An assessment framework for SUDS-based storm water management in urban areas

Abstract

Globally, there is an ongoing trend to improve the live-ability of cities. Furthermore, the importance of sufficient urban response systems for storm water is growing due to climate change and urbanization. Sustainable Urban Drainage Solutions (SUDSs) are seen as a key tool to tackle multiple urban challenges. This is as their design is multi-objective, focusing on water quantity, water quality, amenity, and biodiversity. However, currently knowledge is lacking amongst decision makers on how SUDS affect the urban environment. Therefore, this research aims to develop an assessment framework for SUDS-based storm water management in the urban landscape to help Dutch municipalities improve their decision making to improve the live-ability of the urban environment.

To evaluate the performance of SUDS, assessment frameworks include Key Performance Indicators (KPIs). KPIs are measurable indicators demonstrating how effective SUDS are in achieving their objectives. This research highlights that there is no universal or even country based standard assessment framework for SUDS. Furthermore, there are few examples of the translation of the scientific assessment methods of SUDS to engineering practice available. The assessment of the full effect of SUDS therefore remains unclear to practitioners.

This research proposes a new framework (”extended framework”) to assess the performance of SUDS, building on the existing framework (”conventional framework”) which assesses cost and water quantity currently used in engineering practice. The extended framework adds KPIs assessing the remaining three objectives of SUDS design. Firstly, water quality is assessed with the KPIs Site Pollution Index (SPI) and Pollutant Removal Capacity (PRC). Amenity with the KPIs Thermal Comfort Score (TCS) and impervious area. Thirdly, biodiversity is assessed with the KPI Biotope Area Factor (BAF). Furthermore, it improves the assessment of water quantity by replacing the currently used KPI with Expected Annual Damages (EAD). With the choice of KPIs in the extended framework, it is ensured that their assessment methodologies are suitable to engineering practice. Furthermore, by including KPIs that assess the multi-objectiveness of SUDS, the co-benefits are included in the extended framework.

With the application of both frameworks on the municipality of Alkmaar, this research substantiates the positive influence of SUDS on urban areas. The case study shows improving performance for water quantity, water quality, amenity and biodiversity if the number of SUDS increases.

To assess the effect of the extended framework on the decision making process, the MCDA type Compromise Programming (CP) is applied to the results of both frameworks. With the identification of the best choice of design based on the performance results of either the conventional or extended framework, the outcome of the CP method showed that using the extended framework as opposed to the conventional framework sometimes led to different design choices.

It is demonstrated that the extended framework indeed improves the decision making process to improve the live-ability of the urban environment. Even though the extended framework is more time consuming and may result in more costly designs, using this framework to base decision making on is likely to result in better quality of life for humans with a reduced negative impact on the associated natural environment. This framework better equips decision-makers to face
emerging urban challenges. However, both frameworks are of use in engineering practice. The ultimate choice of using either one of the frameworks is dependent on the goal of the project, the client, and the amount of time and money available.