A Critical Review of the Effects of Motorway River-Crossing Construction on the Aquatic Environment

The construction of river crossings to facilitate road schemes can potentially impact upon adjacent aquatic ecosystems. Such construction activity can pose a risk both to the physico-chemical and ecological quality of the aquatic environment. The EU Water Framework Directive requires member states to ensure that there is no further ‘degradation in water quality’ and to maintain ‘good ecological and chemical status’ of surface waters by 2015. In this context, it is important to understand the potential impacts of river-crossing construction and the methods for mitigating such impacts. This paper presents a critical review of current knowledge on such impacts, which is presented under three headings: water quality, river hydraulics and aquatic ecology. The review has identified knowledge gaps in all three areas, with the issue of the impact of suspended solids on aquatic ecosystems being a priority. The review concludes that some water quality standards may not provide sufficient regulatory control of discharges to the aquatic environment from river-crossing construction activities.