Stream Base Level • base level can erode is the lowest point to which a stream – sea level - when the stream pours out into the ocean is the base level • local or temporary base level can occur ultimate – a formation resistant to erosion forms the stream bed • (water falls develop)– a dam is installed • raising base level– tectonic uplifting results in sediment deposition • dropping base level relative to the ground surface results in erosion and down cutting of the stream bed • longitudinal profile changes if base level changes
Longitudinal Profile of a Stream • The longitudinal profile of a stream is the gradient in elevation of a stream along its length.– Head: upgradient, the profile is usually concave and the stream slope is usually steeper– Downgradient toward the mouth, the stream gradient flattens and has a lesser slope.
Changes in base level can change the longitudinal profile of a stream
Stream valleys • V-shaped narrow valleys– form when the stream is far from base level where the high gradient results in rapid flow and thus down cutting • rapid flow = high competency = large bed load and thus rapid erosion– features include rapids and water falls. • Wide valleys– Form when the stream is near base level so shallow gradient, slower flow, and thus little downward erosion– Features: erosion from side-to-side forms meanders and a floodplain With time a V-shaped valley can transform into a wide meandering river
Meandering Rivers • follows a winding and twisting course with large sweeping bends (meanders )– usually flowing on low slopes in plains or lowlands
Meander Features • cut bank-zone of erosion outside of bend– where velocity is fastest • point bar- zone of deposition inside of bend– where velocity is the slowest • cutoff- meander bypassed • oxbow lake-abandoned bend filled with water– meander scar - dry oxbow lake • bar- sediment accumulations inside the channel
Meander Features • cut bank-zone of erosion outside of bend– where velocity is fastest • point bar- zone of deposition inside of bend– where velocity is the slowest • cutoff- meander bypassed • oxbow lake-abandoned bend filled with water– meander scar - dry oxbow lake • bar- sediment accumulations inside the channel
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Studied by 13 people
