GROUNDWATER Flashcards
Two big problems in terms of groundwater
1) Massive mining of groundwater ==>
massive land subsidence
2) Groundwater contamination - hard to detect + cleanup is costly and hard
ground characteristics
- Porosity (30 - 40%) - Volume of potential water storage
- General permeability / conductivity - allows water to disperse through it
- Made up of different materials - The smaller the grains of soil/rock, the harder it will be for water
to move through it (aquitard) e.g. clay
Porosity and permeability vary with depth
decrease with increasing depth
Groundwater vs “Underground water”
- Groundwater - water in the saturated zone under ground
- “Underground water” - all water beneath the surface
whats the Water table
the surface of the saturated zone underground
how does groundwater flow
- Ground water flows to a lower point with gravity - directly down through unsaturated zone
- flows more complicated when reaches the saturated zone – Governed by gravity and pressure
2 areas of groundwater
source (or recharge) area +
drainage (or discharge) area - Water from these areas
flows to oasis discharge points
whats the cone of depression
area where pumping from a well in a water table aquifer lowers the water table near the well
- groundwater flows towards the well into cone of depression
*land above COD = area of influence
how does permeability effect the cone of depression
- High permeability –> Shallow cone of depression
- Low permeability–> Deep cone of depression
what does darceys law explain
- steeper slopes deliver more water
- more permeable materials deliver more water
how does groundwater vary in Arid vs Humid climates
- Arid climate: Losing stream –> streams recharge
groundwater (recharge area) - humid climate: Gaining stream –> ground water
discharges into streams (discharge areas)
what are springs and the 4 types
locations of natural groundwater discharge
- Contact Springs: water table intersects the land
surface - at the contact between high- and low- permeability layers
- Fracture Springs: water-bearing fractures intersect the surface
- Fault Springs: Where a fault juxtaposes permeability contrasts
- Solution springs
how does a spring emerge
emerges between geological units of different porosity and permeability
what are Hot Springs and Geysers
- Where deep groundwater surfaces along faults
- In geothermal regions linked to shallow magma
– Circulation returns heated groundwater to the surface
whats An aquifer and its 2 types
Sediment or rock that contains and transmits water easily
- Unconfined aquifer: local rainwater percolates directly from land surface to the zone of saturation
- Confined aquifer: overlain by an impermeable layer / aquitard - results in Artesian well due to aquifer being under pressure
whats an Aquitard
Sediment or rock that hinders water flow
how do Concentrations of dissolved ions in groundwater vary overtime
increase - reacts as it flows through an aquifer
what does ‘hardness’ refer to
Ca 2+ and Mg 2+
how do Artesian wells tap groundwater
– Upland (higher) recharge pressurizes the aquifer
– A well casing below the potentiometric surface will flow without pumping
*Water distribution systems mimic these artesian aquifers
whats the Safe yield
pumping rate that does not deplete ground
water
- measured with the conservation of mass equation:
I - O = DS
Recharge - Pumping-Discharge = change in ground water storage
whats an artesian well
induces an upward flow of groundwater without any pumping
when will a dry well always occur
whenever the base of the well is above the water table
