Outline two factors that influence the development of drainage patterns.

KCSE Geography Paper 1 2012 Section B Question 9.

​(a) (i) Outline two factors that influence the development of drainage patterns.

• Direction of the slope of the land.
•  Difference in rock resistance /hardness.
•  The arrangement of rock layers/rock structure.
•  Faulting/fault guided. 

(ii) Outline five characteristics of a river in its youthful stage.

•  the river has a steep river gradient.
•  the river channel is narrow.
•  the river has deep/steep-sided/V-shaped valley/gorges
•  the river flows at a high speed/high stream velocity.
•  the vertical erosion/down cutting is dominant.
•  the river channel is generally winding.
• Rapids/waterfalls/cataracts/cascades/interlocking spurs/potholes/plunge pools
•  the type of flow is torrential.
•  the river has a small volume of water.
•  the river has a small load.

(b) Describe the following processes of river erosion:
(i) attrition; 
(ii) corrasion. 

• (i) Attrition: As rock materials are transported downstream, they constantly collide against each other.
• The materials gradually wear down/reduce in size.
• (ii) Corrasion: As solid rock materials are transported downstream, they are hurled against the banks and dragged along the river bed.
• The rock materials scour/erode/chip off pieces of rock from the channel and the river bed.
• The rock materials scour/smoothen/grind the river bank/bed.
• Eddy currents rotate pieces of rock around the hollows breaking/grinding the river bed.

​(c) Explain three negative effects of rivers to the human environment. 

• When rivers flood, they destroy a lot of property/crops/may lead to loss of human Iife/displace people.
•  Wide/deep rivers are a barrier to transport especially where bridges have not been constructed.
•  River water can be a medium of spreading water-born diseases, since flood waters may spread chemicals from farms/human waste which contaminates sources of water
•  Some rivers are habitat to dangerous animals which may attack human beings/destroy crops.

​(d) Your class is planning to carry out a field study of a river in its old stage.
(i) State three reasons why it would be necessary to pre-visit the area of study.

• helps to assess the suitability of the area of study.
• helps to draw up objectives/hypothesis for the study.
• helps to prepare a route map.
• helps to design a working schedule.
• helps to identify the probable problems/how to solve problems.
• helps to estimate the cost of the study.
• helps to identify suitable methods of collecting data.
• helps to identify appropriate equipment to be used during the study.

​(ii) State three activities you would carry out to determine why deposition occurs at this stage.

• Measuring of gradient.
•  Finding out the nature of the load.
•  Finding out the amount of the load.
•  Establishing the velocity of the river.
•  Observing obstacles in the stream channel/distributaries.
•  Measuring of the width/depth of the river,

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