River Management

Re-alignment

Re-alignment is one of the channelisation where the natural river channel is changed into another specific path to reduce flood. It refers to the straightening of the river channel. It removes the meander and reduces the length of the river channel.

Realignment is able to control the flood occurrence as it increases the speed of the river flow, allowing the water to flow away from the area more quickly and smoothly. Hence, it is able to minimize the localised flooding. Besides, it washes away the sediments that accumulate at the river bed which may shallow the river. It helps to deepen the river channel, allowing more water to be hold, hence reducing the chances of the occurrence of flood. For example, the Mississippi River, USA has been reduced its length by 240km after re-alignment to reduce the occurrence of flood.

However, the sudden increased of the speed of river flow causing the river downstream to overflow and flood eventually because it cannot hold the sudden increased of volume of river water. In addition, the increased speed of the river flow has more energy to wash away more sediment which will prevent sunlight from reaching the river bed in order to affect the marine lives. By straightening the river channel, the area of the wetlands may disappeared and result finally in loss of habitat of marine life. For instance, the government of USA discourages it by implementing a “no nett loss in wetland” policy.

As a conclusion, re-alignment is only effective to a certain extent because effectiveness weights almost equally as the ineffectiveness.

Re-sectioning

Re-sectioning is one of the methods of channelisation of river which means changing the natural river channel to another specific path to reduce the occurrence of flood. It refers to the widening and deepening of the river channel in order to hold more water.

Re-sectioning helps to increase the ability of river to hold water, thus decreasing the occurrence of flood. It also increases the amount of surface-runoff from the surrounding area entering the river at one time without causing a flood. Besides, the river channel will be smoothened by replacing the sands and stones in the river bed using the cements and granites. The speed of river flow can be increased as the river channel becomes smoother and less friction happens. For example, the Singapore River is being re-sectioning to reduce the chances of flood.

On the other hand, re-sectioning will prevent the sunlight from reaching the river bed as the river channel is being deepened. This will affect the marine lives especially the aquatic plants which required sunlight to produce food. Without sunlight, they may eventually die and others aquatic animals may be affected because of losing their natural habitat and food source. Thus, the aquatic food chains will be influenced as a result. // * Conclusion…. © Pin 2010

Bank protection

Bank protection is one of the methods of channelisation of river which means changing the natural river channel to another specific path to reduce the occurrence of flood. The purpose of bank protection is to prevent the flood from occurring and reduce the soil erosion along the river bed. Generally, there are two main types of bank protection which are the build of artificial levees or dykes and the build of gabions and revetments. They are all built along the rivers which often overflow by walls of sand, stones or concrete.

By building bank protection likes artificial levees and dykes, less sediments will be washed away and hence the capacity of the river to hold water is increased and thereby the chances of flooding will be reduced. For example, the dykes are built in the lower course of the Yellow River, China to reduce the occurrence of flooding. Besides, the Singapore government also uses the bank protection method in East Coast Park, Singapore to reduce chances of flooding.

However, the built of the dykes have not been very successful because the continual build-up of the sediments on the river bed causes the channel to be shallower. This has caused the water level to rise above the dyke walls over years and river may overflow eventually. This causes the dykes to have regular maintenance. // conclusion…..

Planting vegetation

Planting vegetation is one of the methods of channelisation of river which means changing the natural river channel to another specific path to reduce the occurrence of flood. Vegetations are planted along the river to help to hold the soil together firmly and prevent erosion.

By planting vegetation, the amount of sediment being eroded is reduced and thus the channel will not become shallower. Hence, the occurrence of flooding is reduced. Furthermore, the vegetation also slows down the rate of the surface runoff. This helps to prevent large amount of surface runoff from flowing into the river at one time and eventually overflow the river. Hence, the ability of the river channel to hold water is increased and less flood will occurred. To stabilise the embankment of the Mekong River, some countries including Laos, Cambodia, Thailand and Vietnam have launched a joint initiative to protect the mangroves situated along the river.

Meanwhile, the weight of the vegetation, especially the trees could add on to the bank stresses and cause the collapse of the banks. Moreover, excess vegetation can blocked the sunlight and prevent it from reaching the river bed. This will affect the marine life such as the aquatic plant will die and the aquatic chains will be affected. Hence, a destroy can happen to the ecosystem in our natural environment.

Planting vegetation is effective to a large extent because the effectiveness overweighs the ineffectiveness.

Dam construction

Dam construction is one of the methods to reduce the occurrence of flood. Dams are often built along the course of a river in order to control the amount of discharge. The walls of dams have gates which can hold back or release the river water from a man-made reservoir behind it.

By building a dam, the amount of the water that flows downstream in the river is controlled. This also allowed the river upstream to hold more water. Hence, it is able to reduce the occurrence of flood downstream. For instance, the largest dam in 2006, The Three Gorges Dam is built to tame the Yangtze River. It is effective that it helps to reduce the occurrence of flooding of the floodplains along the Yangtze River. Besides, it also reduces the amount of damage that suffered by the people living along the river especially in the Hunan province.

However, the dam construction can destroy the natural environment on the upstream of the river. The animals and plants may lose their natural habitats and hence the marine life will be affected. The ecosystem will be influenced as the aquatic chains are affected.

* Conclusion….