Uncertainty and risk-based decision-making tools for water quality regulation compliance in the urban drainage sector

Ecological thresholds are often used in environmental protection regulations, particularly in the context of pollution control to prevent ecosystem damage. One example of threshold-based regulation is the Fundamental Intermittent Standards used in the UK to define if environmental harm has been caused by intermittent sewer overflow discharges. The thesis explores the impact of predictive uncertainty and risk appetite plays in understand weather and the extent of environmental harm has occurred. This thesis concludes that as both data and parameter uncertainty, as well as risk appetite, can alter the final dissolved oxygen and unionised ammonia Fundamental Intermittent Standards exceedance count and therefore can alter one's understanding of whether environmental harm has occurred. It also concluded that sensitivity to uncertainty and risk is location dependent. A new term was created called Parameter Threshold Ratio (PTR) to investigate the extent to which measured water quality concentration interacted with the regulatory threshold at different locations, which can be used to engage with stakeholders around the abstract concepts of uncertainty and risk. Interviews were conducted with practitioners in the UK to understand the role uncertainty and risk plays in the decision process when assessing for and building solutions to counteract environmental harm caused by storm overflows. It was concluded that industry is risk-averse, favouring to over-design solutions, and that it is currently operating opaque manner where this risk-aversion is not discussed with regulators or documented. The impact of uncertainty and risk appetite is believed to be important because not only does it have consequences for regulating sector, but also economic implications such as sensor selection, maintenance regimes and the size and choice of solutions. The largest economic impact of uncertainty and risk is around the decision whether environmental harm has occurred, and therefore whether a solution is required to be designed and implemented.