HomeMy WebLinkAboutDrainage Reports - 02/01/1980REVISED DRAINAGE REPORT FOR
PLATTE RIVER POWER AUTHORITY
FORT COLLINS, COLORADO
Prepared for:
EDAW, Inc.
240 East Mountain
Fort Collins, Colorado 80524
Resource Consultants, Inc.
P. 0. Box Q
Fort Collins, Colorado 80522
February 1980
Ref : 976
l
REVISED DRAINAGE REPORT FOR
PLATTE RIVER POWER AUTHORITY
FORT COLLINS, COLORADO
Introduction
' This study has been made to revise the previous study completed by
this office in 1976 for the Platte River Power Authority (PRPA) complex
' located at the corner of Horsetooth Road and Timberline Road in Fort
Collins,.Colorado. This study was conducted using the new storm drainage
' criteria of the City of Fort Collins. The study was initiated in order
to revise the site master plan based on new site development; thus, this
drainage report revises the runoff estimates previously compiled to include
the additions to the building and parking lot on the site.
' Site Description
' The general layout of the PRPA office complex is shown.in Fig. 1.
Currently the site contains two storm -water detention areas --one is an
' existing pond (Pond #1) on the southern portion of the site, and the
other (Pond #3) is in the landscaped area on the northeast corner of the
site. The current developed portion of the property is approximately 7.5
' acres. Approximately 7 acres to the west is owned by PRPA but is currently
undeveloped and there are no current plans to develop it.
' The proposed changes in the site planning include building an addition
to the main office building. A parking lot is to be added on the north
' side of the entrance road, and a new driveway and garage facility are to
be added in the corporation yard portion of the property.
' In order to accommodate the current drainage criteria of the City of
Fort Colins, the entire site drainage was reevaluated. Based on this
study, drainage improvements were proposed which include construction of a
pond (Pond #2) on the undeveloped portion of the site to contain the runoff
' from that area. In addition the pond at the northeast corner of the site
would be enlarged and deepened to accommodate the larger amounts of runoff.
-1� RESOURCE CONSULTANTS INC
i
l
���T• N1.H. I _ I
coMl31NED r-toW I
fPZ)M CCOH P Ni3 '
ANP AF `A h1°5
lo0 12. PWAK.
. I
,
u.yne
I �
�1J
i-
L
Design Hydrology
' Due to the complex drainage pattern of the site and the three detention
ponds that would be included in the drainage plans, the design hydrology
was developed using the Storm -Water Management Model. This model accounts
for detention routing.and has the advantage that it can be applied to
' large or small areas.
' The entire site was divided into five major drainage areas with three
storm -water detention areas and three open channels. In addition the out-
flow from Pond #3 was routed into the existing storm sewer which runs along
' the west side of Timberline Road north of this site. Appendix A shows the
stage -volume curves and outlet rating curves for each detention pond.
The'design storm was developed for the 2-year and 100-year runoff com-
putations. These storms.were 1 hour in length and the design storm patterns
that were used are shown in Table 1. A 1-minute time interval was used within
the Storm -Water Management Model, and the intensity during each 5 minutes
' of rainfall was assumed constant over that 5-minute period.
A brief analysis was made of historic runoff from this site prior to
' development. A drainage area was assumed of 14.3 acres with a 5 percent
impervious area. Utilizing this watershed a 2-year peak flow of 1.6 cfs
was calculated using the Storm -Water Management Model. Details of this
analysis are shown in Table B-1 in Appendix B.
' An analysis was made of the runoff based on developed conditions assum-
ing the revised development plan. The site was divided into five drainage
subareas in seven channel and detention pond elements. Table 2 shows a
list of each element and the parameters used for the model. These elements
are also numbered and shown on Fig. 1. The outflow point is element #7
which is the 15-inch storm sewer north of this site. In addition, the
' analysis assumed that the east one-half of Timberline Road from the corner
of Horsetooth Road north to the north boundary of the site would drain into
this storm sewer also. This analysis showed that even during the 100-year
flow the depth in a 6-inch curb along the west side of Timberline Road
would only be 4 inches.
-3- RESOURCE CON ULTWM INC
Table 1
Desien Storms
Time
Intensity of rainfall
interval
(in./hr.)
(min.)
2-yr.
100-yr.
0- 5
0.84
2.16
5-10
0.96
3.00
10-15
1.80
5.04
'
15-20
3.24
9.00
20-25
1.32
3.72
25-30
0.60
1.68
30-35
0.48
1.56
35-40
0.48
1.44
40-45
0.36
1.20
' 45-50
0.36
0.96
50-55
0.36
0.84
' 55-60
0.36
0.60
1
'
-4-
--.- .-
RESOURCE COM ULTME INC
II
i
Ja w
0
w v
OJ
ro ro
N 0)
A10 S
m A
Cro 0)
J G
(L) ro
Nm
S4 C
ro ti
11, m
ro
! A
O
m
J)0
•rH
F�a
it
■
1
In
ESz.+Ia a aj
i.ic!-OiO OOO
x¢mlmmmm:
Iz 010 0 O'0
. > 0:0 0 O',O
W
IiL
Y
zz
•OL O O o O1O
'•+ z V7.. 4. 47 VI'47
� z -
cc
�s
'J z
H
z L 0'0 O O'O
z X .1 . . .lo
IM .
Q M''M M MiM
,z z
> O'O O 0'0
u: 00 0OO
W M,M M M M
IC9
jEn 1
W1200000
U w W O O O O O
LLz
Ze
Im
it - I I
O > O O O O'O
1-it 4700047
UW NC4 NjN
W LL 'I I
W
U
z ,
¢ >
r s •O
W i. .
U) 00 000
c+LL - -0 .
Wn�
Wl 00000
LL W M a O N O
0 00 - •1M
�-1 0'0 0 0 0
(A 11 • i • • • r .
Z > to V) CO V)
W it -
U W V) •O a
w a. N MV)
MJ�
W =
u r
I
I
I
Q + M�•O 47 0.•0
LLJ U
CL Q V) •O .r M
I
,2 O;O O 0'0
I H 0.0 m O N
M v .yl I
3 ! i
jj
W I
z
x
m!J- jO
\ILL U. w
•LW ...
z J3
¢
WA
cz
0
Z ;M
M .y
Iz z 'o
z i.
¢
F
to Cr
W W O
LL> re
0
U) I
1
W N :O
u � _j
H cc
m'O
: I
I
F W♦- 0
CC LL W
W O \ 'O
> J !- 'O
I
FI
a
0
0
M I
M
i
.y
o I
o,,
o
,01 I a
I
O -
O
M�
-I n
MI
•
o
of
J
1 .a
O
O
O
O
O
O
I
o;oo0
V)IO 47 N
N 4
O' O •0 M
Q Q ..
0000
0000
M M M •
I M
0000
a V) a C.
0000
0000
z cn L�
.o :
c
I
x
�-
o'
o
o'
0000
o�
0 1
0
0
N10rJ0
Z U.
:
3 •1
3N
3.r
O
O
O
Z
IJi
4
lJi
2Qr
OJ-
O)-
O J-
O O OM
u uW
001
OIL
ON
MM.+.+
M,
:o
3
3
3
I J I
J
IJ
! J
J!
J
..
LL
..
LL
L
Q-
m
(n
m
O
Q
N
J J J
!n
(n
m
W W W
> 1
>
>
z z z
w
w
J.J
z z z w
(L I
i1
11 /—
¢ ¢ ¢ iY
•+W
H W
w
.+W
x x xt4
LL w
LL W
LL W
U U U LL
LL
L.
w
W
W
W
u
U
U
u
u
U
i
Q
¢
¢
N z
N z
z
.,
..
W
W
W
j
(O 0W
O
O
¢ .
Q
Q .
0
O
0
O
0
F•
H
N
EnLO
m
LL
iY
iL
iL
a
V)"O
M-O
•0"O
0000
.z
O
O
O
>
>
>
l[ I
IL
l[
W I
W
W
Jn
En
m
W :
W
W
LL
LL
Lc:
Z
1 i
Ire O
1
W F
H U
,?
V)
N
V7
M NO
I
t7 Z
O
U
rr c
W W
FL
•+
N
M
cN"0n
bl
rol
C21
J
-H
m
w
0
I
J
�
O
F.i
I
!
NI
Ol
to
nl
N
W
LL
LLCL
�
0
J
m
G
\
N
w
7
J
m
�
x
Jll'
w'
0
(Z
W
a.
41
m
r
n
1
z
Q
~
v
w
�
I
I
There is also the model analysis shown in Table 3. This table shows
the results of the 100-year storm analysis on each drainage element. Fig. 1
also shows the peak flows at critical points within the drainage system.
Fig. 2 is the hydrograph in the storm sewer at the north edge of the property.
This assumes that the street flow from Timberline Road would be intercepted
by the storm sewer at this point. This is not currently the case.
Summary and Conclusions
The revised drainage analysis for the PRPA site showed that in order
to maintain historic 2-year flows off of the site during a 100-year storm,
enlargement of the pond on the northeast corner of the site and construction
of a pond on the undeveloped portion of the site are necessary. Using these
drainage improvements the outflow from the 100-year storm is 1.9 cfs.
Including drainage from Timberline Road the total inflow to the storm sewer
at this point would be 5.8 cfs.
In addition to the 10-inch outflow pipes from detention ponds #2 and
#3, overflow spillways were designed for each of the three ponds. Appendix
A shows the stage -volume curves for each pond as well as the outflow rating
curves. Appendix B shows the results of the 2-year calculations for the
historic and fully developed conditions.
-6- RC50URCC CONSULTANTS INC
Table 3. -
100-Yr. Storm Hydrographs for each Drainage Element
HYLIROGRAF'HS ARE LISTED FOR THEFOLLOWING 7 POINTS
--- -- --
_ THE UF'F•ER NUMBER IS DISCHARGE IN CFS
THE LOWER RUi1IFER IS DEPTH ABOVE_INVERT IN FEET
THE LETTERS (S)v UENOTES STORAGE IN ACRE -FT FORDETENTION
PONDS (numbers indicate drainage elements on Fig. 1)
1--
0
1.00
.00
.00
.00
.00
- .00
.00
.00 _
.00
.00
.01
.01
.0!
.01
.00
0
6.00
.00
.01
.04
.00
011
.23
.1i
.00S
.00S
.00S__
.00_
.07
.08
.14
'
0
11.00
.04
.C+6
.41
_
.00
_
- 1.33
_
1.10
1.4G
.04S
.01S
.02S
.00
.32
.16
.41
0
16.00
.00
.16
.92
.00
3.02
2.73
3.51
'
.105
.03S
.085
.00
0.50
•24
•68
0
21.00
.00
.44
1.23
.00
7.38
4.53
-' . 84
`
I'-
.24S
.09S
.18S
.00
0.80
.30
.98
0
26.00
.00
.74
1.39
.00
4.47
2.55
_
4.01
VIO
.34S
.14S
.25S
.00
0.62
.23
.74
31.00
.00
1.02
1.49
.00
3.75
1.36
2.88
.39S
.20S
.315
.00
0.57
.18
.EO
O
36.00
.00
1.27
1.58
.00
3.75
1.01
2.60
.43S
.25S
.36S
.00
0.57
.16
.57
0
41.00
.00
1.41
1.64
.00
3.60
_ .85
2.50
'
.475
.29S
.40S
.00
0.55
.15
.56
0
46.00
.00
1.43
1.68
.00
3.40
671
2.40i
.505
.335
.44S
.00
0.53
.14
•54'
I
0
51.00
.00
1.44
1.71
.00
3.10
.58
2.29
\�
.52S
.37S
.48S
.00_-_
0.51 -
.12
.53
O
56.00
.00
1.46
1.74
.00
3.00
.48
2.22
;_i
.54S
41S
51S
00
1'■.
1
1.00
.00
1.47
1.76
_ .00
3.29
.
�11
36
`.52'
.13
.56S
.44S
.53S
.00
_
0.44
.10
.51
S
1
6.00
.00
1.48
1.78
.00
- 1.57
.18
1.97
6
.57S
.46S
.56S
.00
0.36
.07
.49
7
1
11.00
.00
1.49
1.79
_
.00
1.56
.09
_
1.89
a
.57S
.48S
.57S
.00
0.36
.05
.48
9
1
16.00
.00
1.49
1.81
.00
1.56
.05
1.86
h.
.58S
.50S
.59S
.00
0.36
.04
.47
++I
1
21.00
.00
1.50
1.82
• 00
1.55
.03
! . 85
.585
.515
.60S
.00
0.36
.03
.47
I+_
+=
1
26.00
.00
1.50
1.83
.00
1.55
_
.02
1.85
.58S
.535
.62S
.00
0.36
.02
.47
+-
1
31.00
.00
1.51
1.84
.00
1.54
.01
1.86
+•
.58S
.54S
.635
.00
0.36
•02
.47
+=
1
36.00
.00
1.51
1.86
.00
1.53
.01
1.86
18
.58S
' .54S
.64S
.00
0.35
.02
.47;
�+=
1
41.00
.00
1.51
1.87
667
1.52
_
.01
1.,87
�•�
.59S
•55S
.65S
.00
0.35
.01
.47
2+�
1
46.00
too
1 .52
less
.00
1 1.51
.00
1.88
-_'
.5�i� .55-
.00
0.35
.0
.48
'.
1
51.00
.00
1.52
1.88
.00
1.50
.00
1.89
.59S
.56S
.67S
.00
35
.01
.48
z��5b.00
_•�,
.0-2�1.52�8'00
.59S
.56S
.67S
.00
-.50
1.35
.00
.01
1.897
.48-
-7-
M M M�M M I iM M M M
of
0I0
CO
1 N
I
1
I
,I
to
I
I
I I � •-1
II
1
I
I
i
;
I
II
I
I
'1 �O
I
1
I
I
it
I P
M
I� rl
'
1
I
d
II
I N
M •
ll..i
I
I
ce
O
L
1
x
o
I o
u I
LJ i
1
In
W
ro
I
L
N
I
J..I
m
O
l
L
'
ro
1
I
co
I
P
so+
�I
•O
x
li
I
li
g
I'
o
W
1.1
jl
7
I
O
1
ca
ro
1
41
I N
yy
E
I
I
!F I
iE
•1f
�
1E O
7••I
M M M M M
I M FI
M M H
Fq Fq M
M I M
M I-1 H
Fp M M,M
M I
M FI
�1 M M
M M iF
4
10
O
O
O
10
O
O
O
j•0
v
NI
i •
IW LL
O
Z
C1
Z
N
IL
O
U46
�
_
J
APPENDIX A
Stage -Volume Curves
and
Outlet Pipe Discharges
for
Ponds 1, 2, & 3
to
�-
b
ILui
W
-
-
S _
0,0
__ - --
-
-
in
to
-
A-1
090
OOa
JL
1
_
140
Ul
to tf)
V fn n! -----T
A-2
II
II
1
U
0
7
'
�
Q
N
�
D
O�
S�z
O �Z
O
3
0
O
uo��on al.�
LL
U
Q
A-3
;t,
uo
a
o-�
S 'Z
o,
O Z
b
3
s�
L
N
O
o
'0
o
o
00
to
tc)
tO
W)
' ----- -- - u 01 DA a/.3 — -
' J Get „ -�, ��'_
••
�
•.
•._ �
- _-..--•�!
%_
�
_
_r-.• •___._ _ __-.._ __!. _._.. ♦
...- u _.
._ '
_. _..
00
9*0
LL
tp
— i
~"
-- - -- -
suol�Dn a/-3--
` - . .
_---'--
--
- ------ i
r-77
- - --
- -
- - -
--
-A-S
_
/
r
------------------------------
Ole
Uo
1
_
APPENDIX s
Hydrographs
n
2-Yr. Hydrograph for Historic Conditions
.� HYDROGRAPHS ARE LISTED FOR THE FOLLOWING 1 POINTS
16.
THE UPPER NUMBER IS DISCHARGE IN CFS
I THE LOWER NUMBER IS DEPTH ABOVE INVERT IN FEET
THE LETTERP (S)r DENOTES STORAGE IN ACRE -FT FOR
DETENTION PONDS
TIME 1
0 1.00 600
.00
V
O.VV
.VV
too
0
11,00
.04
.05
0.16.00
.60
0
21.00
1.56/
5
.37
0
26.00
1.26
33
0
31,00
.81
0
36.00
.56
.21 .
0
41,00
.44
0.46.00 .36 '
.16
V .J1. VV
.Qj
.15
0 56.00
.29
.14 -
1 °..1.00.
-.27.
.
.14
1 6.00..
.19
.li
1 11,00
.13
.07 .
1 21.00
.06
.06
1 26.00
.04
.05
1 31,00
.03
.04
1 36.00
.02
:03
1 41,00
.02
.03 -
1 46,00
.02
.03
1 51,00
.01 --- -
.02
1 56,00
.01
' B-1
Table B-2
)ed Conditions
DR.OGR.APHS ARE LISTED FOR -THE FOLLOWING 7 POINTS
THE UPPER NUMBER IS DISCHARGE IN CFS
THE LOWER: NUMBER: IS DEPTH ABOVE INVERT IN FEET
THE LETTERS (S) v DENOTES STORAGE IN ACRE -FT FOR DETENTION PONDS
TIME
1,
- 2
q
5 ..:.:..,
6 .:
7
10
1.00
.00
.00
100
.00
.00
100
.00
.01
001
.01
.00
.00
.00
.01
6.00
.00
.00
.00
.00
100
.00
400
,O
.00S
.00S
.00S
.00
.00
.00
.01
0
11.00.
.00
.01
.02
.00
.04
..11.
.08
.00S
IOOS
.00S
.000
.04
.06
.10
SO
16.00
.00
.03
421
.00
.63
.57
.72
102S
.O1S
.01S
.00
.21
.12
.29
0
21,00
.00
.08
.65
.00
1.57
1410
1
.05S
IO1S
.04S
.00
.35
.16
.45
0
26.00
..00..
.10
1.86 .,
.00
1.14
,.71
1.59
.08S
.02S
.06S
.00
*29
.14..
.43
0
31.00
.00
.10
.88
.00
.71
.41
1.31
.09S
.02S
I06S
.00
.23
.11
.39
0
36.00
100
.11
.89
100
.52
.29
1.18
.10S
102S
•07S
000
.19
.09
.37
10
41.00
.00
.11
.90
.00
.44
.24
1.13
.lOS
.02S
.07S
.00
.17
008
.36
0
46*00
.00
Ill
.90
.00
.39
.19
1.09
Ills
.02S
.07S
.00
.16
.07
.36.
L
51.00.
.00
.12
089
.00
.36
.17
1.07
Ills
•02S
.07S
.00
.15
.07
.35
56.00
.00
.12
.89
.00
.34
.16
,1.05
'0
.12S
.02S
.07S
.00
.15
.07
.35
1
1.00
10.0
.12
.89
.00
.33
.15
1.64
.12S
.02S
.07S
.00
.15
.07
.35
,1
6.00
.00
.12
.88
.00
.26
.09
.97
.12S
.02S
.06S'
.00
.13
.05
.34
1
11.00. ,..:.``.:..00
Ili
.87
` .00
.20
.05
.92
:12S.
.02S
.06S
.00
<.11
.04
.33
'1
16.00 r
.00
.11
.86
.00
.16
.03
.89
113S
.02S
.06S
.00
.09
.03
.32
121.00
000
.10
.84
.00
*14
*02
.86
.13S
.02S
.05S
.00
.09
.102
.32
1
26.00
.100
.10
.77
.00
112
.01
-
.79
.13S
.02S
.05S
.00
.08
.02
.30
11
31.00
.00
.10
.70
.00
Oil
.01
.72
113S
.02S
.04S
100
.OS
.01
.29
1
36.00
.00
109
*64
000
oil
.01
.65
.13S
.02S
.04S
.00
.08
.01
.28
1
41.00,.
.00.
.09
.58
.00
.10
.00
.59
•.
..13S
.02S
.03S_
000
.07
.01
.26
1
46.00
.00
.09
.53
.00
.10
.00
.54
.1S
.02S.
.03S
.00
.07
.01
.25
1
51.00
.00
008
.49
000
.09
.00
.49
.13S
.02S
.03S
.00
*07
.01
.24
�5a.00
.00
.0$
.44
.00---*
6
_
.13S
.02S
.03S
100
.07
.01
.23
B-2