Streams Flashcards
What are the processes involved in the hydrologic cycle?
Evaporation
Precipitation
Infiltration
Runoff
Transpiration (moisture released by plants)
what are streams
considered a body of water that carries rock particles + dissolved ions + flows down slope along a clearly defined path (channel)
Why are streams important?
Deliver much of the water from land to sea
Erode lots of sediment particles + transport them to lower elevations
- Being important in the formation of sediment + sedimentary rocks
They sculpt Earth’s surfaces through processes of erosion + deposition
Carry dissolved ions (weathered from rocks on land) to the sea (this is why the sea is salty)
what can water that falls onto the ground as precipitation do?
Water that falls to the ground as precipitation can:
Evaporate back into the atmosphere
Soak into the ground (becoming groundwater)
Flow on the surface as runoff
What is a sheetflow
Runoff initially moves over the surface in a thin, continuous sheet (sheetflow)
what is a rill?
The flow of sheetflow eventually becomes confined to tiny channels called rills
what is a channel flow
Rills merge into larger, more permanent, stream channels
what are drainage basins
Stream systems can collect water from large areas
The water catchment area/region for a given stream system is called a drainage basin
what is the area bounding drainage basins called?
divides
Streams tend to erode ____ in effort to reach base level (sea level)
downward
- the greater the elevation above sea level, the greater the rate of downcutting
where does erosion tend to dominate?
at headwaters (highest elevation above base level)
what is the gradient of a stream
The gradient (slope) tends to be higher at the upper reaches of a stream (headwaters) than its lower reaches (close to its mouth)
This concave-upward profile is called a “graded” profile
In what 2 ways can streams carry clastic sedimentary particles?
bedload
suspended load
what is a bedload
large and/or dense particles that remain on the bed of a stream most of the time, but can move by tumbling + saltation (in turbulent layer)
what is a suspended load
small and/or light particles that are suspended in water most of the time (in turbulent + laminar layers)
waht happens to volume + sediment grain size of bedloads and suspended load as it goes downstream
decreases w/ increasing distance from primary sediment source
what are the 2 types of flows that occur in streams
turbulent( non-linear)
laminar (linear)
what are turbulent flows?
Turbulent (non-linear) flow dominates near the bottom + sides of a stream channel where swirling eddies are generated around elements of surface roughness
what are laminar flows?
Laminar (linear) flow dominates water that is out of reach of turbulent eddies
eddies (swirling of a fluid)
How are valleys in Highland
River channels are bounded on either side by valleys
Valleys reflect the erosive action of streams, which undercut + destabilize their banks
Destabilized material tumbles down into stream channel, providing sediment particles for the stream to transport as bedload or suspended load
At highest reaches (in mountains), slot canyons can form due to extreme downcutting
As river continues down mountainous terrain, tend to be deep + v-shaped due to rapid downcutting
Meandering pattern not pronounced
what is meandering pattern?
meander is a bend in a river channel
What are the characteristics of a headwater channel in highlands
Small, shallow, channels
Coarse bedload
Turbulent flow dominant
Overall velocity often low bc drag affects most of water column
what are the characteristics of lower course channel in lowlands
Large, deep, wide channels
Fine bedload
Laminar flow dominant
Overall velocity high bc drag is confined near the stream bed (well below the surface)
what are the characteristics of highland streams
At slightly slower gradients (e.g. feet of mountain slopes)
- Large volumes of bedload are deposited in cone-like bodies called alluvial fans
Continuing on their downstream course, highland streams remain small + shallow
Bc they are choked w/ coarse bedload, streams are often diverted + form shallow, braided channels
what are the characteristics of lowland streams
Valleys in lower parts of stream’s course (closer to base level) tend to be broad due to little downcutting + greater lateral movement
Meandering pattern more pronounced
The “flatness” of the valley floor is accentuated by the deposition of sediment during floods
Areas adjacent to the channel that are built up by sediments during floods are called floodplains
how does the meandering stream system work?
The path of highest flow velocity (called the thalweg) veers toward the outer bank of a meander
- This creates an area of highwater pressure at outer bend
- The inner bend is the zone of slowest flow, representing an area of low water pressure
To relieve the differences in pressure, water flows rapidly downward at outside bank, across the bottom of the channel + up the inside bank
- Produces helical flow (circulating in a corkscrew fashion)
what are cut banks
area of erosion
(outer bend)
Strong flow erodes the outer bend, producing a steeply sloping cut bank
what are point bars
area of deposition
(inner bend)
Weaker flow on the inner bend deposits sediment
how does meander move in the direction of the cut bank?
laterally
What are oxbow lakes
Meander loops become more pronounced through time, resulting in cutoffs
When a meander is isolated due to a cutoff, it can form an arc-shaped lake called oxbow lake
what is a floodplain
flat area next to river or stream subject to flooding
what is floodplain deposition
During a flood, water spills over river’s banks
Sudden reduction in the speed of water allows sediment to be deposited on the floodplain
Sediment deposits are thickets (+ coarsest-grained) in natural levees on either side of a flooded channel
How does sediment enter the sea
In lowest part of stream’s course, it is deprived of coarse sediment but still carries lots of fine-grained sediment as bedload + suspended load
When river enters the sea (or other body of standing water)
- Flow velocity suddenly drops + sediment is deposited
Bodies of sediment deposited in this way are called deltas
