water Flashcards
porosity
the percentage of pore space that a rock contains
permeability
a measure of the rate at which a fluid will flow through the rock
primary porosity
the pore space at the time the sediment was deposited
secondary porosity
develops after in the rock, and includes cavities or fractures that have formed
effective porosity
the total porosity minus any cement and this contributes to fluid flow through the rock
capillary pressure
the force which exists across the interface which separates two immiscible fluids
connate water
trapped in the pores of a rock as the rock formed
groundwater
water occupying pore and other spaces in rocks and sediments which is derived mostly from rainfall percolating into the underlying rock
water table
the surface separating unsaturated rock above from the saturated rock below
hydrostatic pressure
the pressure at a point in a body of water due to the mass of the overlying column of water
hydrostatic gradient
the difference in the hydrostatic pressure between two points divided by the distance between them
aquifer
a body of porous and permeable rock capable of storing and yielding significant amounts of water
recharge zone
the area of an aquifer open to the atmosphere, allowing replenishment of water
artesian basin
a large, synclinal confined aquifer under hydrostatic pressure
artesian well
holds water under hydrostatic pressure, which rises up the well to the piezometric surface on release
piezometric surface
an imaginary surface to which groundwater rises under hydrostatic pressure, to produce springs
abstraction
the removal of water from any source
cone of depression
occurs when there is a lowering of the water table in the vicinity of a well, usually due to abstraction of water
acid mine drainage
water containing toxic metals such as lead and cadmium from abandoned coal and metal mines
what are the 3 types of aquifer?
unconfined, confined, perched
perched aquifer
sits above the natural water table but is underlain by e lens of impermeable rock
spring
occurs where the water table intersects the surface
lithological spring
Result of a change in rock type. Where a permeable rock overlays an impermeable rock. A spring will occur at the boundary.
springs at faults
Forms if a fault brings a permeable and impermeable rock together. Pressure causes water to rise up fault line to surface
seeps
low density hydrocarbons can seep naturally to the surface
what are the problems caused by groundwater extraction? x4
lowering of the water - cone of depression
subsidence + reduced porosity- water taken out of rock causing it to collapse downwards
saltwater encroachment
saltwater encroachment
where aquifers are near the coast fresh water sits on top of see water as it less dense. Pumping can disturb this and cause them to mix
what are the 2 main threats to groundwater supply?
over pumping
pollution
why does some groundwater not need treatment?
pore space acts as a natural filter to groundwater, removing chemical impurities
name 4 sources of pollution
nitrates and pesticides
hydrocarbons and solvents
toxic fluids from landfill waste
Acid Mine Drainage
factors affecting porosity x4
degree of sorting
amount of diagenesis
grain shape
packing of grains
factors affecting permeability
porosity
temperature
secondary permeability capillary pressures
