Rivers and Coasts

Waterfall – high force, river tees

Waterfall retreats upstream leaving a steep sided gorge

A waterfall is formed by diffentical erosion between the hard rock (dolerite) and soft rock (limestone). The hard rock erodes less from erosion processes such as abrasion. And because soft rock erodes quicker the waterfall begins to form. Vertical erosion starts to make the plunge pool this is helped by rocks in the plunge pool creating abrasion. Erosion also creates undercutting this is due to the high levels of energy that lead to lots of hydraulic action. Mass movement happens as the overhang falls are its support has been removed it falls due to gravity, causing the waterfall to move upstream.

Bangladesh (LEDC flooding)

Bangladesh, 1998, river Ganges

Causes:

·         The snowmelt from the Himalayas, the ganotri glaciers are retreating an average of 25 meters yearly which is very quick. This caused a significant discharge increase into the river. Thus causing the banks of the river to overflow and flood.

·         The urbanisation of Dhaka on the confluence of the rivers. With an urbanisation rate of 3.5% it is very high this means that there are lots of impermeable surfaces meaning that the water travels as surface run-off which is faster than in the ground therefore the water reaches the river faster. 

Impacts:

·         60% of Bangladesh was flooded and Dhaka the capital city was completely submerged which lead to approimently 800 deaths due to drowning and many more due to waterborne deceases spreading quickly as the floodwater was polluted with sewage exposing 5 million to serious health hazards and a reported 100 deaths.

Management/sustainability:

·         Cluster villages where set up which were raised above the annual flood height and where made of bricks so they were not knocked down easily. And with the help from NGOS they become self-sustainable as they can grow food and they built a school.

o   Sustainable as the school educates the children in the village which gives them skills which makes them more employable thus helping to get people out of the poverty cycle which in turn will make them more resilient to future floods.

·         Long term stone slopes where made on the west side of the river, this means that the embankment is smoother therefore increasing bank full and reduces friction so water can move quickly.

o   Economically sustainable as it saves important buildings within the city and leaves the city flood free and means the cost of building the slopes is offset by the cost to rebuild the city. However , this solution does nothing to protect the east side which will be flooded for 2 months.

Shrewsbury (MEDC flooding)

River Severn, Shrewsbury MEDC flood 2000

Causes:

·         There is a steep gradient that surrounds the river, going from 900m to 160m in 45km from the plylimina hills. This caused the water to travel as surface runoff so that rainfall travelled quicker into…