Modification of drainage cycle Flashcards
Due to dams, there is an increase…
of evaporation. E.g. Lake Nasser loses 1/3 of its water by evaporation.
Increased urbanisation leads to…
reduction in evapotranspiration due to lack of vegetation but increase in evaporation due to higher temperatures.
Deforestation leads to…
a decline of surface storage, reduction in evapotranspiration.
Afforestation may have a negative…
impact, as in river Severn catchments sediment loads increased 4x.
Increased erosion due to afforestation decreased…
as the trees grew up.
Infiltration is up to…
5x higher under forest compared to grasslands.
Grazing leads to decline in…
infiltration due to compaction and pounding of the soil.
Ploughing increases…
the infiltration as it loosens the soil.
When the water table is close to the surface…
evaporation of water leaves salts behind and it may form an impermeable crust.
Increase surface storage in urban areas due to…
large-scale dams.
Problems with dams:
- salinisation
- increased erosion
- local changes in the climate
Over-abstraction may lead to…
the drying of rivers, falling water tables and saltwater intrusion in coastal areas.
In Malta, most underground can no longer be…
used because it is contaminated by the saline intrusion.
The saline intrusion is…
the movement of saline water into freshwater aquifers.
Irrigation is the main…
cause of groundwater overexploitation.
(Aswan Dam) Allow good crops in…
dry years e.g. Egypt in 1972 and 1973
(Aswan Dam) Irrigation-
60% of water is used for irrigation and up to 4000km of the desert are irrigated.
(Aswan Dam) Hydro-electric power accounts for…
7000 million kW hours per year.
(Aswan Dam) Space for recreation and…
tourism.
(Aswan Dam) Water losses are extensive that…
dam provides less than half the amount of water expected.
(Aswan Dam) Due to salinisation…
crop yield has been reduced and more fertilizers are needed.
(Aswan Dam) Seismic stress-the earthquake in…
1981 is believed to be caused by the dam.
(Aswan Dam) Erosion of the Nile delta is…
taking place at a rate of about 2.5 cm each year.
(Aswan Dam) Sardine yields decreased by…
95%.
In California over…
80% of ov water is used for agriculture.
(California) In some areas, there is no…
phreatic zone, which gives cohesion and soil moisture budget.
(California) Most of the population is…
in South (2/3)
(California) Most precipitation fall in…
North (2/3)
Loss of phreatic zone results in:
- increased lag time
- loss of hydrostatic pressure
- removal of water increases the number of gases in the soil
- increased slope instability
