HomeMy WebLinkAboutWESTBURY PUD - PRELIMINARY - 11-94 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTDATE: MARCH 1994
BASIN RUNOFF COMPUTATIONS FOR THE 2 / 10 / 100 YR. STORM EVENT
WESTBURY STORM RUNOFF RATES HISTORIC/DEVELOPED
FOR: Linder Real Estate & Development
BY: Stewart & Associates
GENERAL NOTES:
If C x Cf > = 1 then C x Cf = 1 (constants listed below)
SUBBASIN TIME OF CONCENTRATION ....
D. Pnt. SlopeOverL eng OverL Tc Chan.LenOt I Tc Chan. Tcc Total Total COMMENTS
(%) - (feet) (min.) (feet) (min.) (min.) OVERLAND TIME ONLY
H13-1 1.00 0.20 200.00 22.9
Tc 1.80 0.20 225.001 20.01 42.91 OVERLAND + CHANNEL
0.20 = C (Land) 0.20 = C (Chan.
D. Pnt.
HB-1
Area
(acres)
1.22
C Cf
0.20
0.20
I (2yr.)
(in/hr)
1.16
I (10yr.)_
(in/hr)
2.08
I (100yr.)
(in/hr)
Basin Q
(cf s)
0.28
0.51
Comb. Q
(cfs)
COMMENTS
031
:::_,0;5
---
2 yr. runoff
10 yr. runoff
0.25
3.35
1.02
A 0
100 yr. runoff
0.20 = C 1.00 =Cf(2,10) 1.25
SUBBASIN TIME OF CONCENTRATION
D. Pnt.
Slope
I (%)
C * Cf
OverL LengV
(feet)
HB-2
2.50
0.201
240.00
Tc
_1_._00
-0.201
0.20 = C (Land) 0.20 = C (Chan.)
OverL Tc 1han.Lenght Tc Chan. Tc Total COMMENTSmin. C (feet) (min.) (min-)
18.51 _ I OVERLAND TIME ONLY
1 1200.00 56.11 74.61 OVERLAND + CHANNEL
D. Pnt.
Area
(acres)
C Cf
I (2yr.)
(in/hr)
I (10yr.)
(in/hr)
I (100yr.)
(in/hr)
Basin Q
(cf S)
Comb. Q
(cf S)
COMMENTS
HB-2
5.05
0.20
0.97
1
2 yr. runoff
0.20
1.381
1.39
1.4
10 yr. runoff
0.25
2.18
2.75
100 yr. runoff
0.20 C 1.00 =Cf(2,10) 1.25 =Cf(100)
HB�� 2,
Specializing in
Development Properties
Linder
Real Estate and
Development Co.
MARK LINDER
4355 W.C.R.50E
Fort Collins, CO 80521
Bus. (303) 229-0544
Res. (303) 493-5624
WE5T NAI3-IONY R(S.4D
GR055 ACRES 245
5F LOTS 56
MF LOTS 20
LOTS 16
DENSITY 31
SOLAR LOTS 51 (6lz)
LOTS MEETING SOLAR
ACCESS REQUIREMENTS
%1 PROPOSED TREES
EXISTING TREES
(APPROX LOCATIONS)
Interceptor drain
Relocate part of the ditch and move Thayer
headgate south to Thayer property line
Mr. Willis Smith
February 17, 1994
Page 2
4. My lots on the west side of the ditch will drain to the
street and the stormwater runoff will be carried in the curb
and gutter across the box culvert to our detention pond
along Shields. The rear portions of some of these lots that
are downhill from the level of the street will drain into
the ditch on an undetained basis. This will be an
insignificant amount of water and less than drains there
now.
5. We will monitor our test holes once the ditch.begins to run
and design our drainage plans to minimize and hopefully
eliminate any seepage problems with homes with basements
adjacent to the ditch. I will put notice and advisory
language in the protective covenants that recommends sump
pumps in basements for lots close to the ditch. Before
final approval, we will have to have a hydrologist report on
our design. Based on the soils information from the
preliminary report, we will propose to do an interceptor
drain along the east side of the ditch, probably in the
tract, that will intercept and carry any seepage water to
the detention pond. You will have final design approval on
such things and be asked to sign off on our utility plans.
I believe that summarizes our discussion. If I have misstated
anything, please let me know and I shall correct this letter.
Very truly yours,
.�&aJ�oe-�
Mark Linder
ML:cll
Enclosure
cc: Ed Wendel
Steve Olt
t
10
Linder
Real Estate
February 17, 1994
Mr. Willis Smith
President
Pleasant Valley Lake and Canal Company
c/o Norwest Bank
401 South College Avenue
Fort Collins, CO 80524
Dear Willis:
Thanks for meeting with me this morning to talk about the ditch
issues on my proposed development project (as yet unnamed) near
Harmony and Shields. This letter will serve to document the
points we discussed and your agreement on how we propose to
handle the various issues.
1. We will, on the plat, dedicate a 40' tract as a formal non-
exclusive easement for the ditch. This tract will be
measured as 15 feet from the center line on the west or
uphill side, and 25 feet on the east side. We will build an
access road within the tract on the east side when we do
that phase. This tract will ultimately either be owned.by
the Homeowner's Association or the City, depending upon the
desires of the City.
2. We will cross the ditch as shown with a local street and a
box culvert. The size of the culvert will be determined by
my engineers, Stewart & Associates, and the City Engineering
Department. I would expect it to be similar to the 4' x 8'
box culverts used at the Harmony and Wakerobin crossings.
We will also be crossing the ditch with the utilities for
the lots west of the ditch with the water and sewer lines
going under the box culvert.
3. We will straighten and relocate a small section of the ditch
as shown to eliminate a troublesome, leaky corner. The
relocated portion will be lined with 12" of suitable clay
material as approved by my soils engineers, Empire
Laboratories. We will also relocate the present Thayer
property headgate at that corner south to their property.
They are in agreement with this, and I will work with them
and Ed Wendel as to a satisfactory design.
Specializing in Development Properties
3500 J.F.K. Parkway #221 ❑ Fort Collins, Colorado 80525 0 (303) 229-0544
Mr. William E. Elliott
March 1, 1994
Page 3
As Glen explained to me, the advantage to you of this is that I
will be doing for you, at my cost, what should have been done by
you in 1983 when your swale system was built, or would have to be
done by you now if you expand and add other buildings now that
the Wastewater Utility's policies have become better defined. We
are simply formalizing an existing situation (the historic flows)
and bringing both of our properties into conformance with the
current City Stormwater policies.
Bill, thanks for your consideration in this. I shall have my
engineer do the calculations and size the swale and easement and
prepare a drawing for Jack Hale and the Board of Cooperative
Services and School Districts.
Please feel free to call me if you have any questions. I would
be happy to walk the site with you and my engineer if you like at
any time. I shall copy Glen Schlueter with this letter as he
indicated that he would be happy to speak with you and answer any
questions that you might have.
very truly yours,
Mark Linder
ML:cll
cc: Glen Schlueter
Mr. William E. Elliott
March 1, 1994
Page 2
My development of the 25 acres to the west will increase the
impervious surfaces on my property (roofs, driveways, roads) and
increase the volume and rate of runoff from the property compared
to its present status as an irrigated hayfield. I will provide a
detention pond on the lowest corner of my property, just west of
Shields Street to collect stormwater runoff and detain it (slow
it down). This water will be released from my detention pond
through the existing pipe under Shields and flow onto your
property at no faster than the 2 year storm rate off of
undeveloped land. At.present, this water appears to "sheet flow"
across your property to the drainage swales you constructed
around your parking lots. This is what triggered the concern on
the City's part. My development will somewhat increase the
volume of water crossing your property after major storm events
which could potentially cause increased erosion, sogginess and
maintenance problems. At present, this water looks like it
follows someone's tire tracks across the middle of the field
south of your driveway over to the parking lot swale and then
goes on to Mail Creek.
Glen Schlueter and Dick Rutherford, my engineer, and I have
looked at this situation, and what we would propose would be to
pick up the water at the pipe at Shields in a ditch or Swale,
route it around the gas pumping station easement over to the
south property line (avoiding the tree rows), and run it east
down the property line to a point south of the corner of the
parking lot in a small ditch, then turn it north in a widened
swale (for ease of maintenance purposes) to the existing swale.
I will have .a drawing prepared that illustrates this. The City's
minimum drainage easement width is 201. Since these flows are
not large at all, this probably would suffice, but the easement
size will ultimately be determined by the engineer's
calculations. This seems to be the logical route given the
existing topography.
As you and I discussed, this would correct an existing problem
(the sheet flows) and maximize the building potential of your
site by moving these flows south to the property line. The
drainage easement would be non-exclusive and much of it will be
along the existing road right-of-way or along the property line
where, if you platted anything like a building site, you would be
routinely required to dedicate a general utility easement anyway.
All of the engineering costs, construction costs and re -
vegetation costs would be at my expense. We would require a 50,
temporary construction easement for a short time to do the work,
and I agree to restore the ground to its present condition.
•
OLInder
Real Estate
March 1, 1994
Mr. William E. Elliott -
Manager of Administrative Services
Front Range Community College
Larimer Campus
P.O. Box 270490
Fort Collins, CO 80527
Dear Bill:
Thank you for meeting the other day with me to discuss the
granting of a drainage easement across the Front Range Community
College property. This letter will serve to document the various
issues we discussed and the course of action needed to gain the
necessary approvals. It is my understanding that you have
discussed the easement with Mr. Jack Hale, the Executive Director
of the Larimer County Board of Cooperative Services, and Eric
Reno, the Vice President of the Larimer Campus, and that the
three of you see no problem at this point with the easement, and
that I should proceed to generate a drawing and easement document
for consideration at next month's executive board meeting.
I am proposing a 76 lot residential development on 25 acres
across Shields Street to the west of your campus. This property
has historically drained to the east through a pipe beneath
Shields Street onto and across your property.and into Mail Creek.
Mr. Glen Schlueter of the Fort Collins Stormwater Utility has
requested that I formalize this easement across your property to
conform to current Storm Drainage policies, which require
drainage easements for drainage flows until they reach a natural
watercourse like Mail Creek on the northeast corner of your
property. All of these properties are in the McClelland - Mail
Creek Storm Drainage. Basin. This drainage water has a "right" of
sorts to flow this way called a prescriptive easement, and all
the City really wants us to do is to formalize or legitimize this
easement and direct the flows in such a manner that they can be
safely and properly handled.
Specializing in Development Properties
3500 J.F.K. Parkway #221 ❑ Fort Collins, Colorado 80525 0 (303) 229-0544
P-411"
Lail
U 100
0
O C/)
50
O
O
WESTBURY
THIS IS THE MASS DIAGRAM FOR THE DETENTION BASIN REQUIREMENT
iu.0
TIME IN MINUTES
MTotal Runoff Vol. M Allowable Discharge Vol.
NOTE: Discharge plot does not appear linear since time are not uniformly spaced
THIS MASS DIAGRAM TABLE IS FOR USE IN ESTABLISHING THE STORAGE VOLUME
REQUIRED FOR THE 100 YR. STORM EVENT
PRELIMINARY WESTBURY DETENTION SIZING
. .r n..__a i„N 911 97 = Aran tar-rPsl 7.00 = Release Q(2)***
0.40
TIME
= nui tuu
INTENSITY
C*Cf*A
RUNOFF
OUTFLOW
STORAGE
min
in/hr
s .ft.
cu-ft
cu-ft
cu-ft
5.0
7.00-
1.3.09
27487.7
2100.0
25387.7
10.0
7.00
13.09
54975.4
4200.0
50775.4
15.0
6.10
13.09
71860.7
6300.0
65560.7
20.0
5.20
13.09
81677.7
.8400.0
73277.7
25.0
4.68
13.09
91887.4
10500.0
81387.4
30.0
4.15
13.09
97777.6
12600.0
85177.6
35.0
3.83
13.09
105277.8
14700.0
90577.8
40.0
3.50
13.09
109950.8
16800.0
93150.8
45.0
3.25
13.09
114859.3
18900.0
95959.3
50.0
3.00
13.09
117804.4
21000.0
96804.4
55.0
2.80
13.09
120945.8
23100.0
97845.8
60.0
2.60
13.09
122516.6
25200.0
97316.6
70.0
2':33
13:09
1r28092.6
` 29400 0
986....
80.0
2.05
13.09
128799.5
33600.0
95199.5
90.0
1.88
13.09
132883.3
37800.0
95083.3
100.0
1.70
13.09
133511.6
42000.0
91511.6
110.0
1.58
13.09
136496.0
46200.0
90296.0
120.0
1.45
13.09
136653.1
50400.0
86253.1
135.0
1.33
13.09
141011.8
56700.0
84311.8
150.0
1.20
13.09
141365.3
63000.0
78365.3
165.0
1.13
13.09
146430.8
69300.0
77130.8
180.00
1.05
13.09
148433.5
75600.0
72833.5
*** NOTE: -if C * Cf > = 1 , then C * Cf = 1 is used
SUBBASIN TIME OF CONCENTRATION
D. Pnt. Slope C * Cf jOverL Lengt� overL Tc han.Lenght Tc Chan. Tc
I
SITE -2.001 0.45 120.00 10.21 1 OVERLAND TIME ONLY
Tc 1.001 0.90 1 1900.001 15.71 25.91 OVERLAND + CHANNEL
0.45 = C (Land) 0.90 = C (Chan.)
D. Pnt.
Area
(acres)
C Cf
I (2yr.)
(in/hr)
1 (1 Oyr.)
(in/hr)
1 (1 00yr.)
(in/hr)
Basin 0
(cfs)
Comb. O
(cf S)
COMMENTS
SITE
24.50--
0.45
0.45
2.05
3.60
22.60
39.69
Z 39.7
2 yr. runoff
10 yr. runoff
0.56
5.80
79.93
79.] 01
100 yr. runoff
0.45 = C 1.00 =Cf(2,10) 1.25 =Cf 100
SITE.,
NOTE: These assumption are for planning purposes only. Details will be added
when final design is undertaken.
Detention will be required in the Southeast corner of the site.
m
HISTORIC CONTINUED
SUBBASIN TIME OF CONCENTRATION
D. Pnt.
Slope
N
C * Cf
Overt Length
(feet )
Overt Tc
(min.)
han.Lenght
f (feet)
Tc Chan.
(min.)
Tc Total
I (min .)
COMMENTS
I
HB-6
1.50
0.20
200.00
��2OO
I
I OVERLAND TIME ONLY
Tc
1.80
0.20
220.00
19.81
39.81
OVERLAND + CHANNEL
F- 0.20 = C (Land) 0.20 = C (Chan.)
D. Pnt. Area C * Cf I (2y
(acres) (in/
HB -6 3.91 0.20
0.20
0.25
0.20 = C 1.00 =Cf(2,1
SUBBASIN TIME OF CONCENTRATION
D. Pnt.
Slope
N
C * Cf
Overt LenFh
(feet)
HB -7
0.60
0.20
160.00
Tc
2.40
0.20
0.20 = C (Land) 0.20 = C (Chan.)
1 (1 0yr.)
1 (1 00yr.)
Basin Q
Comb. Q
COMMENTS
On/hr)
(in/hr)
(cf S)
- (cfs)
1.21 f7TF777T�j
2 r. runoff
2.19
2.21
74.44
- ........ . - 2.2
10 r runoff
10 vr. runoff
3.52
10
100 r. runoff
1.25 =Cf(100)
Dverl- TC
han.Lenght
Tc Chan.
Tc Total
COMMENTS
(min.)
� (feet)
(min.)
24.31
1
1
OVERLAND TIME ONLY
46.4 OVERLAND + CHANNEL
D. Pnt. Area C * Cf I (2yr.) I (I 0yr.) 1 (1 00yr.) Basin Q Comb. Q COMMENTS
(acres) (in/hr) (in/hr) (in/hr) (cfs) (cfs)
HB-7 1.89 0.20 1.10 1.11 IrPROM" 2 yr. runoff
0.20 1.97 1.99 10 yr. runoff
0.25 3.16 3.99 ,,,,,,>,,,> ::r:4;0. 100 yr. runoff
0.20 = C 1.00 =Cf(2,10) 1.25 =Cf(100)
ACRES IN HISTORIC BASIN, EXCLUDING 50'ROW ALONG SHIELDS AND HARMONY
2 yr. historic runoff
7.0
10 yr. historic runoff 12.2
100 yr. historic runoff 24.41
R
BBASIN TIME OF CON
D. Pnt. Slope
- 3 2.60
fc-- -1.30
0.20 : �(Land�
L
'RATION
Cf Overt Lengt Overt Tc
(feet) (min.
0.20 385.00 23.1
0.20
0.20 = C (Chan.)
Lenght Tc Chan. Tc Total
yet) (min.) (min.)
635.00 37.4 60.5
MENTS
D TIME ONLY
)+ CHANNEL
--Krea
(acres)
2.24
Cf
0.20
0.20
0.25
-(2yr)
(in/hr)
0.91
(in/hr)
-
1.62
(I 00yr.)
(in/hr)
2.60
Basin Q
(cf S)
0.92
1.64
3.28
Comb.
cfs
COMMENTS
D. Pnt.
HB -3
0
:Ena
2 vr. runoff
10 vr. runoff
100 yr. runoff
0.20 C 1.00 =Cf(2,10) 1.25
3:: -
SUBBASIN TIME OF CONCENTRATION
D. Pnt.
Slope
%)
C * Cf
10verlLengt
-
feet
HB-4
3.90
i
0.20
310.00
To
0
4i1ii
0.20
Land 0.20 = C (Chan.
0.20 = C ()
Tc han.Lenght Tc Chan. Tc Total
feet in.) (min.)
18A
;;As nn 1 35.0 53
COMMENTS
RLAND TIME ONLY
LAND + CHANNEL
D. Pnt.
-
Area
-
C Cf
-
I (2yr.)
1 (1 Oyr.)
I (I 00yr.)
Basin Q
Comb. 0
COMMENTS
(acres)
(in/hr)
(in/hr)
(in/hr)
(cfs)
cfs
HB-4
5.46
0.20
1.00
1.01
::::1:.0
- 2 yr. runoff
0.20
1.78
1.80
:4. 0
10 yr. runoff
0.25
2.85
3.60
;i 3.6
100 yr. runoff
0.20 = C 1.00 =Cf(2,10) 1.25 =Cf(100)
SUBBASIN TIME OF CONCENTRATION
D. Pnt.
Slope
N
C * Cf
Overt Lengt
feet
HB-5
2.90
0.20
685.00
Tc
0.000.20
0.20 =
9.20 C (Land) C (Chan.
Overt Tc han.Lenght Tc Chan. Tc Total
(min.) feet min. min.)
29.7
0.001 0.0 29.7
MENTS
D TIME ONLY
)+ CHANNEL
D. Pnt.
-HB-5
Area
(acres)
3.50
C * Cf
0.20
0.20
I (2yr.)
(in/hr)
1.49
1 (1 0yr.)
(in/hr)
2.61
I (I 00yr.)
(in/hr
Basin Q
cfs
1.50
2.64
Comb. Q
cfs
COMMENTS
F 1--5
� F777777A
y
2 r. runoff1 10 yr. runoff
0.25
-
4.20
5.30
5.3
100 yr. runoff
0.20 = C 1.00 =Cf(2,10) 1.25 =Cf (100)
Storm Drainage Report
Westbury P.U.D.
Page 4
Mr. Mark Linder's, the developer, letter to the College is
included as an addendum to this report.
A major hydraulic design feature in this project will be the
construction of a crossing of the Canal. Discussions with the
officials of the ditch company are anticipated to guarantee that
all possible design consideration are understood and addressed
prior to moving forward with crossing. Preliminary approval has
been granted by the Canal company President for this concept.
CONCLUSION
There are no significant obstacles that would present
themselves as insurmountable in designing a storm drainage system
consistent with the requirements of the City of Fort Collins
Storm Drainage Design Criteria and Construction Standards.
Additionally, the project does seem consistent with assumptions
made during the development of the Major basin study in usage
type and intensity.
Should question arise during your review of this report,
please feel free too contact Alex Evonitz or myself so we may
assist in your understanding of the preliminary design concept.
Respectfully,
Richard A. Rutherfor , P.E. & L.S. #5028
STEjp•F`��p'•�.
*� 5023
,�J�•AZ & ;•, +Iinder.rpt
Fuiii����,,�
Storm Drainage Report
Westbury P.U.D.
Page 3
This fact will be addressed during final design to ensure
adequate consideration of all offsite design features.
HYDRAULICS
Street curb capacities are assumed as capable of handling
the direct runoff from the developed site. This would negate the
need for piped storm conveyance. Confirmation will be part of the
final analysis of the complete storm water management
system.
Flows will be directed, by design, to move from the North
end of the project to the detention pond located in the Southeast
corner. Release from the pond (7.0 cfs) will be directed by
surface means, to an existing 15" RCP that crosses Shields, South
of and adjacent to the project site. Current capacity, and the
requirement following development will be addressed in detail, to
ensure no immediate risk of damage by allowing the new detention
facility to release into this existing 15" piping. Discharge from
the detention pond.will be routed through the Front Range
Community College property along their South Property line, and
then North to the existing drainage swale, built in 1983. The
swale then runs Northeast to intersect Mail Creek. The
administration of the College has reviewed the proposal, the
easement will be discussed at their executive board meeting in
April.
Storm Drainage Report
Westbury P.U.D.
Page 2
HYDROLOGY
In the historic condition dense rangeland grasses cover the
site that is gently sloping from the Southwest corner, a knoll,
to the East and North. Traversing the site and flowing from the
North to South is the Pleasent Valley and Lake Canal (the Canal).
This natural hydraulic barrier will be crossed with most of the
developed runoff from the area above the Canal. Currently,, flows
from this area are not hydraulically linked to the area East of
the Canal.
A runoff coefficient of C = 0.20 is the assumption for the
existing condition across the entire site. Without considering
the aforementioned hydraulic break for this preliminary analysis
a historic 2 year release of 7.0 cfs is indicated from the
Rational Method. Using the zoning implied runoff coefficient (C =
0.45) for the developed conditions, 100 year direct runoff of
79.9 cfs is possible. For this preliminary analysis a single
basin was assumed to size the major feature of this design, the
detention pond.
Backlot developed flows from 13 lots above the canal are
being allowed to flow undetained into the Canal, while the
remainder of the developed flows from the area above the canal
will be conveyed via the street system. This design feature was
not included as part of the preliminary detention sizing. Also,
no offsite consideration has been included since it is not seen
as a major factor to the general storm drainage system.
PRELIMINARY STORM DRAINAGE REPORT
FOR
WESTBURY P.U.D.
GENERAL SITE
This proposed residential development is.located in the
Northeast 1/4 of Section 3, Township 6 North, Range 69 West of
the 6th P.M...The property is located near the Southwest corner
of the intersection of West Harmony Road (Harmony), and South
Shields Street (Shields). East of the site is the Front Range
Community College, East of Shields,. and the Gress Gallery on the
West side of the Shields. North of Harmony is the yet to be
constructed regional detention pond in Pineview P.U.D., while
West of the site is The Ridge P.U.D. residential development.
South of the project is an existing non developed parcel.
The development falls within the "McClellands and Mail Creek
Major Drainageway Plan" (Major Basin). The incorporation of
detention is a certainty for the intensified usage proposed.
Release from this ± 24 acre site will continue to be part of the
Major basin, with the historic 2 year, undeveloped runoff rate
the maximum allowed. Proposed is a mixed residential use of
townhomes (20 units), patio homes (4 units) and single family
(52 units).
T -
Preliminary Storm Drainage Report
for
Westbury P.U.D.
u
March 1994
STcwArgASSocUM-cS
Consulting En3ineers and Surveyors
103 South l e&lum Si4eet
f o/.i Cottin s,o Coioaado 80521
3031482-9331