![]() The higher the hill, the more gravitational energy there is to drive the stream. Streams flow downhill due to the force of gravity. Streams erode dirt and rocks, transport the sediment, and redeposit it in new locations, shaping the earth’s surface into a system of stream valleys. Most valleys on earth are the product of streams. Over longer intervals of time the same processes we’ve imagined on the construction site have built systems of streams and stream valleys on the surface of the earth. If not prevented, the channels may continue to deepen and erode soil from the construction site. A network of streams, including tributaries, has formed. Soon, the water excavates small channels, known as rills, in the dirt. ![]() At first the water saturates the ground and begins to flow downhill across the surface of the slope in a thin sheet. It is interesting to watch water on a recently bulldozed construction site with a slope. A small brook in a meadow and the Amazon River are both streams. What Are Streams?Ī stream is flow of water, driven by gravity, in a natural channel, on land. By eroding sediment from uplifted areas and creating landforms made of deposited sediment in lower areas, streams shape the earth’s surface more than glaciers do, more than waves on a beach do, and far more than wind does. Streams sculpt and shape the earth’s surface by eroding, transporting, and depositing sediment. This approach is applicable to a wide variety of Quaternary settings where prior stratigraphic techniques have resulted in ambiguity.Streams have a major role in geology. Alluvial sediments are differentiated in a manner that successfully integrates geomorphic, sedimentologic, and pedologic data into significant stratigraphic models. Surface horizons of alluvial soils are all similar (ochric epipedons), but subsoil horizons are chiefly stratified parent material on the MAG (Entisols), cambic horizons on the DS (Inceptisols), and minimally developed argillic horizons on the WAT (Alfisols).Īllostratigraphy provides an objective method for definition of geologic units that contain genetically related, but heterogeneous sedimentary deposits. Lithofacies and sedimentary environments are dependent on fluvial process, and a suite of meander belt environments can be identified within each alloformation. Preserved deposits consist of channel lag, point bar and scroll bar, channel fill, and overbank sequences. The valley fill consists of a lower sandy and upper silty facies. Three alloformations, identified as Magnolia Bridge (MAG), Denham Springs (DS), and Watson (WAT), can be differentiated by unconformable boundaries, landscape morphology, and relative pedogenic development. This procedure extends classical terrace mapping concepts to conform with formally defined stratigraphic procedures.Ī meander belt segment of the middle Amite River valley in southeastern Louisiana was selected to test the applicability of alloformation mapping in part of a regional-scale (5,000 km 2) drainage basin. Alluvial morphology and stratigraphy can be linked to flood-plain evolution through the use of alloformations, unconformity-bounded stratigraphic units. Geomorphological studies in drainage basins of the northern Gulf of Mexico coastal plain have indicated similarities in flood-plain character and comparable influences on basin evolution.
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