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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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A fluvial system ideally has three main components: (1) a drainage basin or sediment- and water-source areas, (2) a river or conduit for the waste of the drainage basin, and (3) a site of sediment deposition in the piedmont
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or coastal zone.
The nature and quantity of sediment produced from the source area determine the morphologic character of the river, and a river can be classified into five patterns dependent on type of sediment load. The (1) straight and the (2) sinuous-thalweg patterns reflect relatively low values of sediment transport, of bed-load to total-load ratio, and of stream power. The (3) meandering pattern reflects relatively low to moderate values of sediment transport, of bed-load to total-load ratio, and of stream power. The (4) meandering-braided transitional pattern and the (5) braided pattern reflect relatively high values of sediment transport, of bed-load to total-load ratio, and of stream power.
Throughout geologic time fluvial systems have had complex erosional and sediment-production histories as a result of external and internal influences. The external variables that most significantly affect the fluvial system are tectonic, eustatic, and climatic. The response of the fluvial system to changes in these controls is not necessarily simple; rather a complex response involving both erosion and deposition will ensue and the morphologic character of a river will change as the character of the sediment delivered from the source area changes. The exceeding of intrinsic geomorphic thresholds also produces episodes of high sediment movement.
The character of sedimentary deposits (piedmont, deltaic, or nearshore) will reflect the geology, morphology, and erosional history of the source area as well as the type of river transporting the sediment. Abrupt changes in amount and type of sediment reflect not only the complexity of the erosional evolution of the area, but also the dynamics of the sediment-producing and transport zones of the fluvial system.
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