HomeMy WebLinkAboutKINGSTON WOODS PUD FINAL - 58 91A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE REPORT
for
KINGSTON WOODS P.U.D_
Fort Collins, Colorado
March, 1992
prepared by
T70F2'TI-iF 2N ENC;1[N0F'R2NG SERVSCES 2NC
420 South Howes, Suite 106
Fort Collins, Colorado 80521
(303) 221-4158
In
/n
February 26, 1992
Mr. Glen Schluter
Stormwater Utility
City of Fort Collins
235 Mathews
P.O. Box 580
Fort Collins, Colorado 80522-0580
re: Kingston Woods P.U.D.
Final Drainage Report
Project No. 9123.00
Dear Glen:
Northern Engineering is pleased to submit this Drainage Study
for your review. It represents a study of the existing and
proposed runoff characteristics of the proposer Kingston Woods
P.U.D.. Study of soil erosion at the site is also included in this
report.
Your interest and input during the design phase of this
project have been greatly appreciated. If you should have any
questions or comments as you review this report, please feel free
to contact me at your earliest convenience.
Sincerely,
NORTHERN ENG]PIEE / SERVICES, INC.
I [�
Michael F.,Ydn P.E.
z1-N
o 25033
YkA
W
I. GENERAL
Final Drainage Report
for
KINGSTON WOODS P.U.D.
Forth Collins, Colorado
March, 1992
This report summarizes the results of a stormwater and erosion
study conducted for the proposed development of Kingston Woods
P.U.D., located in the Southeast quarter of Section 27, Township
7 North, Range 69 West of the 6th Principal Meridian, in Fort
Collins, Colorado.
Methods outlined in the City of Fort Collins' Storm Drainage
Design Criteria and Construction Standards were used in the
calculations for the stormwater runoff portion of this study, while
the City's Erosion Control Criteria was used as a guide in
preparing the erosion control plan. Additional references were
made to the Urban Drainage and Flood Control District's Urban
Storm Drainage Criteria Manual as needed. Summary calculations and
other supporting material is contained in an appendix to this
report.
The Rational Method was used to calculate stormwater runoff
from the -site, whine calculations based on the Modified Universal
Soil Loss Equation (MUSLE) were used in the erosion study.
II. SITE DESCRIPTION
The project site occupies approximately sixteen acres of open
ground bounded on the south by Horsetooth Road and on the west by
the Pleasant Valley and Lake Canal. To the north, the site is
bounded by Wagon Wheel and Casa Grande residential developments.
The eastern portion of the site is bounded by a platted
residential/commercial P.U.D., Horsetooth Commons, which has not
been developed.
Kingston Woods P.U.D.
Final Drainage Report
page 2
II. SITE DESCRIPTION (Continued)
The land is mostly covered with short grass and slopes
downward to the northeast corner of the site at approximately 1.6
percent. Near the ditch bank and along the southern border stand
several mature trees of various types. A small frame home and
several out -buildings occupy the south central portion of the site.
The site lies in the Foothills Master Drainage Basin, Basin G,
Reach 4.
III. HISTORIC DRAINAGE
Approximately 0.88 acres of the western portion of the site
is occupied by banks of the Pleasant Valley and Lake Canal and
drains into the canal. Approximately 2.30 acres in Historic sub -
basin H 6 flows off to Horsetooth Commons to the east, while about
0.49 acres flows off from the site into Wagon Wheel. Stormwater
runoff from Horsetooth Road west of the irrigation canal flows into
the canal. Runoff from Horsetooth east of the canal flows east
into Horsetooth commons or into the improved curb at the eastern
end of the site. These flows are tabulated in Table A.
The majority of the site, approximately 11.96 acres, drains
to the northeast corner. This study found the 2- and 100-year
historic runoff flows from this portion of the site to be 5.01 cfs
and 14.76 cfs, respectively. Previous drainage design work in the
area for Horsetooth Commons, Casa Grande and Chaparral PUDs has
allowed for a 100-year release flow from the site of 9.5 cfs. This
flow is to be conveyed through a storm sewer on the north boundary
of Horsetooth Commons to daylight into a reverse -crown drive in
Casa Grande. From there it is to flow into a 24-inch storm drain
which will convey it to the southeast pond, basin 5, of the
Chaparral PUD. Pertinent sections of the drainage reports for
these improvements are contained in the appendix to this report.
IV. PROPOSED IMPROVEMENTS
The proposed development of the site will place 52 new single-
family lots on 16.09 acres. A street system will tie Seneca Street
from Wagon Wheel to Horsetooth Road and will stub out Patterson
Drive to the east for future connection.
Kingston Woods P.U.D.
Final Drainage Report
page 3
IV. PROPOSED IMPROVEMENTS (Continued)
The existing Pleasant Valley and Lake Canal will be realigned
along the south border of the site to allow for widening of
Horsetooth Road. An extension to the existing box culvert in
Horsetooth is proposed as part of this project. At the
recommendation of the soils engineer for the project, ditch walls
will be limited to a maximum slope of 2:19 which is steeper than
those of the existing ditch section. At the request of the
irrigation company, the bottom width is to be narrowed from eight
feet to six in order to maintain the flow velocity. Bends for the
realigned section will have increased radii for better flow.
Contact with the irrigation company has indicated that they
will rarely run more that about twenty cfs in the ditch, with an
estimated high flow of 25 cfs. For hydraulic design purposes,
however, a figure of 55 cfs was used. This is based on the
improvements immediately upstream in Rossborough Subdivision.
Improvements for Rossborough included canal importation and a side -
flow weir which is designed to divert flows in excess of 55 cfs
into their drainage improvements. This implies that stormwater
flows will increase the ditch flow to 55 cfs before it will be
diverted out of the ditch.
A backwater curve for the water surface in the ditch at 55 cfs
was produced using the. Standard method as shown by Liggert and
Morris. (See Appendix.) These calculations show that the maximum
water surface for the ditch, at 55 cfs, will be 104.68 feet. The
ditch banks were, therefore, set at 106 feet to allow for a one -
foot freeboard. It should be pointed out that the banks on the
west side of the existing channel, which are not a part of this
project, are lower than this and it is recommended that —these
banks be raised to 106 feet when that property develops.
Hydraulic analysis of the channel and flows indicates that rip
rap bank protection will not be required, based on the velocity of
flows.
The majority of the site will be graded so as to allow runoff
to be conveyed in the street gutters into a proposed detention pond
at the northeast corner of the site. The largest concentration of
street flows occurs to the west of Design Point 2. (See Drainage
Plan, attached.) Calculations show that the developed flows at
this point will be within City standards for gutter flow and street
encroachment. Other gutters will have a combination of lesser
flows and steeper slopes and will be adequate for runoff flows.
Kingston Woods P.U.D.
Final Drainage Report
page 4
IV. PROPOSED IMPROVEMENTS (Continued)
Table A summarizes runoff calculations for the Historic and
Developed Basins and the Design Points shown on the Drainage Plan.
From Design Point 2, runoff will be routed through Storm Sewer
Line A into the detention pond. An overflow area on top of Line
A will convey any spill -over from Design Point 2 into the pond
should the storm sewer inlet become blocked.
Release from the pond will be limited to a maximum of 9.5 cfs,
as provided for in other downstream projects. (See Appendix.)
Storm Sewer Line B is designed to carry the pond release through
an existing drainage easement across the north of Horsetooth
Commons. as described earlier. Release from the pond will be
controlled by the entrance into the 15-inch Line B. Should the
entrance to this pipe become blocked, over -flow from the backed -
up pond would spill over into the drainage swale (reverse -crown
drive) to the north, slightly upstream from the intended release
point.
Required pond volume was calculated by the mass diagram
method. (See appendix.) Maximum required volume for a 100-year
storm was found to be 63,968 cubic feet. A volume of 70, 496 cubic
feet has been provided at a pond elevation of 90.75. At the
required volume, the estimated water surface elevation will be
• 90.48. At an impoundment level of 91.00 feet, this would allow for
i a freeboard of 0.52 feet and a reserve capacity of approximately
12,650 cubic feet. Since, due to sanitary sewer elevations, the
buildings in the vicinity of the pond are raised to a finish grade
i elevation four feet higher that the high water in the pond, it is
requested that a_variance be granted to the one -foot freeboard
requirement.
By grading the site. to convey runoff inward, 100-year release
flows from developed Sub -Basins 3 and 6 have been kept near or
below historic 2-year levels.
Flows from Horsetooth Road west of the irrigation ditch have
increased due to the widening to arterial standards, but the
irrigation company has allowed for these flows to continue to be
conveyed into the canal. Street flows east of the canal, however,
will increase from an historic 2-year flow of 0.79 cfs to a
developed 100-year of 3.66. This flow will be conveyed east in the
Horsetooth gutter to Richmond Drive, where it will be conveyed into
the Horsetooth Commons detention pond and released into the 36-
inch storm drain in Shields Street. Since the majority of this
Kingston Woods P.U.D.
Final Drainage Report
page 5
IV. PROPOSED IMPROVEMENTS (Continued)
increased flow is due to the City -mandated widening of Horsetooth
Road and since conveying the excess flows to the Kingston detention
pond would pose a hardship for the developer, it is requested that
a variance be granted to allow the developed runoff to remain as
shown.
V. EROSION CONTROL
It is anticipated that the improvements for Kingston Woods
will be completed by the fall of 1992. Construction of homes on
the project will begin as soon as possible and will likely continue
into spring of 1993.
During construction of the improvements and houses on the
lots, the detention pond will be modified to be used. as a
sedimentation pond. During this time, maintenance may be required
to prevent sediment from reducing the pond's detention capacity.
Once construction has been completed, the pond can be final graded
and landscaped.
Other structural erosion controls during construction include
a gravel barrier at the inlet to storm sewer Line A and gravel
gutter dikes in the streets, including off -site on Horsetooth and
Seneca. These improvements will need to be monitored during
construction and maintained as necessary.
Once over -lot grading has been completed, it is recommended
that any lots which are to stand longer than thirty days prior to
house construction shall be seeded and mulched to prevent wf d'and
rainfall erosion. It is also recommended that gravel curb dikes
be placed in the street gutters immediately downstream of any
construction areas and that the condition and effectiveness be
monitored.
Recommended seed mixture would consist of 55% Fairway
Wheatgrass at 7.2 drilled pounds per acre and 45% Smooth Brome at
16.1 drilled pounds per acre. This planting may be revised by the
developer based on seasonal or other conditions with the approval
of the City.
TABLE A
STORNWATER RUNOFF
KINGSTON WOODS PUB
I
I
OVERLAND
I
GUTTER/PIPE
I
SWALE
S V
I
tc I
Tc2 Tc100
1
1
12
1100
I I
I C I
oZ
0100
D.P.I
AREA
I C
L
S
tc2
tc100 I
(yin) I
L
(ft)
S
(1) (f/5)(1in)
V
tc I
I
L
(ft)
ltl
(f/s)(Iie)
IUinl
(Bin)
Ili/bl(i/D)
I.____I(cfs).
(cfs)
I
(ad
I (ft)
(1) (min)
----•---------•---•-------•---•
..............
I
H 1 I
0.88
I
10.30
25
1.0
7.5
I
6.8 I
I
0.0 1
920
0.01
0.68
I
22.5 1
30.0
8.1
29.3
1.9
I
11.48
13.30
4.10
1.00
I
10.30 1
10.71 1
0.39
0.56
I,I1
1.19
H 2 I
0.24
10.30
15
10.0
2.1
2.4 I
0.0 1
0.0 1
360
0,50
1.1
5.5 1
0.0 1
14.1
13.3
12.12
6.10
10.30 1
0.31
0.90
H. 3 1
0.49
10.30
120
1.4
1.8
14.7
27.5
13.3 1
14.9 1
0.0 1
680
1.90
1.5
7.6 1
35.1
32.5
11.35
3.98
10.31 1
5.01
14.16
H 4 1
11.96
10.30
500
2.7 1
0.0 1
110
1.40
1.2
9.9 1
12.8
12.5
12.30
6.50
10.70 1
0.19
2.23
5
H 5 I
0.49
0.49
10.30
IB
10.0
2.9
0.0 I
0.0 1
29.2
26.4
11.51
4.60
10.35 1
1.22
3.70
H 1
2.30
10.30
520
1.0
22.9
9.9
26.4 I
7.4 1
0.0 1
920
0.01
0.68
22.5 1
30.5
29.9
11.48
4.18
10.25 1
0.27
0.77
D I 1
10.30
10,20
25
20
1.0
1.0
7.5
7.1 1
350
0.4
1.5
3.9 1
0.0 1
11.
1.
12.40
.0
10.11 1
0.16
.18
O 2 1
D 3 I
0.41
0.15
10.15
15
10.0
4.1
4,0
I IO
0.4
1.5
0,1 I
0.0 I
4.12
1
44.11
16.5
11.50
11.49
7.00
10.42 10.16
10.76
1 1.31
0.44
72
23.66
0 4 1
13.64
10.15
1110
2.5
17.6
16.9
1 900
1
1.8
1.5
8.3 1
8.0 I
240
0.50
I
4.0
0.0
16.9
116.9
16.5
11.00
5.60
5.60
10.16
11.31
3.66
0 5 1
0.86
10.15
25
1.0
8.9
8.5
5.1
1 720
1 10
0.4
0.4
1.5
0.1
1
0.0
1 5.6
5.3
12.50
7.00
10.36
1 0.16
0.13
0 6
1 0.29
1 13.64
10.20
10.15
40
180
7.5
2.5
5.4
11.6
16.9
1 900
1
1.8
8.3
1 240
0.50
1
4.0
1 29.9
19.2
11.49
4.19
10.38
1 7.12
21.72
1
2 a
I 1.44
10.15
180
2.5
11.6
16.9
I 900
1
1.8
8.3
1
0.0
1 25.9
25.9
25.2
15.2
11.60
11.60
4.60
4.60
10.38
10.38
1 4.52
1 7.65
13.01
22.01
2b
1 12.59
10.15
180
2.5
17.6
16.9
1 900
1
1.8
2
8.3
4.5
1
1
0.0
0.0
1
1 27.5
21.8
12.30
6.50
10.38
1 3.16
8.94
3 a
1 3.62
10.15
190
2.5
18.0
17.3
11.3
1 540
1 540
1.1
1.1
2
4.5
1
0.0
1 22.5
11.8
12.30
6.50
10.38
1 4.15
11.13
3b
1 4.75
10.15
190
2.5
18.0
5.4
5.1
1 10
0.4
1.5
0.1
1
0.0
1 5.6
5.3
12.50
7.00
10.36
1 0.16
0.73
4
5
1 0.29
1 0.15
10.20
10.15
40
25
7.5
10.0
4.1
4.0
1 10
0.4
1.5
0.1
1
0.0
1 4.2
4.1
12.50
7.00
10.42
1 0.16
0.44
6
1 0.86
10.15
15
1.0
B,9
8.5
1 720
0.4
1.5
8.0
1
0.0
1 16.9
16.5
12,00
5.60
10.16
1 1.31
3.6(
7
1 0.41
10.20
20
1.0
7.5
7.1
1 350
0.4
1.5
3.9
1
0.0
1 11,4
11.0
12.40
6.90
10.77
1 0.76
2.11
8
1 0.74
10.25
25
1.0
1.9
7.4
1
0.0
1 920 0.01
0.68
22.5
1 30.5
29.9
11.48
4.18
10.25
1 0.21
0.r
NOTES:
I. OP 2a: Flow from west gutter only
1. OP 2b: All flow into inlet
3. OP 3a: Flows from east gutter only
4. DP 3b: All flows reaching this point
5. OP 4: Sum of all flows leaving site from Sub -Basin 0 6
6, DP ): Sum of all flows leaving site from Sub -Basin 0 3
1
I.
Runoff calculations .....,,,.^,,,..,^..,,^,,....,,.
,...
4
2.
Detention Pond ,.. ,..^ .^ . ^^ . , .^ . ^ . , ^ , , ,
, . . .^ . ^ ^ , , , ,,^,,
3.
Box Culvert and IrrigationCanal .......................
6
8
4,
Gutter Capacities . .,, .,^ ^,^., ^,^..^^,^^.
,,,^.,,.,^^`^`
�,
Storm Sewer Lines � �� B .,^,.,^....,^,.^,.,.,.,^,^,^.,,
8
1@
6.
Erosion Calculations
^
14
7,
References , . , , ^ ^ , ^ , . ^ , ^ . . , , . . . ^ , ^ , ^ ^ ^ ,``
^�```'^^^^
'``
8^
'Wagon Wheel Drainage Excerpt ...^^,,..,
^.,,,,.,.,,^ . ,^^
16
9.
Horoetootlx Commons Drainage Excerpt . ^,,^^^,^,.^^,.,,.
.
17
10.
�
Chaparral Drainage Excerpt ...........................
19
11.
BomslUoroog]b Drainage Excerpt . , . , ^ ^ ^ , ^
. , . , ^ , . , , , , , , ^ , ^ ,
22
-&/igert Backwater .,,,...,^,.,..^^^,^,,I,._..
24_��~__�_�
13,
Nomograp|bm, Tables Used ..,^,^^^,..,,,^.,,,...,.,
. ^.,.,
27