SAQs
Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering these questions.
Rewrite the paragraph below using terms from the list provided to fill the gaps.
aquifers, condenses, evaporation, groundwater, hydrological, percolates, precipitation, run-off, transpiration.
Water on the Earth’s surface moves in an unceasing cycle through rivers, oceans, clouds and rain called the water or ……………… cycle. The heat from the sun causes ……………… of water from oceans and from lakes and wetlands on land. Plants lose water through their leaves by ……………… Water vapour in the atmosphere ……………… to form clouds which are moved around by wind. Rain and snow, collectively known as ………………, fall from the clouds. Some water that falls on the ground forms ……………… which collects into streams and rivers and some ……………… through the soil to become ………………, which is held in layers of rock called ………………
Water on the Earth’s surface moves in an unceasing cycle through rivers, oceans, clouds and rain called the water or hydrological cycle. The heat from the sun causes evaporation of water from oceans and from lakes and wetlands on land. Plants lose water through their leaves by transpiration. Water vapour in the atmosphere condenses to form clouds which are moved around by wind. Rain and snow, collectively known as precipitation, fall from the clouds. Some water that falls on the ground forms run-off which collects into streams and rivers and some percolates through the soil to become groundwater, which is held in layers of rock called aquifers.
Name the three main types of water source that people use and explain how each would be affected by an extended period of drought.
The main sources of water are surface water, groundwater and rainwater. Rainwater collection is obviously not possible during times of drought. The water available from surface water sources such as rivers and lakes will be reduced by drought because there will be no run-off so the volume of water in rivers and lakes will fall and they may even dry up. Groundwater reserves will also be reduced by drought although not as immediately as surface water. If there is no rainfall to recharge the aquifer and water continues to be extracted then the water table will gradually drop.
Town A has does not have a convenient water source for its residents. You are part of a team that has been tasked to select a water source for development to meet the water needs of Town A. List four points that you need to consider as part of the selection process.
You might have considered the following four points:
- Water quantity and reliability; there must be sufficient quantity of water to meet current and future needs.
- Water quality; the water must be free from contamination; fluoride levels may be relevant in some locations.
- Socio-cultural considerations; there may be local beliefs and practices among users that should be considered.
- Technical requirements; the practical feasibility of developing the source is important; operation and maintenance in the future should also be planned.
Which of the following statements are false? In each case explain why it is incorrect.
- More fresh water is held in lakes on the Earth’s surface than is held in aquifers as groundwater.
- Demand for water tends to increase as countries develop economically.
- In rainy seasons, surface water sources are topped up with fresh water therefore they are less likely to be contaminated with pathogenic micro-organisms than groundwater sources.
- Ethiopia has plentiful supplies of fresh water but it is not evenly distributed across the country.
- Globally, the demand for water is increasing but the volume available to meet that demand is not.
1 is false. From Figure 4.2 approximately 30% of fresh water is groundwater and only 0.4% is surface and atmospheric water. The volume of water held in lakes is approximately two-thirds (67.4%) of this 0.4%, and therefore there is much more water in aquifers than in lakes.
3 is false. Rainwater will wash all types of contaminants including pathogenic micro-organisms into rivers and lakes, so they are more likely to be polluted than groundwater. It is possible for groundwater to be contaminated but if pathogens are present, most are removed as the water trickles down through soil and rock.