Hydrologie Applications of Remote Sensing in China
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Hydrologie Applications of Space Technology (Proceedings of the Cocoa Beach Workshop, Florida, August 1985). IAHS Publ. no. 160, 1986. Hydrologie applications of remote sensing in China YANG JICHENG Remote Sensing Applications Center, Ministry of Water Resources and Electric Power, Beijing, China Abstract There are a lot of big rivers, lakes, and reservoirs in China. Remote sensing has been widely used for hydrology. Uses include the following: (1) study of sediment deposition and flood regulation capacity in Dong Ting Lake—the second largest freshwater lake in China; (2) study of estuary, intertidal habitat deposition and river courses variation in the Yellow River, Yangtze River, and Pearl River; (3) rapid mapping of flooded areas (monitoring of flood); (4) study of the Three Gorge Reservoir of the Yangtze River; and (5) study of temperature traverse of cooling water at electric power plants. General China is a country with many mountains. Plateaus and mountainous areas cover 59 percent, hilly areas 10 percent, plains 12 percent, and basins 19 percent of the total territory. The whole country has an area of 9-6 million square kilometers. The topography of the country is of high altitude in the western part, low altitude in eastern part. One hundred million hectares of cultivated lands are concentrated in the three main plains of the country—the Northeast Plain, the North China Plain, and the Middle and Lower Yangtze River Plain—and the Pearl River Delta as well as some island plains. China's climate is strongly influenced by monsoon. It is wet in summer and dry in winter. Annual mean precipitation decreases from 1500-2000 mm and more in the southeast region to 200 mm and less in the northwest region. In the deserts of Xingjiang there is often no rainfall during the whole year. The annual mean precipitation of the whole country is about 630 mm, most of which is concentrated in four months only. The precipitation varies from year to year as well. China has a large number of rivers. Among which the Yangtze River, Yellow River, Huai River, Hai River, Pearl River, Liao River, Heilong River, Songhua River, Yaluzangbu River, Lancang River, and Nu River are the longer ones. Moreover, there are some inland rivers in the arid areas in the northwest. These inland rivers originate in the snow covered mountainous areas, so the runoff often disappears and they become seasonal rivers. And there are some rivers flowing out of our national boundary in the southwest, northeast and northwest of the country (Table 1.). In summer and autumn the wet currents from the Pacific Ocean and Indian Ocean bring about abundant rain, while in winter and spring the dry and cold currents from the central part of European-Asian Continent and the Mongolian Plateau bring about less rain. The coastal areas in the eastern and southern parts of China are humid in climate and rich in rainfall, while the northwestern inland areas are dry in climate and with less rainfall, because of interception of the monsoon penetration by mountains. This is the basic climatic difference between the south and the north, the former is rich in water and the latter is poor in water. This difference in climate is a 269 270 Yang Jicheng Table 1.—The main rivers of China River Length Catchment Area Annual Runoff (km) (10^ sq km) (109 eu m) Yangtze 6,300 1808.5 921 Yellow 5,460 752.4 47 Heilong 3,101 886.9 (119) Lancang 2,354 164.8 69 Pearl 2,210 442.6 307 Talimu 2,179 198.0 Yaluzanbu 2,057 240.5 138 Nu 2,013 134.9 64 Songhua 1,956 545.6 76 Liao 1,390 219.0 22 Hai 1,090 264.6 23 Huai 1,000 296.1 39 main factor for the uneven distribution of water resources either in space or in time. The amount of water resources is very unevenly distributed from region to region. If classified according to annual mean precipitation, China can be divided into five different regions, i.e. more rain, humid, semihumid, semiarid, and arid. The distribution of surface runoff in China is basi cally similar to that of precipitation, but with an even higher degree. Table 2.—Regions classified according to precipitation and runoff in China Classified Annual mean Annual mean Classified Serial according to precipitation runoff depth according No. precipitation (m m) (m m) to runoff I more rain >1600 >900 abundant water II humid 800-1600 200-900 more water III semi-humid 400- 800 50-200 intermediate IV semi-arid 200- 400 10- 50 less water V arid < 200 < 10 arid Remote sensing in China 271 LEGEND NO PRECIPITATION RUNOFF HII I II I I MORE RAIN ABUNDANT H II I II 1 HATER f=| II HUMID MORE WATER Y///A IIJ SEMI-HUMID INTERMEDIATE Itllillll IV SEMI-ARID LESS WATER 1 1 V ARID ARID FIG.l Map showing the regional classification of precipi tation and runoff in China. The criteria for these classifications are given in Table 2, and the sketch map of classifications is shown in Figure 1. Remote Sensing Applications Remote sensing has been widely used for water resources, hydropower and electric power studies, such as the analysis of viater resources; mapping of surface water; measurement of water quality and pollution; study of soil moisture and évapotranspiration; measurement of snow cover; rapid mapping of flooded areas; study of engineering geology; study of lake, estuary, intertidal habitat deposition and river course variation; study of tempera ture traverse of cooling water at electric power plants; and study of ground water. Chinese scientists of water resources, hydropower and electric power are fully aware of the urgency of finding solutions for the above problems and of the necessity of employing the newest and most satisfactory techni ques. Recently multispectral imagery, IR color imagery, thermal infrared imagery, and SLAR imagery have been used to analyze some of these problems and have gained some achievements. The hydrologie applications of remote sensing are emphasized in this paper. Study of sediment deposition and flood regulation capacity in Dong Ting Lake.—Using digital image processing system, mosaiced, rectified and ratio enhanced maps have been made of Dong Ting Lake—the second largest fresh water lake in China. Different optical processing images have been made by the optical equipment, 20 different times CCT's were used, and much ground truth data were collected. Investigations are being made on the volume of this lake and the land use, at different seasons. Studies are carried out on the flood regulation capacity. More than 30 software packages have been developed for this subject, which will provide new data for water resources planning and exploitation. The study of sediment deposition show that the sediment of Dong Ting Lake mainly comes from Yangtze River, and another four big rivers flowing into Dong Ting Lake are relatively clean. 272 Yang Jicheng Study of estuary, intertidal habitat deposit and river course variation in the Yellow River, Yangtze River, and Pearl River.—Air photos of the estuaries of the Pearl River and the Yellow River were taken by multispec- tral and color infrared scanning. Supervised classification of these photos was done by the digital image processing system. Using air photos and landsat images, the water depth of seashore at Pearl River was classified. There are six different kinds from 0.5 m to 5.0 m. The classified maps are very useful to select places for reclamation, navigation and cultivation. In the estuary of the Yangtze River and Yellow River, the sediment deposi tion and the sand bar were displayed very distinctly (Plate 4). Rapid mapping of flooded areas and flood hazard (monitoring of flood).—In vestigations have been made on the flooded areas and flood hazard at the San Jiang Plain, Northeastern China, in September 1981 by landsat imagery and on Hefei Region in Anhui Province in 1984 by Polar Orbit Meteorology Satellite HOAA-7 imagery. Data are processed by photoprocess and digital image processing methods with ground data to divide the extent of inundation and flood hazard. The methods that were used are false color image, density slicing, information extraction and classification (Plates 5 and 6). Study of the Three Gorge Reservoir of the Yangtze River.—For the biggest dam for hydropower in China, the inundation of the reservoir was investi gated by different schemes. Color infrared airphotos were obtained at 1:30,000 scale and enlarged to 1:10,000, 1:5,000, and 1:3,000. The back water curves were calculated and located to color infrared airphoto. Study of temperature traverse of cooling water at electric power plants. The Dou He, Da Gang, Wang Ting electric power plants have gained some achievements by thermal infrared image which have been processed by density slicing method (Plate 7). .