Question

What are the important geomorphological features found in the river valley plains?

Answer 1

Alluvial fans are formed when streams flowing from higher levels break into foot slope plains of low gradient. Normally very coarse load is carried by streams flowing over mountain slopes. This load becomes too heavy for the streams to be carried over gentler gradients and gets dumped and spread as a broad low to high cone-shaped deposit called an alluvial fan. Usually, the streams which flow over fans are not confined to their original channels for long and shift their position across the fan forming many channels called distributaries. Alluvial fans in humid areas show normally low cones with gentle slope form as a low cone.

Delta is like alluvial fans but develops at a different location. The load carried by the rivers is dumped and spread into the sea. If this load is not carried away far into the sea or distributed along the coast, it spreads and accumulates. Such areas over flood plains built up by abandoned or cut-off channels contain coarse deposits. The flood deposits of spilled waters carry relatively finer materials like silt and clay. The flood plains in a delta are called delta plains.

Floodplain is a major landform of river deposition. Large-sized materials are deposited first when the stream channel breaks into a gentle slope. Thus, normally, fine-sized materials like sand, silt, and clay are carried by relatively slow-moving waters in gentler channels usually found in the plains and deposited over the bed and when the waters spill over the banks during flooding above the bed. These river valley plains have a fertile alluvial soil cover which supports a variety of crops like wheat, rice, sugarcane, and jute, and hence, supports a large population.