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Flooding, one of the most disastrous natural hazards.

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Introduction

Geog Summer Assignment- Essay Question 2 Stella Kwok (7) Flooding is one of the most disastrous natural hazards. Take Huang He Basin in China as example, originally, intense rainfall in summer is one of the main causes of flood. With rapid urbanization and population growth, the built environment and the socio-economic characteristics is getting more important in contributing to flood hazards. To minimize the impact of flooding, take Huang He Basin in China as example, some preventive measures, such as flood control projects, are carried out. Flooding refers to the inundation by water of any land area not normally covered with water owing to a relatively rapid change of the water level. It often happens in the lower course of Huang He Basin. Firstly, physical environment is one of the main factors leading to flooding. Meteorologically, snowmelt in the upper course in spring causes sudden increase in discharge and blocking of ice-floes in river channels. In summer, the rainfall is concentrated in July and August, being highly variable. ...read more.

Middle

Runoff increases as a result of deforestation. This causes rapid concentration of discharge, reaching flood stage and peak discharge. Landslides are common, which dam river channels and block channel flow, causing the river to overflow its banks. Besides, the Huang He has dissected the loess plateau region in the middle course. Therefore it carries heavy sediment load to the lower course and flood plain. Hence there is heavy silting and deposition in the lower course and flood plain in river channels, raising the river channel floor and so water level along river banks during flood, hence building up leeves which may breach under great stress on the surrounding floodplain. Together with the perception of people in the region, who are ignorant of the likelihood of floods and their disastrous consequences and are prepared to take a calculated risk that the protective measures will save them from most floods. Yet the risks of flooding are under-estimated. Harmful effects could be disastrous. ...read more.

Conclusion

Area of arable land is increased because cultivation can be extended into marginal lands. Despite the economic benefits, some ecological problems are always resulted from the projects. To begin with, flood control and silt retention result in loss of annual addition of nutrients to the flood plains, so the nutrient status of soil is lowered. Secondly, sediments trapped behind dams cause silting of reservoirs, the aquatic ecosystems are upset. Thirdly, with increasing productivity, the use of fertilizer is widespread, thus causing stream pollution. Moreover, excess irrigation water raise the ground water table, causing water-logging and salinization of soil, this leads to changes in soil and in habitats. Not only are this, increase of irrigated fields causes increase in evaporation and relative humidity, microclimate is then changed. All in all, flooding can badly affect both the ecology and the economy of a country. Preventive and flood control measures can by no means be neglected. However, it seems that people are still more economic-conscious and at the same time ignoring the effects imposed on the ecological balance through the projects. ...read more.

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