Siltation

About: Siltation is a research topic. Over the lifetime, 1420 publications have been published within this topic receiving 20983 citations.

On harbour siltation in the fresh-salt water mixing region.

Abstract: In this paper a novel series of field measurements are presented, which are the first to elucidate the processes influencing siltation in Botlek Harbour. Botlek Harbour is situated at the limit of saline water intrusion in the Rotterdam Waterway. Normally, after the ebb tide fresher river waters are found in the Rotterdam Waterway at the location of Botlek Harbour. On the flooding tide, the tip of the salt wedge is advected along the Rotterdam Waterway towards the mouth of Botlek Harbour. Hence on flood, a lock-exchange mechanism operates between Botlek Harbour and the Rotterdam Waterway. On the flood tide, when there is a supply of suspended particulate matter (SPM) associated with the presence of the estuarine turbidity maximum (ETM) at the mouth of the harbour, the survey data show exchange of SPM into the harbour. This lock-exchange process is found to be the dominant cause for SPM transport into the harbour. This is further substantiated by an analysis of the mass transport mechanisms. In this analysis, the vertical profiles of the instantaneous velocity, salinity and SPM concentration fields, recorded during the surveys, were decomposed into advective and dispersive transport components. The results of this analysis indicate that the correlation between the lock-exchange mechanism on the flood tide with the availability of SPM for exchange and efficient trapping, dominate the total exchange of SPM (97%). Hence, the increase in measured near-bed SPM concentration within the harbour is ascribed to tidal advection of saline water and the ETM along the Rotterdam Waterway. Tidal advection controls the density difference between the estuary and harbour, as well as the availability of SPM for exchange at the entrance to Botlek Harbour. The location of the ETM at the tip of the salt wedge is a key factor in supplying SPM to Botlek Harbour. Consequently the timing of the availability of SPM at the mouth of the harbour needs to be considered in siltation studies. The survey data suggest that Botlek Harbour basin has a 100% trapping efficiency. Analysis of 5 months of data, from a measuring rig located within the harbour, show excursions of the limit of the salt wedge and ETM. These excursions are likely to affect siltation of upstream harbours. Salinity-induced density gradients control the transport and subsequent trapping of SPM in the estuary in close proximity to the harbour entrance, the exchange of SPM between the estuary and harbour, and the trapping of SPM in the harbour basin.

Short and long term changes in estuary capacity

Abstract: Changes in capacity have been examined in the Lune, Ribble, Mersey and Humber estuaries to assess the role played by land-derived sediments in coastal accretion. The engineering concept of dynamic equilibrium is introduced and shown to imply that land-derived sediments should contribute exclusively to coastal accretion. The various factors responsible for changing estuary capacity are also introduced. Capacity changes over the last 100 years show that all the estuaries considered have suffered large scale siltation, with the majority of the sediment being derived from coastal and offshore sources. In the case of the Lune, Ribble and Mersey estuaries, engineering works have been responsible for large permanent changes in capacity. The situation in the Humber is less clear and siltation is probably a result of natural infilling; the estuary having been over-deepened by glacial and fluvial action in the past. A detailed study of the Mersey suggests that the estuary was also over-deepened and over-widened and has only been tidal for the last 9000 years or so. Calculations suggest that a new equilibrium will be achieved in about 250 years time and that the estuary may then be in a state of dynamic equilibrium. The much smaller Lune estuary may already have achieved this state, although detailed evidence is scarce.

A sediment level sensor for erosion and siltation detection

Abstract: A sensor for continuous monitoring of sedimentation, or erosion, of marine sediments, has been developed and tested. The method uses the difference in the electrical conductivity of seawater and sediments (up to a factor of 4). The conductivity change grossly distorts the voltage field generated by a current source placed close to the interface. The sensor takes the form of a thin rod carrying ring electrodes along its length. The sensor is driven into the sediment and responds to the position of the sediment/seawater interface along the rod. One of the sensors tested had a resolution of 1·0 cm and full range of 50 cm. Sensors based on this method could be used in a wide range of sediment transport studies, including beach profile measurement.

Analysis of potential impacts on coastal areas due to changes in wave conditions

Abstract: This study examines the main physical processes related to coastal and port engineering that could be altered by future changes in wave parameters as a consequence of climate change. To estimate the order of magnitude of the potential changes in these processes, several assumptions and simplifications are made and, in most cases, they are assessed by using simple, empirical state-of-the-art expressions. The studied processes are grouped in three categories according to whether they affect beaches, harbors or coastal structures in general. The changes in these processes are estimated as a function of the deepwater variations of the main wave parameters: wave height (H 0), wave period (T) and wave direction (θ 0). A moderate range of variation is assumed for these parameters at deep water (±10 or ±20 % in H 0 and its square root in T, and ±10o in θ 0), taking into account recent studies of future wave projections. The results indicate that potential changes in wave height will strongly affect overtopping discharge, stability and scouring of rubble-mound structures and, to a lesser extent, siltation, wave transmission and longshore sediment transport. Changes in wave direction will affect longshore sediment transport in particular and, at a lower magnitude, processes related to port operability (agitation and siltation). Siltation is the only process affected significantly by changes in T alone.