The practical uses of PODDS

Practical uses of PODDS

Neil CroxtonPrincipal Modelling Engineer

Civil EngineeringUnited Utilities

The practical uses of PODDS

Prediction Of Discolourationin Distribution Systems

Agenda

• Overview of the discolouration problem

• introduction to PODDS• project• Theory• modelling

• practical uses

Background

Preston

Liverpool

Crewe

Manchester

Carlisle

Crewe

Carlisle

ManchesterLiverpool

PrestonPreston

Liverpool

Crewe

Manchester

Carlisle

Crewe

Carlisle

ManchesterLiverpool

Preston

• 5,400 square miles• a population of over 7 million• Over 2,500 district metered areas• 455 service reservoirs• 626 pumping stations• 127 water treatment works• treating 2,000 million litres of water daily• 1,444 kilometres of aqueduct• 40,000 kilometres of water main

The discolouration problem

2008 ~ 2,000 complaints2009 ~12,000 complaints2010 ~10,000 complaints2011 ~ 4,000 complaints

Water, usually supplied like this

sometimes like this…

The discolouration problem

Discolouration - where from and why?

• corrosion products / biofilms• historical output from treatment works• complex water chemistry• poor cleaningWhy?• bursts• operational changes• operator error• increased demand• illegal use

1 NTU1 NTU 4 NTU4 NTU

90 NTU90 NTU 190 NTU190 NTU

40 NTU40 NTUTurbidity – what does it look like?

1. a research project undertaken by Sheffield University

2. a theory of how discolouration happens

3. a predictive software tool

PODDS – 3 aspects to consider

• a research project undertaken by Sheffield University

• supported by some UK water companies

• a theory of how discolouration happens• principal proponents: Prof Joby Boxall & Dr Stewart Husband

• the aim is to predict where discolouration is likely to occur -how much? when?

PODDS – the research project

PODDS – the theory

= discolouration= discolouration

normal flow

increase to well above normal flow

giving > 0.7 ms-1

increase to well above normal flow

giving > 0.7 ms-1

TRADITIONAL sediment theory

= discolouration= discolouration

normal flownormal flow

ANY value above normal flowANY value above normal flow

the PODDS theory

• discolouration arises due to the erosion of layers of cohesive “sticky” material that builds up on the pipe walls

• Layers get used to the normal daily flow

• anything above this “conditioned” flow erodes the layers, causing discolouration

PODDS – the theory

“conditioned” flow; no l removed

No discolouration on 1st dayal shears ayers

pipe is NOT conditioned to 2nd day higher flow; discolouration occurs

peak flow 1st dayflow broadly similar overprevious few months

peak flow 2nd day

pipe wall

build-upof material

flow through pipe

PODDS theory – in motion

• EPANET based– public-domain open-source software

• simple or complex models

• hand-built or exported from other software

• Currently building up a set of field test based turbidity parameters

• searching for the ideal set based on pipe characteristics

PODDS – the software

all mains modelall mains model

Calibrating the PODDS model

simple modelsimple model

sourcesource

demanddemand

flow

Imposing the flow and monitoring the turbidity

portable self-contained turbidity monitoring

equipment x2

portable self-contained turbidity monitoring

equipment x2

turbidity – 2 daysturbidity – 2 days

Model Calibration to WQ data

modelled turbiditymodelled turbidity

imposed flow to create

turbidity response

imposed flow to create

turbidity response

measured turbiditymeasured turbidity

flow - 2 daysflow - 2 days

PODDS Model parameters altered so that model = reality

(most influential being the value which represents the rate at which material is mobilised)

PODDS Model parameters altered so that model = reality

(most influential being the value which represents the rate at which material is mobilised)

Practical uses of PODDS

some examples…

EPAnet400 l/s400 l/s

+50 l/s+50 l/s

+50 l/s+50 l/s

+50 l/s+50 l/s

+50 l/s+50 l/s

movement of turbidity across the network

EPAnet

09:00

normal flownormal flow

EPAnet

10:00

+50 l/s for 30 mins+50 l/s for 30 mins

+30NTU+30NTU15NTU15NTU

2NTU2NTU5NTU5NTU

EPAnet

11:00

back to normal flowback to normal flow

5NTU5NTU2NTU2NTU

EPAnet

12:00

5NTU5NTU2NTU2NTU

EPAnet

13:00

5NTU5NTU

2NTU2NTU

EPAnet

14:00

5NTU5NTU

2NTU2NTU

EPAnet

15:00

5NTU5NTU

2NTU2NTU

EPAnet

16:00

5NTU5NTU

2NTU2NTU

EPAnet

20:00

5NTU5NTU

2NTU2NTU

EPAnet

24:00

5NTU5NTU

2NTU2NTU

EPAnet

28:00

5NTU5NTU

EPAnet

31:30

back to normal turbidity levels>20 hours after 30 min flow eventback to normal turbidity levels>20 hours after 30 min flow event

one more to construct

Uses of PODDS – priority ranking

0

4

8

12

16

20

24

0% 10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

mod

elle

d Tu

rbid

ity (N

TU)

extra Flow (%)

Ranking of trunk mains using potential to cause discoloured water- modelled Turbidity (NTU) against increase in Flow (%) -

pipe 1

pipe 2

pipe 3

pipe 4

pipe 5

pipe 6

4 NTUnetworkPCVfailure

4 NTUnetworkPCVfailure

PIPE 610% increase in flow = 4NTUHIGH RISK

PIPE 610% increase in flow = 4NTUHIGH RISK PIPE 1

>100% increase in flow = <4NTULOWER RISK

PIPE 1>100% increase in flow = <4NTULOWER RISK

Uses of PODDS – priority ranking

Uses of PODDS – reducing the risk

1. Allows flow increase while maintaining a low turbidity response2. Facilitates gradual removal of deposits, effectively “cleaning” or reducing the

risk of future discolouration – increases the headroom.

• to compare the potential discolouration risk• to determine where the greatest investment need is required.• cost savings by avoiding or deferring mains replacement

• operational charts used to gradually increase flow• operational charts used to lower the risk of discolouration

• “cleaning” the pipes while maintaining the flow

• PODDS theory in a wider sense is being used regularly in the design of engineering solutions.

• mitigating risk in operational changes and enabling works

• large-scale cleaning of small diameter plastic mains• using “conditioning” flow to design robust flushing schedules

Uses of PODDS - summary

Summary

• the discolouration problem

• introduction to PODDS • project• theory• modelling

– field trials– calibration

• practical uses – priority ranking, getting the best use out of our finances– lowering the risk– regular use of PODDS concepts in engineering design

Neil Croxton, Principal Modelling Engineer,Clean Water Network Modelling

Engineeringand Capital Delivery United Utilities

Thanks, any questions?

Uses of PODDS – operational chartsChanging flows in large diameter mains

data lines produced by running scenario versions of the PODDS model with different initial conditioning flows e.g. 100, 150, 200 etc