The Development of an Economic Costing Methodology for Stormwater Management Within a Spatial Decision Support System Used to Evaluate the Impacts of Urban Development

The key innovation reported in this paper is the development of a catchment scale method for assessing the stormwater management costs associated with urban development. This research extends current international practice which typically operates at the scale of individual stormwater management devices. The method has been developed for incorporation in a catchment-scale spatial decision-support system (SDSS) which being developed by the National Institute of Water and Atmospheric Research (NIWA) and the Cawthron Institute to aid in the evaluation of impacts of urban development on receiving water bodies. The SDSS aims to express indicators of impacts on receiving water body environment values, and will use this system to integrate the measurement of environmental, social, economic and cultural wellbeings. Two key factors which influence economic wellbeing are stormwater management costs and economic benefits to society that arise from stormwater management measures. The economic costing methodology has been developed using a life cycle cost assessment approach. Methods for estimating relevant costs associated with different urban development scenarios within the SDSS are described.