1. CE 3372 Water Systems Design
EPA SWMM– Pumps and Lift Stations

2. Purposes
To lift stormwater to higher elevation when discharge of local collection system lies below regional conveyance.
To lift stormwater to higher elevation when terrain or man-made obstacles do not permit gravity flow to discharge point.

3. Pond and pump station

4. Types Submersible Wet-well / dry-well Lower initial cost
Lower capacity
Smaller footprint
Wet-well / dry-well
Higher initial cost
Easier inspection/ maintenance

5. Submersible lift station
Module 14

6. Wet-well / dry-well lift station

7. Design criteria
Size the pumps and the wet-well (sump) storage capacity to accommodate inflow variability and detention time limits.
Match the pumps to the flow and head requirements.
Provide ‘near-absolute’ reliability
Automated controls
Redundant systems
Alarms
Regularly scheduled, preventive maintenance
Assess and mitigate environmental factors
Flood risk, noise pollution, visibility

8. Site plan and facilities
Protected and accessible during a major flood
Redundant power supplies
Intruder-resistant with controlled access

9. Wet-well (sump) dimension design
Height
Inflow pipe elevation
Ground elevation
Excavation costs
Cross section
Constant
Variable
Module 14

10. Pump capacity Greater than average flow Less than the maximum flow
Depends mainly upon
Inflow variability
Marginal costs of increasing sump volume

11. FHWA-HDS
Detailed “how-to”
Reviews hydrology
Reviews hydraulics

12. Pump System Hydraulic Operation
Runoff enters the collection system and is conveyed to the storage unit and wet well of the pump station. For a period of time there is no outflow as the runoff is stored within the storage unit and wet well.
The water level in the wet well rises and a hydraulic gradient develops based on the rate of inflow, the water level in the wet well, and the conveyance capacity of the storage unit and collection system.
The first pump starts when the water level in the wet well reaches a specific elevation. The pump evacuates the flow at a rate that varies with the pump characteristics and total dynamic head.

13. Pump System Hydraulic Operation
The inflow rate will vary as defined by the inflow hydrograph. If the pumping rate is lower than the inflow rate, the water level in the storage unit and wet well continues to rise and the volume stored in the system increases.
Additional pumps start at predetermined elevations as the water level rises.
At some point, the inflow rate will be lower than the total pumping rate. The water level in the wet well drops as water is evacuated from storage.

14. Pump System Hydraulic Operation
At preset elevations, as the water level drops, individual pumps are stopped and the discharge rate drops accordingly.
When the water level drops to the minimum level required for submergence, the last pump is stopped. The last pump off is usually the first to have been switched on, although different switching schemes are feasible.

15. Lift Station Design Process
Design criteria include:
Design frequency
Peak outflow
Station type
Design philosophy
Minimum storage volume
Maximum allowable highwater
Discharge velocity
Criteria must be established before design of storage and pump system (FHWA-HDS pg 4-9)

16. Lift Station Design Process
Hydrologic Analysis:
Drainage boundary and area
Runoff characteristics
Design runoff hydrographs
Cumulative inflow

17. Lift Station Design Process
Trial Pumping Configuration:
The design is typically iterative
Minimum of two pumps recommended

18. Lift Station Design Process
Hydrologic/Hydraulic Analysis/Estimates
Inflow hydrograph
Inflow mass curve
Stage-storage relationship
Trial pump/switching scheme
Mass curve routing
System head curves
Pump selection/operation

19. Hydrographs – review
A hydrograph is a graphical representation of discharge (volume/time) with time
The area under the hydrograph curve represents the total volume of runoff during the time represented
The highest point on the graph is the peak discharge

20. Hydrographs – review

21. Storage
Storage is collection system, plus any sump (wet well) on suction side of lift station.

22. Time distributed discharge
Route inflow hydrograph through lift station (and collection system) to generate the time distributed discharge.

23. Basic assumptions
Pump station hydrologic design is conceptually identical to reservoir routing design
Inflow-outflow=change in storage
Inflow is the hydrograph produced by the storm sewer system
Outflow is derived from the sump geometry (stage/storage) and Pump Performance Curves for the pump or pumps in the station
Module 14

24. Lift Stations in SWMM
Used to “lift” water from a low elevation to a higher elevation.
Lift provided by pumps, usually centrifugal.
Pumps modeled similar to EPA-NET

25. Lift Stations in SWMM

26. Lift Stations in SWMM
Lift stations are modeled as special links (like in EPA NET).
Page 40 of the SWMM manual described the conceptual model used – there are 4 “kinds” of pumps in SWMM

27. Lift Stations in SWMM Type 1 Pump Rule
Semi-realistic (see next slide); actual operation would likely be by stage (depth)

28. Lift Stations in SWMM Type 2 Pump Rule
Realistic rule: can use a PLC and transducer to control the pump; assumes discharge into free (open) pipe

29. Lift Stations in SWMM Type 3 Pump Rule
Realistic rule: Like in EPA-NET. Assumes suction and discharge submerged – discharging into a force-main. This is the “kind” of pump you had in fluids and earlier in this course.

30. Lift Stations in SWMM Type 4 Pump Rule
Realistic rule: Archimedes (screw) pumps work exactly like this rule. Reasonably common in wastewater treatment plants for initial lift into the reactors (then gravity flow rest of plant).

31. Lift Stations in SWMM Woodlands Ditch C Subdivision.
As-is drainage model, using 2-yr design storm.
Suppose the goal is to keep ponding less than 2 feet.

32. Lift Stations in SWMM 3:15 into the storm Greater than 2 feet deep
Ok to be deep in the ditch

33. Add relief sewers 3:15 into the storm Used a 8X16 box culvert
To “store” water in the sewer
Lift station here
For the example
Ok to be deep in the ditch

34. Run once to find lift station need
3:15 into the storm
Lift station here
For the example
Probably need 100 cfs
(5 low-head pumps)

35. Run again with the lift station
3:15 into the storm
Lift station here
For the example
Probably need 100 cfs
(4 low-head pumps)

36. Then Check Is such a lift station feasible? How many pumps?
Force main diameter (4-foot this simulation), kind of big
How much power?
Other alternatives (in this case a gravity relief sewer probably makes more sense)

37. Exercise Download the No-Relief-Sewer file and run the program.
Then design a relief sewer(s) to keep all the storage nodes at 2 foot ponding depth or less.
Require at least 5-foot cover (storage nodes are at grade, other nodes below grade).