River Processes Flashcards

Question

how are waterfalls/ gorges formed?

Answer 1

- a river falls over a hard rock edge, meeting a band of softer, less resistant rock at the bottom. - processes of erosion, mainly abrasion and hydraulic action, cause undercutting. the underlying, soft rock is eroded more quickly - the more resistant rock is left unsupported and overhangs. Hydraulic action causes a plunge pool under this rocket form - eventually the more resistant rock collapses onto the river bed - a steep sided river valley is created called a gorge. this process is repeated and the river/ waterfall retreats upstream

Answer 2

include: - slowest flow - fastest flow - beach - deposition of sand on inside bend - shallow water - deep water - bank worn away - erosion on outside bend causing undercutting - flow - river cliff

Answer 3

- a river rarely flows in a straight line, it will bend around something in its course, e.g a tree or hard rock - this results in areas of slower and faster water movement - the river flows faster on the outside, because this is where water is pushed (more water= more energy = faster flow) and erodes these outside bends by processes such as hydraulic action and abrasion, forming a river cliff - the river flows more slowly on the inside bend of a river channel and deposits some of its load, creating river beach - continuous erosion on the outer bank and deposition on the inside of a river creates a meander in the river - over time, meanders become larger and more recognisable

Answer 4

- in meander, the water is pushed to the outside bend, so processes such as abrasion will cause lateral erosion - continual erosion on the outside bend narrows the meander neck (neck of land) - the river floods, and takes the shortest route, cutting through the neck - the fastest current is now in the centre of the channel - deposition occurs along the banks of the river, eventually making the meander cut off, leaving an ox bow lake - the ox bow lake will slowly dry up, unless rainfall is very high

Answer 5

- deltas are located at the mouth of a river as it enters a sea or lake - on reaching the sea, it suffers a loss of energy as its velocity decreases and so deposition occurs - sea water is denser and salty, which helps the sand particles to bind together, becoming heavier and sinking to the sea bed - sometimes deposition occurs in the main channel and blocks it. the river then has to divide into a series of smaller channels called distributaries in order to reach the sea - over time deposition of silt occurs in and on the banks of the distributaries to form islands and levees - as a river approaches the sea it has the energy to carry huge amounts of sediment as suspension - eventually the delta grows both upwards and outwards into the sea to form new land often colonised by vegetation. the growth of this vegetation raises it above sea level.

Answer 6

- the sediment load in the river must be substantial (due to active erosion in the upper course) - needs to be a sheltered sea/ lake where there are no strong tides or currents - the supply of sediment must be greater than the rate at which tides or currents are able to remove it from the mouth of the river

Answer 7

- Levees occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs. - Sediment that has been eroded further upstream is transported downstream. - When the river floods, the sediment spreads out across the floodplain. - When a flood occurs, the river loses energy. The largest material is deposited first on the sides of the river banks and smaller material further away. - After many floods, the sediment builds up to increase the height of the river banks, meaning that the channel can carry more water (a greater discharge) and flooding is less likely to occur in the future (natural embankments)

Answer 8

silt, sometimes alluvium (good for farming as is fertile)

Answer 9

- very low lying (70% of its land area is less than 1m above sea level and 80% is floodplain) - receives large amounts of water passing through it - three major rivers (the Ganges, Meghna and Brahmaputra), with the Ganges and Brahmaputra converging and forming a huge delta - has a monsoon climate and the annual torrential rains from June to September often cause rivers from exceeding their capacity and flooding. - in the spring, melting snow from the Himalayas increases flood risks as torrents of melting snow enter the rivers at their source - the ground is baked hard before the monsoon season, making it impermeable, meaning there is more surface runoff

Answer 10

- intense deforestation in the Himalayas has led to less trees and therefore more soil erosion. this means less interception and more water and silt in the river - Bangladesh is an LEDC and its lack of money and heavy national debt means that little money is available to spend on flood protection and many existing defences lack upkeep and are of questionable use - population growth, leading to increased population density and more urbanisation, which reduces infiltration and increases surface runoff - poor transport and communication skills means there is not good warning or evacuation due to lack weather warnings - global warming means that more snow on the Himalayas melts

Answer 11

- 50% of country flooded - 7 million homes destroyed - 30 million people were homeless - wells were polluted (clean water contaminated and as a result 100,000 people suffered from water Bourne diseases) - 750 people died

Answer 12

- people had no electricity for weeks - 1 million people were forced to live in temporary accommodation - crop were ruined, leading to food shortages - total damage accounted to 7 billion dollars

Answer 13

- boats to rescue people - emergency supplies for food, water, tents and medicines - fodder for livestock - repair and rebuild houses, as well as services such as sewage etc. - aid from other countries

Answer 14

- reduced deforestation in the Himalayas - built 7 large dams in Bangladesh to store excess water, costing 30-40 million dollars + 40 years to complete - built flood shelters to accommodate the population - built 350km of embankment- to reduce flooding along the main river channels - developed an effective flood warning scheme

Answer 15

- slow drizzle all day - soil that is dry before the rain storm - chalk (a porous rock which stores water) - woodland and trees in the drainage basin - gentle slopes that water flows off slowly - the countryside, with fields full of crops

Answer 16

- heavy rainfall for several hours - soil that is saturated (soaked) before the rainstorm - granite (an impermeable rock which doesn't store water) - very few plants in the drainage basin - steep slopes which drain quickly - a built up area with many tarmac surfaces