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Earth Systems and Resources
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broadly, it is a river that receives more sediment than can be transported
four characteristics of an alluvial river
erodible channel and bed; sediment supply is equal to or greater than transport capacity; huge sediment storage; channel forms patterns easily
what are the five alluvial channel types?
cascade, step-pool, plane-bed, pool and riffle, dune-ripple
which alluvial channel type is the most common?
pool and riffle channels
how are alluvial channel types ordered?
based on decreasing gradient and average level of sediment the flow can carry
pool and riffle channel characteristics
alternating sequence of pools and bars; tend to meander
small headwater channels at tips of network that are dominated by sediment transport via landslides
steepest of mountain channels; tumbling flow, individual boulders; disorganized streambed
channels that accumulate coarse sediment that form "steps" sequence
lack well-defined bedforms; displaying long reaches with no pools
what are the two types of channels the average mountain stream has?
colluvial (sediment from hillslope) and alluvial (fluvial transport)
how often do riffles and pools alternate?
every 5-7 channel widths
how often do steps and pools alternate?
every 1-4 channel widths
deepest point in a channel
what are the four channel patterns?
straight, meandering, braided, and anastomosing
what two factors does a channel's pattern depend on?
if the channel is straight or sinuous; if the channel divides or is single
represent young rivers that are confined by topography/geologic structures; relatively rare due to erosion patterns (rivers Want to bend)
more common (especially in alluvial channels); self-reinforcing series of bars and bends that lead to cut banks and point bars, meander belts, and huge floodplains
where does a meandering channel erode in a bend?
on the outside of the bend, where velocity is highest
where does a meandering channel deposit in a bend?
in the inside of the bend, where velocity is lowest
the fucking around of a river on a floodplain (think of it like a snake thrashing)
is there a cap to how much a meander can grow?
no; only limitation is if it cuts itself off and an oxbow lake forms
characteristics of a meandering river's floodplain
very fertile with seasonal flooding
big meanders tend to have...
a low gradient and fine substrate
small meanders tend to have...
a higher gradient and coarser substrate
channels that are relatively straight but with streams that converge and diverge around mid-channel bars constantly
three characteristics of braided channels
high BEDLOAD compared to discharge; constantly changing course due to erosion and redepositing of beds; floodplain occupied entirely
where are braided channels typical?
areas with easily erodible banks/beds that have high sediment loads nearby (glaciers/mountains)
what four factors determine a channel's broad patterns?
longitudinal, latitudinal, vertical, and temporal (time) factors
is a river's channel one type from start to end?
NO! a river can change at different areas of its run depending on the four broad factors