river

Question 1

Assess the effectiveness of re-alignment as one method of river management

Answer 1

1. Refers to the straightening of river channel.
   2.removes meanders and reduces length of river channel in order to increase the speed of the river.
   Helps the river and sediments to flow away from the area quickly to reduce the chances of flooding.
   3.channels are also deepened to hold more water.
2. the volume of water flowing downstream is increased.
3. The channel downstream may not be able to hold the increased water flow, flooding may occur.
   (3) . Channelization may protect one part of the river course, flooding may occur in other parts.

Question 2

Assess the effectiveness of re-sectioning

Answer 2

1. Refers to the widening and deepening of the river channel.
2. Increases the river’s ability to hold water, lowering the possibilities of flooding.
3. River bed and banks are smoothened by granites and cement to increase the speed of the river. Flow away more quickly to prevent flood.

Isar river in Bavaria and Germany

1. But as the river flows faster and with more energy, the sediments are removed from the river bed and banks to be washed downstream.
2. the sediments accumulate in the sea or ocean and block the sunlight from reaching the seabed. Marine lives are thus affected

Question 3

Assess the effectiveness of bank protection

Answer 3

1. Artificial dykes which are walls of sand, stone or concrete are built along rivers that overflow their banks, to prevent erosion against the river banks.
2. the structures increase the capacity of rivers to hold water. Reduce the chances of flooding.
3. Gabions which are walls made if stone, are built along a river channel to divert the flow of water form the river banks to the center of the river.
4. River banks become protected from being eroded, thereby reducing the amount of sediments that flow into the river.
5. The constructions of dykes and Gabions also cause sediments to cumulate behind these structures. Overtime, the river channel becomes shallower, reducing their effectiveness in flood control.

In china, dykes are built in the lower course of yellow river. However the continuous building-up of sediments on the river bed, making the channel shallower, lifting up the river bed and it’s water level. Hence more dykes have to be built regularly to prevent flooding.

Question 4

Assess the effectiveness of plating vegetation

Answer 4

1. Roots of trees and other vegetation planted along the river banks can hold the soil together and prevent soil erosion .
2. Vegetation also slows down the rate of surface runoff as it allows water to infiltrate into the soil while its roots absorb the water.
3. Planting too much vegetation along the river banks can prevent sunlight from reaching the river bed, killing aquatic plants and affecting aquatic food chains.

Question 5

Define hard engineering

Answer 5

Construction of structures such as seawalls,breakwaters，groynes

Question 6

Define soft engineering.

Answer 6

Application of knowledge of natural processes to stabilize the coast and reduce erosion