A framework for implementing surface water treatment trains for large developments

Abstract

Urban growth and the associated urbanisation has led to increased pressure on the natural environment. Associated with climate change, the development of large urban and industrial areas has been found to be responsible for water quality degradation and recent flooding of watercourses. In parallel, increased pressure on land and costs associated with developments tend to place pressure on the space allocated to amenity in cities. This is despite the fact that amenity has been found to act positively on residents in terms of their wellbeing by raising living standards. Within this context, urban drainage has a key role to play by providing water quality, water quantity and amenity benefits according to the SuDS triangle philosophy. However, it is felt that urban drainage could potentially offer more than its current benefits by implementing SuDS in series; a treatment train. Indeed, despite environmental regulator guidance (CIRIA, 2007) a significant proportion of sites in Scotland are developed with a single “end-of-pipe” pond. Within this context, the research undertaken aimed to develop a framework which may be used by an environmental regulator to implement treatment trains and maximise potential water quality, water quantity and amenity benefits while preventing excessive constraints for other stakeholders involved in SuDS implementation. In this regard, the fears and expectations of stakeholders are investigated using structured interviews and questionnaires. This step allowed underlining drivers and barriers to SuDS implementation to be identified and a set of quantitative benchmarks to be developed including cost of construction and maintenance, land take, pollutant removal, attenuation volume and the willingness to pay for amenity benefits. To determine how the benchmarks interrelated, two case studies were investigated in Scotland: The Dalmarnock Road Area in Glasgow and the Houston Industrial Estate in Livingston. Based on water quality modelling using MUSIC and hydraulic modelling using Infoworks CS, it has been shown that the benefits, in terms of water treatment and attenuation, should be seen in the context of increased land take and/or costs for the area considered for virtually all the SUDS techniques. iii Based on the conclusions of the investigations, a general framework was formulated to optimise SuDS treatment trains for large developments. The framework, based on iterative water quality and hydraulic modelling aims to identify the relationship between drivers and barriers to SuDS implementation. The final decision regarding the extent to which the treatment train can be implemented can then be taken knowing its implications for all the stakeholders.