Determining the Level of Flood Resilience Required for UK Water Assets, using Risk Analysis

As the UK continues to suffer from unseasonal weather patterns, serious flooding is a very real possibility. This can have a severe impact on water assets and services.

Halcrow, a CH2M HILL company, has developed a programme to mitigate the consequences of severe flooding in the UK. It determines the risk faced by critical assets such as water treatment works and pumping stations and weighs it up against the cost of appropriate preventative measures. @RISK is used to quantify the uncertainties in this process.

Halcrow first identifies the likelihood that a site will be subject to fluvial flooding and quantifies the vulnerability and consequence of failure for each asset. Recommendations to improve flood resilience may include adaptive solutions, such as designing structures to reduce the consequences of flooding by facilitating recovery from it. Alternatively, resistance, which aims to prevent flooding in the first place, might be more appropriate for some sites.

For example, rectifying the consequences of a flooded water treatment plant can be very expensive. The physical damage to pumps and equipment needs to be repaired, and there are additional costs that may be incurred, such as bottled water supply while the plant is out of action, and customer compensation for lack of service. Working out the costs of these consequences will help to determine the right solution for the individual site. However, it is difficult to quantify the exact costs so @RISK is used to quantify the variations in the figures.

@RISK is also used to measure levels of uncertainty for other key aspects that have bearing on the eventual outcome. For example, there are uncertainties around the direct damage costs and the expense of responding to customer contacts associated with the incident. At the same time it is important to understand the level of uncertainty in the costs of intervention, such as building a floodwall.

Halcrow set out to understand what it was realistic to mitigate against and therefore what could be achieved in terms of the costs and benefits of improving the current levels of resilience. The nature of the task means that each stage of the calculation is subject to uncertainty, but @RISK enables it to measure each eventuality and make an informed decision on the best course of action.

» Case study: "Halcrow uses @RISK to determine level of flood resilience required for UK water assets"

» Related: How can the UK public services prepare for unpredictable, extreme weather?
 

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