Flashcards in Water Deck (65)
Why is water becoming so scarce?
- low, variable rainfall and high evaporation rate, and climate change
- rapid population growth, increasing demand for supply
- economic growth, increase water for industrial use
Why are dams so important?
They provide our water requirements
what is the purpose of large storage dams and inter-basin transfer schemes?
For irrigation, domestic and industrial water supply and hydroelectric power
Why is the Gariep dam important?
supply of water to drier parts of the vaal, fish and sundays river
What are the negative impacts of dam?
- Large cost
- creates a reservoir , which disrupts functioning of river ecosystem
How do dams effect environment?
- Natural habitats are flooded
- organic material limited
- Surface area of water is increased, rate of evaporation increased
- large quantities of methane gas are produced.
what does reduced natural flooding prevent?
-flood water from bringing beneficial silt and nutrients to the crops
- silt in rivers being flushed out and washed down to beaches
What are wetlands?
Areas where teresstrial and aquatic ecosystems come together
What does a wetland consist of?
- water table,near the surface of the ground. Land with shallow water.
-areas be fresh water, forming vleis, bogs, pans, marshes, swamps and floodplains
why are wetlands so impotant?
-purify the water, act as filters, removing pollutants and excess nutrients.
- act as sponges, storing water. Help to recharge underground aquifers when water released to downstream areas.
- prevent severe damage during floods. soak up excess water.
What is causing wetland destruction?
-by need for development by humans e.g crop prodution,pastures etc.
- 'reclaimed' for industrial use, construction of airports, harbours, housing development
What is the Ramsar Convention?
an international agreement for the conservation and wise use of wetlands and their resources
what farming practices, results in the loss of protective vegetation and causes erosion?
- ploughing of marginal lands
- cultivation without protecting lands from excessive run off.
- allowing cattle to form paths, which soon form gullies.
What is the cause for the loss of availability of water?
- excessive runoff
- sedimentation in storage dams when valuable topsoil is washed away from sediment in streams. reduces capacity in storage dams
What are floods?
An overflow of a large amount of water over dry land.
How are floods caused?
- heavy rains
- human interferences, impact on flooding.
Why are floods important?
- provide water to irrigate crops
- replenish the soil in flood plains.
What is a drought?
An extended period of months or years where water availability falls below requirements for a reigon.
What happen in drought?
a region consistently receives below average rainfall
more severe by humans using more water than is available in particular.
what are exotic plants?
specie growing in an area where they do not naturally grow.
What is a plantation?
even-aged monoultures grown over a large area/
What varieties does Plantations include?
- Crops such as tea, coffee, cotton, tobacco, sugar cane.
- Trees such as pine, eucalyptus and acacia are planted because of their:
* Fast growth
* tolerance of rich or degraded land
* potential to produce large volumes of timber for industrial use
How do plantations affect water availability?
trees may reduce the amount of goundwater, lowering the water table because:
- deep root systems, which absorbs more water that natural vegetation
- Groundwater is drawn by the large number of leave transpiring
What is groundwater?
Water found in pores, cavities and cracks in hard rocks and soil off aquifers
What factors cause plantations to deplete the water table?
-What species make up the plantations
- What type of vegetation is being replaced
- The properties of the soil
What is a water table?
topmost level of groundwater
What is an aquifer?
A layer of earth and rock that holds water
What is the main source of aquifers?
How do boreholes affect aquifers?
- groundwater is reached through wells or pumped out through boreholes.
- water is abstracted and water table is lowered.
-Borehole yields then drop, wells begin to dry up, groundwater is depeleted.
- supply of water is reduced.