basinThe water network system composed of all rivers, lakes and other water bodies is called water system.Among them, the water that finally flows into the ocean is called outflow water system, such as the Pacific Ocean water system and the Arctic Ocean water system;The water flowing into inland lakes or disappearing into deserts is called internal water system,[1]Such as Tarim River system[2]，Amu Darya、Syr RiverAral Sea water system[3]。Drainage areaCan be determined according toTopographic mapDraw out drainage basinWatershed, and then calculate the area surrounded by the watershed.riversThe drainage area ofControl section, the dam site of the reservoir or the confluence of any tributary.
From the shape, the water system can be divided into the following types.
Dendritic drainage
The trunk and tributaries are dendritic, which is the most common type of water system development. They are generally developed in sedimentary rock or metamorphic rock areas with consistent erosion resistance.asXijiang RiverUpstream admissionLiujiang, YujiangGuijiang RiverAnd other tributaries.
Fan-shaped drainage system
The outline of the drainage basin formed by the combination of trunk and branch rivers is like a fan shaped water system.asHaihe Riverriver system.North Canal、Yongding River、Daqing River、Ziya RiverandSouth CanalFive major tributaries converge atTianjinNearby, then into the sea.This kind of water system converges in a concentrated time, which is easy to cause rainstorm disasters.
Feathery drainage
The tributaries on both sides of the main stream are evenly distributed, which is similar to the feathery water system.Long convergence time, after rainstormfloodThe process is slow.For example, in the southwest longitudinal valley area, the main stream is strong, and the tributaries are short and symmetrically distributed on both sides, which is a typical representative of the feather water system.
river system
parallel river system
A water system in which tributaries flow into the main stream in approximately parallel arrangement.When the rainstorm center moves from upstream to downstream, it is very easy to flood.asHuaihe RiverThe water system above Bengbu.
Lattice drainage
It is developed by the trunk and tributary along two groups of vertically intersecting tectonic lines.asthe minjiang riverriver system.
In addition, there are comb like water systems, that is, the tributaries are concentrated on one side, and the other side has few tributaries.Radial drainageAnd centripetal drainage system, the former is often distributed incraterAround, the latter is often distributed inbasinMedium.usuallyGreat RiverIt is composed of two or more water systems.
Internal and external water systems
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From the final result, the water system can also be divided into internal water system and external water system.
Internal drainage system
Final inflow of waterInland lakesOr disappeared in the desert, it is called internal water system.Such as Tarim River system[2]，Amu Darya、Syr RiverAral Sea water system[3]。
Outflow drainage system
The final flow of water into the ocean is called outflow water system.Such as the Pacific Ocean water system and the Arctic Ocean water system.[1]
characteristic parameter
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The characteristics of the water system can be expressed by various calculation parameters. ①River network density。The ratio of the total length of the water system to the distribution area of the water system represents the length of the river per square kilometer.Its size is related to the climate, lithology, soilvegetationCovering and other natural environments, as well as various measures taken by human beings to transform nature.Under similar natural conditions, the greater the river network density, the greater the river runoff.
② River system development coefficient.The ratio of the total length of tributaries at all levels to the length of the main stream.Primary tributaryThe ratio of the total length to the length of the main stream is called the primary river network development coefficient, and the ratio of the total length of the secondary tributaries to the length of the main stream is called the secondary river network development coefficient, and so on.The greater the development coefficient of the river, the more the length of the tributary exceeds the length of the main stream, and the more favorable the regulation effect on runoff.
③ Uneven coefficient of river system.The ratio of the total length of the left bank branch of the main stream to the total length of the right bank branch indicates the degree of asymmetry of the river system.The larger the nonuniformity coefficient is, the more unbalanced the water quantity flowing into the main stream on both banks is.
④lakeAnd swamp rate.In the water systemLake areaOr the ratio of swamp area to distribution area of water system (drainage area).As lakes or marshes can regulate the flow of river water, the change of river water volume over time tends to be uniform, so as to reduce flood disasters and ensure water use in dry seasons.Therefore, the greater the lake rate and swamp rate, the more significant the regulation effect on runoff.
