Answers – Rivers and Drainage Basins

(i) River discharge formula:

width × depth × speed of flow

precipitation × volume of river

speed of flow × amount of erosion

groundwater flow × overland flow

(ii) From Fig. 6:

• Maximum rainfall during 30 minutes: 15 mm
• Time when river most likely to start flooding: 17:30

(iii) Why rivers continue to flood after heavy rain ends:

Water takes time to flow from far places to the river. Some water goes underground first and moves slowly. The ground is already full of water so new rain runs straight to the river. All this water keeps coming even after rain stops.

(iv) How increased discharge affects erosion and transportation:

More water makes the river flow faster. Fast water has more power to pick up rocks and mud from the bottom. It can carry bigger pieces of rock. The strong water also breaks away the river banks.

(i) Definitions:

• Drainage basin: The area of land drained by a river and all its tributaries
• Watershed: The high land that separates one drainage basin from another
• Tributary: A smaller river that flows into a larger river

(ii) Problems caused by deforestation in Oregon:

Problems for people:

• Increased flooding as trees no longer intercept rainfall
• Water pollution from soil erosion getting into rivers
• Loss of jobs in forestry and tourism
• Damage to property from landslides on steep slopes

Problems for natural environment:

• Loss of animal habitats and food sources
• Soil erosion as tree roots no longer hold soil together
• Climate change as fewer trees to absorb carbon dioxide
• Loss of biodiversity as species lose their homes

Name of river: River Thames

Opportunities:

• Water supply: Fresh water for drinking, washing and industry
• Transport: Ships and boats can carry goods and people cheaply
• Agriculture: Fertile soil in the flood plain for growing crops
• Fishing: Source of food and income from catching fish
• Tourism: River cruises and water sports bring visitors and money
• Industry: Water for cooling in power stations and factories
• Trade: Ports and harbors for importing and exporting goods
• Hydroelectric power: Using flowing water to generate electricity
• Recreation: Swimming, boating and fishing for leisure
• Settlement: Flat land for building houses and cities