Trapping of sediment in tidal estuaries

Abstract

An estuary is an ideal habitat for various aquatic species. At the same time, estuaries and adjacent rivers are used as fast navigation routes between the coastal and inland territories. The fast industrial development and the subsequent growth of cities and trade have led to large-scale anthropogenic alterations of estuarine systems. Estuaries are streamlined and deepened to ensure a safe navigation for larger ships. Dams are constructed to protect the farmland, households and industrial buildings from floods. Moreover, land reclamation, deforestation and various agricultural activities result in higher sediment and freshwater input into estuaries. All these activities lead to fundamental alterations of the hydro- and sediment dynamics, mixing and circulation processes within estuarine systems. An estuarine system, taken out of its natural balance, is always trying to restore this equilibrium or reach a new balance. This can result in, for example, an increased siltation such that the estuarine depth has to be constantly maintained via annual dredging activities. Engineering interventions are expensive and they create a substantial load on the local ecosystem, because a biological system cannot readjust to new conditions within a short period of time. Hence, these activities pose many problems from both the ecological and economic point of view. A proper understanding of estuarine processes is essential to minimize the negative consequences of human influence and to develop a long-term restoration and development plan for many problematic estuaries. The main objective of the thesis is to investigate physical mechanisms in the along-estuary direction that result in the trapping of suspended sediment in partially and well mixed tidal estuaries and to analyze the influence of individual mechanisms on the trapping location.