Distribution Of Sediment Transport Rate Research Articles

Longshore sediment transport rate from the field measured wave and sediment characteristics along the coast of Karaikal, India

ABSTRACT The change in the shoreline greatly influences the coastal developments such as maritime trade, fishing activities, coastal transport, and tourism. Due to the requirements of vast developments along the coast near major habitat zones, such as the Karaikal coast along the east coast of India, it is essential to understand the longshore sediment transport (LST) movement to plan for any coastal systems to protrude. A detailed LST estimate has been made with the predicted wave climate using the wind-wave model, WAM. The wave characteristics are compared with the field measurements off the coast considered herein. The LST rates computed using five different sediment transport formulae and the method of integrating the distribution of sediment transport rates within the surf zone have been computed to understand the variations of the estimate in each method. Although the predominant direction of sediment movement is towards the north, there is a seasonal variability of LST based on the prevailing monsoon wind direction. Monitoring and analysis of the LST are important as it is required in designing coastal structures.

Monitoring and modeling sediment transport in space in small loess catchments using UAV-SfM photogrammetry

Sediment transport rates are widely used in studies of soil erosion, hydrological simulation, and regional ecological assessment. Although traditional field hydrological stations can provide a global sediment transport rate for observation areas, quantifying sediment transport rates in space is still challenging. This study presents a work frame for monitoring and modeling sediment transport in space using recently ongoing UAV-SfM photogrammetry. First, the DEMs of difference (DoDs) were obtained by repeated UAV surveys. Then, we used the root mean square error (RMSE) and precision map (spatially distributed errors) to detect topographic changes at different confidence levels and analyzed the relations between detected changes and the thresholding of confidence level. Finally, we compared different routing solutions for inferring the sediment transport rates in space based on the observed topographic changes. Results show that the thresholding of confidence level will lose observations and may underestimate global sediment transport rates. The sensitivity of observation loss to the confidence level by using the precision map is lower than that by using RMSE, suggesting that the use of the precision map is more suitable for topographic change detection. In terms of the spatially distributed sediment transport rates, the multiple flow routing based on slope exponent (MFD-se) shows superior performance than the multiple flow routing based on maximum downslope gradient (MFD-md) and eight-node (D-8) routing. The negative sediment transport in the study areas ranges from 2.53% to 7.85% by using MFD-se routing. Moreover, the use of thresholding of confidence level is beneficial to reduce negative transport. The proposed work frame can conveniently provide a detailed spatial distribution of sediment transport rates, which would provide a new perspective for studies of earth surface processes.

Morphodynamic response of nearshore bars to a shoreface nourishment

The autonomous nearshore bar behaviour along the barrier island of Terschelling, The Netherlands, is characterised by the presence of net seaward cyclic migrating sand bars generated near the shoreline. In 1993, a perturbation of the cyclic bar system was introduced by the implementation of a 2 Mm 3 shoreface nourishment supplied to the nearshore bar zone, filling up the trough between the middle and outer bar. The morphodynamic response of the nearshore bars to the nourishment perturbation is investigated using a bathymetric data set with an alongshore extent of 12 km and sampled for 10 years. Bar behaviour is quantified in terms of bar crest position in relation to morphometric parameters such as bar depth, height, width and volume. Along with a pronounced development of a three-dimensional bar system unseen in the autonomous behaviour, the nearshore bars exhibited a 6–7 year arrest in their migrational behaviour during which bar morphology remained stable at immediate pre-nourishment morphometric values. At the subsequent onset of bar movement, bars resumed their migration at a rate predicted by autonomous behaviour in parallel development with morphometric parameters along their predicted trends. It is shown that the observed onshore transport of nourished sediment in the 6–7 year arrest results from a gradual deepening of troughs. Cross-shore sediment transport modelling is used to assess the effect of the nourishment on yearly averaged onshore (short-wave nonlinearity) and offshore (undertow) sediment transport rates. The gradual reappearance of the pre-nourishment bar-trough morphology is shown to engender a normalisation in the cross-shore distribution of sediment transport rates to pre-nourishment rates.

A general framework for modeling sediment supply to coastal dunes including wind angle, beach geometry, and fetch effects

A series of spatially explicit equations are derived that form the foundation of a modeling framework that provides insight into how the interaction of the fetch effect and angle of wind approach leads to tradeoffs that govern the magnitude of aeolian sediment transport across beaches of different geometry. The spatial distribution of sediment transport rate per unit width at any point on the beach is shown to vary predictably as a function of wind angle, critical fetch, and beach geometry; and this has evident implications for the total volume and distribution of sediment transport into the dunes behind the beach as well as the proportion of sediment lost from the beach-dune system at the downwind margin. As the wind field shifts from onshore (shore perpendicular) to oblique (shore parallel) approach angle, total sediment transport rate across a dune line segment will reflect a tradeoff between transport reduction because of the cosine effect and transport enhancement because of potentially longer fetch distances traversed by the wind prior to encountering the dune line. This tradeoff is most evident on long, narrow beaches when beach width is less than the critical fetch. For such beaches and with onshore winds, the total sediment transport rate across the dune line will be less than that predicted for a wide beach because of the constraint imposed by the fetch effect. However, as the angle of wind approach becomes oblique, the available fetch becomes progressively longer, transport limitations imposed by the fetch effect are negated, and transport enhancement across the dune line is to be expected. With very large angles of wind approach, the cosine effect dominates the interaction and transport reductions across the dune line occur until the wind is shore parallel and sediment supply to the dunes ceases altogether. This sequence of adjustments and tradeoffs were only partially understood prior to this study, and yet they form the foundation of coastal dune modeling. The framework proposed in this paper serves to place future studies of process-form interaction in beach-dune systems on a robust theoretical foundation. It also facilitates the testing of various alternative hypotheses regarding the uneven spatial and temporal distribution of dune height and growth rate in coastal environments.

Distribution of Sediment Transport Rate over Alternating Bars

Distribution of Sediment Transport Rate over Alternating Bars