Sediment Transport & Reactivity in a High Capacity Flume

Industrialized, macrotidal estuaries across the globe have high retention capacities for cohesive and non-cohesive sediments that may contain a legacy of contaminant metals discharged over many decades. Although many estuaries currently receive lower discharges of metals, a potential long-term threat exists from the remobilisation and transport of contaminated bed sediments into fertile coastal waters. Managers of large estuaries, such as the Mersey, have few decision-making tools to assist in evaluating options for dredging and disposal or predicting the likely impact of modifications of estuarine hydrodynamics arising from the effect of sea level rise or changes in fluvial inputs.

Bed sediment is the critical reservoir since it receives and/or supplies particulate contaminants via deposition or erosion, thereby determining the overall residence time for contaminated sediments in estuaries. However, there are many gaps in our understanding of the key processes required for the precise modelling of estuarine flows and sediment transport. Predicting the behaviour of contaminated sediments in estuaries, including their long-term transport, could be achieved using coupled hydrodynamic-geochemical models. However, metal partitioning algorithms for these estuarine models have originated from small scale laboratory experiments, using reactors whose volumes are typically <1 L.

On the other hand, experiments designed to improve the prediction of the dynamics of cohesive and non-cohesive sediments, including those contaminated with radionuclides, have been often conducted in large flumes where water volumes can be up to several tens of m3. Thus, in order to achieve simultaneous monitoring of chemical and sediment dynamics, the chemical component requires extrapolation to a more environmentally-relevant scale, such as a flume, thereby upscaling laboratory experiments by about four to five orders of magnitude.

To address these gaps in knowledge, two separate research grants, linked by a unified project proposal, were awarded to Millward and Turner at the University of Plymouth (EP/C512324) and to Lin and Falconer (EP/C512316) at Cardiff University. Previously, Falconer and Lin were awarded an NERC research grant (GR/C513269/1) to develop and implement a state-of-the-art high capacity flume. The key objective was to improve the predictive capabilities of coupled hydrodynamic-geochemical models by conducting flume experiments that may better quantify the transport and reactivity of contaminated estuarine sediments.