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River terrace

2015-03-23 00:20 | Author:gzzjd | Reading:amount |


1-River terrace

The river erodes in the down-cutting way and the former river valley bottom (flood plain or riverbed) goes beyond the general flood level, and are distributed on the valley walls in a ladder manner, such landform is called as river terrace.



Form element table of river terrace
R:River bed; P: Flood plain; A. Front edge of terrace; D:Rear edge of terrace; ABD: Terrace surface; AF, ED: Terrace scarp
h1: Height of front edge of terrace; h2: Height of rear edge of terrace; h3: Height of front edge of the 2nd class terrace


2-Types of river terrace

Types of terrace classified according to their structures and form characteristics.

(1) Erosion terrace.It consists of bed rocks and there are no or just only some scattered sediments on the terrace, so it is also called as rock terrace.


(2) Basement terrace.Basement terrace consists of two layers of different substances, with river sediments on the upper layer and with bed rocks or other genetic type sediments on the lower layer. (T3, T4 and T5 in the diagram).


T1: Superimposed terrace; T2: In-laid terrace; T3: Bed rock-seated terrace; T4, T5: Overlying bed rock-seated terrace
1. Loess; 2. Red loam; 3. Washout sand gravel; 4. Slope debris; 5. Clay sedimented by still water; 6. Bed rock


(3) Accumulation terrace.Accumulation terrace consists of alluvial deposit, most commonly seen in the downstream of the river and mostly are the latest low terrace. According to different down-cutting depth of river when the terrace was formed, accumulation terrace can be classified into superimposed terrace (no cutting the sediments in the earlier stage) and in-laid terrace (just downcutting into the valley bottom in the earlier stage) (T1 and T2 in the diagram)


(4) Buried terrace

I.e. the terrace formed in the earlier stage is buried by the sediments in the later stage, doing like this time and again which then leads to form into multilayer buried terrace.

River bed

Cut-in-bedrock terrace
Fill terrace
Cut-in-fill terrace
Nested fill terrace
Cut-in-bedrock terrace (Erosion terrace, rock terrace)
Fill terrace (Accumulation terrace)
Cut-in-fill terrace (Basement terrace)
Nested fill terrace (Intrenched terrace-superimposed terrace, in-laid terrace)

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