Rob Mustard discusses the decision-making balance between service, risk, cost and some of the interventions Scottish Water is making
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Author: Rob Mustard, general manager, Waste Water Strategic Services, Scottish Water

Scottish Water has a large and diverse asset base with a total Modern Equivalent Asset Replacement Value (MEAV) which runs into billions of pounds. Two-thirds of the MEAV is linked to the replacement of Scottish Water’s 50,000km long sewer network with some dating back to the early 19th century and the majority dated to about the 1940s. The effective and efficient optimisation of capital maintenance and operational investment across such a vast network of ageing assets is a significant challenge.

It is not feasible or practical to replace every asset that exceeds its notional lifetime as the cost to the customer would be too great. There is the constant pressure between delivery of legislative compliance and customer service against a backdrop of stable customer prices and other downward pressures on capital investment.

Water Framework Directive


Furthermore, these important business drivers change over time, with a broadening range of legislative issues under the Water Framework Directive to manage, and rising customer expectations to be considered, in any future investment portfolios. For many buried infrastructure there is always a challenge around ‘out of sight equals out of mind’. So how do you get the intelligence to make informed decisions on sewer network maintenance?

When service issues arise on the sewer network they tend to be visible and cause high levels of customer disruption and angst; whether an issue leads to sewer flooding within a customer’s property or pollution of a water course. Historically, Scottish Water has had a largely reactive response to these types of sewer network issues. Responding quickly and effectively to restore service to normal after an event has occurred and carry out necessary clean-up of customers’ properties or the surrounding environmental landscape.

However, over the past few years we have focused our combined efforts to reduce the number of service failures. Good root cause analysis has helped determine the appropriate activity. This has led to significant improvements with a two-thirds reduction in pollution events over the last regulatory period through a focus on understanding the true cause of failure.

Reducing impact from internal and external sewer flooding


In preparing for the current regulatory period (2015-2021), through dialogue and engagement with our customers, one of the high priority areas for them was to put a focus on reducing the impact from internal and external sewer flooding. This has led to a review of how we approach network maintenance, which is now being focused on risk management and proactive intervention. This should see less service interruptions and fewer pollution events.

Scottish Water has asked itself three questions in this area of activity:

  1. What can we do in the network?
  2. What gives us the most benefit?
  3. What manages risk?

In any sewer catchment there are a limited number of areas that you can work on to address service outcomes:

  1. Renewal- this is a long-term programme and has limited short-term impact on service;
  2. Maintenance – this gives a number of opportunities to impact service – it’s about understanding what to do and where and for how much;
  3. Flooding investment and surface water removal are closely linked – one is often the root cause of the other;
  4. Customer education impacts a lot of service issues on the network – but the issue is to how to change behaviour long term;
  5. Capacity – linked to growth.

The key is getting the balance right between these areas of activity to manage the balance between total investment outlay, the return on that investment in terms of service benefit and the residual level of risk that remains. An example is, should you invest more in a customer education programme or in a sewer cleaning programme? One requires less investment but has a less certain outcome. So how do you choose? Historically, there was a simple relationship: you made an intervention, you could see the outcome. But with so many things happening in a catchment, how can you be sure which one of your interventions resulted in the service improvement?

Identify clusters of network where sewer blockage and service contacts are more common


We know that after cleaning a sewer you get a reduction in service contacts, but where to clean to maximise the benefit? Scottish Water has adopted an evidence-led approach to assist selection of interventions in this case. Analytical approaches have been used to identify clusters of the network where sewer blockage and service contacts are more common and tend to repeat. Analytics can help break down the network by identifying statistical significant relationships between network and geographic features and the likelihood of service contacts.

Through this approach an area can then be targeted for cleaning with a high likelihood of giving a positive service outcome. This is much more focused and cost effective than relying on gut feel. What was surprising was how little of the sewer network was identified for cleaning as a result – only one per cent in our analysis to date. This presents a big opportunity for Scottish Water to more wisely and surgically deploy its sewer cleaning activities and, at the same time, up its stakes in some other potentially cost-beneficial activities.

One of these activities is real time management of the sewer network. Scottish Water is investing in 24/7 staffing of its state-of-the-art Intelligent Control Centre with waste water risk technicians. Their role is to interpret what field data is coming into the control centre and to instigate actions as needed to maintain service. One activity that is already improving service is in flood response.

Through real time field sensors, Scottish Water is able to detect when sewer levels are rising in key parts of the network and to send support if necessary to maintain service. As a result of this, internal sewer flooding in one area of Glasgow that has suffered sewer flooding in the past through high rainfall events, has been averted through a proactive response.

Condition of high consequence sewer assets


Scottish Water has also identified the importance on improving evidence of our asset condition. Sewer assets have a long service life but cannot be ignored as the consequences of failure can be high. As a result we are looking to understand the condition of more of our high consequence sewer assets. This will allow better financial scenario planning for the future. Again advanced analytical approaches are being used.

Data on thousands of historic sewer collapses and structural defects are being linked to sewer attributes such as age, material type to build predictive models of sewer deterioration. As well as growing our understanding of our asset condition through analysis we are building up an extensive library of frontline CCTV investigations of critical areas of our sewer network. We are also looking to understand the available hydraulic capacity in extreme conditions.

By linking this to the wider Flood Risk Management Act (FRMAct) duties, we and other public bodies can work together to manage flood risk. A key output of this approach in the current regulatory period will be to understand the flood risk to all properties in Scotland from sewer flooding. With this intelligence, Scottish Water will be able to engage customers on agreeing future investment priorities as well as engage public bodies on progressing FRMAct activities such as surface water plans. By understanding the level of resilience of the network under different flow conditions, Scottish Water will be able to plan the future of the network under different climate change scenarios.

This intelligence on resilience and asset condition give an understanding of service risk on the network. This is part of their journey of focusing less on dealing with known problems and issues to having a better understanding of risks. This allows Scottish Water to operate in a more planned way, have richer discussions with customers and stakeholders on the future direction of the service and ensuring how customer charges are invested wisely to maintain and improve service.

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Author: Rob Mustard, general manager, Waste Water Strategic Services, Scottish Water Scottish Water has a large and diverse asset base with a total Modern Equivalent Asset Replacement Value (MEAV) which runs into billions of pounds. Two-thirds of the MEAV is linked to the replacement of Scottish Water’s 50,000km long sewer...