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Describe the changes of characteristics of the river channel after channelization. Evaluate the pros and cons of channelization on the river channel and its neighbouring areas. Suggest ways to reduce the negative effects that may have occurred.

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Describe the changes of characteristics of the river channel after channelization. Evaluate the pros and cons of channelization on the river channel and its neighbouring areas. Suggest ways to reduce the negative effects that may have occurred. Give appropriate examples.

Channelization is carried out to modify a channel, usually to regulate river flow. However, this will cause great impact on the river system and also its neighbouring areas. Nevertheless, there are still ways to minimize negative effects of Channelization and people will adopt different measures to carry out channelization.

Characteristics of river channels will be changed after channelization. Firstly, rivers before channelization are usually winding and meandering. However, after channelization, the river channel would be straightened and less meandering. Secondly, the narrow river would also be widened after the modification. Thirdly, because the river was made less meandering, the channel length would become shorter than before. Fourthly, channel gradient would be increased and it will be steeper. Fifthly, the rugged channel bed will be smoothened after channelization taking place. These changes were contributed by the removal of obstructions along the river channel by human effort. As a result, the river flow would become faster and the capacity of the river would increase.

There are different advantages for rivers to be channelized, firstly, it will provide more navigable waterways for ships. The stream will be more suitable for navigation and large ships which previously cannot pass through the channel can now pass through the river.

Secondly, channelization can also control flood. This promotes efficient irrigation and drainage of farmland along the river channel. The decrease in the danger of flood made the lands along the river more appropriate for agricultural purpose.

Thirdly, channelization can also reduce natural erosion at the concave banks of the river. There are often rapid erosions at the concave banks of meandering rivers, after the curves are removed, the water can flow straightly and erosion can be reduced.

However, there are also negative effects triggered after channelization. Despite the decrease in erosion at the concave banks, the general erosion rate at the bank might increase because the river has more energy. As a result, rate of mass wasting of slopes will increase and more sediment will enter the river channel.

Also, velocity increases after channelization, therefore, there will not be enough shelter for breeding. This creates negative effect on the habitat of the fish in the river and affects the eco-system.

In addition, the increase in sediments is river channel will cause flooding in the lower course of the river. These loads will be deposited in the lower course of the river because the velocity of the channel drops. Then, the lower course might be prone to flooding due to channelization.

Water table might be lowered in neighbouring areas as a result of channelization. The channel will draw groundwater beneath the adjacent floodplain, groundwater storage will then decrease. As ground water storage decreases, the soil becomes more compacted, reducing capacity of soil to store water.

Lastly, channelization may worsen the water quality of the river. After channelization, higher turbidity was promoted and this usually has negative impacts on the channelized section of the river.

There are different ways to reduce negative impacts of channelization, one way is to carry out afforestation. By planting more trees, more tree roots are available to hold the soil and help reduce soil erosion at the river bank. With a decreased silting rate, the sand content in the river will decrease the danger of flooding in the lower course could be reduced.

Constructing dams can also minimize negative effects of channelization. A pool would be formed and this will allow river water time to return as ground water storage in neighbouring areas so that water table can rise and the soil would become less compacted.

By placing boulder back to the river channel can reduce negative effects of channelization. These boulders can provide fish with shelter, they can seek breeding ground and resume to their habitat and the ecosystem could be maintained.

Creation of an artificial bank could also reduce the harmful effects channelization. With the artificial bank, the problem of silting would be improved. One example could be the Shing Mun River, where a section of 250m embankment was planned to reduce the problem of silting.

In conclusion, channelization as a modification by human effort can help bring positive effects to the channel in theory. But it can only help river channels improve relationship only if certain measures were carried out in order to reduce the negative effects brought along.

This student written piece of work is one of many that can be found in our AS and A Level Hydrology & Fluvial Geomorphology section.

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