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Accumulation and dispersal of suspended solids in watercourses


The four national road administrations for the United Kingdom – the Highways Agency, the Scottish Executive, the National Assembly for Wales and the Department for Regional Development Northern Ireland – have the responsibility of ensuring that discharges of runoff from motorways and trunk roads meet the relevant legislative requirements and good environmental practice. In order to meet these responsibilities, the Highways Agency has over the years commissioned research into the nature of highway runoff, its environmental effects and treatment. The next Phase of the environmental research is concerned with assessing the ecological effects of the soluble and insoluble components of runoff on the ecology of receiving waters.

The Highways Agency wishes to provide authoritative advice on the circumstances in which runoff is likely to have a significant ecological effect, whether treatment measures are necessary and whether ecological indicators can be used to assess potential impacts. To be in a position to do this a procedure is required whereby the potential impact of the sparingly soluble pollutants in accumulated sediment from highway runoff can be assessed.

Highways Agency Project No. 00Y91925 Specification and Study Brief


Highway runoff contains a complex mixture of toxicants (e.g. metals, PAHs) that have the potential to adversely impact the biota of receiving waters (Ref previous studies at PPB). There is a need, therefore, to establish guidance on the circumstances in which highway runoff is likely to have a significant ecological effect. To meet this need, the Highways Agency and Environment Agency have sponsored three linked projects: the first investigates the delivery of pollutants from highways to discharge points; the second examines the effects of soluble pollutants in highway runoff on the ecology of receiving waters; the third, this project, is concerned with assessing the ecological impact of contaminated sediments in highway runoff.

Many contaminants in highway runoff are associated with particulate material, the dispersal, accumulation and re-distribution of which depend on the hydraulics of both the highway drainage system and the receiving watercourse. The impact that these contaminated sediments have on the biota of receiving waters depends on how contaminants are partitioned in the environment, how bioavailable they are, and to what extent they bioaccumulate in organisms.

In this project we characterise temporal variations of both highway runoff (flow quantity and quality) and receiving watercourses, to determine the particulate contaminant load in runoff and predict its distribution and behaviour in receiving watercourses. In addition, we use a combination of field studies, in situ bioassays and laboratory experiments to determine the ecological significance of runoff-contaminated sediment and to establish causality.

The fundamental research questions are:

  • Are stream organisms exposed to accumulated highway-derived particulate matter?
  • What are the apparent ecological impacts of contaminated particulate material on receiving waters?
  • What processes produce and control the observed impacts and how are they mediated?

Having addressed these questions, phase three of the programme aims to devise an assessment and prediction procedure for the impact assessment of the ecological effects of sediments arising from highway runoff on receiving watercourses.


Further information / web links:

Poster presentations

SETAC-Europe, Lille, April 2004

  • Characterising impacts on receiving waters of contaminated sediments derived from highway runoff: Field survey.
  • Using in situ bioassays to monitor the effects of highway runoff.

SETAC-Europe, The Hague, May 2005

Highways Agency/Environment Agency Funded


Professor Lorraine Maltby,

Department of Animal and Plant Sciences, University of Sheffield

Professor Ian Guymer

School of Engineering, University of Warwick

Appointed Researcher:

Dr Paul Gaskell,

Department of Animal and Plant Sciences, University of Sheffield


Contact: Professor Ian Guymer


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