HomeMy WebLinkAboutDrainage Reports - 03/01/1989FINAL DRAINAGE REPORT
FOR
POUDRE R-1 SCHOOL DISTRICT
1990 ELEMENTARY SCHOOL
ENGINEERING PROFESSIONALS INC.
Fort Collins • Colorado Springs
FINAL DRAINAGE REPORT
FOR
POUDRE R-1 SCHOOL DISTRICT
1990 ELEMENTARY SCHOOL
MARCH, 1989
Prepared For:
Dulaney Architecture
5261 South Quebec Street
Suite 210
Englewood, Colorado 80111
Prepared By:
Engineering Professionals, Inc.
2000 Vermont Dr.
Fort Collins, CO 80525
FINAL DRAINAGE REPORT
FOR
' POUDRE R-1 SCHOOL DISTRICT
1990 ELEMENTARY SCHOOL
LOCATION
The proposed school is to be situated on 10.0 acres located approximately 1500 feet
west of South Taft Hill Road and 200 feet north of West Horsetooth Road, within the Horsetooth
West Masterplanned area. More specifically, the site is located within the southeast quarter of
section 28, Township 7 north, Range 69 West, which puts it in the upper third of the Spring
Creek Basin (See vicinity map).
EXISTING CONDITIONS
' The site presently drains by overland flow to the northeast. Two offsite basins (denoted
as OS1 and OS2 on the plan) with a combined area of 4.62 acres located southwest of the site
contribute overland flow to the site along the south and west property lines. The property has
moderate slopes ranging between 1 % and 2.5%, with ground cover generally being sparse
grasses. The site is not located within any designated floodplain.
The school is located within an area assumed to contribute flow to the Rossborough
Subdivision at historical rates, identified as offsite basin 2 in the Drainage Report for
Rossborough Subdivision, prepared by Stewart and Associates, dated April 13, 1979 (see
appendix). A drainage channel was constructed within the Rossborough Subdivision along the
east side of Taft Hill Road to accept runoff from this basin, route it around the subdivision, and
direct it to the Trend - Cedar outfall to Spring Creek. Currently, flow from this basin is directed
to the west side of Taft Hill Road north of West Horsetooth Road where it appears to pond
before ultimately flowing to the north and possibly overtopping South Taft Hill Road. To our
knowledge, no operable culverts under South Taft Hill Road exist in this area which direct flows
to the Rossborough channel.
PROPOSED DRAINAGE
■ School Site
The school site will be drained in such a manner so as to maintain the existing drainage
patterns as much as possible. The school site is divided into 3 basins (1, 2 and 3) with each
basin having its own detention pond. Flows are directed by swales, gutters and concrete pans
to the detention ponds which are generally located along the east side of the property adjacent
to the proposed collector street. The total runoff released from the 3 ponds will be the historic
2-year runoff for the site (3.3 cfs) in addition to the historic runoff from the offsite areas. The
' ponds and release weir structure will be sized to handled the onsite flows with the offsite flows
spilling over the top of weir. The released flows will be directed to the west flow line of the
proposed collector street by a sidewalk chase and covered channel. The following tables
' present the proposed developed school property drainage basin and detention pond data.
di.
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VICINITY MAP
'
SCHOOL SITE DRAINAGE BASIN DATA
BASIN
AREA (acres) C Q10 (cfs)
Q100 (cfs)
'
1
1.48 . 0.72 4.8
9.7
2
3.27 0.39 3.6
7.0
' 3
5.25 0.40 4.8
9.8
OS1
3.03 0.25 1.2
3.1
OS2
1.59 0.25 0.9
1.9
DETENTION POND DATA
' POND NO.
VOLUME REQ'D RELEASE RATE
HIGH WATER ELEV.
(cubic feet) (cfs)
' 1
11,430 0.37
5138.3
2
9,200 1.76
5133.9
3
20,310 1.17
5135.2
Collector Street
Three basins, S1, S2 and S3, in addition to the school site area (and offsite basins) will
ultimately direct runoff to the collector street. The boundaries of these basins were determined
by discussions with the land planners for the Horsetooth West Master Plan as well as the
topography of the area adjacent to the street. Historic flows were assumed from basins S1 and
S3 while developed flows were projected for basin S2 and the, street itself (basins S4 and S5).
' Detention storage for basin S2 and the street will ultimately be provided for within the
Horsetooth West regional detention pond to be located adjacent to South Taft Hill Road.
It is anticipated that Horsetooth Road will be improved in the near future. The City's
design for Horsetooth Road calls for a storm sewer to be constructed with an inlet located at
the northwest corner of the collector street intersection. This inlet will intercept runoff from the
north side of Horsetooth west of the collector street and direct it to the east. This storm sewer
along with the grading at the south end of the collector street will prevent Horsetooth Road
runoff from impacting the collector street. The following table presents data for the drainage
basins directly contributory to the collector street.
■ COLLECTOR STREET DRAINAGE BASIN DATA
BASIN
AREA (acres)
C
Q10 (cfs)
Q100 (cfs)
S1
0.76
0.25
0.4
0.9
S2
2.34
0.70
7.5
11.9
S3
0.46
0.25
0.3
0.5
S4
0.64
0.95
2.7
4.5
S5
0.64
0.95
2.7
4.5
' Historical runoff from the school site will combine with the street drainage and be
directed to a low point in the collector street adjacent to the school. The 10 and 100 year
recurrence interval design flows at the upstream end of the cross pan to be constructed at the
' low point are 6.7 cfs and 9.2 cfs, respectively. All flows will then be directed to the curb return
constructed for future Bronson Street. From this point runoff will be via a temporary earthen
swale to the west side of Taft Hill Road. The 10 and 100 year design flow for the swale are
' 16.9 and 25.6 cfs, respectively. Ultimately, this runoff will be directed to the aforementioned
regional detention pond by Bronson Street and a possible storm sewer system. In the interim,
this runoff will flow through a culvert under Taft Hill Road which is to be constructed south of
' Bronson Street in the near future as part of the Taft Hill Road improvements. This culvert will
direct the runoff to the Rossborough channel east of Taft Hill Road. These culverts will greatly
improve the existing drainage west of Taft Hill in this location.
' Erosion Protection
It is anticipated that stripping and rough grading of the site will occur early in the
' construction process. As a result of this grading, points of runoff concentration will be formed
at the locations of the pond outlets. Hay bales will be positioned at these points to filter
sediment from the runoff. The hay bales will be maintained in these locations until the site
' ground cover has been established.
' CONCLUSION
The 'proposed drainage scheme for the Poudre R - 1 School District 1990 Elementary
' School safely routes minor and major storm flows through the site. Furthermore, the drainage
design for the site is in accordance with the City of Fort Collins storm�e criteria and is
compatible with future improvements planned for the immediate
®o`.�� KR
ENGINEERING PRQItvAL5��{f�lj6
f 400
Steven L. Kraushaar; ` `apoqE c� �v
1
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DETENTION POND VOLUME CITY OF FORT COLLINS
PROJECT NAME: 1990 ELEMENTARY SCHOOL
N� PROJECT NO: 761.1
BY: SLK
DATE: 3/3/89
DESIGN STORM:
100 YEAR
RELEASE RATE (cfs)
0.37
�
0�
RAINFALL
AVERAGE
INFLOW
OUTFLOW
POND
TIME
INTENSITY
INFLOW RATE
VOLUME
VOLUME
VOLUME
(in/hr)
(cfs)
(cf>
(cf>
(cf)
N� 5
8.00
10.6
3192
111
3081
� 10
7.20
9.6
5746
222
5524
15
6.00
S.
7182
333
6849
N� 20
5.18
6.9
8267
444
7823
�
m� 25
4.71
6.3
9396
555
8841
30
4.16
5.5
9959
666
9293
35
3.80
5.1
10613
777
9836
N� 40
3.50
4.7
11172
888
10284
4.3
11671
999
10672
11970
1110
1086(-
N� 55
2.79
3.7
12245
1221
11024
� 60
2.60
3.5
12449
1332
11117
65
2.42
3.2
12553
1443
11110
70
2.3O
3.1
12848
1554
11294
N� 75
2.18
2.9
13047
665
11382
80
2"06
2.7
13151
1776
11375
85
1.96
2.6
13295
1887
11408
� 9�
�
1.87
2.5
13430
1998
11432
95
1.78
2.4
13494
2109
11385
100
1.70
2.3
13566
2220
11346
U� 105
1.62
2.2
13574
2331
11243
110
1.57
2.1
13781
2442
11339
115
1.50
2.0
13766
2553
11213
U� 120
1.43
1.9
13694
2664
11030
DETENTION POND VOLUME
CITY
OF FORT COLLINS
0� PROJECT
NAME: 1990
SCHOOL
PROJECT
NO: 671.1
BY: SLK
DATE:
�m
3/3/89
N�
DESIGN STORM:
100 YEAR
�
RELEASE RATE
(cfs) 1.76
Cf*C*A (acres):
1.59
�|
RAINFALL
AVERAGE
INFLOW
OUTFLOW
POND
TIME
INTENSITY
INFLOW RATE
VOLUME
VOLUME
VOLUME
(min)
(in/hr)
(cfs)
(cf)
(cf)
(cf>
�
5
8.O0
12.7
3816
528
3288
1O
�1.4
6869
1056
581315
.0
ilI
9.5
8586
1584
700220
. 8
8.2
9883
2112
7771
25
4.71
7.5
11233
2640
8593
30
4.16
6.6
11906
3168
8738
N� 35
3.80
6.0
12688
3696
8992
40
3.50
5.6
13356
4224
9132
45
3.25
5.2
13952
4752
9200
N� 50
3.00
4.8
14310
5280
9030
55
2.79
4.4
14639
5808
8831
60
2.60
4.1
14882
6336
8546
65
2.42
3.8
15006
6864
8142
N� 70
2.30
3.7
15359
7392
7967
75
2.18
3"5
15598
7920
7678
80
2.06
. 3.3
15722
8448
7274
N� 85
1 .96
it. 1
15894
8976
6918
m� 90
1 .87
3.0
16056
9504
6552
95
1.78
2.8
16132
10032
6100
N� 100
1 .70
2.7
16218
10560
5658
105
1.62
2.6
16228
11088
514()
110
1.57
2"5
16476
11616
4860
115
1.50
2.4
16457
12144
4313
N� 120
1 .43
2.3
16371
12672
3699
'�-
DETENTION POND VOLUME DETERMINATION - CITY OF FORT COLLINS
m� PROJECT NAME: 199O ELEMENTARY SCHOOL
PROJECT NO: 761.1
BY: SLK
N� DATE: 3/3/89
DESIGN STORM:
100 YEAR
N�
RELEASE RATE (cfs)
1.17
f
Cf*C*A (acres):
2.62
'
RAINFALL
AVERAGE
INFLOW
OUTFLOW
POND
TIME
INTENSITY
INFLOW RATE
VOLUME
VOLUME
VOLUME
w� (min)
(in/hr)
(cfs)
(cf)
(cf)
(cf)
5
8.08
21.0
6288
351
5937
10
7.20
18"9
11318
702
10616
N� 15
6.00
15.7
14148
1053
13095
� 20
5.18
13.6
16286
1404
14882
25
4.71
12.3
18510
1755
16755
30
4.16
10.9
19619
2106
17513
35
3.80
10.0
20908
2457
18451
40
3.50
9.2
22008
2808
19200
45
3.25
8.5
22991
3159
19832
3.00
7.9
23580
3510
20070
w� 55
2.79
7.3
24122
3861
20261
60
2.60
6.8
24523
4212
20311
N� 65
2.42
6,3
24728
4563
20165
70
2.30
6.0
25309
4914
20395
75
2.18
5.7
25702
5265
20437
80
2.06
0.4
15907
5616
20291
N� 85
1.96
5.1
26190
5967
20223
90
1.87
4.9
26457
6318
20139
95
1.78
4.7
26583
6669
19914
N� 100
1.70
4.5
26724
7020
19704
�
105
1.62
4.2
26740
7371
19369
110
1.57
4.1
27148
7722
19426
N� 115
1.50
3.9
27117
8073
19044
�
~= 120
1.43
3.7
26976
8424
18552
I
3 5-8
/,o 0-9 -t-
- ------- ---
/2 5e-z>
April 13, 1979
Drainage Report
Rossborough Subdivision.
Fort Collins, Colorado
Rossborough Drainage
Fort Collins, Colorado .
Rossborough is a proposed residential subdivision at the southwest
city limits of Fort Collins, Colorado. It is on a 156 acre site at
the northeast corner of Taft Hill Rd. and W. Horsetooth Rd. (See Exhibit
No. 1). The present use of the property is for agricultural purposes;
it being the old Ross farm.
The slope of the land is from the southwest to the northeast and then
northerly. The sub -basin within which the parcel lies is in the Spring
Creek watershed. The Pleasant Valley and Lake Canal flows southeasterly
across the site from a little east of the northwest corner to a little
north of the southeast corner.
The majority of the site is proposed for single family residences with
zoning for multi -family at the southwest corner. A small commercial site
is located on Horsetooth Rd. at about the mid -point of the .south portion
of the property. The northeast corner of the project is devoted to open
space being a combination detention basin for drainage control and
proposed City of Fort. Collins park. The park site is the southern portion
of that approximately 14 acre parcel located on the drainage thalweg at
the downstream portion of the site. .(See Exhibit No. 2).
Offsite drainage flowing onto the site is from the southwest in two
separate patterns separated by a divide extending southwesterly from the
intersection of Taft Hill Rd. and Horsetooth Rd. There are 192 acres
draining onto the site across Taft Hill Rd. from the west and 83 acres
draining onto the site across Horsetooth Rd. - from the south.. The thalwegs
of these two drainages combine on the Rossborough site north and east of
the Pleasant Valley and Lake Canal and then the combined drainage flow is
northerly across the proposed future Cedar Village 5th filing subdivision,
then through earlier filings of Cedar Village, and on to Spring Creek at
Drake Rd. .(See Exhibit No. 3). The area shown as No. 1 on Exhibit No. 3,
is now mostly developed as a mobile home park and a large lot rural sub-
division. The area shown as No. 2 on Exhibit No. 3, is now mostly farm-
land west of Taft Hill Rd. and north of Horsetooth Rd. with that portion
lying south of Horsetooth Rd. being part of a mobile home park. The
southernmost tip of areas 1 and 2 are undeveloped at this time.
The topographic information utilized in this study was from the United
States Geological Survey Quadrangle Map, the City of Fort Collins Aerial
Photography 100 ft., 2-ft. contour interval, mapping, and spot elevations
determined by.our field crews. The soils information used as a reference
in this study was from the Empire Laboratories, Inc. soils report Empire
Labs No. 3258-78.dated October 3,. 1978 and No. 3481-79 dated March 2, 1979,
along with supplements to Report No. 3258-78 dated December 26, 1978 and
January 19, 1979. .
The 2-year return frequency event and the 100-year return frequency event
are the two runoff conditions analyzed in this study. The Colorado Urban
Hydrograph Procedure (CUHP) was used in the hydrologic routing and deter-
mination of conditions at various points of concentration throughout the
watershed. The Rational Method was used in the analysis and design of
-1-.
storm sewers and open ditches throughout the project. Where results
of the design analysis with the Rational Method differed from the results
obtained at the same point of concentration through the Colorado Urban
Hydrograph Procedure the Rational Method output figures were adjusted
to match the CUHP quantities.
The analysis of runoff events were for the conditions of the historic
situation in the present and/or past and for the fully developed con-
ditions as now -proposed or to be expected in the future. Peak rates of;,
flow for the four interval conditions analyzed entering and leaving they
site are shown on Exhibit No. 3.
The City of Fort Collins requires detention of storm water runoff in
order to reduce the peak flows from the developed condition to or.less
than those that would be experienced during the historic analysis. The
mechanics of utilizing a detention basin require that the surface flows
be collected and concentrated in a basin and then released either into
some natural or man made acceptable channel -or discharged back upon the
surface at the outlet of the site. As the downstream end of the drainage -
way in Rossborough at its northline is a swale across a farm and not a
channel the discharge waters need be replaced upon the surface. Cross
sections of the existing ground at the thalweg at the northline of
Rossborough were subjected to a hydraulic analysis by the Manning's Method.
Exhibit No. 4 shows the depth, the velocity, and the width of the water
surface at the northline when the existing thalweg is subjected to the
historic 100-year peak runoff and the historic 2-year peak runoff of the
entire watershed at that point of concentration. This exhibit is a guide
in the design of the outlet works of the drainage channels and conduits
from Rossborough to the north into the future Cedar Village Fifth filing:
The off site drainage from the west 192 acres is proposed to.be collected
along Taft Hill Rd. and drained to the north in an open ditch along the
east side of Taft Hill Rd. and then turned easterly along the northline
of Rossborough to the area of Dunbar Ave. and the emergency spillway
ditch of the detention basin as shown on Exhibit No. 2._ This flow along
with a small amount from Rossborough itself directly along the path of the
ditch bypasses the site storm water collection and disposal system. As
the City of Fort Collins policy is that all new development will need
installed detention facilities so that peak flows outletting any property
are equal to or less than historic flows that bypassing will have no.
adverse affect on the properties downstream to the north and therefore
those waters need not be handled in the Rossborough detention facilities..
The flows from the south, however, do not lend themselves to bypassing and
are planned to be received directly into Rossborough across Horsetooth
Rd. at the existing low point west of the proposed Dunbar Ave.. The
offsite flows from the south are carried together with the onsite flows
along Dunbar Ave. in a storm sewer system with a 2-year runoff capacity,
or, overland in the street for those waters from events in. excess of
2-years. The northwest portion of the site drains easterly across the
canal from Birmingham Dr. and Devonshire St. to Hertford Circle and then
to Dunbar Ave. The southeast portion of the site drains northerly across
the PV&LC from Birmingham Dr. at British Circle doom Downing Ct. to London
St. and then to the west where it connects with the flows from Dunbar Ave.
travelling east on London St.. The combined flows at this point then move
north into the detention basin. What is left then of the Rossborough site
is the area between Dunbar Ave. and the Pleasant Valley and Lake Canal
from Bedford Circle north in the center of the site that drains northerly
-2-
and whose flows joins the bypass flows from the west of Taft Hill Rd.,
both leaving the site without detention. This small northerly area
runoff not being detained is a trade-off for the offsite waters in the
83 acres to the south, a part of which are from lands developed without
consideration being given for detention facilities.
The basic control elevations of the detention basin are shown on Exhibit
No. 5.
All the culverts considered on this.project are planned to be reinforced,
concrete with precast concrete end -sections. All storm sewer is-coasideYed
to be reinforced concrete pipe.
Melody Homes Inc. of Broomfield, Colorado have agreed to allow Rossborough
to daylight the bypass open ditch to the north in an open cut through the
proposed Cedar Village Fifth filing. They have also agreed to the
providing.of an easement for the 15" storm sewer draining the sump in
the detention basin. Melody Homes is.the proposed developer of the Cedar
Village Fifth filing property owned by Miller Properties; Miller being
the original developer of the previous Cedar Village Subdivision.
Entering the site then, across Taft Hill Rd. and W. Horsetooth Rd. we have
proposed.culverts under the pavement to carry the 2-year flows. These
2-year flows are then carried across the Rossborough. properties along .
__with site generated.runoff waters through a system of storm sewers, culverts,
open ditches, and a siphon, all of 2-year runoff capacity. For the 2-year
event the ditches are proposed to have freeboard. The waters in excess
of the 2-year event are proposed to enter the site across Taft Hill Rd.
and W. Horsetooth Rd. pavements and continue across the site and join
with site generated waters and flow overland to the detention basin or
north and west in the bypass ditch around the west and north portions of
the Rossborough site. For the 100-year event no freeboard is considered
in the open ditches. Waters flowing over streets are considered to not
exceed the City of Fort Collins criteria of 1.5 foot depth above the gutter
flowline along with other requirements for numbers of lanes to be kept
open on various category streets or depths of water over the crown of the
streets as listed in city.regulations..
Outletting the site then, from one direction we have waters flowing north
at the terminus of the bypass ditch at Dunbar Ave. (this particular flow -
stream to the north could be on the west side of Dunbar Ave. or the flow
could be carried under Dunbar in a culvert for release to the north on
the east side of Dunbar Ave. as the details are worked out in the future
between the Cedar Village and Rossborough developers and their engineers
and the city'of Fort Collins). Additional waters outletting the
Rossborough site are proposed to be, one, carried underground from the
Rossborough detention basin.sump to the existing storm sewer system in
Cedar Village discharging directly to Spring Creek through the Cedar Village
detention basin located on the south bank of the creek, and, two, in the
two culverts at the thalweg through the dam bank of._the Rossborough.
detention.basin.
A further outlet of storm waters from Rossborough to the north is shown
on Exhibit No. 2 along the existing thalweg as the emergency spillway
outlet of. the detention basin.
The basic equation for storage in a detention facility is that the storage
- 3-
at any one time is equal to the inflow minus the outflow. In these
hydraulic calculations it is necessary to determine -a stage volume curve
that gives the volume or capacity of the detention facility at various
elevations above a set datum and a hydraulic performance curve of the
outlet works which shows the rate of outflow of these facilities at
various elevations above the same set datum. In addition to these two
curves the inflow runoff hydrograph to the basin showing the instantaneous
rate in cubic feet per second at various times of concentration from the
start of the storm are needed. The inflow runoff hydrograph is used to
determine various volumes of runoff entering the facility in certain
small increments of time. The elevation the water might rise to in that
time as determined from the stage volume curve when applied to the outlet
performance curve givers a release rate. Inflow and outflow are balanced
against each other and a net instantaneous volume of stored waters is
obtained. Exhibits 6 through 11 show the various curves and the results
of the routing through the basin: Exhibit 12 is a summation of the
results of the routing and shows that the storage volume achieved is more
than the city requirements and that the combined peak flows outletting
the site after development are less than the historic peaks.
In the event there is a runoff situation in excess of the 100-year return
frequency event or there is more than one 100-year event back to back on
a daily basis or if the outlet works are plugged in the detention basin
an emergency spillway is provided. Exhibit No. 13 shows the situation
in the event the spillway is activated while passing a flow in the
neighborhood of 500 cubic feet per second (cfs). The 500 cfs shown in
the exhibit while not checked by an actual routing should be more than
adequate to handle the 100-year inflow peak as attenuated by the surface
of water pounded in the basin under that type condition. Exhibit 14 shows
additional dimensions and elevations of the spillway and outlet ditch
including expected water surface, sections, and profiles, while handling
a flow in the magnitude of 500 cfs.
Exhibits 2, 15, 16 and 17 show proposed gutter flowline finished street
grades at various points and routes through and around the site. These
grades are set so as to provide a* potential balance in earthwork on the
site and so as to control the runoff waters into the bypass ditch and
from the site into the proposed detention basin as required. Exhibit No.
15 shows the plan and profile of the proposed bypass ditch including the
two year runoff capacity siphon under the Pleasant Valley and Lake Canal..
That exhibit also shows the existing and proposed culvert crossings of
Taft Hill Rd. and a profile of the flowline of Taft Hill Rd. itself which
is proposed to control, direct, collect and dispose of the bypass waters.
Exhibit 16 shows -the proposed profile of Dunbar Ave.. including the high
point required north of London St. to divert surface runoff waters
easterly along London street to the detention basin as well as the Dunbar
Ave.storm sewer and the proposed siphon to carry the Pleasant Valley and
Lake Canal irrigation waters under and across Dunbar Ave. Exhibit 17
shows the proposed gutter flowline elevations and drainage facilities
proposed at Horsetooth Rd. in plan and profile.
In the routing of the major (100-year) storm runoff waters through the
site the analysis showed that some streets needed to be wider, than City
minimum standards in order to pass these waters safely without innundation
of proposed buildings (homes). Certain relationships need to also be
maintained throughout the site to keep the waters separated as they flow
-4-
to and from and bypass the detention facility. City standard street
sections proposed during study period were:
Classification F.L./F.L. Gutter R/Id
Place 32' .50'
Local 36' 54'
Collector 44' 62'
Arterial 60' 100'
While minimum city standards will suffice at other locations Exhibits
18 through 21 show minimum cross sections that must be maintained at
specific locations throughout the site., Exhibit 20 shows the basic design
criteria used in the Manning's Equation approach to the analysis of street
carrying capacity. A minimum longitudinal street gutter flowline slope
was assumed of 0.004 feet per foot (0.4%) in this analysis. The bypass
siphon along the Rossborough northline and the storm sewers in Dunbar
Ave. and in Downing Ct. are proposed to -handle the runoff from a 2-year
event. Waters in excess of those quantities are proposed to flow overland.
The excess waters in the bypass ditch over and above the 2-year storm
siphon capacity will flow directly overland into the Pleasant Valley and
Lake Canal. The similar excess waters from the low point at Birmingham
Dr. and Devonshire Street and from the low point at Birmingham Dr. and
British Circle are proposed to flow overland in a drainageway directly .
into -the PV&LC channel through open swales as shown on Exhibit No. 21.
The major onsite excess water surface runoff along Dunbar Ave. is proposed
to be carried over the canal on the street surface. Cross -sections taken
of the existing Pleasant Valley and Lake Canal showed it to have a
capacity equal to approximately 55 cfs when flowing bank full as determined
by the Manning's Equation. The maximum potential depth of water in the
canal at this capacity at existing conditions was found to be 4 feet.
As the expected overland flows entering the irrigation canal will be in
excess of its capacity alterations will be necessary in order to contain
and control these flows and direct their release. The basic approach to
this is to maintain the west and.south bank of the canal height at a point
4 feet above the existing flowline. .The north and east bank of the canal
is proposed to be heightened outside of the waterway (widened) and side
overflow weirs located at strategic points to direct the excess waters
out of the canal and down streets planned for that purpose for. disposal
either in the bypass system or the detention system_The throttling
control to activate these side overflow weirs is proposed to be a siphon
carrying the irrigation (plus some excess storm waters up to an amount
equal to canal capacity) waters under Dunbar Ave -for the north portion of
the proposed development. While the heightening of the irrigation canal
bank is proposed downstream from Dunbar to the east line of Rossborough
no such control to activate the side overflow weirs is proposed in the
Rossborough improvements. However, if such a control device is established
by others offsite, protection to the Rossborough development and to the
canal owners is provided in the overflow at Downing. The work on the
Pleasant Valley and Lake Canal proposed in this report is shown on Exhibits
22 through 24.
This initial drainage study gives envelopes, minimums, criteria, assumptions,
approximations, and other preliminary drainage factors. The design
engineer preparing the construction drawings for the site development
-5-
purposes (utility plans) will extend the intent of this study. Exhibits
25 through 27 (design curves) are presented for his use at that time.
Q 7! ��-�- n .� r 1 !- I t v r
1, ....
a
� � I
--6l EOGE OF FUTURE
I1 ORCA60N STREET ROW W
IA'/6,OE6LOYE i5
L '/J J mRl r9
^..03
O[Nt4c(s 0 1.30EGlN
I^IIAV1A-ll')�,I/vyR^YV�1 V. 9.9 TK
Ouner SWALE OETA/L
HT6
NDre BwALE To BE 6EALE0 Scale 1" : 50'
SU86EOt/EN/W CONSTR(JCTION
M
V ,
�YVHI a.ab �,
I IAA ld
F
\� \>
HILL ROAD
III I / I p'oo •ZSL ciShc a60V6 TAFT
�J i a LJ c=1
0 S.'E / III/¢ / e BASIN DATA
jJ •c\t /yy / •V / %' / / / I/� BASIN AREA (acres) C Q10 (cfs) Q100 (Cfe)
/ I 1 1.48 0.72 4.8 9.7
DWICN PoIN1 Q SO (C[a) Q 00 (Cfa) 3
.20.39 ..
2 5.25 0.4.8 9.8
1 6..OS1 1.0.25 1.2 3.1
3 16.9 5.6 08.59 0.25 0.9 .9
076 0.25 4 0
S2 2.34 0.70 7.5 11.9
S3 0.46 0.25 0.3 0.5
SCHOOL SITE \'(-`V I l / II"� % •1 I • I� 1HISTORICAT RUNOFF D M 94 0.64 0.95 2.7 4.5
�,\ N �� I I` 1 / / / ' FFP• 1 I r SS 0.66 0.95 2.7 4.5
AREA - 10.m ACRES
TC - 35 1OYCes
\ I Cfs
04fBNTIDN
Q SO - 5.8 [a POND DATA
Q 100 - 11.9 CIS
FOND N0. VOILic feet) RELEASE RATE HIGH WATER ELM.S$ cubic feet) .fs)
////`♦ // \ 1 1 I + II I / 2 18,075 1.,415 00
/E9
- � a.n � ' yd-u•�� -.
LEGEND
BASIN DESIGNATION
I __-all,fl/ / /[j BASIN AREA
�.
�. 2.36
BASIN BOUNDARY
DESIGN POINT
8l
ill, \ \ \�--
__ �e___ _______ _ _ �_______�..._���-�»_-__ne.
r N - --I .-- �- � --- S T Hd�7S_ TOOTFI � F7QAD----- \---------
_____________ R
LUTUse, C/PY STORM SEWER FOR W NO.PSEIDOTN ROAD Y Y e
N0. REVHRONS BY DAiE aw[nuco uliofx THE 4Y[m5gx i s CLIENT: TITLE : All W.
z96Dvomnm Dme RA°'"'a"BBe Sou" RGP 1990 ELEMENTARY SCHOOL 761.1
Q(r'I'�J(j(y' Fon Coal OrIo N 80525 Wtir= Sppnirss.. COIJ 8"He nl 6ssraNn SLK mSLK a..c 1"=5o' POUDRE SCHOOL DISTRICT. R-I DRAINAGE PLAN 66Tw
prCfec InC. JIM)2zs3a52 pI91 s9o--sass CSP MTEMARCH 1989 I
6x I 6leere