River network of Lianshui County, Huai'an City, Jiangsu Province

river network

This data is reviewed by the project of data compilation and application of Science Encyclopedia of science popularization in China.

The river system is composed of densely distributed crisscross rivers.

River network classification

River network classification factors

1) Network characteristics. Network is a complex linear structure pattern composed of nodes and edges. In a certain area, each path is closed to each other to form a closed loop, which is called "loop" network. The network in river network refers to the loop composed of two river sections starting from a certain node, searching according to their flow direction and converging again. Network is a typical feature of network river which is different from other forms of river network. (2) angle analysis. Angle refers to the angle between intersecting rivers, which reflects the intersection characteristics of rivers at all levels. Different types of river network have different statistical characteristics of river intersection angle. For example, most of the tree river network is acute angle, while there is obvious approximate right angle intersection in the square river network. 3) flow direction analysis. The flow direction reflects the geological structure of the area where the river flows. In the regional river network, the mainstream flow direction is dominant, which represents the overall trend of the river network and affects the development of other river flows. According to the analysis of the river flow direction in the river network, the river network types can be distinguished, such as the parallel river network has similar mainstream flow direction, and the primary tributary flow direction is relatively consistent. 4) tortuosity coefficient. The tortuosity coefficient reflects the degree of curvature of linear elements and is the statistical feature of their distribution. The meandering coefficient of a river can be simply considered as the ratio of the total length of the river to the straight-line distance from its starting point to its end point. The river here refers to the river with relatively independent semantics after hierarchical classification. Generally speaking, the tortuosity coefficient of a river refers to its total tortuosity coefficient, that is, the ratio of the length of the river to the length of its closed straight line. 5) length, average length and length frequency statistics. Length is the basic feature of linear elements.

River network classification method

The hierarchical structure method of river network classification is to use different factors to classify. If the classification can not be completely distinguished, another factor is used to distinguish again until all the categories are determined. Firstly, the river network can be classified into network structure and non network structure by using network features; secondly, the non network structure can be classified into acute angle river network and approximate right angle river network by using angle features; thirdly, the acute angle river network and approximate straight angle river network can be classified into radial, square grid and parallel river network by using river flow direction classification; Finally, tree river network and ring river network are classified by tortuosity coefficient. According to the length characteristics and its distribution, the river network type can be preliminarily tested.

stream order

abstract

specifies the numerical order for grid segments representing branches of a linear network.

usage

· if the input River grid data and the input flow direction grid data are obtained from the same surface, the output quality of river network classification will be higher. If the river raster data is obtained from the rasterized River dataset, the output may not be available because the flow direction of each pixel does not correspond to the position of the river pixel. · the grid river network can be created using the results of the flow tool by selecting pixels with high cumulative flow by applying threshold. For example, pixels flowing in more than 100 are used to define a river network. Use the conditional function or set to null function tool to create a river network grid, where the flow values greater than or equal to 100 are merged into one value, and the remaining flow values are put into the background (NoData). The generated river network can be used in river connection and grid river network vectorization. An analytical method for determining the corresponding thresholds for river network delineation is described in tarboton et al. (1991).

grammar

StreamOrder(in_ stream_ raster,in_ flow_ direction_ raster,{order_ method})

Typical river network structure -- Yangtze River Basin

The density of river network in the Yangtze River Basin varies greatly from region to region. Under the influence of uneven distribution of regional precipitation and runoff, the general trend is decreasing from east to west. The river network density of the plain in the middle and lower reaches of the Yangtze River is generally above 0.5 km / K ^, and the hilly area is favorable for the development of water system, and the river network density can exceed 0.7 km / K ^. The river network density in most areas of the upper reaches of the Yangtze River is less than 0.5km/km2. It's flat on the ground. the river network structure of the Yangtze River Basin is a huge dendritic water system. The Yangtze River runs through the hinterland of the Qinghai Tibet Plateau to Haikou, and winds through the three steps of the Chinese mainland, such as the main tree. However, due to the complexity of geological structure, bedrock properties and surface morphology, different river network structures appear in some areas. For example, the river network in the source area of the Yangtze River develops into a fan-shaped turbine under the influence of the Qinghai Tibet Yunnan "evil" shape rotation and torsion structure and the chair like terrain; the Jinsha River and the Yalong river run through the parallel fault area in the west of Sichuan and the north of Yunnan, and the main stream developed along the structural line and the short parallel tributaries formed under the control of topography and structure form a pinnate river network; the Jialing River is located in the middle of Sichuan Basin Under the influence of basin topography, a typical fan-shaped river network is formed; when Minjiang River and Tuojiang River flow through the piedmont alluvial fan in the western edge of Sichuan Basin, a divergent river network is formed from one point to the outside; the tributaries of Wujiang River and Xiangjiang River also form a feather like river network, some of which pass through the karst geomorphic area where the subsurface flow develops, and some of them submerge underground, forming a peculiar Duanwei river or Duanwei river Under the influence of long-term human activities, the rivers of touhe River, Yangtze River Delta and Jianghan Plain interweave and form a network of rivers. different river network structures often have different effects on the hydrological changes of river network, especially in the speed of flood concentration after rainstorm, the emergence momentum and duration of flood peak, etc. For example, at the confluence point of fan-shaped river network, the flood peak converges rapidly and the water potential rises sharply; the tributaries of network river network are evenly dispersed and the water potential changes gently; in the divergent river network, the flow changes from concentrated to dispersed and the water potential changes from turbulent to gentle, resulting in a large amount of sediment deposition; in the network river network area, the terrain is low and flat, the flow communicates with each other and the water potential changes gently, but it is prone to waterlogging in case of concentrated rainstorm. There are many large tributaries in the middle reaches of the Yangtze River, which gather the water from the main tributaries of the upper reaches. The floods meet in the flood season. The Jingjiang River and Wuhan river reach, which are the confluence points, have limited drainage capacity, and the low and flat terrain on both sides of the Yangtze River is very easy to cause floods. Therefore, they become the key areas for flood control of the Yangtze River.