Bristol Water

Minimising disruption to water supply at Bristol Water

Over 1.2 million people who live in the City of Bristol and surrounding areas in the west of England rely on Bristol Water to provide clean, fresh drinking water every day. In a comprehensive survey in 2017, Bristol Water’s customers stated that they wanted water that was always on tap with no interruptions and that any interventions represent best value.

Innovyze and Bristol Water have worked closely together to ensure these priorities are met.

In order make sure water is always ‘on tap’ with no interruptions, Bristol Water works to achieve certain key objectives:

  • Provide extra resilience by reducing the number of pipes whose failure could affect a population in excess of 10,000 to zero by the end of AMP 8 (2030)
  • Improve reliability by reducing the number of interruptions
  • Maintaining a high level of customer satisfaction

Resilience is essentially the ability to react to and recover from an incident, such as a leak or a shut down for maintenance or repair. Improving resilience in water distribution networks to ensure continuous supply means identifying and mapping the critical pipes that could lead to supply being disrupted. The goal is to keep the
number of customers affected to a minimum. Bristol Water uses InfoWorks WS Pro (IWS Pro) from Innovyze to assess the pipes that are most critical to the network and its customers.

The Challenge

Every water supply network has pipes and other assets (pumps, valves, etc.) that could be considered critical. This may be because of the number of customers affected if the asset or pipe fails, the type of customer affected (such as hospitals, schools, care homes etc.) or how difficult it is to repair because of their location. Understanding the impact calls for ‘Critical Link Analysis’– a consideration of the importance of assets as links in the network.

Critical Link Analysis (CLA) informs the modeller how important individual pipes are to the whole network. The CLA feature in IWS Pro shows the impact of individual pipe failures on the hydraulic performance of the network.

To assess the impact of individual component failure on the Bristol Water network, the Network Asset Modelling team ran independent hydraulic simulations. Kevin Henderson, Network Asset Modelling Manager for Bristol Water explained, “Critical Link Analysis is about understanding who is at risk when an asset fails – preferably before it happens – and taking decisive action to protect communities.”

As part of its investment plans to mitigate key risks relating to its critical assets, Bristol Water proposed a number of measures. These include additional manual and smart valves and/or the laying of additional pipes so that all major population centres have a backup supply in case the usual source fails or is unavailable. Building redundancy into the network is a significant investment and requires careful planning and analysis to ensure the best return.

That is where hydraulic modelling comes in. It empowers water professionals to identify the hydraulic impact when a pipe or other asset fails and see how many customers are affected.

The Project

As part of the development of the PR19 Business Plan, the company needed to assess the level of Asset Resilience. This exercise was part of a wider piece of work around providing long term resilience in the round. Previously, network resilience investigations were undertaken using externally provided models. To aid the assessment for PR19 the Network Asset Modelling team was given the challenging task to provide a full suite of models comprising every treatment works supply zone across the whole network, in a relatively short period. The models were to be used to answer questions such as:

  • Which mains would affect the highest number of customers if it burst and extenuating circumstances led to an extended repair period of 24 hours? Real life examples of this have included not being able to isolate a burst immediately due to fire brigade disallowing site access due to gas being smelt. On another occasion, a ferocious overhead thunderstorm prevented immediate isolation because of the risk to operatives’ safety.
  • Where should we divert the water from to compensate for an isolated main while it is being repaired or replaced?
  • Where do we enhance the network to provide full resilience for customers downstream of assets supplying a population of 10 000 or more.

Resilience is a major factor in PR 19, the UK regulator Ofwat’s 2019 Price Review. Where previous price reviews had looked only at how customers were affected by above ground assets like treatment

works, PR 19 considers individual pipes affecting 10,000+ consumers. The first task for the team at Bristol Water was to identify which mains served those numbers. Kevin and his team had to look at

every single main in the company’s network – some 175,000 pipes, in isolation groups of four to one. Creating isolation groups was a major investment in time and computer power, and the team was under a great deal of pressure to get it done quickly.

The Network Modelling team ran the Critical Link Analysis in InfoWorks WS Pro for every main in the company area. To carry out the analysis, the tool closes either end of a single pipe or an isolation area at a time. It runs a simulation and then compares the result with a base simulation. They ran a 48-hour simulation for each isolation group, and each isolation was from 6 a.m. for a 24-hour period. Any properties that dropped below 3m pressure for at least 30 minutes were added to the ‘critical count’ against those mains. If any reservoirs emptied as a result of the 24-hour isolation then all properties downstream were also counted towards the ‘critical count’ A simple calculation converted this figure to the population affected by the loss or failure of each component.

Once the critical count was established for each main, a four-phase approach was adopted for evaluation.

Pipe Criticality Overview

Once the individual pipe results for all treatment zone models have been calculated, the network files are combined to give a view for the whole company area. This cannot be ‘run’ as a model but can be used to provide an overview of results for further analysis by experienced Network Asset Modelling Engineers with a good knowledge of the company’s hydraulic network.

Phase 1. Analysis of results – High Level Criticality Removal

As the models do not have built-in algorithms to automatically reconfigure the network with potential rezones (valving, pump switching, etc.) during the modelled 24-hour isolations, pipes could be flagged with a criticality count where, in reality, no customers would be affected.

The company overview is scrutinized, based on a good knowledge and understanding of the network, to remove criticality counts on pipes where a high level rezone options are known.

Phase 2. Analysis of results – Rezoning (Additional Valves) Mitigation Options

Evaluate where rezone options are available for pipes at risk of affecting ≥ 10 000 population. 

Size additional manually operated valves and/or new dynamic control valves to maintain at least 3m pressure for full 24-hour period on failure of pipe at risk.

Phase 3. Analysis of results – Mains Laying Mitigation Options

Evaluate where rezone options are not available for pipes at risk of affecting ≥ 10 000 population.

Assume pipe reinforcement required to be laid in parallel to pipe at risk. Size new pipe to maintain at least 3m pressure for full 24-hour period on failure of pipe at risk.

Phase 4. Cost Benefit Analysis

Outputs are passed back to the PR19 team to evaluate appropriate inclusion in the Bristol Water Business Plan. In reality the outputs were fed back to the PR19 team as soon as available from each model.

As a result of this process, the modelling team has requested some enhancements to the Critical Link Analysis in IWS Pro, including:

  • The ability to see a timeline of numbers of properties affected during the 24-hour isolation for each main. This will vary depending on system hydraulics and reservoirs emptying.
  • The next level of analysis to include automatic assessment of potential rezoning options

'Infoworks WS Pro has been invaluable in aiding our understanding of the location of the most critical pipes in our network and has also been used to evaluate mitigation options for these pipes.'

Kevin Henderson,
Network Asset Modelling Manager
Bristol Water

The Results

Bristol Water was able to make a direct comparison of the improvement in performance when using Critical Link Analysis in Infoworks WS Pro against the previous 32-bit Infoworks WS. For the previous price review, PR14, Bristol Water had attempted to use the Critical Link Analysis for a single snapshot in time on a ‘simplified whole company model – reservoirs and pumps replaced with fixed heads’. However, the process was slow and there was little confidence in the results. “We saw massive improvements in performance for PR19,” said Kevin. “The improvements to the Critical Link Analysis algorithms in IWS Pro made our analysis significantly quicker.”

The project identified key capital funding requirements on mains and control valves over the next two AMP periods 2020 – 2030, to upgrade the network and reduce criticality to acceptable levels.

The work was completed by the Network Modelling team within the required timeframe and was fed back to the PR19 team for consideration in the business plan. The technology meant that Bristol Water could put together a robust business case for its resilience plans with greater confidence than previous AMP periods.

Key Benefits

Advanced analysis capability

In-built Critical Link Analysis within InfoWorks WS Pro automatically tests and reports the eff ects of failure of a selection of links within a network. By testing network nodes against defined Level of Service Criteria, WS Pro users can identify which pipes are the most important to monitor and maintain, improving the resilience of the water supply network.

Engineered for increased performance

InfoWorks WS Pro multi-processor simulation capability exponentially increases the throughput of results for network-wide impact analysis. This industry-leading innovation is particularly useful for performing composite runs, where multiple simulations run in parallel to analyse diff erent scenarios on the same network.

Strengthen capital investment plans

The modelling capabilities of InfoWorks WS Pro show the impact of investment in the networks, allowing water companies to plan investment programs with greater confidence.

'We saw massive improvements in performance for PR19. The improvements to the Critical Link Analysis algorithms in IWS Pro made our analysis significantly quicker'

Kevin Henderson,
Network Asset Modelling Manager
Bristol Water

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