Water Resource Modelling

The core objective of the WRSE is to identify how best to share available water resources at a regional level.  We look further afield, working with neighbouring regions and water companies to explore inter-regional water transfers.

The water supply network within south east England is a complex pattern of different water company areas and water resource zones. This is a result of the historic development and integration of local systems over more than a century, plus the fact that division of the region after privatisation did not necessarily align with catchment or water resource system boundaries. Therefore, the fundamental approach of the WRSE is to ignore water company boundaries, and look across the region, to assess best ways to share available water.

Many of the water resource zones across the South East currently, or in the future, will experience shortfalls in water availability. However, there are also areas that have water that can be shared. By looking at a regional scale we can try to maximise the benefits of sharing of water resources across the area, and in doing so, reduce the need for new water schemes or developments, and reduce existing abstraction.

Our modelling work help us to understand which options might be best for the south-east in the long-term (such as strategic schemes that are not necessarily justifiable on a single company basis but would be beneficial on a regional scale) which will help the region become more resilient to drought, outage and the environment.

With this in mind, the core work of the WRSE is to perform regional water resource modelling, which is summarised below.

Addressing the future need for water

For the PR19 planning cycle, the WRSE is looking over a very long horizon of sixty years (from 2060 to 2080) exploring different factors such as:

  • a greater range, and severity, of future droughts
  • different population growth forecasts
  • greater protection of the environment through reduced abstraction
  • effects of poor water quality
  • resilience to extreme events
  • reducing water demand and leakage rates still further

This is done via several plausible “what if?” scenarios to examine potential future water demand using an optimisation model. An optimisation model seeks to minimize the total economic costs of meeting future water demands for these future scenarios, by selecting a portfolio of options, from a choice available to it that cover both supply and demand management schemes. Using such a model allows the development of strategies to address future water needs; it has been a standard approach of the water industry for many years.


Over previous cycles of work, the WRSE has developed and used its own bespoke EBSD optimisation model as a key tool to help find the least cost solutions for customers and the environment in the South East of England. The model’s results have formed the basis of the WRSE regional strategy over successive years, which water companies then use to inform and guide their own long-term water resource plans.

For PR19 the WRSE has used the same model as the core approach to examine water resources but with amendments to be more strategic, look further into the future (2020 to 2080). This is because looking further into the future helps us to make better decisions in the long run in terms of what types of options may be needed.  Another critical amendment is that the model is being used in conjunction with “Info Gap” advanced decision-making approach, to reflect latest developments in the water industry that calls for the need to ‘stress test’ model outputs to determine how the selected portfolios of options are resilient for a range of possible futures, not just the one modelled.

 What we’ve done

There have been numerous phases of the EBSD optimisation modelling work for PR19, allowing us to continuously inform our knowledge and better our understanding. This work was undertaken by Jacobs on behalf of the Group. Below is a summary.

Modelling to explore all options

This phase incorporated over 1000 potential options into the EBSD optimisation model from all member water companies, covering demand management, resource developments and transfer scheme to allow the model to select from very wide range of choices. The purpose of this phase of modelling was to take a broad, extensive examination of all the options that have been outlined or defined but not yet implemented, taking a ‘blank sheet’ approach, to see what might be useful to meeting future water demand.

Twelve different possible future scenarios were scrutinised, based on different combinations of the key influencing factors affects the demand and supply of water, including population, the type of droughts that we might experience in the future, and whether abstraction will be reduced to protect the environment and water quality. Each scenario would require a different amount of water in the future, and the EBSD optimisation model created a portfolio of options that together would meet the demand.

The results showed that some options were always chosen for every scenario modelled; others were sometimes chosen; and a number were never chosen. Examining why some options are always chosen helps us to understand what schemes might be ‘no regret’ developments for the future.

The choice of options selected by the model shows where and what schemes might the best choices, at a regional level, to develop and provide water to other areas of the region. The importance of these schemes might not otherwise be realised from single water company plan looking at a specific area. The results also highlighted which water resource zones were more vulnerable than others, indicating that it would be beneficial to increase the connectivity of the water supply network to allow transfers to take place could help move water around the region.

The stress testing of certain portfolios of options, showed that some fared better than others when assessed for their resilience in meeting conditions that are more demanding or difficult than their original scenario design. This helps us to understand what might be the best value choice of groups of options to implement, given the uncertainties of some key factors driving water demand, such as climate change and population.

Modelling to explore feasible options only

After the completion of the above phase, further modelling was undertaken to use recently updated datasets that had been updated, such as population forecasts and potential abstraction reductions, also termed Sustainability Reductions or Changes. For this modelling exercise, the options in the model were restricted to only those which have been screened as feasible by each water company, and which were being considered for inclusion in the dWRMPs. Further new options or schemes that had been just developed by the water companies were also incorporated.

The purpose of this phase of modelling was to use only those options which had been subject to examination to ensure their feasibility, from an environmental or water volume perspective, and assess which would be selected by the optimisation model in its search for a regional solution to future water demand by 2080.

For this phase, the WRSE first explored the possible water demand to 2080 from over 140 scenarios to explore the full range of possible futures and resulting water deficits. This ‘capacity analysis’ has given insights into the vulnerabilities across the region on a water resource zone-by-zone basis, and identified which zones require transfers to solve their deficits and which zones have surplus that can be shared.

Optimisation modelling was performed on 10 scenarios to see what groups of options were the best choice to satisfy the deficit, and to test their resilience. The scenarios are based on a medium population forecast and incorporate known sustainability changes, but differ according to the severity of the droughts that are expected over the 60-year planning horizon (severe or extreme), whether water companies can take more water from the environment during drought episodes, and whether unconfirmed sustainability changes have been included. One scenario explored a situation that met demanding regional targets for the reduction of leakage by 15% by 2025 and a reduction in water consumption to 110 litres per person per day by 2050. The other scenarios examined future situations using existing plans for reducing leakage and per capita consumption.

The outputs of this modelling phase have been used to set a strategy for the WRSE area, based around the central planning scenario where there is medium population growth in the south east, drought become sever in nature, and where water companies are not permitted to abstract more water from the environment during drought episodes.

Modelling to explore the effect of customer consultation, and regional targets for water consumption and leakage

Further regional modelling has been undertaken, exploring more scenarios to assess the feedback from customers. In addition, the scenarios being explored include a range of regional targets to assess the effect of meeting the recommendations from the NIC and Defra on leakage and per captain consumption in terms of option selection.

This work is currently ongoing. Preliminary outputs have been produced and these are being subject to close examination, as per all previous phases, to ensure robust confidence can be placed in the results. When the review period is completed, the findings of the revised modelling work can be used to update the WRSE’s strategy.

Developing an innovative cutting-edge simulation model for the future

To take advantage of advances in computer power and incorporate cutting edge innovation into our work, the WRSE also commissioned Atkins and the University of Manchester to develop a regional simulation model, built from first principles.

A regional simulation model allows robust testing of the performance of different portfolios of options or solutions, to satisfy the need for water for different possible future scenarios. It offers more flexibility than other modelling approaches, to explore what might be optimal approaches to different existing and future challenges.

As there was no existing simulator, the WRSE adopted a developmental approach: continue to use the existing optimisation method for its core modelling work for PR19 as explained above, but at the same time, commission Atkins and the University of Manchester to develop of a regional simulation model and its testing during PR19, so that the model is ready to inform PR24.

The WRSE regional simulation model involves a representation of the water resource network in south east England, covering all six member companies. This has been coupled with the advanced decision-making approach “Robust Decision Making” (RDM) to stress test the model outcomes for their resilience.

The WRSE will continue to explore this simulation model, in tackling the issues and challenges facing the region.