Ranking strategies for stormwater management under uncertainty: Sensitivity analysis

Abstract

The disadvantageous consequences of stormwater perturbations of receiving water quality in urban environments can be attenuated by exercising control at various locations across the sewer network, wastewater treatment plant, and the stream itself. As part of a long-standing programme of research on developing an integrated approach to the management and real-time control of water quality in river basins, the paper examines the sensitivity of the associated strategies to model uncertainty. Specifically, results are presented for a case study based on a 10 km stretch of the River Cam as it passes through the city of Cambridge in eastern England. The options for control are restricted to design and operational features of the wastewater treatment facility. Assessment is according to maximum and cumulative values of mass flows of ammonium-N and biochemical oxygen demand, together with the duration of dissolved oxygen concentration below 4.0 gm-3, at the downstream boundary of the system. A straightforward analysis of the sensitivity of these criteria to changes in the parameterization of a model for receiving water quality shows that the ranking of strategies is robust in the face of model uncertainty. Minor differences in ranking occur as a function of whether judgement is based on ammonium-N or the other two attributes of water quality and whether attention is focused on the treatment plant in isolation or performance across the system as a whole. However, such conclusions must be qualified by noting that our analysis has been limited in its scope and elementary in its treatment of uncertainty.; The disadvantageous consequences of stormwater perturbations of receiving water quality in urban environments can be attenuated by exercising control at various locations across the sewer network, wastewater treatment plant, and the stream itself. As part of a long-standing programme of research on developing an integrated approach to the management and real-time control of water quality in river basins, the paper examines the sensitivity of the associated strategies to model uncertainty. Specifically, results are presented for a case study based on a 10km stretch of the River Cam as it passes through the city of Cambridge in eastern England. The options for control are restricted to design and operational features of the wastewater treatment facility. Assessment is according to maximum and cumulative values of mass flows of ammonium-N and biochemical oxygen demand, together with the duration of dissolved oxygen concentration below 4.0 gm-3, at the downstream boundary of the system. A straightforward analysis of the sensitivity of these criteria to changes in the parameterisation of a model for receiving water quality shows that the ranking of strategies is robust in the face of model uncertainty. Minor differences in ranking occur as a function of whether judgement is based on ammonium-N or the other two attributes of water quality and whether attention is focused on the treatment plant in isolation or performance across the system as a whole. However, such conclusions must be qualified by noting that our analysis has been limited in its scope and elementary in its treatment of uncertainty.