Drainage and Wastewater Management Plans (DWMP)

The Challenge

The development of Drainage and Wastewater Management Plans (DWMPs) is driving a more unified and systemic approach to the integrated management of wastewater assets and services. As pressure on existing infrastructure increases due to population growth and urban creep, and climate change makes rainfall events more intense and variable, Water and Sewerage Companies (WaSCs) face the difficult task of deciding which investments provide the best value now and in the future. They do so whilst meeting immediate expectations associated with new legislation, customer expectations, sustainability and social added value.

The Solution

The BMA approach enables planners to take a systemic view of catchments and define the mathematically optimal trade-offs for a variety of traditional and innovative interventions and controls, considered against multiple objectives.By utilising the output of geographical information systems, hydrological models and risk assessments, and by applying financial and operational constraints, the BMA DWMP decision support tool can recommend what, where and when to invest in the network over a 25-year horizon.

Solutions can be applied at two different levels in the DWMP process.A catchment area assessment requires the integration of an operational model, to determine which parts of the network are at risk of coping with extreme weather events, with a long-term strategic view, to understand how demand and environmental conditions will change in the future. The combination of operational and strategic views gives the opportunity to planners to determine which investments have the capability to deal with immediate challenges, while providing value and resilience in the future and generating overall best valuefor customers.

The Outcome

Recommendations for a mix of capital solutions and system enhancements are based on a strategic understanding of other contextual factors such as environmental legislation, budget limitations associated with the impact of ever more stringent regulatory price reviews and by factoring in social and environmental benefits. This is in line with the Water UK guidelines for the DWMP, which indicate that the benefits delivered should go “above and beyond what is solely required for DWMP purposes”. These types of less tangible social and environmental factors can be modelled with the use of biases, weighted factors, constraints and monetised benefits of different interventions.

A higher level, company-wide solution looks at the all the interventions and options recommended by the catchment assessment solution and support managers with their prioritisation. At this level the trade-off to determine overall bestvalue is based on factors such as:

• Criticality of interventions: for interventions that are mandated by regulatory requirements, a hard constraint can be set to force the model to choose them.
• Multiple benefits: solutions that generate benefits against multiple objectives, such as social or environmental (not just economic), can be given a higher relative score to favor their selection.
• Willingness to pay: going through an iterative process, water companies can capture the feedback of all interested stakeholders to assign a higher score to more favorable interventions.
• Business objectives: outcome delivery incentives and penalties can be built-in to ensure interventions are in line with published performance commitments, benefitting shareholders and the wider reputation of the company.

The Benefits

This solution allows a water company to demonstrate a fully integrated bottom-up system-thinking approach, whichembeds in a single plan the local requirements of catchment areas with the high-level commitments the company makesto customers and regulators. In line with the DWMP guidelines, the system can be maintained and continuously updated during new business cycles, ensuring continuity and consistency of decision-making processes and integrity of data.The online interactive dashboards provided by BMA also allows clients to easily communicate results to different audiences, from customer engagement groups to company executives.

At a strategic level, the penalties and incentives associated with both standard and bespoke Performance Commitments that are associated with the overall performance of the catchment, can also be considered by the model. Such functionality provides further insight into the overall financial benefit and risk associated with the introduction of DWMPs and, where required, additional business case justification for an integrated approach to the deployment of interventions and controls.