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A river delta is a landform, ... the importance of turbulent bed friction beyond the river mouth, ... Such deltas are characterized by a tripartite structure of ...
The geology of the Pearl River Delta is rock sequences plus superficial sediments, emplaced in an alluvial delta, occupying the Pearl River Estuary. The unconsolidated sediments which dominate the delta are largely derived from continental materials exposed across the Pearl River basin, and range in size from fine particles such as mud to larger fragments like gravel.
The foreset bed is formed when a stream carrying sediment meets still water. When the stream meets the still water, the velocity of the water is decreased enough so that the larger sediment particles can no longer be carried and are therefore deposited. The deposited sediment builds up over time, and a delta is formed.
An example of a deltaic lobe is the bird's-foot delta of the Mississippi River, pictured at right with its sediment plumes. As the deltaic lobe advances, the slope of the river channel becomes lower, as the river channel is longer but has the same change in elevation. As the slope of the river channel decreases, it becomes unstable for two reasons.
A bedform is a geological feature that develops at the interface of fluid and a moveable bed, the result of bed material being moved by fluid flow. Examples include ripples and dunes on the bed of a river. Bedforms are often preserved in the rock record as a result of being present in a depositional setting.
The cuspate deltaic lobe is defined by its abrupt rate of discharge from river to body of water, and the creation of multiple cusp systems built up into separate but active distributaries. [9] One such example of a cuspate delta is the Tiber River delta of Italy. The river was formed first as a deltaic lobe cusp prograded from the river mouth.
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In the lower flow regime, the natural progression is from a flat bed, to some sediment movement (saltation etc.), to ripples, to slightly larger dunes. Dunes have a vortex in the lee side of the dune. As the upper flow regime forms, the dunes become flattened out, and then produce antidunes. At higher still velocity, the antidunes are flattened ...