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Water Resource
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Remote Sensing Monitoring on flood damanages and its evaluation system
Various regional types of flood risks and prevention countermeasures can be divided according to their different environment backgrounds such as climate, hydrology and river pattern in China. Therefore, the counter measures of flood control and disaster relief should be in line with the local conditions.
- Bursting type. This kind rivers flow through the plain areas with dense population and highly developed industry and agriculture. The dikes are highly built mainly for river bursting control. The riverbeds are gradually silted up, migration frequently, and so many dangerous sections are formed. Their are bursting fans and pools all over scattered outside dikes. The river formerly wildly ran on the alluival fans are artificially restrained and its antagonistic contradiction produced. With the raising of the dikes, the hidden danger becomes bigger. The flood preventing counter measures are focused on flood peak adjusting and controlling in the upper reaches to reduce the mud and sand deposition and simulate bursting plan so as in lessen the losses of disasters. For the lower reaches, the counter measures such as flood diversion, storage, cut off and river course changing are implemented so as to prevent dangerous sections from bursting. In 1988, we completed flood real time monitoring and digital terrain model base of the Yellow River between Zhenzhou and Jinan city; and all-weather monitoring and multielement geographical database of the Yangtze River between Yichang and Wuhan. Compared with the experimental monitoring system of the Yongding River between Beijing and Tianjing in 1986 and the Liaohe River between Shengyang and Yinggou, much more experiences have been obtained.
- Overflowing type. The river courses are divorced into distributaries in the delta areas of estuary because of the tide effect. Natural dikes are highly developed. The elevation of precipice is low. The conditions of marshiness and salinization are serious. Shipping and harbor construction are affected due to unstable lower reaches. The flood preventing counter measures are mainly to make estuary stable: to control mud and sand deposit; to extend land areas; to make irrigation system perfect 'to reduce water logging ime' to wash salt and alkali' to improve soil quality; and to irrigate under ground water back etc. The most typical type is the new delta of the Yellow River. Since 1986, we have built up micro terrain database and studied the problem of ice-flood. Although the estuary of the Yangtze River and the Pearl River have experienced reconstruction in recent thousand years, these characteristics are still remnant.
- Water logging type. The Lakes where rivers converge play a role in toring flood and adjusting flood peak naturally. However, because of eclaiming fields from the lakes and mud and sand depositing, the flood torage capacities are gradually lessened and flood diversion courses staffer o that the flood adjusting capability is reduced the dikes are increased. And raised and the inside terrain becomes relatively lower and lower then the outside riverbed. Since the water discharge is not affluent in ordinary lines and underground water level raised, various close wetland management and ecosystem have been formed. Therefore, they can be taken as independent original units when flood prevention and disaster relief are considered.. The gting Lake area is just made up of 39 dike arounded areas of this kind. there are the industrial and agricultural bases which need to be protected from good damages and also some transient flood diversion areas which would be given up so long as catastrophic flood coming. With the development of econimics, the industrial and agricultural bases which need to be protected live established digital terrain model for dikes and river courses to research on the all-weather monitoring plan. The Poyang Lake and the Hongze Lke have almost the same problems.
- Reservoir type. Reservoir is a kind of artificial lake. It is requirement to given rpedictive evaluation for reservoir flood damage. The key problems are to select dam site and to decide stair-reservoir scheme since sometimes irrigation and damage compensation could reach 40-60 percent of total investment. Meanwhile. It is requested to analyze the benefits of flood control and the requires for irrigation energy in the lower reaches of the dam. For demonstrating the Three Gorge Project of the Yangtze River, be have used SPOT, TM and aerial remote sensing images to provide landuse surveying maps ( 1:10,000) and data for the dams at different heights of 150, 175 and 180 meters. We have modified the flood damage evaluation for the Longtan Reservoir in the upper reaches of the Pearl River by using color infrared images. Finally, we have compared 21-stair development project along the Heilongjiang Amur River by using the images taken from Chinese satellite.
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