Coastal processes Visit our website: http://www.sliderbase.com/ Free PowerPoint Presentations for teaching and learning Coastal processes are the set of mechanisms that operate along a coastline, bringing about various combinations of erosion and deposition. The land water interface along the coastline is always in a highly dynamic state and nature works towards maintaining an equilibrium condition. The energy due to tide, waves, wind and currents is constantly working in the coastal zone. Dissipation of energy (due to tide, wind, waves and current) is often provided by the beaches, mudflats, marshes and mangroves. Introduction Human use of the coasts also requires space and herein lays the conflict, which results in unstable coastal systems. This induces coastal erosion, sediment transport and accretion. Coastal processes are highly unpredictable and is a challenge to coastal scientists. Some of the coastal processes are Sediment transport currents Denudation Deposition Erosion Flooding Diffraction Refraction Sediment transport is the one of the important coastal process. The analysis and prediction of sediment transport have great commercial, aesthetic, social, and scientific importance owing to the sustainable development and coastal zone management. accretion - natural or artificial deposition of sediment in a particular location beach nourishment - the restoration of a beach by the mechanical placement of sand on the beach for recreational and/ or shore protection purposes. cross shore transport - the displacement of sediment perpendicular to the shore erosion - the removal of sediment from a particular location by the action of wind or water. Sediment Transport and Coastal Processes Definitions longshore bar - offshore ridge or mound of sand, gravel or other loose material running parallel to the shore which is submerged (at least at high tide) and located a short distance from the shore. tombolo - the combination of an offshore rock or island which is connected to the beach by a sand spit. sand spit - low tongue of land or a relatively long, narrow shoal extending from the land. Changes in water level Tides Waves Currents Stream outflow Normal condition prevail most of the time, and the wave energy is easily dissipated by the beach’s natural defence mechanisms. When storm conditions generates waves containing increased amounts of energy, the coast must respond with extraordinary measures, such as sacrificing large section of beach and dune. Alternate erosion and accretion may be seasonal on some beaches; the winter storm waves erode the beach, and the summer waves rebuilds it. It is the movement of sediments most often sand, along a coast parallel to its shoreline - a zig-zag movement of sediment along the beach . The largest beach sediment is found where the process begins, updrift, and the smallest, most easily moved, downdrift. Where waves are strong, the coast will be eroded and sediment carried away and where they are weak sediment will be deposited. Longshore drift can have undesirable effects for humans, such as beach erosion. To prevent this, sea defences such as groynes or gabions may be employed. Where beaches have become severely eroded by longshore drift and little material is replaced by natural processes, then the material may be artificially replaced by beach nourishment Energy flux model Energetic model Suspended transport model It is the simplest model used for the calculation of total amount of material moved along the shoreline. It is based on the amount of energy available in the waves arriving at the shoreline. The flux energy in the wave direction is determined to be as Ϝ dl, where Ϝ -the energy flux of the waves per unit crest width(Ϝ=ECg), E - the energy per unit surface area= ξgH2/8 ρ –the water density where θis the angle the wave ray makes with the onshore(y)direction. Now it is supposed that the energy flux in the alongshore direction is responsible for the longshore sediment transport; therefore we multiply the energy flux per unit legth(dx=unity) of beach by sinθ to obtain Ϝcosθsinθ= Pl=ECgsinθcosθ= (ρ gCgsin2θ)/16 Onshore offshore drift and longshore drift deposit and shape debris to produce a variety of landforms. A spit is an elongated deposit that extends from the land edge out to sea. It may be shaped to produce a distinctly curved end, as in Cape Cod. Another landform that attaches an island to the mainland is known as a tombolo, while deposits may also accumulate to create barriers such as a bay barrier. Coastal engineers, physical oceanographers and geomorphologists generally carry out measurements of sediment transport using the following methods : Wave refraction studies Determines places of wave convergence or divergence and provide quantitative measurement. Using geomorphic indicators Based on geomorphic indicators sediment transport direction is decided. Sediment transport measurements

• published: 05 Jan 2016
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