Sediment Dynamics and their Influence on the Design of Monitoring Programmes

Sediment Dynamics and their Influence on the Design of Monitoring Programmes 

5 How Should we Monitor Sediment Flux in Europe References 

The Water Framework Directive Ecological and Chemical Status Monitoring Edited by Philippe Quevauviller, Ulrich Borchers, Clive Thompson and Tristan Simonart 2008 John Wiley Sons, Ltd. ISBN 978-0-470-51836-6 

The initiation of sediment movement depends on a supply of energy from raindrop impact, overland or river flow, or a mass movement of soil. Similarly, deposition occurs when sufficient energy is not available to maintain sediment particles in motion. The energy thresholds for initiation and cessation of sediment movement are not the same, being influenced differently by a range of conditions such as flow depth, velocity and turbulence, and sediment characteristics such as cohesion, particle shape and particle density. 

There are many equations which allow calculation of sediment transport rate within a water body, or sediment flux (see for example Task Committee of Computational Modeling of Sediment Transport Processes, 2004 for a review). However, these equations tend to be for a uniform sediment distribution, which is far from the variable source supply of material seen in events when the majority of sediment is moving. It is also generally considered that a particular flow has a maximum capacity to transport sediment, although the concentration this relates to depends again on sediment characteristics. Hence tliere are examples in China where sediment concentrations can reach several tens of thousands of parts per million for very fine particles, whereas a flow may become saturated with sand-sized particles at far lower concentrations. Rivers are often considered to be either capacity- or supply-limited in terms of their sediment transporting dynamics. However, in practice for most rivers, most of the time, sediment transport is limited by a complex and dynamic pattern of sediment supply. 

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