Spatial evaluation of the multiple benefits of sustainable drainage systems

Traditional approaches to understanding the multiple benefits of sustainable drainage systems often rely on value transfer. This converts each benefit into a monetary value, which can then be compared with the cost of the project. The approach, while well-developed, is limited because it does not systematically incorporate the spatial nature of the benefits. This paper discusses the development of an alternative way of evaluating and comparing benefits, allowing spatial distribution and local context and circumstances to be taken into consideration. The suggested approach is to create a score for each benefit category, which is normalised against a defined initial condition state on a scale of 0 to 10. This approach allows a direct comparison of the relative magnitude of benefits for a given location and provides a clear understanding of how and to whom multiple benefits accrue. The approach allows a singular significant benefit to be compared against many minor benefits. It can also easily be modified to reflect local preferences by weighting each benefit category appropriately. The method is demonstrated by three case studies in Newcastle, UK.