HomeMy WebLinkAboutDrainage Reports - 02/01/1991SHIELDS AND SWALLOW
DRAINAGE STUDY
PREPARED FOR
THE CITY OF FORT COLLINS
STORM WATER UTILITY DEPARTMENT
PREPARED BY
ROCKY MOUNTAIN CONSULTANTS, INC.
P.O. BOX 1649
ESTES PARK, CO 80517
FEBRUARY, 1991
1
11
I
one
engineers • planners • surveyors
February 14. 1991
Mark Sears. P.E.
City of Ft. Collins
Engineering Dept.
P.O. Box 580
Fort Collins, CO 8OS22
' Re: Shields and Swallow Drainage Study
1
Dear Mark:
Enclosed you will find a copy of Rocky Mountain Consultants., Inc. Storm
Drainage Study for the South Shields and West Swallow Subbasin, part of the
Spring Creek Drainage.
Additional copies of this report have been sent to Glen Schluter of
Stormwater- Utility and Jay Holmann of Poudre R-1. We have enjoyed working
with you on this project.
If you have anv questions, please do not hesitate to call..
Sincerely,
ROCKY MOUNTAIN CONSULTANTS. INC.
Gary A. Odehnal
Civil Engineer
Reviewed by-
/ j
Ker M. Prochaska_. P.E.
Pro ect Engineer
GAO/tst
Enclosure
Rocky Mountain Consultants, Inc.
Post Office Box 1649, Estes Park, Colorado 80517 303-586.2458
Offices also in Denver and Longmont, CO Metro line: 825-8233 Fax No. 825-8912
I
TABLE OF CONTENTS
PAGE
I.
INTRODUCTION .................................
1
II.
STUDY AREA ...................., .............
2
III.
EXISTING STORM DRAINAGE FACILITIES...........
2
A. Street Conveyance .......................
2
B. Wagon Wheel Detention Pond and Outfall..
2
C. P.U.D.'S and Subdivisions ...............
3
D. Silver Plume P.U.D........ 6.............
5
E. Rocky Mountain High School ..............
5
F. Cimarron Square Channel and 42" Outfall.
6
IV.
DESIGN CRITERIA .............................
7
V.
ALTERNATIVES AND COSTS .....................
11
A. Alternative 1...........................
11
B. Alternative 2...........................
11
C. Alternative 3...........................
14
D. Alternative 4...........................
16
E. Alternative 5... .....................
18
VI.
RECOMMENDED ALTERNATIVE...' ...................
20
APPENDIX A - CALCULATIONS
APPENDIX B - SWMM RUNS
I
'I. INTRODUCTION
This storm drainage report was developed to support planned street
' improvements for South Shields from Casa Grande to Davidson. The widening
and upgrading of South Shields required a detailed analysis of storm
' drainage conditions and evaluation of the existing collection system.
Rocky Mountain Consultants, Inc., (RMC) was retained by the City of Fort
Collins to develop a storm drainage study, following is a brief outline of
our Scope of Services.
' A. Data Collection
1. Collect existing storm drainage reports and plans for
contributing subdivisions from existing City of Ft. Collins
files.
2. Collect existing data for the Rocky Mountain High School
site.
3. Review reports and site plans, incorporate relevant
information into subbasin model.
B. Hydrology and Hydraulics
1. Develop a SWMM computer model of the subbasin, model the 2,
10, and 100-year events.
2. Incorporate planned street improvements into the SWMM model.
3. Determine street flows from hydrological data.
4. Size storm sewer inlets and piping system.
C.. Existing Stormwater Interceptor
1. Evaluate the capacity of the existing subsurface collection
system.
2. Determine energy losses and hydraulic grade line's for
existing system.
D. Alternative Analysis and Improvements
1. Develop design alternatives to evaluate routing of surface
flows, detention ponds, subsurface piping and surface
collection to handle the 2-yr and 100-year storm events.
2. Provide a preliminary construction cost estimate for
proposed storm drainage improvements.
3. Develop a design report presenting findings from our
investigation, alternative analysis, costs, and
recommendations.
1
' II. STUDY AREA
' The subbasin that was investigated for this study consists of approximately
175 acres of developed, undeveloped and Poudre R-1 School District
property. The area is located on the .southern edge of the Spring Creek
Basin and drains north to the Cimarron Square Subdivision and east to South
Shields. The basin topography is very flat, falling gently at less than 1%
' to the northeast. The area has a history of agricultural use, as evidenced
by abandoned.irrigation laterals and farm structures. Refer to Figure 1
' for a vicinity map of the study area.
' III. EXISTING STORM DRAINAGE FACILITIES
A. Street Conveyance
' The primary surface conveyance features consist of West Swallow, Rocky
Mountain Way and South Shields. These street prisms collect surface
flows or outfalls from adjacent properties and transfer these flows to
' South Shields. West Swallow acts as the main collection element as
numerous upstream subdivisions and P.U.D.'s drain onto the street,
' including undetained flows fom the Rocky Mountain High School site.
Field cross sections were used to calculate street carrying capacities
for these elements, calculations are in Appendix A.
B. Wagon Wheel Detention Pond and Outfall
' A subsurface piping system begins at the outfall of the.Wagon Wheel
detention pond and parallels the westerly edge of pavement on South
' Shields. The pipe sizes range from 18" RCP to 24" HERCP and continue
2
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34 SOBS
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cy� e
VICINITY MAP SCALE I"_=2,0001 N
W E
S
SHIELDS a SWALLO R M C
STORM DRAINAGE FIGURE
IMPROVEMENTS I
northward to the intersection of South Shields and Rocky Mountain Way.
' Inlets located .at this intersection capture surface flows and the pipe
turns northeasterly crossing under Shields to parallel the easterly
' flowline of the street. The pipe continues north as a 30" RCP to
empty into an open channel on the south side of the Cimarron Square
development. The entire outfall line is very shallow with the crown
' of the pipe less than 1 foot from the surface. A detailed hydraulic
analysis was performed on the pipe and is available for review in
' Appendix A. This analysis shows that the upstream elements of the
pipe system (manholes 1 and 2) will be surcharged during the 2-year
' storm event. Figure 2 shows a schematic of the system.
' C. Contributing P.U.D.'s and Subdivisions
Numerous developments contribute flows to this sub -basin area. Per
City of Ft. Collins standards, these areas release at the 2-year
historic rates: The differences between the 2-year release rate and
the 100-year storm is detained on site in ponds or parking lots.
' Table 1 gives a run down of all existing or planned developments with
approved two year release rates. All developments contribute at some
point in the system, with the exception of Cimarron West and Cimarron
Sam. These subdivisions outfall directly to the open channel at
Cimarron Square. Please refer to Figure 2 for a sub -basin diagram.
LJ
' 3
Table 1
Development
Silver Plume A P.U.D.
Silver Plume 3rd Filing
Gables at Silver Plume
Jon -El P.U.D.
Wagon Wheel -north detention pond
Kinder Care
Cimarron West (Pond 2b)
Cimarron Square
4
Release Rate (2 yr)(cfs
1.7
1.23
1.21
0.90
15.0
0.18
6.42
6.8 (2yr)
20.4 (100 yr)
SILVERPLUME
3rd FILING
1
.�O
cccecc�f 1.2
GABLES AT
1
SILVERPLUM
°A° P.U. D.
PEACE w/
CHRIST
LUTHERAN
CHURCH
3 LEGEND
m0 ==�>DIRECTION OF SURFACE FLOWS
MUM= DRAINAGE DEVIDES
OPEN CHANNEL
O DRAINAGE" CONCENTRATION POINTS
(SEE TABLE 2a3)
CIMARRON WEST
Z/1
c``,bN EL
J
JJJ>
MH-7J/ O CIMARRON SQUARE
278 LF 30" RCP 0.52 % I TO WOOD WEST
35 DETENTION POND
MT. VIEW VET
KINDER
71
u
� I
392 L� I
24�� HERCP --�I
aQ 0.23%
GI I
MH-3
246LF I
18" RCP
n M-H-21
347 LF
24!' HERCI
Q 0.47%
rWAGON WHEEL)
DETENTION POND
DETENTION POND 15
15
OUT FLOWS
r EXISTING DETENTION
POND
SUBSURFACE PIPE SYSTEM
lO
464 LF
�—I RCP
a 0.13%
I
f WOOD WEST.
0
a
0
w
z
0
0
MH-6
,75 LF 30'1 RCP
Q 0.71 % N
WAY A>�
14>1
W E
S
N.T.S.
li-1 SUBCATCHMENTS AND
POINTS OF CONCENTRATION
FIGURE 2
' D. Silver Plume P.U.D.
As part of the subbasin modeling drainage reports and site plans were
reviewed for all contributing areas. All existing drainage reports
were complete with the exception of the Silver.Plume P.U.D. This
' report was submitted to the city in'Aug. of 1979 by M & I Consulting
Engineers. Subsequently, these plans were revised with no
corresponding update of the drainage report. A 10" PVC outfall line
from the gouthPa4terly detent�np pond was installed and drains to the
northern curb flowline on West Swallow, adjacent to Rocky Mt. High..
tHydraulic analysis of the outfall revealed that the maximum capacity
of the outfall is only 1.7 cfs under full ponding conditions. Our
calculations show that the 2-year historic release rate is 2.7 cfs.
' Greater than the release rate of the outfall line. The as -built
capacity of the pond is currently unknown, if the pond does not have
' the ability to detain accumulatad stormflows during the ma.ior event,
' overtopping of the embankment will occur. The actual release rate
from the pond will be somewhere between the 1.7 cfs and the 100-year
event release of 37.4 cfs, further analysis will be required to
determine the actual release rate.. This extra water will overtop the
' detention pond berm and flow into the playing field areas of Rocky Mt.
High School. Please refer to Appendix A for all associated
calculations.
' E. Rocky Mountain High School
The high school site currently has no provisions for either rooftop or
surface detention. All storm water falling on. the site is collected
' as surface flows or accumulated in the rooftop drains and piped to the
1 5
flowline of Swallow. The parking areas on the east side of the school
drain to Rocky Mountain Way, concentrate in the flowline and drain
northward to the intersection at South Shields. The rational method
was used to determine the actual historic flows from the site, grading
plans obtained for Poudre R-1 files were used.to establish the
undeveloped points of concentration. The 2-yr historic release rates
were calculated to be 2 cfs (on Swallow) and 5 cfs t the NE corner of
the property, draining to Rocky Mountain Way. N/ .0-ro- +�e_
F. Cimarron Square Channel and 42" Outfall
All flows accumulated in this sub -basin concentrate as surface flows
or pipe outfalls into the open channel on the south side of Cimarron
Square. This channel falls eastward to a large drop structure and 42"
RCP at the far southeasterly corner of the Cimarron Square. Stormwater
is accumulated at this point and flows into the subsurface collection
system of the Wood West Subdivision, eventually outfalling in the
Woodwest Detention Pond. The channel has a capacity of 225 cfs (with
one foot free board) and the pipe has a capacity of 120 cfs.
9
' IV. DESIGN CRITERIA
The basin hydrology was simulated using EPA's Storm Water Management Model
(SWMM), modified by the Missouri River Division of the Army Corps of
' Engineers. The model computes runoff utilizing overland flow and channel
' routing routines.
Hydrologic analysis including analyzing the runoff from the 2, 10, and 100-
year storm events. These storm events were developed based on
precipitation intensity duration curves for the Ft. Collins area. In order
' to accurately model the basin, the entire area was broken into
subcatchments. Figure 2 shows the boundaries used for these subcatchment
divides. A total of 19 separate subcatchments were used along with
' detention ponds, storm sewer and channel elements.
' Infiltration, surface storage and decay rates were obtained from the Spring
Creek Masterplan study. These factors were used to accurately reproduce
' results from the Spring Creek study due to the fact that this subbasin is
part of larger Spring Creek Drainage Basin.
' For the purpose of this study, the 2-year release rates were modeled with
SWMM, the results were checked against the rational method release rates
and adjusted if necessary. These 2-year release rates were used as "point
raisch�es" d and
undeveloped parcels in the basin, with the exception of the release from
the Rocky Mt. High School site. The runoff from this site was considered
historical, even though the site is presently developed and detains no
' 7
1
storm water. 'This resulted in high runoff quantities from the high school
site, -which closely models all present conditions. Table 2 shows the peak
' flows computed from the design storms under existing conditions. In. order
to accurately model fully developed conditions, existing undeveloped land
' in the area was modeled with only the 2-yr historic release rates
to simulate onsite detention for these sub -catchments. Table 3 shows peak
' flows under fully developed conditions. Concentration points referenced in
' Tables 2 and 3 are shown on Figure 2.
'
8
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1
TABLE 2
COMPUTED PEAK FLOWS AT VARIOUS
POINTS WITHIN SHIELDS & SWALLOW SUBBASIN,
(EXISTING.CONDITIONS)
PEAK FLOWS
POINT LOCATION 2-YR 10-YR 100-YR
A West Swallow -west of 3 11 23
Rocky Mt. High
B
West Swallow -in front of
14
46
Rocky Mt. High
C
15' Inlet -west flowline
3
4
of S. Shields
D
West Swallow -between
14
39
Rocky Mt. High and S. Shields
E
Souh Shields north of
15
40
West Swallow intersection
F
Open channel overflow to
1
6
Woodwest Subdivision .
G
Rocky Mt. Way north
10
21
of school parking lots
H
Open fields and some
8
34
parking lots from high school
I
Rocky Mt. Way east of
17
51
field areas
J
Intersection of Rocky Mt.
7
72
Way and.S.'Shields
K
Open channel at
41
107
Cimarron Square
9
86
7.
83
76
19
34
92
116
178
216
TABLE 3
COMPUTED PEAK FLOWS AT VARIOUS
POINTS WITHIN SHIELDS & SWALLOW SUBBASIN
(FULLY DEVELOPED CONDITIONS)
PEAK FLOWS
POINT
LOCATION
2-YR
10-YR
-100-YR
------------------------------------------------------------
A
West Swallow -west of
3
11
23
Rocky Mt. High
B
West Swallow -in front of
14
.35
67
Rocky Mt. High
C
15' Inlet -west flowline
3
4
6
of S. Shields
D
West Swallow -between
14
34
65
Rocky Mt. High and S. Shields
E
Souh Shields north of
15
38
70
West Swallow intersection
F
Open channel overflow to
1
6
19
Woodwest Subdivision
G
Rocky Mt. Way north
10
21
34
of school parking lots•
H
Open fields and some
7
30
67
parking lots from high school
I
Rocky Mt. Way east of.
17
51
116
field areas
J
Intersection of Rocky Mt.
7
72
166
Way and S. Shields.
K
Open channel at
41
107
204
Cimarron Square
NOTE: Current undeveloped areas within the subbasin have been
modeled with the 2-yr release rates to simulate fully developed
detention of these areas. The high school site was modeled
as currently existing with no detention of roof or surface flows.
10
' V. ALTERNATIVE ANALYSIS AND COSTS
' A. Alternative #1 - Do Nothing
In order -to develop baseline points and analyze the existing condition
the 100-year event was run with no improvements other than S. Shields
' Street improvements. All undeveloped areas were modeled to closely
simulate fully developed conditions with 2-year release rates, and on -
site detention with the exception of flows from the high school site.
Figure 3 shows the -results from this computer.simulation. Flows
' accumulated on West Swallow and Rocky Mountain Way will overtop the
' crown on S. Shields and flow east into the Wood West Subdivision.
Surface runoff spilling east onto Rocky Mountain Way will total over
120 cfs, overtop the street and flood homes adjacent to South Shields.
Flooding can also be expected on the west side of Shields north to the
' detention pond at Cimarron West.
Alternative #1 has no associated cost for drainage improvements.
' However, should a major storm occur, the damage to surrounding homes
and businesses could be substantial.
B. Alternative #2 - Modify Pipe
' The first improvement alternative involved replacement of undersized
' pipe and addition of 500 if of 34" HERCP. Approximately 670 if of 30"
RCP would replace 18" and 24" RCP between manhole 2 and manhole 4.
' The.increased pipe size will allow inlets.at the intersection of South
Shields and West Swallow to.capture a larger quantity of surface
' flows. Flows would still be anticipated to overtop South Shields,
11
approximately
15 cfs would flow east onto West Swallow.
'
The 500 lf.of
34" HERCP 42" RCP)
(equivalent would share manhole.5 and
run north to a
new manhole and then turn east under South Shields to .
exit in the Cimarron
Square channel. The increased pipe capacity -
would carry surface.
flows col lPc -d in -inlets at Lock*-Ho»n , p way_
and South Shields.
Runoff could be expected to overtop the crown at
'
this intersection,
20 flow Rocky
approximately cfs would east onto
'
Mountain Way.
Flooding of buildings on the west side of South Shields
could also be
expected due to ponding of flows at the intersection.
Figure 4 shows
Q's expected during the 100-year storm event. Table 4
gives drainage
improvement costs.
1
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1
1
1
1
' 12
O�
SILVERPLUME
3rd FILING
J
�Qv v,4
CIMARRON WEST
SILVERPLUME
11A" P.U.D.
ROCKY MTN. HIGH SCHOOL
PEACE w/
CHRIST
LUTHERAN
CHURCH
Flooding MH-7.� CIMARRON SQUARE
278 LF 30° RCP
® 0.52 % : TO WOOD WEST
34 DETENTION POND
MT. VIEW VET. 1
Flooding, 55 MH-6 Flooding -
KINDER CARE 01 75LF 30"RCP
Flooding MH-5 aQ 0.71% N
67 ROCK 241 MT. WAY
116 W E
Floodingf S
I lO
392LF I f N.T.S.
24" HERCP 464 LF
aQ 0.23% �--15RCP
I 3 Qa 0.13%
I
11-4 WOOD WEST
15
• OI
I cn
} 19
w
3 4'1
2R
�� RCP
aQ 0.34% I
Y ~
U
O
MH-3 N C-)
a
246LF I o
18" RCP 1 ai
42 Z
O
n MH-21
WEST SWALLOW
T 30 -
67
JON — EL
347LF
w
P. U.D.
24'�HERCP
a'
® 0.47% ALTERNATIVE N2 I
MH-I
3
LEGEND
DO NOTHING
m
DIRECTION OF FLOW
WAGON WHEEL
15 6
O EXISTING INLET
DETENTION POND
FIGURE 3
O PROPOSED INLET
O DRAINAGE CONCENTRATION POINT
.1
1
1
1
1
1
1
1
1
1
i
1
.1
1
1
I
CIMARRON WEST
SILVERPLUME
IAA" P.U. D.
ROCKY MTN. HIGH SCHOOL
4
l_,44vqr
SILVERPLUME
3rd FILING PEACE w/
CHRIST
LUTHERAN
CHURCH
WEST SWALLOW
w
a
3 LEGEND
m DIRECTION OF FLOW
O DRAINAGE CONCENTRATION POINT
❑ PROPOSED INLETS
0 EXISTING INLET
i
I JON — EL
P.U.D.
50OLF 34 MERCP
aQ 0.68 % _�
278LF 30"RCP
Qa 0.52 %
MT. VIEW VET. .
Flooding
i
KINDER CARE
'MH-5
Flooding
ROCKY
I�
vLic �_
MH-7 TO WOOD WEST
O
DETENTION POND
1 MH-6
,75LF 30°RCP
aQ 0.71 % N
MT. WAY /4�
I 10
392LF
24° HERCP �-15"RCP
464 LF
aQ 0.23% I
Qa 0.13%
�
I
MH-4�
f
35I
I
663LF
I
U)
J
a
3
30° RCP
Q0.60%
417LF
w
N
24 RCP
7--A @ 0.34%'
Y
�
m
MH-3
N
246LF I
18'l RCP
aQ 1.11% ,
42
65 MH-
WAGON WHEEL
DETENTION POND
347 LF
24°HERCPI---
0.47%
MH-I
WOOD WEST
19
F-
U
a
c�
0
cn
w
z
0
0
ALTERNATIVE N2 2
MODIFY PIPE
FIGURE 4
'
TABLE 4
ALTERNATIVE
#2
PRELIMINARY COST
ESTIMATE
1
,Item Description
Unit Quantity
Unit
Price
Total
Price
30" RCP
LF
670
$38
$25,460
134" HERCP
LF
500
$70
$35,000
5' Manhole
1
EA
4
$1000
$42000
10'Type R Inlet
EA
2
$2800
$5,600
'20'Type R Inlet
EA
2
$4200
$8,400
Concrete Headwall
CY
6
$400
$2,400
' with Wingwalls
20% Contingency
$16,200
'Total Project Cost
.......... ...............................
$97,000
1
1
1
'
13
1
1
1
1
1
C. Alternative #3 - Divert - Detain Pipe
r
This solution requires the construction of a small detention pond in,
the northeasterly corner of the high school property. A small area
inlet would capture flows and the 15" RCP would be designed to release
at the.historic 5 cfs rate. Runoff collected in the north flowline of
West Swallow would be diverted north onto Rocky Mountain Way by
removal of the existing crosspan and minor modifications to the street
crown. Water collected in the south flowline of West Swallow would
continue to the intersection of South Shields where approximately 10
cfs would overtop South Shields.
Surface flows at the intersection of Rocky Mountain Way and South
Shields would be intercepted by inlets and handled by a new 36" RCP,
following the same -alignment as outlined in Alternative #2. The
addition of the detention pond and diversion flow onto Rocky Mountain
Way will reduce peak flows adequately, only 7 to 10 cfs can be
expected to flow into the Wood West Subdivision. Figure 5 shows peak
flows, Table 5 gives the cost estimate.
14
CIMARRON WEST
SILVERPLUME
IAA" P.U. D.
ROCKY MTN. HIGH SCHOOL
/,4N
SILVERPLUME
3rd FILING PEACE w/
CHRIST
LUTHERAN
CHURCH
WEST SWALLOW
W
a
w LEGEND
m _ DIRECTION OF FLOW
O DRAINAGE CONCENTRATION POINT
O PROPOSED INLETS
O EXISTING INLET -
DETAIN
3.3Ac.ft.. C
r
n
n
n
n
n
n
n
2
`CCfCc�ccc-ccc fcc
Q
3
}
Y
U
O
It
1 1 DIVERT
35cfs
JON = EL
P.U.D.
WAGON WHEEL
DETENTION POND
50OLF 36 RCP
® 0.68 % �,�
278 LF 30" RCP
Q 0.52
n�
MT. VIEW VET. I
i
KINDER CARE
' MH-5
0
392LF
24°HERCP
aQ 0.23%° i
MH-4 C
81
I N
0
J
w
417LF _
24°RCP.' �
QQ 0.34% I
D
O
MH-3 N
246LF I
18" RCP -
aQ I.I%
��I� 2E
1301 MH-21
347 LF
24!'HERCP
& 0.47%
MH-I
15 6
i
CIMARRON SQU
r MH-7 TO WOOD WEST/
134 DETENTION POND
MH-6
,75LF 30ofRCP
aQ 0.71 %
r J 'MT- WAY
to
464 LF
—15" RCP
IQo 0.13%
WOOD WEST
F-
U
Q
c�
0
w
z
O
U
ALTERNATIVE N2 3
DIVERT -DETAIN -PIPE
RE
FIGURE 5
Inc
'
TABLE
5
ALTERNATIVE
#3
PRELIMINARY COST ESTIMATE
Unit
Total
'
Item Description
Unit
Quantity
Price
Price
36" RCP
LF
500
$42
$21,000
'
15" RCP
LF
,470
$20
$99400
5' Manhole
EA
3
$1000
$39000
'
4' Type C Inlet
EA
1
$1000
$1,000
'
10'Type R Inlet
EA
2
.$2800
$5,600
15'Type R Inlet
EA
2
$3500
$3,500
'
Concrete Headwall
CY
6
$400
$2,400
with Wingwalls
'
Earthwork for 3' Berm
CY
1700
$5
$8,500
Asphalt
TN
50
$60
32,000
'
20% Contingency
$122200
Total Project Cost ..............
........................$73,100
15
1
..
' D. .Alternative #4
This alternative was designed to divert all flows from upstream basins
into a detention pond on presently undeveloped property. Diversion of
flows onto Rocky Mountain Way would require vertical modifications of
West Swallow and Rocky Mountain Way. `These modifications would
involve transitions of the roadway over a 1 foot berm needed to
channelize runoff into a large detention pond as shown of Figure 6.
Additional berming would be required behind the east curb head on
Rocky Mountain Way and around the tennis court area of the high _.
school. A 15" R(`P aid area inlet would be used to drain the detention
pond per historic rates. Table 6 shows costs associated with this
design. A minimum of 2 acres would be needed and raw land costs are
very high ($1.20 - 1.50/sq. ft.) in this area. Extensive earthwork
and street grading would also be required to direct surface flows into
the pond.
16
1
1
1
1
1
1
1
SILVERPLUME
3rd FILING
SILVERPLUME
11
A11 P.U. D.
w
a
w
0
m
PEACE w/
CHRIST
LUTHERAN
CHURCH
LEGEND
CIMARRON WEST
ROCKY MTN. HIGH SCHOOL
WEST SWALLOW
<M STREET REPLACEMENT AND MODIFICATIONS
Ucccccccccc EARTH BERM ❑ PROPOSED INLET
DIRECTION OF FLOW 0 EXISTING INLET
JON = EL
P.U.D.
WAGON WHEEL
DETENTION POND
CIMARRON SQUARE
MH-7
278 LF 30RCP
Q 0.52%' TO WOOD WEST
34 DETENTION POND
MT. VIEW VET
i
i
KINDER
RE
elzN
MH-6
�75 LF 30° RCP
Q 0.71 %
i ROCKY MT. WAY
IDETAIN IO
6.1 Ac..ft..
tl 392LF
24° HERCO 464 LF
aQ 0.23% �15" RCP
I Qa 0.13%
� V I
MH-4�
�cccccUlc�
15
I m
0
J
w
'1 R _
24�� RCP N
Qa 0.34%' I
j 0
MH-3 O 0
246LF I
18 RCP
Qa I.il% H
NIH-2�
347 LF
24!'HERCP---'
Q 0.47%
MH—I
WOOD WEST
r 7cfs
It--
t—
U
Q
C9
0
w
z
0
U
7
ALTERNATIVE N2 4
DIVERT —DETAIN
FIGURE 6
IQ
TABLE
6
'
ALTERNATIVE
#4
PRELIMINARY COST ESTIMATE
Unit
Total
Item Description
Unit
Quantity
Price
Price
6" Asphalt
TN
700
$40
$28,000
'
Excavation
CY
109000
$2.50
$25,000
'Haul
& Place Berm
CY
2,000
$2.50
$52000
Haul Excess
CY
89000
$2.00
$169000
Purchase Land
SF
90,000
$1.30
$1179000
15" RCP Outfall
LF
300
$20
$62000
'
20% Contingency
$392400
'
Total Project Cost
.......................................$236,400
1
17
' E. Alternative #5
' The design of these drainage improvements were evaluated with
consideration of possible problems associated with the alteration of
' the high school playing fields. Flows from the north curb line on
West Swallow would be diverted north onto Rocky Mountain Way as.
explained in Alternative #3. However, rather than .being diverted into
' a detention pond or routed to the South Shields intersection, these
flows world be collected and detained in the street and adjacent
fields during the major storm event. This would be accomplished by
' the modification of the vertical alignment of Rocky Mountain Way and
the addition of berming along the east side to the street and onto the z
school property behind the tennis court area. Water depths in the
street would be shallow enough to allow buses and vehicles to safely
' exit the parking areas in the southeast corner of the school property.
Figure 7 shows associated flows expected during the major storm event
and Table 7 gives costs associated with the improvements.
1
18
1011-1-7,,e
4v
SILVERPLUME
3rd FILING
4(vi
SILVERPLUME
I'A" P.U. D.
PEACE w/
CHRIST
LUTHERAN
CHURCH
w
CIMARRON WEST
ROCKY MTN. HIGH SCHOOL
WEST SWALLOW
wI LEGEND
oi DIRECTION OF FLOW rcccalcec EARTH BERM
m
PROPOSED INLET
0 EXISTING INLET
0 DRAINAGE CONCENTRATION POINT
STREET REPLACEMENT AND MODIFICATION
mmmmmmmmmmm�
278 LF 30" RCP
0.52 % TO WOOD WEST/
34 DETENTION POND
MT. VIEW VET.
rr MH-6
rr
re,
Irr DER CARE ol �-��75LF 30 RCP
r,rvilk dN. @ 0.71 % N
r.
r-64�
ROCKY MT WAY
I S
LF O
392N.T.S.
24HERCP 464LF
@ 0.23% �-15" RCP
@ 0.13%
MH-4
WOOD WEST
cn
19
w
3: 2417L4'1RFCP U) �E
F-:
@0.34%.
0
MH-3 cn
0
0
246LF 1 1
18" RCP V)
ui
DIVER @ 1.11% 26 z
35cfs 0L)
30 mH-2
7T--------
JON — EL 347LF
244'HERCP
P.U.D. @ 0.47% MH—I ALTERNATIVE N2 5
% STREET a SITE DETENTION
IH-2 -
WAGON WHEEL
DETENTION POND FIGURE T
R MCI
1
TABLE
7
ALTERNATIVE
#5
'
PRELIMINARY COST ESTIMATE
'Unit
Total
Item Description
Unit
Quantity
Price
Price
'
6" Asphalt
TN
240
$40
$90600
Earth Berm
CY
3700
$5
$18,500
'
15" RCP
LF
400
$20
$89000
5'T7pe C Inlet
EA
1
$1100
$10100
'
EA
3
$2800
$8,400
10'Type R Inlet
Channel Enhancement
LF
500.
$2.50
$1,250
for Rocky Mt. Way
'Concrete
Curb and
Gutter
LF
400
$9
$3,600
Purchase Land
SF
25,000
$0.50
$129500
'
or Slope Easement
20% Contingency
$12,600
'
Total Project Cost.........................................$759550
1
'
19
1�
VI. RECOMMENDED ALTERNATIVE
' Alternative #3 is recommended as the most desirable solution due to design
constraints and costs. Construction of berming in the high school playing
' field area could easily be accomplished, berming would be required on the
'east and north sides of the fields. The area of ponding is large and the
berm would only have to be 3 feet .high. The addition of inlets at West
' Swallow and South Shields will handle 2-year runoff volumes with
modifications of the inlet pine in the Wagon Wheel detention Dond. This.
modification will require construction of a Type "C" area inlet over the
'existing 15" RCP at the pond invert. A 8" orifice plate would be built
the box invert to allow 3 ofs to pass during the 2-year event. The outfall
line from the pond would then have adequate capacity to transfer two Year
flows expected to be intercepted by these inlets. New 15' Type "R" inlets
at the intersection of Rocky Mountain Way and South Shields would easily
' capture 2-year flows and transfer to a new 36" RCP running north following
the alignment of an abandoned irrigation ditch.
During the major storm event (100-year) the Wagon Wheel outfall line would
' be at capacity and some crown topping at West Swallow and South Shields
' could be expected. The volume overtopping and flowing east .onto West
Swallow would be relatively small, approximately 10-15 cfs. Inlets at
' Rocky Mountain Way and South Shields would intercept surface flows and the
36" RCP could transfer 55 cfs to outfall in the Cimarron Square Channel.
The subsurface pipe system is also sized to.handle the 2-year release rates
from adjacent properties and the 5 cfs outfall from the high school
detention pond.
ME
' This design also has the advantage of being developed in stages. The first
stage would-be construction of inlets and 36" outfall'pipe and manholes.
This would be accomplished in conjunction with planned South Shields
improvements scheduled for the spring of 1991. The construction of the
school detention pond and outfall line could wait for negotiations and
funding.
1
' 21
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Adapted from Bureau of Public Roads Nomograph
MAY 1984 cot-�_r or cc
5-10 v�' DESIGN CRITERIA
Of�% r1-JDy'
APPENDIX B
c ROCKY MOUNTAIN CONSULTANTS, INC.
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ENDPROGRAM
PR06RAN CALLED