Dam construction is multi-purpose and not a solely channel management strategy. It is effective in controlling flood. The three gorges dam across Yangtze River was built in 1998 to manage Yangtze river flood. The 1998 Yangtze River floods was a major flood that lasted from middle of June to the beginning of September 1998. In 2007, Three gorges dam release little amounts of water into Yangtze and trapped excessive rains. Yangtze did not flood. Another advantage of the project is to generate power to keep pace with China’s economic growth.
It is estimated that China’s power output must rise by 8 percent annually to keep pace with 6 percent annual increase in gross national product. On the other hand, this river management strategy have its own limitations. Firstly,Chinese officials estimate that the reservoir will partially or completely inundate 2 cities, 11 counties, 140 towns, 326 townships, and 1351 villages. About 23800 hectares, more than 1. 1 million people will have to be resettled. Secondly, It will threaten the river’s wildlife.
The dam will alter the natural environment, and therefore, an almost infinite number of species will be affected by the project. Thirdly, The dam will disrupt heavy silt flows in the river. It could cause rapid silt build-up in the reservoir, creating an imbalance upstream, and depriving agricultural land and fish downstream of essential nutrients. Despite high cost, technological expertise required, I feel that dam construction is an effective river management strategy.
However, to ensure effectiveness, ecological rehabilitation like afforestation in mountainous areas and upstream arable land has to be practices to reduce surface run-off from yantze. The Mississippi River is the largest river system in North America. Since flooding occurred in this river, correct river management strategy must be used. The most significant floods on the Mississippi River result from regional rainfall and snowmelt. For over two centuries, structural measures dominated the US response to flooding.
Louisiana in the early 1700’s until the early 20th century, the principal and frequently only approach to flood damage reduction was the construction of levees. In the early 20th century, levees were augmented by channel work to speed floodwaters to their ultimate destinations The 1936 flood in prompted the federal government to assume responsibility for flood control throughout the nation with a clear structural focus – construction of levees, floodwalls, channel work, floodways and flood storage in reservoirs. On the other hand, there is another method to deal with the meandering river- realignment.
Re-alignment is the straightening and shortening of the river channel. It shortens the river channel by removing meanders along a winding river course and hence reduces length of the river channel. The shortened and deepened river carries away the sediments faster and allows faster flow of the river, therefore, minimising flooding risk. The Mississippi river has been shortened by 240km after re-alignment by cutting off the meander through its neck. This effectiveness of the flood management strategy of Mississippi River is effective .
Flood management measures in themselves have over the years prevented significant flood damages. For instance, In the 1993 Mississippi River flood, the presence of federal projects prevented over $18 billion in damages in the upper Mississippi and Missouri basins. On the other hand, measures to realign the river not for long term purposes. Realignment is a short term measure as rivers will develop meanders over time. These will become pronounced, making the flowing slower and the areas around the river vulnerable to flooding.
Realignment is only effective in one area as flooding problem may persist downstream especially since smoother channel and faster flow may increase sedimentation downstream. This makes the downstream section of the river shallower, reducing its capacity to hold water, causing the river to overflow its banks and hence flooding. Realignment is an expensive method which requires resources. For Mississippi’s case, it lies in a developed country, the USA, where realignment can be afforded. However, it would be difficult for third-world countries to afford.