RIVERS Flashcards
How does a rivers cross profile over its course?
Upper course - narrow and deep (V)
to
Lower course - wide and shallow (U)
How does a rivers long profile over its course?
Steeper in the upper course and slowly levels out (gradient decreases).
How does vertical and lateral erosion change the cross profile of a river.
Vertical erosion makes the river deeper (mainly in upper course, V shape).
Lateral erosion makes the river wider (middle and lower course).
What are physical causes of river flooding?
- Heavy rainfall
- Long periods of rain
- Impermeable rock
What are human factors that increase the risk of river flooding?
- Urbanisation (impermeable surfaces in towns)
- Deforestation (removing trees increases surface run-off)
What is river discharge?
River discharge is the volume of water flowing through a river channel.
What are factors that can increase river discharge?
Impermeable surfaces
Heavy rainfall
Deforestation
Long periods of rain
What do dams do to stop flooding (hard engineering)?
Dams - traps water and can release it in a controlled way.
What does river straightening do to stop flooding (hard engineering)?
River straightening - straightening the river speeds up the water, so high volumes can pass through an area quickly, therefore reducing the chances of a flood.
What do embankments do to stop flooding (hard engineering)?
Embankments - embankments raise the banks of a river so that it can hold more water.
What do flood relief channels do to stop flooding (hard engineering)?
The floodwater flows into the relief channel and is taken either to an area where it can be absorbed, or re-enters the river further down its course
What do flood warnings do to stop flooding (soft engineering)?
Warn people so they can protect their properties and save possessions.
What does floodplain zoning do to stop flooding (soft engineering)?
Allowing only certain land uses on the floodplain reduces the risk of flooding to houses and more important buildings.
How are meanders formed?
Erosion on the outside bend (the arc).
On inside bend the river flow is slower so sediment drops (deposition).
How are ox-bow lakes formed?
An oxbow lake starts out as a meander in a river. A lake forms as the river finds a different, shorter, course.
How are levees formed?
The natural movement of a body of water pushes sediment to the side. This makes the banks of a river are often slightly elevated from the river bed. The banks are made of sediment, silt, and other materials pushed aside by the flowing water.
How are waterfalls formed?
Waterfalls often form in the upper stages of a river where it flows over different bands of rock. It erodes soft rock more quickly than hard rock
How are steep-sided gorges formed?
Streams carve through hard layers of rock, breaking down or eroding it. Sediment from the worn-away rock is then carried downstream. Over time, this erosion will form the steep walls of a gorge.
Why do interlocking spurs form?
Because in the upper course of a river it lacks the power to erode laterally so it winds around the high hillsides which interlock with each other
What are flood plains?
The wide valley floor on either side of a river that occasionally floods
It builds up when water floods, loses energy and deposits material
What are estuaries?
Near the river mouth
Tides rise and deposit silt and sand
Overtime more mud builds up creating large mudflats
What can increase the flood risk of a river?
Prolonged rainfall
Heavy rainfall
Rock type (impermeable)
Land height
Land use
What are estuaries?
Where the river meets the sea
River is tidal so the sea retreats so the volume of the water in the estuary is reduced
Less water so the river deposits silt to form mudflats
