subject: The Yangtze River [print this page] The Yangtze River The Yangtze River
The Yangtze River or Chang Jiang is the longest river in Asia, the third river in the World. It is about 6,300 kilometers (3,915 miles) long and flows from its source in Qinghai Province, eastwards into the East China Sea at Shanghai (Fig 1.) (Wikipedia, 2010). It has the highest source of any of the world's major rivers at over 5,000 m (Owen, 2002) above sea level, on the border of Qinghai Province and Nagqu Prefecture, Tibet. One of the dams on the river, the Three Gorges Dam, is the largest hydro-electric power station in the world.
According to the hydrological, geomorphologic characteristics of the main stream is divided into three sections, as named Upper, Middle and lower reaches. There are also two hydrometric Stations in the Yichang and Datong which considered as the separated points for the three basins.
The Upper Reaches flows from source to the Yichang City of Hubei Province, its distance is 4529 kilometers long, up to 3/4 of the whole length of Yangtze River, the drainage area of this region is 1,006,000 square kilometers, accounting to 55.6% of watershed area (Fig2.) (Owen, 2002). The upper reach goes through mountainous areas with a steep slope of riverbed and, thus, the upper river basin suffers from less flood disaster, whereas the middle and lower reaches flow through plain areas and the riverbed slope is extremely gentle, which makes the middle and lower basin one of the regions suffering the most from flooding in China (Wang, 2004).
The Middle Reaches begin on the East Sichuan Plateau (fig2) and flow steadily downs to the plains of Hubei, the total length is about 2,000 km (1,200 miles) long(Owen, 2002). The middle basin is characterized by its extensive floodplain that are flanked by lower terraces and hills, which changes into a geological depression where the river bed gradient of the Yangtze is reduced to 0.04m/km, where is between Shashi and Yueyang, about 2 m higher than that the ground altitude of its floodplains ((Zong et al, 2000).). At this point, the Yangtze meets the Dongting Lake that collects discharge of four tributaries from the south, then at Wuhan, meets the River Han, which is a large tributary from the north, towards into a narrow valley, afterwards, the Yangtze runs into another floodplain and receives discharge from five tributaries at Poyang Lake (Zong et al, 2000).
The Lower Reaches begins from Hubei Province and end at Jiangsu Province. There are many lakes and connecting waterways in this low-lying region, as s known as "a land of fish and rice" by the Chinese, which is one of China's most fertile, most populous and most affluent region (China Highlights, 2010). Moreover, the middle and lower basin, especially the most downstream Yangtze River Delta with Shanghai as its economic center (Fig 2), is one of the most developed areas in China and has been playing an important role in the national social and economic development. Thus, the emphasis of the flood control in the Yangtze River has been on the middle and lower reaches (Wang, 2004).
1.2 The History of Floods in Yangtze River Basin
According to the historical record, 1092 big flood disaster events occurred since 206 B.C. in China in the period of 2155 years, averaging once in every two years (fig3)(Technical Support Unit, 2004)
Particularly, an exceptionally big flood occurred in the middle and lower reach of the Yangtze River in 1931. All the cities and towns along the river were inundated, over 3 million ha of farmland were flooded, and about 28.5 million people were hit by the flood, of which 145 thousand people died.
Until August 1949, another big flood occurred over the Yangtze River Basin. When the water level in the main stream of the Yangtze reached the highest record, the Jingjiang Flood Diversion Works and Dongting Lake were to divert and store flood water. Finally, the city of Wuhan was protected, but there were 3.1 million ha farmland flooded.
The average annual flood was significant affected on regional agriculture lands during 1950-1990, which was about 7.8 million ha, accounting for about 7.8% of the China's total farmland (Wang, 2004).
As known as the1998 flood is the most noticeable flood, the heavy rainfall covered a vast area with long duration which resulted in big floods in some major rivers as Yangtze, Songhua, pearl and Min River.
After 1949 considerable number of big floods occurred in large rivers such as the Yangtze, Yellow, Huaihe, and Haihe Rivers, yet the losses were far less compared with those before 1949 because of the role of the available flood control projects and efforts made in flood preparedness.
1.3. Objectives of the study
This study aims at looking at the most essential factors that cause floods in the Yangtze River basin in Southern China. The broad objective of the study is; finding out the most significant factors that lead to flooding in the Yangtze River Basin.
The specific objectives of the study are:
Analyzing whether the floods are mainly caused by natural, human factors or both of natural and human factors.
Evaluating the current flood control system, management and related policies
Currently, erosion, deforestation, urbanization, channelization, flow regulation, water transfers, irrigation, sanitization, domestic and industrial pollution, and many other human activities have altered rivers in ways that we do not fully understand. The purpose of this study is to analyze and assess the factors which cause recent more frequent floods in Yangtze River basin. In order to address the problem, there are three aims need to be concerned:
2. Methodology
This research study is mainly based on review of the previous literature studies with relevant secondary data analysis, in order to predict and meet the aims of this study.
In order to assess the causes of the flood, this essay mainly uses literature review method to identify and predict the most significant factors that causes of floods in Yangtze River basin;
As the main purpose of this research study is to focus on the previous flood events, analysis and make comparison, in order to answer and meet the aims and hypothesis of this study. In order to assess the factors/causes of the flood, which are evidently complex in nature, in this case, this essay adapts an overarching approach on the main factors with evaluation of current flood control, management and related policies (Zong et al, 2000).
According to the many studies of floods in Yangtze River basin, I found that most of studies were concerned and discussed the following eight factors as the main causes of floods in Yangtze River basin, which are: changes of climate extremes, precipitation trend, runoff trend, sediment discharge, deforestation, urbanization, human activities, and the factors (such as: Land-use and land cover, policy, regional forecasting system, economic development). This study mainly depends on the previous studies and makes comparison between each factor, in order to predict the most significant factors associated with floods in Yangtze River Basin.
In the section of Literature Review, simply use the internet search engineer, such as: Google, to widely search the relevant studies of Yangtze's floods, total found about 50 reports. However, there are only 36 out of 50 reports have been used into this study and also particularly focus on the case of flood in 1998 and 1 respectively. The rest of 10 reports are irrelevant to the study.
3. Literature Review (in Table display)
According to the existing literature about the causes of flooding in the Yangtze River basin, the following are the main factors that led to the previous flood.
3.1 Changes of Climate Extremes
When looking at the Table1(See Appendix1), the report No. 36 there are different presentations which include; (1) different phase relations are found between annual maximum stream-flow of the Yangtze River and El Nino/Southern Oscillation (ENSO) in the lower, the middle and the upper Yangtze River basin. In-phase relations are detected between annual maximum stream-flow of the lower Yangtze River and anti-phase relations are found in the upper Yangtze River. But ambiguous phase relations occur in the middle Yangtze River, showing that the middle Yangtze River basin is a transition zone. Different climatic systems control the upper and the lower Yangtze River. The upper Yangtze River is mainly influenced by the Indian summer monsoon and the lower Yangtze is mainly influenced by the East Asian summer monsoon; (2) as for the individual stations, different phase relations are found in the longer and the shorter periods, respectively. In the longer periods, the annual maximum stream-flow is more influenced by climatic variability, while in the shorter periods; it is influenced by other factors, e.g. human activities. The results of the study provide valuable information for improving the long-term forecasting of the stream flow using its relationship with ENSO and the Indian Monsoon
