The Hydrosphere - Physical

Question 1

What is residence time?

Answer 1

The average length of time water stays in a reservoir before moving to another reservoir.

Question 2

How do you calculate residence time?

Answer 2

Volume in reservoir / rate of transfer

Question 3

What are the impacts of abstraction from rivers?

Answer 3

• Reduced water supply downstream.
• Reduced downstream flooding. Reduces soil quality.
• Decreased water velocity.
• Increased sedimentation.

Question 4

Why might reservoirs be more suitable than rivers for abstracting water?

Answer 4

Allows storage of water when there is a surplus for when needed in shortages.

Question 5

What factors are important in choosing reservoir location?

Answer 5

• Topography.
• Geology.
• Catchment areas (area of land which rain will flow into river).
• Water supply.
• Pollution risk.
• Sedimentation.
• Infrastructure.
• Land use and conflicts.

Question 6

What are the environmental impacts of reservoirs?

Answer 6

• Habitat change - flooding for reservoir, obstructs migration.
• Changes in river flow - downstream reduced, reduced flooding.
• Sedimentation - loss of sediment downstream, reduced soil fertility.
• Reservoir microclimate - high SHC = reduced temp. fluctuations, reduced insolation as inc. evaporation = reduced temp.

Question 7

What are the properties of an aquifer?

Answer 7

• Rock below water-bearing rock must be impermeable.
• Some rock above must be permeable to allow aquifer recharge.
• Water may be abstracted using a well, a borehole, or may come to surface naturally in springs.

Question 8

What are some problems of reservoirs that are overcome by using aquifers?

Answer 8

• Water underground = no evaporation.
• Less pollution = water percolates through soil.
• Cheaper = less construction.
• Less land use conflict.
• Less climate change.
• Ecological impacts = not a habitat for most species.

Question 9

What is subsidence?

Answer 9

The collapse of the ground surface caused by a reduction in aquifer volume due to over abstraction.

Question 10

What are some potential problems created by unsustainable aquifer use?

Answer 10

• Reduced supplies (rate of extraction more than recharge).
• Subsidence.
• Over abstraction lowers water table.
• Saltwater incursion - seawater flows sideways to aquifer to replace water - cannot be used for irrigation or drinking.

Question 11

What are the two types of water treatment where freshwater is extracted from seawater?

Answer 11

Reverse osmosis = process of osmosis but it travels from low water potential to higher instead (high pressure is applied). Uses a LOT of energy.

Distillation = Salt water heated, will start to evaporate. Water vapour travels through condenser, condenses, left with pure water.
A commercial way uses the cold sea water as the condenser before it enters the heater, allowing it to be a continuous process.

Question 12

describe this: Reservoir, mesh, aeration, flocculation, filtration, carbon treatment, sterilisation, pH adjustment, ion exchange

Answer 12

1) Removes vegetation and litter, usually metal mesh.
2) Removes bad taste / smell from toxic metals.
3) Flocculants added to neutralise clay particles by mixing them quickly with water and passing to clarifier tank.
4) Removes any suspended solids. Sand and gravel layers.
5) Activated carbon filters remove organic chemicals.
6) Addition of chlorine, ozone, or UV light sterilise water + kills pathogens.
7) previous can make acidic water, adjusted with crushed lime.
8) Added sometimes - improves dental health.
9) Toxic ions removed, also used to produce ‘soft water’ (removal of calcium and magnesium ions).