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Concept
Coastal sediment supply
Résumé
Coastal sediment supply is the transport of sediment to the beach environment by both fluvial and aeolian transport. While aeolian transport plays a role in the overall sedimentary budget for the coastal environment, it is paled in comparison to the fluvial supply which makes up 95% of sediment entering the ocean. When sediment reaches the coast it is then entrained by longshore drift and littoral cells until it is accreted upon the beach or dunes.
While it is acknowledged that storm systems are the driver behind coastal erosion. There is a general consensus that human activity, mainly dam and reservoir impoundments on rivers are the cause of indirect human related coastal erosion, along with other local scale effects such as: land use change, irrigation, gravel extraction and river re-alignment.
Worldwide, rivers discharge approximately 35x103 km3 of freshwater into the ocean annually. Transported in this freshwater is 15 to 20 x 109 tons of sediment. This sediment load is not proportionally distributed across the world's rivers, with Asian and Oceanic regions being among those most significantly affected by changing sediment regimes, as they account for 75% of this global sediment budget.
These changing rates of supply/replenishment from the fluvial environment are a dominant factor in controlling the rate of coastal erosion. While sediment supply is actually increasing, due to increased erosion rates, the supply of this sediment to the coastal environment is decreasing.
Fluvial systems are key elements for operating Earth surface change because they convey most of the global fluxes of water and sediment from land to oceans. Human activities can affect the discharge of water and sediment from a river to the coastal environment in many ways. Deforestation and agriculture, as well as urbanization can increase the erosion of a river basin by as much as an order of magnitude. Freshly exposed soil is much less likely to resist erosion by rainfall or moving water, especially in areas where land is often used for agriculture and precipitation is high.
Source officielle
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