1) Too much water can contribute to the instability of a slope. Describe two thi
ID: 283798 • Letter: 1
Question
1) Too much water can contribute to the instability of a slope. Describe two things that water does that could contribute to mass wasting.
2) In what three ways does a stream transport its load? Which contains the coarsest (largest) sediment?
3) Distinguish between capacity and competency.
4) Distinguish between a meandering river and a braided river.
5) How would a river respond to:
A) A drop in base-level?
B) A rise in base-level?
C) Tectonic uplift?
Explanation / Answer
1. a) Excessive amount of water within a slope increases its mass, increasing shear stress within parts of slope, especially along rock fractures tilted in the same direction as the slope surface causing instability ,which in turn results in mass wasting.
b)Too much water can also float the soil/sand grains apart,which in turn reduces the friction between the grains thereby reducing the shear strength and so that any slight disturbance can cause instability and thereby leading to mass wasting.
Also water can flow into the the narrowest of rock fractures and if temperature then drops below freezing ,ice crystals will form, expanding in volume by 9% and this causes a powerful force which can wedge apart rocks, often causing them to fall from steep slopes in mountains and canyons . This phenomena is called ice wedging.
Too much water also reduces the angle of repose to very small values and the material tends to flow like a fluid.This is because the water gets in between the grains and eliminates the grain to grain frictional contact.Water also increases the pore pressure which in turn accelerates the erosion process and resulting in different types of mass wasting like mud flows , landslides etc.
2)Three ways in which a stream transports its load are:
a.in solution b.in suspension c. in its bed load
The Suspension contains the coarsest(largest) load.
3) In hydrology stream competency is a measure of the maximum size of the particles that the stream can transport. It is proportional to the velocity of the flow.
Whereas Stream capacity is the total quantity of sediment that a stream can carry, move, transport. Streams of water carry sediment. Each stream has a capacity for what can be carried by the volume and velocity (force) of water being channelized.
4)Meandering river is a river which takes lots of turns(meanders) and curves(sometimes sharp) as it flows and due to which it creates some water bodies cut off from the main river .
Braided river is a river which consists of a network of small channels separated by small and often temporary islands called braid bars.
5) A) A drop in base level causes the land to emerge from the sea and steepens the gradeint of river and therefore increses the rate erosion due to an increase in potential energy of the stream. Sometimes a waterfall may also occur if the rise in land is more rapid than the river's ability to vertically erode to the new base level
B) A rise in base level reduces the stream’s velocity, leads to deposition, and a reduction of the gradient upstream from the reservoir.
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