2.2 Rivers Flashcards
The hydrological cycle:
- Drainage basin: the area of land drained by a river
- Watershed: the edge of highland surrounding a
drainage basin, marking the boundary between two
drainage basins - Source: the beginning or start of a river
- Confluence: the point at which two rivers or streams
join - Tributary: a stream/smaller river which joins a larger
stream or river - Mouth: point where river comes to end, usually when
entering sea
River processes:
Drainage basins act as a system with:
- Inputs: precipitation
- Transfers: infiltration, percolation, surface runoff,
throughflow & groundwater flow
- Stores: interception, surface storage, soil moisture
storage & groundwater storage
- Outputs: evaporation & transpiration or
evapotranspiration
Characteristics of the River:
- Bed
- Bank
- Width
- Depth
- Speed of flow
- Wetted perimeter
- Channel
- Thalweg
Purpose of river characteristics:
- Bed: The bottom of the river channel
- Bank: The sides of the river channel
- A river has two banks - Width: The distance between the two banks of a river
- Depth: The distance from the water surface to the bed
of a river - Speed of flow: how fast the water in a river is moving;
different speeds arise at different parts
of the river - Wetted perimeter: length of bed and banks in contact
with river - Channel: The route course (between bed and banks)
that a river flows. The flow of the river is
often described as channel flow. - Thalweg: The fastest part of the river, always near the
middle of the river channel, where there is
least friction
Erosion stages:
- Attrition
- Hydraullic Action
- Abrasion
- Solution
Erosion:
- Attrition: large particles such as boulders collide and
break into smaller pieces; occurs at higher part of river - Hydraulic action: the sheer force of the river dislodges
particles from its banks and bed - Abrasion: smaller particles rub against the river banks
and bed like sand-paper; occurs at low part of river - Solution: acid in rivers dissolve rocks; occurs at any
part of river
Transportation stages:
- Traction
- Saltation
- Suspension
- Solution
Transportation:
- Traction: rolling stones along the bed
- Saltation: small particles bounce along bed in a
leapfrog motion - Suspension: silt and clay-sized are carried within the
water flow - Solution: minerals dissolve in the water
Deposition:
- When a river lacks the energy to carry its load; it begins
depositing the heaviest particles - Happens when there is less water or where the current
slows down - Large boulders are deposited at the top, and very small
particles are deposited at the end, resulting in sorting
River profiles:
Upper
Middle
Lower
Upper (of river profile):
- long profile
- cross profile
Long profile:
Steeply sloping towards the lower sections of the river
Cross profile:
Steep sided v-shaped valley, thin river channel, deep in places
Middle (of river profile):
- long profile
- cross profile
Long profile:
Shallow slopes towards the mouth of the river
Cross profile:
V-shaped valley remains with a wider valley floor, river begins to meander, channel is wider and deeper
Lower (of river profile)
- long profile
- cross profile
Long profile:
Almost at sea level, gently sloping to its mouth
Cross profile:
Wide, shallow valley, with large flood plains and meanders; channel is wide deep and smooth sided.
Landforms:
- V-shaped valley
- Potholes
- Meanders
- Waterfalls
- Ox-bow lakes
- Levees
- Deltas
- Flood plain
V-shaped valley:
(landforms)
- Is narrow with a narrow, shallow river channel
- Has steep sides
- Channel has a steep gradient
- Water is mainly slow flowing
- Load is mainly large, angular and rough
Potholes:
(landforms)
Can be found in the upper & middle valley
where a river flows over solid rock
Meanders:
(landforms)
- Wide sweeping bends found in the lower part of the
river - They are formed by a combination of lateral erosion &
deposition
Waterfalls:
(landforms)
- They occur because the river flows over hard rock
which erodes slowly - Beneath is softer rock which is eroded faster to form
a “step” - The force of the water erodes the bottom of the
waterfall to form a plunge pool - The hard rock gets undercut as the soft rock erodes
so that it eventually collapses
Levees:
(landforms)
when a river floods, the coarsest material is
deposited first, on the edges of the river, forming a
natural embankment called a levee
Deltas:
(landforms)
- Deltas occur where a river that carries a large amount
of sediment meets a lake or the sea - This meeting causes the river to lose energy and drop
the sediment it is carrying - Deltas form where river mouths become choked with
sediment, causing the main river channel to split into
hundreds of smaller channels or distributaries
Flood plains:
(landforms)
- Area of alluvial deposits found beside the river in its
lower course - As meanders move slowly down the course of the
river they erode the valley to create a wide valley floor - Deposits layers of alluvial material on the slip off
slopes building up into a large flood plain
Causes of river flooding:
- Steep-sided channel
- Lack of vegetation or woodland
- Drainage basin, consisting of mainly impermeable rock
- Drainage basin in an urban area
- Deforstation, overgrazing and overcultivation, and
population pressures
Steep-sided channel:
a river channel surrounded by steep slopes causes fast surface run-off.
Lack of vegetation or woodland:
surface run-off will be high as trees and plants won’t intercept precipitation.
