Stream Features

What factors control a stream's velocity?
The term velocity means the speed, motion, and quickness of motion. A stream's velocity varies for several different reasons. Rain causes stream levels to rise and possibly flood. Excess water in a stream increases the velocity. A stream will reach maximum velocity while in the middle of the channel. However, the speed will decrease once the water goes around a curve. A stream gradient also affects its velocity. The gradient is based on whether the water will travel downhill or level. The shape of a stream's channel and roughness will impact the stream's velocity. Semicircular channels allow rapid water flow, wide and shallow channels increase friction and slow down the flow, and rocky channels also slow the stream. When the stream's velocity begins to decrease the deposition of sediments may occur.

In what part of a large alluvial fan is the sediment the coarsest? Why?
The sediment is coarsest near the mountains in a large alluvial fan. Gravel and sand are the coarsest sediments and deposited near the upper portion of an alluvial fan. The coarse sediment is deposited after water is gradually lost and enters the alluvial fan. Finer sediments are deposited further away and not grade sized. Alluvial fans form near dry climates at the base of mountains and coarser sediment are deposited in the upper portion because of the stream's velocity and gradient. The gravel and sand build up the base of a mountain.

Describe one way that incised meanders form.
Uplift is a process in which river levels are increased well above base level. The uplift would impact the river's gradient which causes the velocity to increase. Incised meanders don't always form by uplift, but it's a key factor.

Describe three ways in which a river erodes its channel.
A. Hydraulic action transports loads and fragments of sediment with flowing water. The hydraulic force pushing and swirling water can crack rocks and then fragments are carried away. The stream then transports and deposits the sediments in other areas.
B. Solution is a slow but effective process in transporting sediment. Solution causes erosion and deepens a stream channel. The stream flows over sedimentary rocks and can begin dissolving them. The loose fragments are then picked up and carried away by hydraulic action.
C. The abrasion process grinds away rocks in streams with friction. The friction and impact due to abrasion will wear away the sediment near the bottom of the stream and begin to carry it away. Abrasion in streams is similar to taking sandpaper to wood, as the gravel and sand grind the rocks.

Name and describe the three main ways in which a stream transports sediment.
A. The bed load is heavy and large fragments that are carried along the streambed. The sediments roll or slide along the stream which is called traction. The bed load may also be moved by leaps and jumps in the stream called saltation. Rarely will the bed load rise above the streambed.
B. The suspended load is lighter and smaller fragments of sediment that streams transport. The suspended load is lifted and carried in the water instead of sliding along the streambed. The transportation of sediment by suspension has less of an impact with erosion than the bed load.
C. The dissolved load is a process in which soluble products are effected by chemical weathering. Several streams contain ions such as calcium, potassium, bicarbonate, sodium, chloride, and sulfate. The dissolved loads are not visible unless the water evaporates and materials begin to crystallize. The dissolved load carries away sediments and minerals which may reach the ocean or evaporate.