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Sediment supply
The sediment supply to a river delta is one of the most important factors controlling its evolution. Deltas that receive a high sediment supply will prograde, or build out into the sea, while deltas that receive a low sediment supply will retrogress, or erode away. The sediment supply can be affected by a number of factors, including the rate of erosion in the river's watershed, the amount of vegetation in the watershed, and the frequency of floods.
Flow of water
The flow of water through a river delta also plays an important role in its evolution. Deltas that have a high flow of water will be more likely to prograde, while deltas that have a low flow of water will be more likely to retrogress. The flow of water can be affected by a number of factors, including the amount of rainfall in the river's watershed, the size of the river, and the slope of the riverbed.
Local geology
The local geology of a river delta can also influence its evolution. Deltas that are located in areas with soft, easily eroded rock will be more likely to prograde, while deltas that are located in areas with hard, resistant rock will be more likely to retrogress. The local geology can also affect the shape and size of a river delta.
Over time, river deltas can undergo a number of changes, including:
* Progradation: As sediment is deposited at the mouth of a river, the delta will build out into the sea. This process can be accelerated by a high sediment supply, a high flow of water, and a soft, easily eroded local geology.
* Retrogradation: If the sediment supply to a river delta decreases, the flow of water increases, or the local geology is hard and resistant, the delta may erode away. This process can be accelerated by a low sediment supply, a low flow of water, and a hard, resistant local geology.
* Lobe switching: As a river delta progrades, it may form multiple lobes. These lobes can shift over time, as the river's course changes. Lobe switching can be caused by a number of factors, including changes in the sediment supply, the flow of water, and the local geology.
* Channel avulsion: A river delta can also change over time through channel avulsion. This occurs when a river suddenly abandons its old course and creates a new one. Channel avulsion can be caused by a number of factors, including floods, earthquakes, and landslides.
River deltas are dynamic systems that constantly change over time. The rate and magnitude of change can vary depending on a variety of factors, including the sediment supply, the flow of water, and the local geology.