A river flowing between banks composed of coarse material with numerous protrusions and over a bed of large, angular rocks meets with more resistance than a river with cohesive clays and silts forming its bed and banks. As bed and bank roughness increase so does turbulence and therefore a mountain stream is likely to pick up loose material and carry it downstream. Roughness is difficult to measure but Manning, an engineer, calculated a roughness coefficient by which he interrelated the three factors affecting the velocity of a river: What are these?

In his formula known as Manning’s N: V=R0.67 S0.5 n Where V=velocity R =hydraulic radius S = channel slope N = boundary roughness The formula gives a useful approximation: The higher the value, the rougher the bed and banks.

Bed ProfileSand and Gravel Coarse gravel Boulder s Uniform Undulating Highly irregular

River load Suspended sediment load: This is carried with the body of the current. It can consist of suspended bed material, which is fine to medium sands, which have come from the riverbed. The material such as silts and clays is light and can be held in suspension. Bedload: Can be either exogenetic(outside the channel) or endogenetic, and moves by sliding, saltating, or rolling. It is larger than suspended sediment load. Dissolved load: This is held in solution and can come from erosion, pollution, mineral springs and chemical weathering.

Tasks: Complete activities 3 and 4 on page 33. Read and Highlight the sheets on sediment systems and summarise the Exogenetic ways which sediment enters and river in the upper course.