Eastgate Drainage Study
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EASTGATE DRAINAGE STUDY
Dow Addition
City of Salina, Kansas
Mayor
Peter F. Brungardt
City Commissioners
John Divine
Joseph A. Wamer
Carol E. Beggs
Evelyn Maxwell
City Manager
Dennis M. Kissinger
Director of Engineering & Utilities
Don Hoff: P.E.
November 1993
Project No, 10-93142-31
EARLES & RIGGS
Engineers, Planners, and Landscape Architects
Post Office Box 147
Lindsborg, Kansas 67456
(913) 227-3787 - Fax (913) 227-3788
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Eastgate Drainage Study
Table of Contents
Purpose
page 2
Background
page 2
Act~al Construction
page 2
Problems
page 3
Discussion
Page 3
Solutions
Page 4
Typical Ditch X-Section
Page 5
Costs
Page 6
Appendix A - Original Storm Drainage Plan
Appendix B - Existing Ditch Plan & Profile
Appendix C - Existing Ditch X-Sections
Eastgate Drainage Study
page 1
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EASTGATE DRAINAGE
CIIT OF SALINA
E&R File 10-93142-31
Purpose:
To provide a reasonable solution to the drainage problems associated with the holding
pond and ditch located in the Dow Addition to the City of Salina.
Background:
The original drainage study was completed in 1984 by Appleby Architects. This study
focused on the area bounded by Cloud Street on the south, Braidshaw Street to the north,
Ohio Street to the West and the east extends of the Dow Addition to the east (see layout
in Appendix A). The entire area was laid out to drain into an existing drainage swale
located on the east edge of the Dow Addition which drains into a 42-inch diameter pipe
running through the Smoky Hill River dike. To control the volume of run-off: a holding
pond was constructed and sized to detain the runoff differential from a 10 year storm. The
pond was designed to be emptied by pumping the storm water into the drainage ditch
located on the eastern edge of the Dow Addition. A box culvert was to be installed
between the pond and the ditch to act as on overflow device preventing the pond from
over topping the street if the pumps were to fail. The existing drainage swale was then to
be widened to a 30 foot ditch from Courtney Street east along the south side of the Dow
Addition, approximately 550 feet, and then east along the east edge of the Dow Addition
for approximately 1300 feet to north edge of the Dow Addition. The remaining 580 feet
of drainage swale, which carries the flow to the 42-inch pipe, was to be widened in the
future. This ditch was to be graded at a slope of 0.05 % and to flow at a depth of
approximately two feet in order to carry the required volume of runoff. The drainage
pattern for the area was to have Minneapolis Street drain directly into the pond.
Bradshaw and Beloit Streets would drain into the northern portion of East gate Drive and
flow through a flume inlet directly into the newly widened ditch, Louis Lane would drain
to the east into Courtney Street which drains south into the drainage ditch. Ellsworth
Street would drain into the southern portion of East gate Drive, through another flume
inlet and into the newly widened ditch.
Actual Construction:
The ditch was constructed with a 20 foot bottom width at a slope of 0.05%, or 5/8 inch
drop in 100 feet. This widen ditch section was installed from just east of Courtney Street,
east to the east edge of the Dow addition, then north along the eastern edge of the Dow
Addition to the northern edge of the Dow Addition. The remaining 580 feet north to the
42" pipe remained a V-ditch. The two flumes were installed as stated, one on the south
portion of East gate Drive and one on the north. The top of the flumes were constructed
at elevation 1221.78 for the south flume and 1221.88 for the north flume.
Eastgate Drainage Study
page 2
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The pond was constructed with a capacity of3.4 acre-feet of storage below the 1221.00
elevation. A concrete flume was constructed which runs the length of the pond's center
and empties into the lift station. The flow line of the flume at the lift station is 1217.00,
with the floor of the lift station at elevation 1211.83. When the water in the wet well
reaches three feet in depth or at elevation 1214.83 the discharge pumps automatically
switch on and discharge into a double cell2'x4' reinforced box culvert constructed
between the pond and the ditch under Eastgate Drive, which carries the flow into the
drainage ditch. The inflow elevation of this box, pond side, is 1220.85, with the discharge
elevation into the ditch at elevation 1220.68. There are two inlets constructed into the top
of the box which allows the flow along Eastgate Drive to drain into the box.
Problems:
A normal minimum grade required to maintain flow and prevent silting in a grass lined
ditch is 0.40%. The current grade of the Eastgate ditch is 0.05%, considerable less than
the acceptable standard. This low grade is part of the cause for some of the ponding,
however the main reason for the ponding is the condition and width of the ditch from the
north edge of the Dow Addition north to the dike. The ditch abruptly goes from a 20 foot
flat-bottom ditch to a v-ditch at the north edge of the property. The v-ditch then
continues 580 feet to the dike with a grade that varies, but at times is as much as one foot
higher than the flow line of the widened ditch forcing the water to pond a foot in depth in
the Eastgate area before flowing on to the dike. (See Appendix B and Appendix C)
In order for the widened ditch to carry the required flow at a slope of 0.05%, the original
calculations, which were based on using a 30 foot flat bottom ditch, show the depth of the
water to be approximately two feet, assuming no blockage of the ditch. The actual
existing ditch flow lines and flume inlets were surveyed to find out the actual allowable
depth that could occur in the ditch before it flooded the roadway. We found the roadway
elevation near the south flume inlet on Eastgate Drive was at elevation 1221. 78 and the
ditch elevation was 1221.0. At the north flume the roadway elevation was 1221.88 and
the ditch elevation was 1220.5. These elevations at the ditch flow lines with reference to
the street flow lines and the required depth of flow, readily show another reason for the
flooding. The water level in the ditch need only rise one foot and the water is flooding
Eastgate Drive.
Adding to the flooding problem are the pond pumps which turn on immediately upon
receipt of water into the pond. The water is pumped into the west end of the reinforced
box culvert which drains into the ditch. Presently the flow line of the box culvert is
approximately equal to the flow line of the ditch. As the water backs up in the ditch, the
water overflows through the box culvert and flows into the pond. At the same time the
pumps are running, pumping the water into the ditch, and the circulation of water begins.
Another concern is the river. When the Smoky Hill River rises, the flap gate at the end of
the 42-inch pipe under the dike is closed and no flow will exit this ditch. There is
currently no other way to get the flow through the dike.
Eastgate Drainage Study
page 3
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Discussion:
The survey showed that unless the 42-inch discharge pipe was lowered, the maximum
slope that can be maintained in this ditch from Courtney Street to the pipe is 0.05%.
Looking at the roadway elevations in comparison to the ditch grades, it is also apparent
that the maximum depth of flow allowable before street flooding occurs is 1 to 1.5 feet.
In order to obtain the quantity offlow required, realizing that the slope must remain the
same and the depth of flow is limited, the width should be adjusted to create a larger flow
area or a larger holding area must be created to reduce the volume of flow. In order to
maintain the greatest flow in the ditch, the ditch should be keep as wide as possible
throughout it's length and the pond used as a storage and overflow basin. It is our
recommendation that the current v-ditch be widened to a minimum of a 20 foot flat
bottom ditch with 2 to 1 side slopes (see new ditch x-section on the following page).
To reduce the flow in the drainage ditch we suggest the pond's pumps not discharge water
into the ditch until the ditch flow has been reduced by flowing through the 42-inch
discharge pipe. This could be accomplished by use of a time delay switch on the pond
pumps, however this would require some additional water storage capability.
In order to get the maximum use of the pond, we suggest deepening the pond to the
maximum allowed by the water table. If the pond is deepen to elevation 1217.00, the
storage volume below elevation 1221.00 would increase from 3.4 acre-feet to 5.5 acre-
feet, thus allowing for more storage which would elevate some of the flooding problems in
this area.
When the river rises and the pipe discharge is sealed, water will rise in both the ditch and
the pond simultaneously. Once the water elevation reached 1221.00 the water would
begin to flow onto the roadway. The only way to eliminate the problem would be to
pump the runoff from the pond over the dike to the river.
Solutions
Short Term:
1.) Widen north end of ditch from the north edge of the Dow Addition,
north to the dike.
Required - City will be required to purchase 60 feet of drainage
easement, assuming a 20 foot flat-bottom ditch with 2 to 1 side slopes
2.) Widen and deepen the pond below elevation 1221.00 to provide
additional storage capacity.
Required - Removal of concrete flume through the center of the pond
3.) Install time delay switch to pond discharge pumps
Required - Adjustment of discharge pump's high level alarm
Long Term:
1.) Extend pump discharge line over the dike
Required - Establishment of a drainage district and two discharge p!lffiPS .
Eastgäte Dramage Study
page 4
-------------------
Typical Ditch X-Section
20'
Eastga te Drainag.s¿
Ditch (Iypj
Easlgalc Drainage Study
page 5
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Costs:
Short Term:
Item
Excavation
Concrete Removal
Ditch Liner
Pump Delay Switch
Quantity Unit Cost
6200 C.Y. $ 5.00
84 C.Y. $ 30.00
70 S.Y. $ 45.00
1 Each $500.00
Subtotal
15% Contingency
Cost
$31,000.00
$ 2,520.00
$ 3,150.00
$ 500.00
$37,170.00
$ 5.575.00
$42,745.00
$ 8.549.00
$51,294.00
Long Term:
Costs will vary depending on the volume of water pumped. If the current
wet well can be reused and only the pumps replaced and a new discharge
line installed, the total cost could run around $45,000 to $65,000. If the
city decided to pump at a much higher rate, the costs for a completely new
lift station could run between $130,000 to $250,000 depending on the size
and availability of the discharge pumps.
Engineering, Legal, Bonds and Administration (20%)
Total Estimate Probable Cost
Eastgate Drainage Study
page 6
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APPEND IX A
ORIGINAL STORM DRAINAGE PLAN
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