Water resources in namibia Flashcards
1
Q
what is the difference between periodic and episodic rivers?
A
- Periodic only flows during rainy season when water table rises enough to feed the river.
Episodic flows for short periods after heavy rains.
- many in namibia.
- important source of water.
2
Q
Why are lakes an important water resource in namibia.
A
- Valuable for many countries.
- Namibia does not have any real lakes.
3
Q
What are pans?
A
- very common in namibia during or after good rain.
- are shallow basins of water that tend to evapourate easily.
- drying up leaves valuable fertile soil.
4
Q
Importance of dams.
A
- Namibia large and small storage dams.
- supplying water for domestic and agricultural consumption.
- Omdel dam:
- build because seawater leaked into dam water, and the do was there to trap flood water and to allow all sediments to be deposited.
5
Q
What is ground water?
A
- Refers to water that infiltrates surface of the earth and percolates underground where it is stored.
- plays an important part in dry countries.
6
Q
Where is ground water found?
A
- found in aquifers.
- aquifers in gravels and sand is knows as alluvial aquifers.
- aquifers in harder rock, sandstone and limestone, are hard rock aquifers.
7
Q
name the three process of desalination of seawater.
A
- Distillation
- Electro-dialysis
- reverse osmosis
8
Q
Describe desalination in terms of distillation.
A
- seawater is boiled to cause evaporation and leaves salt behind.
- steam is condensed as fresh water.
- is fine for small quantities but not economically viable.
9
Q
Why is permanent rivers permanent?
A
- The river channel reaches water table throughout the year.
10
Q
Describe elevctro dialysis to de desalination.
A
- seawater placed in container with negative electrode at one end and positive electrode at the other.
- negative and positive charged ions move towards electrodes.
- salts become trapped between semi-permeable membranes in the container.
- water on one side of memebrane will be fresh and pumped out.
- left water will be salty and returned to sea.
11
Q
Describe reverse osmosis in terms of desalination.
A
- Pressure is applied to seawater, forcing it through special memebranes.
- only water will pass through and salts will be caught in membrane.
12
Q
Why do farmers irrigate?
A
- To supplement low rainfall in an area.
- to provide water throughout the year where rainfall is seasonal.
- to provide water in areas with high evaporation rate.
- to increase crop production.
13
Q
What is the problems caused by irrigation?
A
- High cost of building and maintaining installations.
- reservoirs have limited life as they slowly fill up with river borne silt.
- may effect quality of the soil.
- great deal of water loss from reservoir through evaporation.
- can rise the water table.
- surface water evapourates, leaving salts behind: salination.
- when raining, salf may spread to other sources of water.
14
Q
name the factors that contribute to pollution of water sources.
A
- Rapid urbanisation
- industrial activities.
- irrigation
- agriculture
- soil erosion.
15
Q
why does urbanisation cause pollution?
A
- lack of toilets
- waste end up in water supply
- more people, more cars truck, diesel oil.
