Alluvial river terrain

The role of the alluvial river 

If the upper reaches of rivers and tributaries are taking too much or carrying sediment force is likely to weaken once the deposition, when the river water flow along the river bed slope can be water from soil erosion to the lower reaches of gravel removal, which discussed the role of the river as follows: 

1. The impact of silt content increased, leading to a reduction in the reasons for removal: 

1) The river flows through the soft rock region 

Silt content of the river will increase, such as the Loess Plateau of China's Yellow River flows through the middle reaches of the sediment concentration increased, resulting in the prevalence of sediment downstream, resulting in Huanghuai Plain. 

2) climate change 

Flash floods, taken off a lot of sediment, such as Taiwan summer and more typhoons, each time after the storm, so that the river sediment concentration increased, in order to defy the power of removal, then precipitation occurs. 

3) the human factor 

Human river upstream logging, such as, inadequate water and soil conservation, rain water erosion, soil erosion, leading to increased sediment downstream. 



 The impact of river flow slowly, moving force resulting weakening of the reasons 

1) to reduce the bed slope 

General river upstream slope but to enter a plain, slope by the sharp decline in velocity from acute slow, handling is also followed weaker. The influence of sediment was deposited in the mountain prevalent, resulting in the foothills of the alluvial fan, such as China's two foot of Tianshan oasis. 


2) river wider range 

Rivers flowing through valleys, a great flow, but out of a canyon, into the plains, flow rates widened, the flow rate slowed down, Sui-sheng deposition. As the Yangtze River by the Three Gorges in Yichang deposition occurred in the east, resulting in the Jianghan Plain. 

3) reduction of river flow 

Removal and river flow is directly proportional. Therefore, to reduce the river flow, its removal will naturally reduce excess sediment deposition will occur, so the river branches, the deposition of very Sheng, such as the Minjiang River in China due to some of the following Guanxian Dujiangyan irrigation works, will be divided into Minjiang inside and outside the two rivers, the flow reduction, removal of power decentralization, Sui-sheng precipitation. 

4) the water flow path blocked 

Landslides or cave-ins, a large number of sand blocking the river so that flow down to form a deposition. 



  Alluvial river terrain 

Because of the topography of the river alluvial from mobile, it is important are: 


1. Deposition cone (a l l u v i a l c o n e) 

Since the height of the mountains, river discharge, the influence of gravel piled up in front steep mountain slope into a range of large and small cone of the terrain is. 

2.Alluvial fan (a l l u v i a l fan) 

Mountain rivers flow radical, one flowing into the ground but leave the valley, the gradient dropped, the flow rate dropped sharply in front of a large number of sediment in the low-width Department Yamaguchi alluvial and fan-so start to form a fan-plain, is called "alluvial fan" such as the Chengdu Plain in Sichuan. 

3. Flood plain (Flood plain) 

Cross-strait rivers often flood during the flood period, when in flood, flood the kidnapped with the river sediment deposited on the proliferation of reach of the ground, the formation of the low edge of the red layer (alluvim), is to "flood plain." Rivers in the flood plain on the flow, because of flooding so that sediment in the river on both sides have a natural levee, called the natural levee (naturallevees).