River Characteristics - Sample Answer

(a) Outline physical factors that might affect the discharge of rivers such as that illustrated in Figure 1. (5 marks)

The Yellowstone River pictured in Figure 1 is in its upper course.  The surrounding land is an area of high relief with steep valley sides.  This will lead to a "flashy hydrograph" with rapid rises and falls in discharge.  The climate of the area will influence the regime of the river, with peak discharge in spring after snowmelt in the mountains. After a period of rainfall, water will reach the main river channel quickly via overland flow adding to the flashy nature of the discharge.  There is little vegetation cover near to the river and so reduced interception will also allow water to transfer rapidly to the main channel contributing further to rapid changes in dicharge.  However, the mountains in the background of the photograph are forested, so this may slow the passage of water and help to reduce discharge in the river.  Finally, the geology of the surrounding area will influence discharge.  Permeable rocks will allow infiltration and percolation and reduce run-off, leading to less rapid rises and falls in discharge since water flows more slowly through the ground to reach the channel.