Author(s): Deonie Allen; Scott Arthur; Heather Haynes; Robert Ellam; Valerie Olive; Kevin Black; Jenny Mant
Linked Author(s):
Keywords: Swale efficiency; Sediment transport; Sediment tracing; Rare earth oxide; Paramagnetic fluorescent particles
Abstract: Vegetated sustainable urban drainage systems (SuD S) are becoming more prominent within the urban form as an aesthetic and functional mitigation strategy for flood risk and stormwater management. Within the UK at present, SuD S are predominantly constructed to meet specific design event discharges for flood risk management purposes. The multiple benefits of vegetated SuD S and their role in the Blue-Green city network are acknowledged by environmental regulators across the world (particularly North America, Northern Europe, Japan and Australia). However, a full understanding of long term, multiple event, potential impact of SuD S on water quality and flood benefits has yet to been reached in the UK. A key indicator of long-term SuD S performance is source to sink mapping of sediment. Sediment monitoring methodologies include particle size distribution and mass change over time, dye tracing, chemical and mineral sediment fingerprinting/tagging, magnetic and synthetic particle monitoring. The chemical fingerprints and particle size distribution of urban sediment and diffuse pollution sources have limited diversity compared to more contrasting land uses (e. g. rural, forest, agricultural and general urban areas). The use of these methods within the urban environment is difficult and potentially lacks clarity. Therefore, the presented field study has focused on tagging methods with multiple traceable unique identifiers, allowing sediment movement from the urban sources to be monitored individually. Despite the breadth of research, only limited field data or published analyses exist to quantify sediment transport through an urban ephemeral vegetated stormwater system. Thus, the presented research tests whether sediment tagging methodology used in agricultural scour and large river sediment transport analysis is transferable to blue-green SuD S network analysis. Urban sediment transport monitoring requires that sufficient unique identifiers be available, to monitor the range of urban surfaces and that particulates have and extended field and time resilience. The two materials trialed, meeting these requirements, are paramagnetic fluorescent (PMF) particles and rare earth oxide (REO) tagged sediment. Field data is presented that compares the performance of PMF particles and REO tagged sediment released in an urban area, transport into and through a vegetated swale over multiple runoff events. The transport properties of sediment within the swale are examined to provide recommendations towards methodological practice for use of tags in long-term SuD S monitoring. This study identifies significant complexities in monitoring urban sediment movement which influence effective data collection, future modeling, calibration and validation. These include: the impervious urban surface/vegetation interface; the ephemeral nature specific to urban SuD S designs and function; and the complications in sediment collection without influencing the SuD S function and/or downstream results.
Year: 2014