This spreadsheet is a tool to help the drainage engineer designs a storm sewer pump station by performing a level pool analysis of the pumping system, and storage areas. The settings of the pumps “on” and “off” points, flows, system storage, the storm hydrograph, rainfall depth, and duration, are parameters that could be adjusted to optimize the size of a pump station.

1. STORM SEWER PUMP
STATION SIZING
SPREADSHEET
Francis Mitchell, M.S., P.E.
F-MITCHELL@ATT.NET

2. Francis Mitchell, M.S., P.E. PAGE 1
STORM SEWER PUMP STATION SIZING SPREADSHEET
Abstract:
This spreadsheet is a tool to help the drainage engineer designs a storm sewer pump station by
performing a level pool analysis of the pumping system, and storage areas. The settings of the
pumps “on” and “off” points, flows, system storage, the storm hydrograph, rainfall depth, and
duration, are parameters that could be adjusted to optimize the size of a pump station.
This spreadsheet can be downloaded through the link below,
https://www.dropbox.com/sh/jf8vsmhhq013mdd/AACJfnUjpiiCieTCusBS0JxEa?dl=0

3. Francis Mitchell, M.S., P.E. PAGE 2
STORM SEWER PUMP STATION SIZING SPREADSHEET
Table of Contents Page
1.0 DESCRIPTION................................................................................................................................3
2.0 INPUT DATA WORKSHEETS..........................................................................................................4
3.0 OUTPUT DATA WORKSHEETS......................................................................................................8
4.0 CASE STUDY................................................................................................................................16
5.0 AUTHOR......................................................................................................................................33
6.0 REFERENCES...............................................................................................................................34

4. Francis Mitchell, M.S., P.E. PAGE 3
STORM SEWER PUMP STATION SIZING SPREADSHEET
1.0 DESCRIPTION
This spreadsheet was developed as a tool to perform the preliminary sizing of storm sewer pump
station and to complement the analysis performed by much advanced software which don’t have
the flexibility of quickly varying the input data. This spreadsheet could be used first to pre-size and
calibrate a pump station and then use the results for further analysis without having the burden of
performing countless trial and error analysis.
The analysis performed by this spreadsheet is a level pool flood routing of a pump station system
given its watershed area, the rainfall depth and duration, the unit hydrograph and peaking factor.
In addition the user can choose different storm hydrograph generating procedure. The pump
station is defined by its geometry, pumps capacities, “on” and “off” setting, and the storage
available in the storm sewer network.
This spreadsheet generates watershed inflow hydrograph output, outflow hydrograph output,
stage duration graph, and displays also the number of times a pump will turn “on” and “off”, as
well as the amount of working hours.

5. Francis Mitchell, M.S., P.E. PAGE 4
2.0 INPUT DATA WORKSHEETS

6. Francis Mitchell, M.S., P.E. PAGE 5
Design Unit
Design unit is either “Metric” or “English”.
Areas
Areas are entered as “Acres” or “Hectares”.
SCS CN
CN (curve number) depends on the type of land cover.
Time of Concentration
The time of concentration is entered in minutes.
Hydrologic Method
Three different hydrologic analysis method can be used.
 SCS – Santa Barbara Method
 SCS – Design Storm
 SCS – Flood Hydrograph
Rainfall Depth
Rainfall depth for the selected storm is entered in inches or millimeters.
Routing Time
This is the duration of the storm in hours.
Flood Routing Time Step
The time step increment for the routing analysis to be performed.
Print Display Time step
The time step for a result to be printed. This option is currently disabled.
Peaking Factor
The SCS peaking factor, and the length of the receding leg of the hydrograph. This variable
is dependent on the hydrologic method selected.

7. Francis Mitchell, M.S., P.E. PAGE 6

8. Francis Mitchell, M.S., P.E. PAGE 7
Top Elevation and Top Area
The pump station top elevation and top area are entered in feet, and square feet, or meter,
and square meter.
Critical Water Level
The stage at which the water level reached a critical value is entered in feet or meter. This
input data is only for graphical representation of the design constraint.
Starting Water Level
The starting water level is the level of the permanent pool of water inside the pump station.
This data is entered in feet or meter. The stage of the starting water level cannot be higher
than the lowest pump starting elevation.
Bottom Elevation and Bottom Area
The pump station bottom elevation and bottom area are entered in feet, and square feet,
or meter, and square meter.
Pumps Settings
The pumps “on” and “off” elevations are entered in feet or meter. The CUMULATIVE flow
for all the pumps are entered at each row. The unit is either cfs, or cubic meter per second.
Additional Storage
The storage within the drainage system is entered at each stage elevation. The unit is feet,
and cubic feet, or meter, and cubic meter.

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3.0 OUTPUT DATA WORKSHEETS

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4.0 CASE STUDY
Project:
The City of Miami Beach, and the Florida Department of Transportation District Six, have decided
to jointly fund the construction of a major storm sewer pump station facility to offer relief from
recurrent flooding events along Indian Creek Drive from 25th Street to 41st Street. These floodings
are mainly caused by the ever increasing high tides, and deficient gravity drainage systems that
were built in the 1940s.
Design Criteria:
 Design storm to satisfy FDOT critical storms duration as per Chapter 14-86.
 Minimum elevation of +3.70 for new pavement.
 Drainage for low lying side streets will need to be accommodated.
Design:
 Total tributary area A=36.81 acres
 SCS weighted curve number CN = 96
 Critical storm is FDOT 1 Hour hydrograph with rainfall depth of 3.60 inches
 Maximum watershed runoff flow is 132.23 cfs at 54.25 hours
 Trunk line length is 4,600 feet divided into a south and north reach.
 The south reach controls the design with a length of 2,490 feet.
 The south reach has 30 manholes risers, and 1 terminal manhole.
 The north reach is 2,110 feet.
 The north reach has 25 manholes risers, and 1 terminal manhole.
 Minimum existing inlet elevation +2.20 NAVD
Step 1
Find pump station preliminary total flow estimated at 70% of the watershed flow.
Qtotal = 132.23 cfs x 70% of inflow = 92.56 cfs
A preliminary headloss – system curve analysis yields a pump station with three pumps
having a total capacity of 93.36 cfs. (refer to step 5)
Step 2
Find trunk line preliminary pipe diameter for a conveyance velocity of 3.0 ft/s to 3.5 ft/s
Diameter for 3.0 ft/s = (92.56 cfs x 4 / (3.0 ft/s x 3.14159))^.5 = 6.3 ft ( 6.0 feet = 72 inches)
Diameter for 3.5 ft/s = (92.56 cfs x 4 / (3.5 ft/s x 3.14159))^.5 = 5.8 ft ( 5.5 feet = 66 inches)
Step 3
Calculate head losses along trunk line

18. Francis Mitchell, M.S., P.E. PAGE 17
Head losses for 66 inches pipe – south branch
Ref: Hydraulic Calculator Software from HYDTRENCH
Manhole risers losses = 30 x 0.15 x ((3.93)^2 / 64.4) = 1.08 feet
Terminal manhole loss = 1 x 0.5 x ((3.93)^2 / 64.4) = 0.12 foot
Manhole 90 deg. Bend to pump station = 1 x 0.7 x ((3.93)^2 / 64.4) = 0.17 foot
Pipe exit losses to pump station = 1 x 1.0 x ((3.93)^2 / 64.4) = 0.24 foot
Losses along length of south pipe = 2,490 feet x 0.0659 / 100 = 1.64 feet
-------------
Total Losses 3.25 feet
Minimum crown elevation of pipe for HGL to be below existing inlet
+2.20 NAVD – 3.25 feet (head losses) = -1.05 NAVD

19. Francis Mitchell, M.S., P.E. PAGE 18
Head losses for 66 inches pipe – south branch
Ref: Hydraulic Calculator Software from HYDTRENCH
Manhole risers losses = 30 x 0.15 x ((3.30)^2 / 64.4) = 0.76 foot
Terminal manhole loss = 1 x 0.5 x ((3.30)^2 / 64.4) = 0.08 foot
Manhole 90 deg. Bend to pump station = 1 x 0.7 x ((3.30)^2 / 64.4) = 0.12 foot
Pipe exit losses to pump station = 1 x 1.0 x ((3.30)^2 / 64.4) = 0.17 foot
Losses along length of south pipe = 2,490 feet x 0.0414 / 100 = 1.03 feet
-------------
Total Losses 2.16 feet
Minimum crown elevation of pipe for HGL to be below existing inlet
+2.20 NAVD – 2.16 feet (head losses) = +0.04 NAVD

20. Francis Mitchell, M.S., P.E. PAGE 19
Step 4
Find crown elevation based on concrete manhole structures placed along new pavement
Frame and cover height 9.0 inches
Brick leveling (2 layers) 8.0 inches
Concrete slab thickness 8.0 inches
Minimum wall height above opening 6.0 inches
Minimum spaces around pipe 6.0 inches
Pipe thickness 7.0 inches
---------------
Total Cover 44 inches (3.67 feet)
Crown elevation based on structure type = 3.70 NAVD – 3.67 = +0.03 NAVD
In order to expedite construction the City has decided to use spiral reinforced HDPE pipe. This pipe
will be placed under water and requires a soil overburden atop the pipe to prevent floatation. The
minimum crown elevation needed to prevent uplift is -1.00 NAVD.
Although the 66 inches pipe is sufficient, the 72 inches pipe will be used with crown placed at -1.00
NAVD, invert set at -7.00 NAVD. The benefit of using the 72 inches instead of the 66 inches will be
less head loss (lower HGL), longer filling time which will translate into longer cycling time between
pumps start.

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Typical project pump station layout
Drawing Sketch Credit: Ribbeck Engineering Inc.
The pumps used are “in tube” axial flow pump. This setting allows lower minimum
submergence depth. As a result the pump station needs not to be set very deep.
The spacing between pumps is also reduced.
Another requirement was to construct the station in a modular fashion. The modular
approach allowed the units to be pre-cast at the casting yard, and transported on
site for setting and installation.

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Step 5 – Head loss at low water level
Pump flow at low water level (maximum head) is 29.57 cfs

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Head loss at high water level
Pump flow at high water level (minimum head) is 32.67 cfs
Average of pump flow for high and low water level is (32.67 cfs + 29.57 cfs)/2 = 31.12 cfs

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Watershed input data

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Pump station input data

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Inflow Hydrograph

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Outflow hydrograph

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Inflow – outflow hydrograph

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Stage duration

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Cumulative inflow – outflow volume

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Pumps running time

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Pumps capacity and “on” “off” setting rating curve

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System storage capacity rating curve

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5.0 AUTHOR
This spreadsheet can be ordered from the following address.
Francis Mitchell, M.S., P.E.
f-mitchell@att.net
Phone: (305) 979-6387
Or by accessing the link below,
https://www.dropbox.com/sh/jf8vsmhhq013mdd/AACJfnUjpiiCieTCusBS0JxEa?dl=0

35. Francis Mitchell, M.S., P.E. PAGE 34
6.0 REFERENCES
Federal Highway Administration, Highway Stormwater Pump Station Design Manual,
HEC-24, 2000. Formerly Highway Storm Water Pumping Stations, Volumes 1 and 2,
FHWA-IP-82-17.
Daugherty, Robert L., and Franzini, Joseph B.: “Fluid Mechanics with Engineering Applications,”
McGraw-Hill Book Co., New York, 1985.
Mc Cuen, Richard:”Hydrologic Analysis and Design”, Second Edition, Prentice Hall, New Jersey,
1998.
Reitz, and Jens:”Design of Urban Highway Drainage, the State of the Art”, FHWA-TS-79-225, Federal
Highway Administration, August 1979.
Shammas, Namir C.; “Mathematical Algorithms in Visual Basic for Scientists and Engineers,”
McGraw-Hill Book Co., New York, 1995.
Soil Conservation Service:”National Engineering Handbook Section 4-Hydrology, (Part 1 of 2, 2 of
2), Engineering Division Soil Conservation Service, USDA, Washington, March 1985.
South Florida Water Management District:”Management and Storage of Surface Waters-Permit
Information Manual Volume IV”.Streeter, Victor L., and Wylie, Benjamin E.: “Fluid Mechanics,”
McGraw-Hill Book Co., New York, 1979.
Mitchell, Francis : “HYDTRENCH, Exfiltration Trench manual”, Miami, 1999.