Delivering and Evaluating Multiple Flood Risk Benefits in Blue-Green Cities



The Blue Green Cities consortium project brings together research leaders from 8 UK Universities to investigate the effectiveness of Blue-Green approaches to urban water management.  This is achieved by using sustainable approaches to water managegement that offer resilience to future changes in climate, landuse, and socio-economic activity in the city. The Heriot-Watt University team are tasked with unwrapping the complexities of long term woody debris and fine sediment pollution interaction in waterways, and the benefits and risks these pose in Blue-Green Cities. To achieve this, multiple field site monitoring programs have been undertaken, within Scotland, England and Portland (USA) to create datasets that support detailed long term pollutant and debris transport analysis.


The Heriot-Watt University team, led by Dr Scott Arthur and Dr Heather Haynes, are investigating the woody debris and fine sediment pollution movement and impact on Blue Green Infrastructure, specifically Sustainable Urban Drainage Systems (SuDS). The key research questions within this project are:

1. How effective, in terms of sediment and debris connectivity, is Blue-Green infrastructure, both singly and as elements in integrated Blue-Green systems?

2. What are the urban land uses and environmental conditions that determine whether a catchment is a significant source or sink of sediment and debris?

3. What sediment characteristics are associated with key pollutants of concern (EU Water Framework Directive, WFD), how far does this sediment travel through a Blue-Green system before it is deposited and stored?

4. During the life cycle of a Blue-Green element, what is the potential for sediment re-suspension and deposition, particularity with regards to loss of flood storage functionality and blockage risk?

5. What benefits, other than those associated with flood conveyance and storage can be generated through enhanced Blue-Green design?

6. What is the potential for implementation of Blue-Green enhanced design to assist in achieving ‘good ecological status’ or ‘good ecological potential’ in urban watercourses, as required under the EU WFD?


The Blue-Green debris and sediment research will create a complex and detailed new dataset that identifies Blue-Green City pollutant and debris movement and impact on flood risk, waterway health and water quality. Key findings from analysis of this field supplied and modelled data include:

  • Statistical definition of small woody debris transport characteristics within small urban waterways (associated with culvert blockage)
  • Visualisation of fine sediment transport and re-suspension within SuDS over multiple rainfall-runoff events
  • Heavy metal concentration and treatment linkage with fine sediment movement in Blue-Green infrastructure

Related Publications

Findings have been summarised in easily accessible Factsheets as well as published in relevant peer reviewed academic journals and were contributors to the new CIRIA SuDS Manual (C697). 

For more information on the Blue-Green cities project visit their project page or contact the project co-ordinator.