geog – rivers

what is a drainage basin?
this is an area of land drained by a river and its tributaries
what is a watershed?
higher land which is the boundary of a river basin which separates two river basins
what is the source?
the point at which a river begins
what is a tributary?
a small stream of river flowing into a main river
what is a confluence?
the place where a tributary joins the main river
what is the mouth of a river?
the end of a river
define transportation
movement of rocks, sediments and eroded materials down the river
define erosion
the wearing away of land
what are the 4 processes of erosion?
attrition, corrosion, corrasion, hydraulic action
what are the 4 processes of deposition?
saltation, traction, suspension, solution
what does traction mean?
large rocks and boulders are rolled along the bed of the river
what does saltation mean?
smaller stones are bounced along the bed of a river in a leap-frogging motion
what does solution mean?
dissolved material transported by the river
what does suspension mean?
fine material, light enough in weight to be carried by the river. It is this material that discolors the water
what does corrosion mean?
some rocks forming the banks and the bed of a river are dissolved by acids in the water
what does corrasion (aka abrasion) mean?
fine material rubs against the river bank. The bank is worn away, by sand-papering action called abrasion, and collapses
what does attrition mean?
material is moved along the bed of a river, collides with other material and breaks up smaller pieces
what does hydraulic action mean?
the sheer force of water hitting the banks of the river
what is the shape of the river and what type of spurs is there?
it is a v-shaped valley with interlocking spurs
what happens after periods of heavy rain?
On the valley sides slowly moves downhill under gravity. The valley forms a V-shape as it deepened faster than it is widened.
what happens in the upper course of the river?
steep, fast flowing river with little water. Lots of erosion
what happens in the middle course of the river?
River starts to slow down. More water. Still eroding
what happens in the lower course of the river?
River very slow. Much more water. Depositing here, NOT eroding
what is an eddy?
Boulders broken off by erosion that sit on the river bed create swirling eddy currents as the water flows past as the river is not strong enough yet to move the boulders by traction.
what do eddies do?
These eddies swirl the boulder round and erode a pothole in the river bed by abrasion.
what is a braided channel?
In the summer months load is dropped by the low volume of low-energy water in the river. These build up to form obstructions in the river and it divides up the flow around them. In the winter, it is likely that the river volume will increase and remove these obstructions.
what is a delta?
This deposition feature is one of the largest. When the flowing river hits the non-flowing sea, energy is suddenly lost. This causes all of the load in the river to drop in the river mouth. This builds up over time to create a delta – an area of land. The river divides into distributaries to continue to the sea which is now some way from its original meeting point. Lagoons and marshes can form.

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