1. InfoWorks CS Enables Design of Hybrid Pressure/Gravity Sewer Systems

2. Background
InfoWorks CS has been used for the functional design of proposed residential and industrial hybrid sewer systems.
Pipeline sizing, pump selection and storage requirements were all determined using InfoWorks CS.
The aim of today’s presentation is to show how the dynamic modelling capabilities of InfoWorks were utilised in functional design.

3. Agenda Definition of Hybrid System Advantages of using InfoWorks CS
Case Study 1: Yarra Valley Water – Wonga Park
Case Study 2: Barwon Water – Industrial Estate
Conclusions
Questions / Discussion

4. What is a Hybrid System ?
GRAVITY SEWER
PRESSURE SEWER

5. Advantages of Using InfoWorks CS
Allows both analysis of pipe-full flow and part-full flow, so that pressure pipes and impacts on gravity systems can be assessed in one model.
Integration with existing gravity system models.
Data import / export tools
Pump controls
Reporting tools

6. Case Study 1: Wonga Park Yarra Valley Water
Existing residential area currently not sewered.
Approximately 500 properties with a mix of gravity connections and pressure pump units
Area is low-density with lot sizes approximately 4000 sq m

7. Modelling Issues Considered
In addition to the usual design criteria the following issues were considered in modelling:
Initial starting conditions
Headloss in property connections and sensitivity analysis considering varying lot control requirements
Peak flows generated from the system upon resumption of power following a prolonged outage

8. Initial Starting Conditions

9. Random Initial Starting Conditions (Reality)

11. Uniform Initial Starting Conditions

12. Uniform Initial Starting Conditions

14. Applying Random Starting Conditions

15. Applying Random Starting Conditions

16. Allowance for Headloss in Property Connections
Wonga Park has very large lots with steeply sloping topography and potentially long property connection pipes.
To improve the efficiency of the model, property connection pipes were not modelled, however the headloss was still allowed for.

17. Hydraulic Grade Line Outlet Property Connection Friction Head
Static Head
Property Connection

18. Static Head
Taken into account by ensuring the pump well levels and pump cut in/cut out levels are accurate

19. Friction Head
Allowed for by subtracting friction loss from pump curve

22. Consideration of Property Control

24. Consideration of Property Control
Solution: two models
Partial Lot control – pump levels and pump curve based on location of existing property
Full Lot control – pump levels and pump curve based on worst case

26. Power Outage Scenarios

27. RTC Rules

28. Typical Flows

29. Depth to Spill

31. Summary Random initial tank level created using inflow hydrograph
Pump curves and pump levels altered to account for headloss in property connections
Two models built to consider different lot control scenarios
RTC utilised to model power outage scenario and report on freeboard to spill

32. Case Study 2: Industrial Estate – Barwon Water
64 Properties. Each with own pressure pump discharging to gravity sewer.
Two main catchments each discharging to an outfall pump station
GRAVITY SEWER

33. Issues Considered Sizing of gravity pipe
System requirements to cater for peak flows following a power outage

34. Pipeline Sizing
Barwon Water recognised the importance of dynamic modelling in determining pipe sizing given that:
Under normal operating conditions only a small number of pumps operate simultaneously
However there are circumstances where pumps can operate simultaneously.
Pipelines were sized based on the flows and velocities predicted by InfoWorks CS, considering usual design criteria

35. Results

36. Results

40. Power Outage Scenario Differences from Case Study #1
All pumps discharge into gravity sewer, there is no head restriction limiting pump operation at the resumption of power.
Discharge rates are potentially higher – potential for inflow volume to exceed tank volume during a prolonged power outage

41. Node Spill Model
Where the wet well is predicted to fill during a power outage it is important to consider the node spill model adopted for the node representing the pressure pump well.
Two applicable options:
Lost
Stored

42. Lost
Once the node representing the pressure pump well fills any additional flow is lost from the system.

43. Stored
Once the pressure pump well fills any additional flow is stored and is returned to the system as the well empties.

44. Lost vs Stored – Difference in Results

46. Which Spill Model to Adopt ?
Requires understanding of:
Likely operation of customers
Rules applied to customers
For example, if customers don’t have additional storage, the lost model would be more appropriate.

47. Summary
Barwon Water recognised the importance of dynamic model in the efficient design of a hybrid system.
InfoWorks CS was used to determine peak flows and size pipelines.
The different node spill models available in InfoWorks allow the modelling of different operational scenarios following resumption of power.
Modelling of the power outage scenario enabled additional storage requirements to be determined.

48. Conclusions
The following aspects of the functional design of hybrid sewer systems were modelled using InfoWorks:
Hydraulic analysis of both part-full flow and pressurised pipes allowing pipeline sizes to be determined
Randomisation of initial starting conditions
Variable lot control scenarios
System outflows following a power outage and associated storage requirements
Consideration of various system operating scenarios by use of a choice of node spill models.

49. Acknowledgements Yarra Valley Water – Chris Saliba
Barwon Water – Mircea Stancu

50. Questions / Discussion