of 0.97 acres on the east side of the P.U.D. Drainage from
these lots is generally to the east into the canal by sheet flow and through
swales created by the grading between the buildings.
A copy of the calculations to arrive at the 2 year historical 100 year
developed flows is included in Appendix A. This illustrates the discharges
projected for the site.
Historically the site does not present any major runoff problem as the
drainage area is small and resulting discharges are also small. The release
point into th canal will be protected by rip -rap to prevent erosion problems.
It is believed that the small contribution resulting from this site can easily
be handled by the canal with the addition of the side outlet spillway.
Calculations for the side discharge spillway are included in APPENDIX A (page
2).
7
APPENDIX A
CALCULATIONS
Historic Flows - 2 Year
A = 2.15 Ac.
D = 300 ft.
Si = 5120 - 5113 = 2.33%
300
C. = 0.25
Tf = 1.870(1.1 - CC�)D1/2 = 1.87(1.1 - 0.25(1.0))3001/2
c S1/3 2.330.33
= 20.8 min
I = 1.90 in./hr.
Q2 = CCfIA = 0.25(1.0)(1.9)(2.15) = 1.02 cfs
Basin A - Developed Flows
A = 1.18 Ac.
D = 300 ft.
Si = 5118.5 - 5115.5 = 1.00%
300
C. = 0.45
1.25 Tc1=1.87(1.1 - CCt)D1/2 = 1.87(1.1 - 0.45(1.25))3001/2
S1/3 1.00.33
= 17.41min
D = 120 ft.
S2 = 5115.5 - 5112 = 2.92%
120
C. = 0.45
1.25 Tc2=1.87(1.1 - CC )D1/2 = 1.87(1.1 - 0.45(1.25))1201/2
S1/3 2 920.33
7.73min
Tctot - 25.14 min.
1100 - 4.8 in./hr.
Q100 - CCfIA = 0.45(1.0)(4.8)(1.18) = 2.54 cfs
Basin B - Developed Flows
A = 0.97 Ac.
D = 125 ft.
Si = 5118 - 5112 = 4.80%
125
C. = 0.45
Cf = 1.25 (100 yr.) 1/2 1/2
T = 1.87(1.1 - CC )D = 1.87(1.1 - 0.45(1.25))125
c S1/3 4.80.33
= 6.7min
I100 = 6 in./hr.
Q100 = CCfIA = 0.45(1.25)(6.0)(0.97) = 3.27 cfs
APPENDIX A
(Page 2)
Side Outlet Weir Calculations
Basic equation for a sharp crested side overflow weir
Q = 3.32 10.83h1.67 Ref. ASCE MOP -No. 37
Page 113 eq. 38
Proposed structure is actually a broad crested weir.
Therefore, c factor must be corrected.
Ref. "Handbook of Hydraulics" by King & Brater
Page 5-24 c = 3.087
Solving for h
h = G. 1/1.67 h = 0.75 ft.
3.087 1
Page 5-46 c = 2.70
1/1.67 h = 0.81 ft.
2.70 1 '
Top of Ditch Bank = 5111.80 field meas.
Top of Exst. Earth spillway approx. 65 ft. east of bike
path bridge = 5110.30 field meas.
Normal High Waterline = 5110.20
(Ref. Resource Consultants' report on Diversion of
Storm -Water Runoff, etc.
Therefore, set crest of spillway at 5110.30 (same as
existing).
Therefore, maximum waterline @ 66 cfs. is 5111.05 to
5111.11 depending on which coefficient is used.
Note: Resource consultants report recommended setting
the crest at 1 ft. below top of bank which would be
0.50 higher than the existing earth spillway.
m
3
X
m
Z
Z
m
CD
0
INTENSITY- INCHES PER HOUR
c�
mD
..
•
n
1
n
�
•
•
n
Z
w
Q
D
A
w
•�
o
v
wr
r
o
n
Z
q�
D°
m�
.
.
a
Z
--�
C/)
_
e
M
o
o
w
o
3
C)
Z
(n
z
a
C
n
O
«
w
>
D�
�
o
N
Z
0
O
L 1 TGRI F
STORM DRAINAGE S"'fS*f-M PRELIMINARY DESIGN DATA s
c --
• y
Q, ro } E
c Basin3
v
E
o c
a
Flory Time
C
o `
c
E
►_ u E
c
U
u -
�
=
E
•
o CC
o'r
°
•
c ...
c
E
E
v) Cr
Street
Pipe
Street
pipe
Remarks
for additional l remarks,
see TABLE 1-2
-
v�c
ao c
i
(2
o =
o
.
=
n• w
c,o
,,
o
a
_
�•
u
av
>
t 1 2 3 4
1 S
6
7
8
1 3
1 10
II
12
13
ra
1 IS
16
1 17
18
19
20
21
1 22
23
IF-1 31.0
31.0
0.501
1. 5111.78R.5
103 24.5
R 24.5
0.50
4.65
11.78
34.2
2IF-T. F-4 2 31.0
4.6(11
35.5
0.50
1.3
14.34
9.3
9.3
1013 24.5
4.6 1
29.1
3.SQ
4.25
14.34?8.138.1
3 F-2 2 22.8
22.8
0.5C
1.7
4.95
4.1
41
100 18.11
18.1
0.50
5.4
-I'a
6.4
F- -
7.5
30.3
0.50
1.45
2).1
14.5.,
"
intpr-ppt In
133 18.1
7.5
25.5
0.5C
4.5
20.1
56.5
cfs as part of final cesion
-
2
5.1-
_
4 ;
n
9V
11 12
Sump -install
10, 24.8
24.3
MC
4.5
7.2"
20.9
inlet
5 F- b
5.4
5.4
3.1E
1
3.7
3.
1.20
6.4
Gutter
1n
5.4
1
1 5.4
0.9
7.0
1.21
10.4
10.
-1 2 1 26 .41
0.4
1
1 25.8
0.591
1.55
4.211
3.3
-
100 1 20.9
0.4
1
21.3
0.501
5.05
4.211
13.3
_
_Z _
3.7
_
^ 1 20.912.7
0.51
4.8E
4.8d
14.8
a
-1- -
S.0
5.2
2.8!
Guttercapacityp .
a
?a
n-
4.
32.2,
2.
1.20
37.1
- -' -
.4
4.
9.8
O.K.
F- 100 20.9
5.4
26.
0.5r4.5
14.0
39.5
5
3
--
11 F-6 2 21.6
2.6
24.
0.5
1.6
4.0
3.3
_
3.
1.20
6.4
_
10-3 17.1
2.6
19.
3.5
5.1
4.0
13.0
13,
12 F-5a F-5b 2 21.6.
4.0
25.5
0.5
1.6
6.0"
4.3
•4rapar
+
100 17.1
4.0
21.1
0.5
5.05
6.3'
19.1
13 F-6a 2 21.6
8.0
29.6
0.5
1.4
8.0
5.8
_
5.
1.10
6.2
_
+ a it
1C0 17.1
8.0
25.1
0.5
4.6
8.0
23.2
23.
_
14 F- F-7 F-6 2 26.4
9.4
35.
0.5
1.3
25.1.
15.4
2
+r2naCcPPd __
130 20.
9.4
30.
0.5
4.2
25.1
66.1
- - -F
2.1�
_
37.9
-
F- -1 100 4^.2
40.1
0.5
3.5 1
72.1-157.8
157. E
16 F-1- - 'fl
1'C
n
Q1 7711')q_n
:i 1
Z
,d48"
_
_
I-
Z)/
BASIM F-2
4.85 AC.
i�
� I
• r
I '
1
,•t
S
6
We
• �/
., .. V
TRACT E <6xlt0000
,
BASIN F-8 334,l r
13.46 AC. 1
- FAIRBROOKE S10. I.D.
of ej
N DESIGN POINT REMARKS
"• �" _' 9 Install 2, 4' curb chases to intercept
law•° = 2.8 cfs. 5.2 cfs to reman ir, street
10 Install 4' curb chase to intercept 1.2 cfs-
r° ...• 4.0 cfs to remain in street.
•w a_
PROSPECT •••" STREET s. r
eev ,
BASIN F-5
15.28 AC. = .
z` BAUDER ELEM. SCHO
I
\ TRACT 0
\\BA5111 F—(6cL
„ •� 4.03 AC.
ae.nn ! J
BASIN F-3a a ...•..•.,-. ...�
BASIN F-1 "" 2.96 AC. /f \
11.78AC.
I �;•r„» �" �• -\ BASIN F-9
\" ,,.•». , ..1 BASIN F-74L \
\
B 0.67 AG. �\ \% S TRACT t
TRACT A \ � � w
a.rrn
TRACT . BASIN F-6c
waft
BASIN F-3b BASIN F-lb \ \� ` ® BASIN
AC.
00
L25 AC. 4-5
l0.21 AC. n AC- — -
\ ..��
`� ` BASIN IN
twoom
F
n�, M
• *R+i_ T a `t 1" 3.0
BASIN F-7c
a•�A 1 r+ 2.9�0 At• ��
v
r a
•.e e, a
K4� � aNPI.
* Install 4' curb chase to intercept 1.2 cfs.
2.8 cfs to remain in street.
14 Install 2, 4' curb chases to intercept
4.2 cfs. 4.4 cfs to remain i:i street.
._� "
Y.l.=. DRAINAGE MAP
f A1REROOKE S.I.C.
,a, r aNan .•e.u+ N
M