Water Flashcards
What is groundwater?
Subsurface water contained within the porespaces of rocks below the water table.
What is the water table?
The level that the water sits within the ground. It is the surface seperating unsaturated rock above from saturated rock below.
What is porosity?
The amount of pore spaces in a rock or sediment, usually expressed as a percentage of the total rock volume.
What factors affect porosity?
Rock type, degree of diagenesis, degree of sorting, grain shape.
What is permeability?
The ability for fluids to flow through a rock. The pore spaces present in a rock may become interconnected and link up to form a pathway.
What factors affect permeability?
Grain size, rock type and degree of diagenesis
What is hydrostatic pressure?
This results from the weight of the overlying water column and increases with depth.
What is hydrostatic head?
The height of the overlying column if water.
What is hydraulic gradient?
The difference in hydrostatic pressure between two points divided by the horizontal distance between them.
What is an aquifer?
A body of porous and permeable rock capable of storing and yielding large quantities of water.
What is an aquiclude?
An impermeable rock that doesn’t transmit water.
What types of aquifer are there?
Unconfined, confined, perched, live and fossil.
What is a recharge zone?
The area of an aquifer open to the atmosphere allowing replenishment of the water.
What is an artesian basin?
A large synclinal confined aquifers.
What is a cone of depression?
It is created as groundwater is pumped out from a well and the level of the water table falls around it.
What is draw down?
The height difference between the water and the level of water in the well.
What affects the cone of depression?
Rate of abstraction, duration of abstraction and hydraulic properties of the aquifer
What problems are associated with water abstraction?
Lowering of the water table, subsidence of the ground at the surface and saltwater encroachment
What threats are there to groundwater?
Overpumping and pollution
What is a spring?
When subsurface water flows onto the surface because the water table intersects the land surface and is a junction between permeable and impermeable rock.
How does lithology create a spring?
They occur where porous and permeable rock overlies an impermeable rock. They also occur where impermeable igneous intrusions cut through porous and permeable rocks.
How do faults create a spring?
Faults can produce springs if they have moved porous and permeable rock into contact with impermeable rock.
How do unconformities create a spring?
If porous and permeable rocks lies unconformably on top of impermeable older rock, the water table will intersect the land surface at the junction between the two rock types
What are the advantages of ground water supply?
Rocks act as a natural filter
No loss of water through evaporation
No need for expensive and damaging dams
Pumping costs for an artesian basin will be low
What are the disadvantages of ground water supply?
Surface subsidence Pollutants have a long residence time Pumping is costly Not all areas have the required geology Groundwater is not suitable in coastal areas is not suitable for drinking
What are the advantages of surface water supply?
Easy to abstract
Water can be treated after use
Dams can be used for hydroelectric power
Reservoirs can be used for recreation
What are the disadvantages of surface water supply?
Water will need treatment Seasonal as volume of water varies Requires sufficient rainfall and large catchment areas Requires construction of dams Requires flooding of land Reservoirs will slit up
What makes an aquifer renewable?
Live aquifers are a renewable resource as long as the rate of replenishment is greater than the rate of use.
