Pollutant Tracking and Blue-Green City Design for Urban
Stormwater Management
Deonie Allen
The Challenge
The Water Framework Directive required ‘good’ water quality status for all EU rivers. The
2015 deadline required catchment management plans to be designed and implemented for a
large number of waterways across the UK. There is potential, through informed integrated
design and decision making, to achieve multiple flood risk benefits through the use of
sustainable urban drainage (SUDS) and Blue-Green infrastructure, and both SEPA and the EA
are supporting greater implementation of SuDS and Blue-Green design as approaches
towards meeting WFD benchmarks. However it is important to understand the benefits and
limitations of these systems, to know what we can expect them to achieve, and what
maintenance costs and requirements will be incurred and to advance design to achieve both
water quantity and quality benefits.
While the flood attenuation capabilities of SuDs are relatively well understood, little is known
about the sediment and pollutant transport dynamics in emerging vegetated and naturalized
urban drainage design. To achieve effective water sensitive city design, the impacts and
implications of incorporating Blue-Green stormwater management principles into urban
design, beyond merely attenuating peak flood volume, need to be considered. This research
explores the functions and dynamics of sustainable urban drainage and urban watercourses,
with a specific focus on sediment transport within the new Blue-Green urban form. In
particular, conveyance, deposition and re-suspension of sediments, as well as choke and
pinch point blockage are key flood risk and water quality considerations of surface vegetated
stormwater management systems. The research conducted here will investigate the extent
to which SUDS, as part of a well-designed Blue-Green network, have the potential to
influence not just flood mitigation in a catchment, but a range of other factors including
water quality, public amenity and safety within the local urban environment.
Our Approach
This research has a strong focus on field data acquisition and the analysis of trends, patterns,
relationships and process dynamics discovered within this data. Using an established Scottish
SuDS network site, the movement of sediment from its source - car parks, road surfaces, roof
areas, to deposition locations are being examined. It has been well established that 85% of
urban pollutants, heavy metals and nutrients, are conveyed by adsorption to urban sediment
particles. Through tracking the movement of sediment through the urban stormwater
drainage network, the movement of a significant proportion of urban pollutants are defined.
An innovative application of a natural tracing methodology is implemented in the urban
environment. Using Rare Earth Oxides (REO), source and time specific sediment transport is
traced through the stormwater drainage network. REO tracing provides multiple unique
identifiers, supporting replication of natural sediment movement through a specified system.
The aim of empirical analysis is to identify the influencing entrainment, deposition and
resuspension characteristics of urban sediment within the blue-green vegetated stormwater
network. Considering sediment movement over multiple events, key deposition locations and
rates will be investigated to further the design and management of SuDS in the Blue-Green
City design in the future.
The Benefits
This research will generate a fuller understanding of benefits and limitations of SuDS
operating within a Blue-Green network. This will support improved design, application and
implementation guidance, maintenance understanding and long term multiple benefit
analysis of SuDS as part of a Blue-Green City and advance sediment management practices
and water quality improvement potential in SuD systems.
The data produced from this work will contribute to the development of industry bestpractice such as CIRIA guidance on Blue-Green Cities multiple benefit and SuDS water quality.
Future Work
This work is under further development,
More Information
This work is produced by Deonie Allen, as part of a wider EPSRC-funded project, Blue-Green Cities. For
more information about Deonie’s http://www.sbe.hw.ac.uk/staff-directory/deonie-allen.htm
work, or about the Blue-Green Cities project
http://www.bluegreencities.ac.uk/bluegreencities/index.aspx
Delivering and Evaluating Multiple
Flood Risk Benefits in Blue-Green
Cities