InfoWorks CS Enables Design of Hybrid Pressure/Gravity Sewer Systems

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.

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

What is a Hybrid System ?

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

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

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

Initial Starting Conditions

Random Initial Starting Conditions (Reality)

Uniform Initial Starting Conditions

Uniform Initial Starting Conditions

Applying Random Starting Conditions

Applying Random Starting Conditions

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.

Property Connection

Hydraulic Grade Line

Outlet

Friction Head

Static Head

Static Head

• Taken into account by ensuring the pump well levels and pump cut in/cut out levels are accurate

Friction Head

• Allowed for by subtracting friction loss from pump curve

Consideration of Property Control

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

Power Outage Scenarios

RTC Rules

Typical Flows

Depth to Spill

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

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

Issues Considered

• Sizing of gravity pipe• System requirements to cater for peak flows following a power

outage

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

Results

Results

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

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

Lost

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

Stored

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

Lost vs Stored – Difference in Results

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.

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.

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.

Acknowledgements

• Yarra Valley Water – Chris Saliba• Barwon Water – Mircea Stancu

Questions / Discussion