| Throughout history, people have foolishy tried to 'control' rivers. These efforts have met various levels of success, but almost always were plagued with more problems than beneifits. One of the most recent examples is that of 'channelizing' rivers and other waterways. When a river is channelized, it is dredged and straightened , removing the curves and bypassing much of the floodplain. Sometimes, the waterway is even encased in concrete to speed the passage of water. These measures are taken to free up the floodplain for development of various types, and presumably to decrease flooding. However, the beneifits almost never eclipse the abundant disadvantages. Here are a few reasons why channelizing a river is a bad idea:
Channelized rivers do not flood less
Channelizing a river supposedly causes the water to leave the system faster, decreasing flooding. However, this is rarely the case. When a river which is usually a mile wide during heavy rains is constricted into a few hundred feet, it becomes a raging torrent. (in many cases, these torrents become death traps - any person falling into the river will not be able to pull themselves free of its grasp, as these rivers are generally free of any bankside vegetation) True, the water is moving faster than in a natural river, but it has less of an area to spread out over. During major flood events, these channelized rivers still overflow. The Los Angeles River, for example, a river totally encased in concrete, is expected to flood most of San Pedro when a major '100 year' flood event next occurs. Many people are calling for raising the levees around this river. However, people do not realize that no matter how high the levees, if the river is higher than the level of the land outside them flooding will still occur. Water actually moves backwards through storm drains and sewer lines and bubbles into the streets. I saw it happen firsthand during one of the El Nino events of the 1990s. The drains actually start regurgitating water and flooding the streets... a situation no number of sandbags can remedy.
Floodplains are natural flood control systems
A river with a healthy floodplain almost never sees floods outside its boundaries. The flood plain, true to its name, floods most years. However, this does no harm if it is expected. The extensive wetlands in the floodplain dampen the effects of the flood. In fact, floods are actually beneificial in these areas. The ancient Egyptians farmed the floodplains of the Nile every year during the dry season, and left the area during the floods. The result was a thick layer of fertile silt deposited on their fields every year. The Aswan Dam was built in the 20th century to curtail natural floods. Now, the farmers can farm all year. But the fields are infertile and unproductive and the poor farmers are forced to buy massive amounts of expensive fertilizer every year.
Floodplains have many beneifits
As the Egyptians can tell you, floodplains are extremely fertile land, if allowed to continue their natural flood cycle. Althoug they make excellent farmland, floodplains are even more productive when left to themselves. In addition to dampening floods and providing fertile soil, floodplains provide excellent wildlife habitat. Although this is implicitly a good thing, it also offers many beneifits for humans. For example, salmon are much more abundant in rivers with lush floodplains. Salmon are a very tasty fish, and often the vast abundance of salmon in a river with a floodplain makes up for the economical losses of not farming the land. Other fish also abound in these areas. In addition, recreational uses for the land such as boating, hiking, hunting, camping, etc, are much more fulfilling in a non-channelized river.
Floodplains, as noted earlier, dampen floods. They also lessen the effects of droughts by creating a vast network of natural water storage in wetlands and groundwater areas. These areas even filter most pollutants out of the water, making the river more useful to anything living nearby.
Once a river is channelized, it is very difficult to repair
The Army Corps of Engineers discovered this fact when they straightened the Kissimee River of Florida. After experiencing the many problems associated with a channelized river, it was decided that the river should be returned to its natural state. This process took millions of dollars and even after its completion, it will take hundreds or even thousands of years for the river to return to its pre-channelized state. It is a worthy task to restore rivers channelized by those less aware of the consequences than us. However, it is better never to have to
In conclusion, channelization of rivers may have some beneifits. However, they are vastly outweighed by its disadvantages, and before even considering doing so, this must be taken into account. If channelization is absolutely necessary, measures to mitigate its damage should be enacted. |
