A cost-effectiveness analysis of stormwater management systems: Isipingo prospection.

Abstract

Flood mitigation measures have become a contentious challenge due to the lack of infrastructure to prevent them after the 10 October 2017 flash floods, which impacted the Isipingo and Umlazi area the hardest within the eThekwini Municipality. The storm which caused the damage were measured as a 1 in 100 year recurrence interval storm or greater, however eThekwini Municipality only caters for 1 in 3 year storms and 1 in 10 year storms at critical points. A capital injection would thus be required to cater for a 1 in 100 year recurrence interval storm amidst a precarious economic climate. The purpose of this study is to determine a cost effectiveness analysis of conventional stormwater management systems, Sustainable Urban Drainage Systems (SUDS) and an attenuation facilities based stormwater management system as alternative configurations for the Isipingo Prospection area. A cost effectiveness analysis will be deduced by means of a multi-criteria decision matrix which enables a holistic incorporation of environmental and social effectiveness of the stormwater management systems proposed instead of costs in isolation. In addition, this approach allows for sustainability and an objective inclusion of preservation of biodiversity, social wellness and comparison of alternatives without compromising the functionality of the stormwater management system. The results show that Sustainable Urban Drainage Systems is the most cost-effective due to the utility of green infrastructure as opposed to a high reliance on grey infrastructure, with a final weighted score of 4.12 and Bill of Quantities (BOQ) estimate of R2 119 047.50, which is highly influenced by the excellent performance in the costeffectiveness criteria. In addition, green infrastructure is able to incorporate environmental and social effectiveness and lower the costs required for mitigating a 1 in 100 year recurrence interval storm in the catchment studied. Conventional stormwater management systems received a final score of 2.22, which reflects the low cost and environmental effectiveness performance of 2.2 and 2 respectively. The BOQ estimate amounted to R5 188 921.33. Attenuation facilities based configuration was the least cost effective with a final score of 1.8, due mainly to the cost required for the underground concrete attenuation facility at a BOQ estimate value of R16 007 209.38. The utility of a multi-criteria decision matrix as a means of conducting a cost effectiveness analysis comes highly recommended by this study as an objective decision making tool for project managers. The alignment of existing strategies and policies requires the filtration to project managers to include green infrastructure to enable integration and sustainability.