In fact, the worst recorded flood in the U. S. history is caused by the breaking of dam in Little Conemaugh River, Johnstown, Panama. The May 31, 1889 tragedy killed about 3,000 people, with the 40-feet high wall of water. The flood in Georgia which killed 39 people was also caused by the breaking of dam on November 06, 1977 (Gore, 1995). Flood Walls/Levees the latest controversy relative to the efficiency of floodwalls and levees on flood mitigation is the case of New Orleans struck by the hurricane Katrina in 1997, where such infrastructures generally failed to serve its purpose.
John Hopkins Magazine reported that 75% of the metropolitan area was inundated y floodwaters, a catastrophe blamed at engineering failure (Keiger, Dale, John Hopkins Magazine, April 2006). Engineers however defended that the levee was designed for category 3 storms (Katrina was category 4 storm). When investigation was done, experts found that the levee was made from organic, peaty soil and clay topped by a floodwall and what was wrong in the design was found to be on the sheet pile. What the investigation concluded was that it was an engineering failure (Keiger, Dale, April 2006).
On the other hand, levees in some cases have been beneficial to flood control as in the case of Rock Island in Illinois which have built its levees as early as 1971, saving them from the damages of flood in July 1993 (Time Magazine, July 26, 1993). The 7000-mile levees built along the Mississippi River the US Corps of Engineers. Hannibal Missouri has also completed a floodwall project which was proven to have been effective in protecting them from the damages flood. In comparison, Davenport was severely damaged by the same flood because of the absence of levees.
The levee along Mississippi however also brought damages to the Mississippi Delta and the Gulf of Mexico because of the alluvial soil being carried by the water. Levee works to divert water flow to certain area which in turn makes it beneficial to areas where the water has been diverted from but damages the areas to where the water is being diverted to. (American Society of Civil Engineering Education Annual Conference, June 20, 2006). Dams- In the United States alone, there are about 2 million small dams and 75 thousand large dams (Allen, David 2000).
Although flood mitigation is just one of the many purposes of dams (hydropower dams, for water reservoir, navigation dams), they have harmful effects to the environment including the damages to marine life and temperature (climate). Dams alter the flow and sediment load of rivers downstream, and thereby may induce changes in channel form in alluvial rivers (Kondolf, G. M. 1997). Dams trap sand and gravel in reservoirs which prevent the normal flow of sediment downstream. Streams have their normal sediment loads which dams consequently reduce by trapping such sediment essential to the marine habitat (Wilcock, P. R. et. al. 1996).
Channels- The Sycamore/Mud Creek Flood Diversion project was designed to mitigate flood in the city of Chico in California which had in 33 years had well-served its purpose. The trapezoidal channel however harmed the other creeks by altering the movement of bed-load materials. The Lindo Channel for example has been deprived of gravel because of the reduction of high flow (Maslin, Paul 1999). The local governments also adopted a zoning program which regulates the construction of any public of commercial structures in floodplains.
This way, the drainage system for the flood water becomes more efficient as no structures or occupants in the area that can possibly interfere to the process. Policies that prohibit the reconstruction of residential structures that have been previously damaged by flood including the emergence of flood insurance are also in the list of flood mitigation efforts. The increase in the area of impervious cover is the main reason why urbanization has caused the significant disturbance in the water cycle and thus its contribution to water pollution.
Through the clearing of the forests and the wide areas of ground cover, urbanization has caused the significant reduction of infiltration, the increase in runoff and the decrease in the volume of water that is being processed during evapotranspiration. As a major indicator of urbanization, population explosion has demanded the conversion of agricultural or agrarian land areas into industrial areas. Such conversion is undergone to give way to the massive construction of residential areas, commercial establishments and industrial sites. In such a way, urbanization is pushing the capacity of the land to the limits.
The construction of structures in order to mitigate flood has never been fully successful as some of these structures have actually caused thousands of lives to perish due to the worsening of floods. The government and other non-government organizations with the help of the experts in the field have joined hands to fight the problem of flood control and the improvement of water management practices. Engineers and researchers have spent several years and are continuing in the efforts to minimize the effect of the alteration of the hydrogen cycle.
Case studies on the different major rivers and lakes such as the Ontario Lake, the Chesapeake Bay and the bodies of water in different highly urbanized cities have been done and some are still ongoing in order to fully understand how things are going and how the elements involved in the cycle have been improving or worsening since water management measures have been implemented. Floods and the pollution of the water ecosystem are just the most evident results of human intervention in the water cycle. They are evident because these are physical changes that caught the human attention and have called for immediate action.
Whether intentional or not, human beings have caused much of the damage in the cycle and as rational beings, we are held highly responsible for this. What has been done can no more be undone as industrialized areas can no more be turned back to its original state. We can no more bring down urban structures in order to plant trees so we can possibly bring back what has been already degraded and grazed. What we can do is to make the individual efforts to practice the best water management measures suggested and implemented by the experts.
The government and groups of scientists and engineers are currently making more studies and researches including experiments on water management. In addition to that, policies have already been implemented in order to minimize the negative impact of urbanization not just in the water cycle but also the other ecological cycles that are somehow interconnected and vital in the human existence. Saving the quality and quantity of water are means of saving our lives and the future the younger generation.
Making the effort to help save the earth in our own little ways will make a big difference in the current situation of the life in the human planet.
Allen, David (2000). Dams and Rivers: Human and Ecological Consequences. Retrieved on September 22, 2007 from http://www. earthscape. org/t1/ald01/ American Society of Civil Engineers (1996). Effects of Watershed Development and Management on Aquatic Ecosystems. New York City. NY. American Society of Engineering Education Annual Conference. Getting an Ethics Charge out of Current Events: Some Doubts about Katrina. June 20, 2006. Pages 1-7