According to Notice of the State Council on Carrying out the First National Water Survey (No. Guofa [2010] 4), the First National Water Survey was conducted on a national scale during 2010-2012 with the basic survey of rivers and lakes as one of the major tasks.
The goals of the basic survey of rivers and lakes were (1) to comprehensively check out such basic situation as the number and distribution of rivers and lakes above certain scale in China; (2) to work out a list of rivers and lakes above designated criteria; and (3) to establish a basic database of national rivers and lakes to provide important and fundamental national information for water conservancy work and national economic and social development.
The specific survey tasks included (1) the basic features of rivers with a catchment area of or above 50km2, i.e., river name, location, length, number and catchment area, among which the natural and hydrological features of a watershed system should be further identified for a watershed area of or above 100km2; and (2) the basic features of lakes with a perennial water surface area of or above 1km2, i.e., lake name, location, number and perennial water surface area, among which the water depth and volume should be further identified for a perennial water surface area of or above 10km2.
1.Key Techniques of Basic Survey of Rivers and Lakes
With the help of lots of existing findings, such as field measured data, recent remote sensing image data of 2m resolution, basic national geographic information data with a scale of 1:50,000, the basic survey covered all the rivers and lakes within the scope of census, supported by 3S techniques of GIS, RS and GPS/GNSS, and adopting the work pattern of combination of comprehensive indoor analysis and field inspection review and top-down and bottom-up workflows
Key techniques included:
1.1 An innovative proposal of a systematic method for the definition and classification of rivers and lakes census objects;
1.2 The first proposal of an objective, practical, non-repeated and non-omission river statistical method;
1.3 The construction of a technical system by integrating DEM and DLG with digital watershed boundary and digital water system production of remote sensing images;
1.4 The proposal of a watershed river division method combining regional division with mainstream and its tributaries division;
1.5 The proposal of a scientific and extendible river system coding method.
2. Major Achievements of Basic Survey of Rivers and Lakes
It was the first time that the basic situation of rivers and lakes above certain criteria was surveyed in China. A most complete basic database of rivers and lakes has been constructed till now.
There are 45,203 rivers in China with a catchment area of or above 50km2, among which 40,503 rivers are mountain ones, accounting for 89.6% of the total surveyed rivers, and 4,700 rivers are plain ones, accounting for 10.4% of the total surveyed rivers. There are 35,958 outflow rivers in China, accounting for 79.5% of the total surveyed rivers, with a total watershed area of about 2/3 of the total territory, while there are 9,245 inland rivers, accounting for 20.5% of the total surveyed rivers, with a total watershed area of about 1/3 of the total territory. There are 22,909, 2,221 and 228 rivers with a catchment area of or above 100km2, 1,000km2 and 10,000km2, respectively.
The total length of rivers with a catchment area of or above 50km2 is 1.5085 million km, and the average river-net density is 0.16km/km2. Among rivers with a catchment area of or above 50km2, the percentage of rivers with a catchment area less than 100km2 is 49.32%, that of rivers with a catchment area less than 200 km2 76.39%, and that of rivers with a catchment area less than 500 km2 90.36%. Among rivers with a catchment area of or above 100km2, rivers with an average gradient less than 1‰, 5‰, 10‰, 20‰ and 30‰ account for 7%, 33%, 57%, 79% and 88%, respectively.
There are 2,856 lakes in total with a perennial water surface area of or above 1km2 in China, and the total lake water surface area is 78,000 km2 (excluding the surface water area of 3,900 km2 of cross-border lakes in foreign countries). Among the lakes with a perennial water surface area of or above 1km2, there are 696, 129, 24 and 10 lakes of or above the respective perennial water surface area of 10km², 100km², 500km² and 1,000km².
3. Application of Survey Results
The survey results including basic data of rivers and lakes were successfully applied in the compilation of Encyclopedia of Rivers and Lakes in China after they were released.
The survey results were applied in the book Major Rivers and Lakes of the 3rd Edition of Encyclopedia of China. According to the survey results, the clauses of rivers with a catchment area of or above 10,000km2 were worked out.
The survey results were applied in the compilation of industrial standards of rivers and lakes. According to the survey results, the lake codes and table structure of river and lake database were compiled.
The key techniques of river and lake survey have been widely applied in the important work of hydrological forecasting of middle and small rivers, and will also be applied in the river shoreline regulation of River Chief System, analysis and evaluation of inflow and storage water of all the catchments in China.
