5.12. (9/23) Fluvial System; Basic Channel Hydrology Flashcards
river and channel types
where is sediment-moving water gathered?
in drainage basins
What is a drainage basin?
- catchment
- where precipitated water gathers
What do rivers do with the water?
- conduits in catchments to move water into ocean
- pick up and move sediment
What are headwaters?
- sediment factory
- creep, debris flows, landslides
- move sediment to transfer zone
What are transfer zones?
- sediment and water carried by river channels
What are depositional zones?
- deltas, beaches, offshore to shallow marine environment
What are the characteristics of the meandering channel pattern?
- carries fine-grained mud
- sticky banks
- stable discharge: same amount of water every day
- low slope
What are the characteristics of the braided channel pattern?
- coarse (sand and gravel) sediments
- loose/unstable banks (fall apart all the time)
- varied discharge: a lot of water one day and not a lot the next
- steep slope
- frequent shifting of sediment, vegetation cannot establish
What is discharge?
volume of water moving per unit time
*cubic meters per second
What kind of channel is a pool and riffle?
- deep pools
- shallow riffles
- step slope
- rocks transverse to flow (bubbling rapids)
- coarse-grained (sand and gravel)
- some mud
- steep slope
- headwaters and transfer zones
- Saucon Creek (many in Pennsylvania)
What is a point bar?
- landform that is made in big meandering loops
- as the river goes around a meandering loop, it deposits sediment whose shape points out into the channel
- inclined surfaces violate steno’s laws
- sediment accumulates laterally/horizontally
What is lateral accretion?
- sequential build-up in a lateral way
- sediment accumulates in a lateral way and builds out into the channel horizontally
What pushes a channel to build its looping meanders?
lateral accretion
What is a levee?
- natural mounds of sediment that form at the edges of meandering channel
- help confine water
- part of the point bar system
- occur there because as the water rises in the channel, as soon as it flows out - speed falls, depth falls, sediment gets dumped
- sediment accumulates vertically
How do things move in the floodplains?
Settling
what does S stand for?
slope m/m = degrees
What does d50 stand for?
average grain size (m)
Where can we find gravel and sand?
channel/bedload
Where can we find silt and clay (mud)?
floodplain
what is bedload?
sediments carried in the bed of the channel
What are the two ways gravel and sand are moved?
rolling: along the bottom
Saltation
*grains must be sticky enough
What is saltation?
jumping - hitting each other
What process takes place in the floodplain?
settling
What is settling?
mud and silt get dumped because water gets stagnant allowing for the material to fall out of the water
What is suspended load?
silt and clay “float” in the water
What does U stand for?
velocity of the flow
how fast water is flowing (m/s)
What does W stand for?
width of a channel (m)
What is baseflow?
where the groundwater intersects the channel
What does Q stand for?
discharge of a channel (measured in m^3/s)
What does h stand for?
depth of the flow/water (m)
What does bankfull mean?
when the water gets to the top of the bank
What is a flood?
when water goes outside a bank
What key parts do we want to measure in a river channel and its floodplain?
W, S, h, d50, Q, U
How do rivers organize the sediment?
they carry heavy stuff in the channel and light things in the floodplain
What defines how high water is in channel?
the height of the water is keyed into the height of the groundwater
What is baseflow?
where the groundwater intersects the channel
What is a flood?
above/outside the bank
What are riffles?
parts that look like rapids
