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"Sedimeter sensors designed and
built by Lindorm are a fantastic
tool for measuring water column
turbidity and siltation." (Gravity)

Beach Erosion and Sedimentation

In the the geologic cycle minerals are combined into rock, the rock is lifted up as mountains, the mountains are eroded, and rivers carry the sediment back to the sea.

Where the rivers meet the sea some of the sand is deposited, while the finer particles are carried further in suspension. Sediment accumulates, is deposited, in the near-shore or offshore depending on sediment size. Some may continue directly as a turbidity current through a canyon to a deep-sea fan.

Sediment that stays on the continental shelf is accumulated, eroded, transported, deposited, resuspended many times. The SediMeter was developed to measure and monitor these processes.

In the hot, humid, and lowland tropics, clay dominates over sand in the river load. For that reason, mudbanks and mangrove tend to be more common than sand beaches.

Sand beaches are most common in desert climates and in temperate climates. In previously glaciated seas the downstream shore tend to contain vast amounts of glaciofluvial sand (i.e., sand transported and sorted by glacial meltwater).

Other sand is created by fragments of coral or mollusc shells, or by chemical precipitation as "ooids". Coral reefs require very clear water with no sediment input from rivers. Also ooids occur only far from rivers, since they cannot form where the water is diluted. A lack of rivers is found both on tropical islands, and in desert climates such as the Red Sea.

Regardless of the origin of the sand, all beaches depend on one more factor, without which they cannot exist: Waves. Waves prevent vegetation from taking over, by stirring up the sand. However, waves can also erode the beach. The beach only exists in a dynamic equilibrium with the waves. The waves shape the beach.

Some waves tend to move sand out to deeper water, others to move it back in. Some beaches have sand that is trapped between headlands, while others receive sand in one end and loose it in the other. The beach exists when these various processes balance each other over some time.

The SediMeter can be used to meausure sediment accumulation and erosion on the underwater part of beaches. The sensor is strong, and if there is very high energy, it can be mounted upside down to minimize the protrusion into the water. The only limitation is grain size; it is not suitable for studying coastal erosion where the bed material is coarser than sand, for various reasons. It can, however, be used to study suspended sediment in high concentrations, such as fluid mud.

The SediMeter data can be a crucial piece of information when estimating sediment transport, especially when the transport takes place as bedload in the for of migration of sandwaves and other bedforms. Knowing the sediment transport rate is essential when contemplating a beach erosion mitigation strategy.

Rio Terraba, Costa Rica
Mouth of Rio Terraba, Costa Rica. Pacific Ocean. Mangroves in the foreground.
El Alamein beach
Ooid beach, El Alamein, Egypt. Mediterranean Sea.
Beach on Surtsey, Iceland
Tephra sand on beach of Surtsey, Iceland. Atlantic Ocean.
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