Chapter 14: The Geology of Running Water Flashcards
stream
any body of running water that flows in a channel
channel
an elongate depression or trough
headwaters
the source of streams (up stream)
mouth
the very end of the stream (down stream)
sheetwash
a thin film of water (a tiny, tiny stream)
runoff
water flowing on the surface of the Earth; includes sheet wash plus the water in streams
substrate
the material water flows over
downcutting
extra flow contributing to sheet wash deepens the channel relative to its surroundings
headward erosion
the process of a stream channel lengthening at its head; happens because the strength of the flow at the head of the stream is powerful enough to down cut OR because groundwater enters the head of the stream channel, causing weakness in the soil/rock in that area, eventually collapses lengthening at the head of the stream
tributaries
new side channels
drainage network
the configuration of tributaries and trunk streams; patterns of these networks include:
- dendritic: looks like a pattern of branches
- radial: form on the surface of a cone shaped mountain peak; flows in all directions
- rectangular: forms in joints
- trellis: cuts through ridges
- parallel: forms in steep vertical canyons that are in a row
watershed
the collection of water over a broad region; feeds into the trunk stream
drainage divide
separates drainage that flows into one ocean from drainage that flows into another
permanent streams
contain water year-round, fed by ground water
ephemeral streams
contain flowing water for only part of the year
discharge
the volume of water passing through a cross section of the stream in a given time
how do streams erode?
- scouring: running water removes and carries away loose fragments of sediment
- breaking and lifting: the pushing or pulling of rock caused by flowing water
- abrasion: sediment laden water grinds away at the channel walls
- dissolution: water dissolves and carries minerals away
sediment load
total volume of sediment carried by a stream
sediment load
- dissolved load: minerals dissolved and carried by the stream
- suspended load: consists of tiny solid grains (silt or clay)
- bed load: consists of large particles that bounce or roll along the stream bed
saltation
bed load movement involving grains/cobbles bouncing along in the direction of flow
competence
refers to the maximum particle size it carries
- high competence: can carry large particles
- low competence: can carry only small particles
capacity
the total quantity of sediment it can carry
alluvium
sediments transported by a stream as fluvial deposits
point bars
crescent shaped bars (elongate mounts of alluvium) that develop along the inner edge of a meander (where the flow slows)
floodplain
a broad flat area bordering a stream; friction slows the water in the floodplain so a sheet of silt and mud settles out as floodplain deposits
stream gradient
the slope of the stream channel
longitudinal profile
a cross-sectional image showing the variation in the rivers elevation along its length
base level
the lowest level elevation that a stream channel’s surface can reach at a locality
- local base level occurs at a point upstream of a streams mouth
- ultimate base level (the lowest possible elevation along the streams longitudinal profile occurs at sea level
stream terraces
in an alluvium filled valley where the surface of the alluvium becomes a floodplain and a streams base level drops or discharge increases so that the stream cuts down into it’s own alluvium, terraces form in the surrounding bedding/canyon/valley (think grand canyon)
alluvial fan
a low area where flow events deposit it’s load, and develop a broad, gently sloping wedge-shaped apron of sediment
braided river
when stream is choked up with sediments and cannot cut into a single deep channel but instead divides into numerous strands weaving back and forth between elongate bars of gravel and sand
meander
the weaving back and forth of a river (the bends in the river/stream)
oxbow lake
a meander that has been cut off from the stream
delta
a wedge of sediment formed where a flowing stream enters standing water
stream rejunivation
occurs when a stream starts to downcut into a land surface whose elevation had previously been close the the streams base level; can be triggered by a drop in the base level, an uplift event, or an increase in stream discharge
stream piracy
when headward erosion by one stream causes the stream to intersect the course of another stream
drain reversal
when the overall slope direction of the drainage network becomes opposite of what it once had been
flash floods
events during which floodwaters rise so fast that it may be impossible to escape from the path of water
annual probability of flooding
indicates the likelihood that a flood of a given size or larger will happen at a specified locality during any given year
recurrence interval of a flood of a given size
defined as the average number of years between successive floods of at least this size
drainage basin
small rivers flow into larger rivers: the 1 to 2 stream types
what controls where the streams and river flows?
- base level
- tectonics
- bedrock type and orientation
dendritic drainage network
areas where rock (or unconsolidated material) beneath the stream has no particular fabric or structure and can be eroded equally easily in all directions
landforms in fluvial systems
- terrace
- floodplain
- channel
v-shaped valley
form as rivers down cut through soft rocks
