Groundwater & Karst Topography Flashcards
Hydrologic Cycle
1) series of storage areas connected by transfer processes + closed/circular system
2) water can cycle through in hours or millions years
3) 99% Earth’s water in storage = oceans, lakes, rivers, ice, aquifers
4) only 2.8% freshwater AND 75% of that water is in glaciers
Describe evaporation precipitation balance
1) over the course of years it does balance + cancel each other out
2) tends to be more evaporation compared to precip over ocean, opposite true for continents
Residence times
amount of time water spends in a certain substance/medium
- may stay stored in ocean or lake for thousands of years
groundwater
1) underground water in subsurface zone where pore spaces completely filled with water (zone of saturation)
2) more than 50% of world’s groundwater within .5 miles underground
source of groundwater
majority of groundwater comes as precipitation from above that percolated into soil or seeped downward from lakes
Porosity
1) quantity of water that can be held in subsurface material
2) more porous = more open space/cracks = more water stored
permeability
1) ability for water to move through soil
2) means the holes/cracks connected
Rate at which water moves through rocks depends on
1) permeability
2) porosity
ex = clay has many small interstices that give it high porosity BUT the interstices bind so strongly to water that water cannot move through it
aquifers
1) PERMEABLE ROCK where water is stored in sediment underground
2) 3 layers = zone of aeration, zone of saturation, waterless zone
aquicludes
1) impermeable materials composed of components like clay which hinder water movement
2) ex = clay + bedrock
3 hydrologic zones for groundwater
1) zone of aeration
2) zone of saturation
3) waterless zone
Zone of aeration
1) mixture of solids, water, air
2) depth varies
3) interstices filled with water + air
4) water that isn’t held by molecular attraction seeps down
zone of saturation
1) pores fully saturated with water
2) water table = top of saturated zone
3) watertable bends to surface above + when it intersects with land –> forms spring
4) humid regions = high water table
Cone of depression
1) well filled with water up to water table
2) if water is taken out faster than flows into saturated rock –> creates a “cone of depression” where no water
Types of aquifers
1) unconfined (able to enter from any location)
2) confined (only able to fill from one location)
How do lakes relate to watertables
Lakes usually depressions that go deep enough into water table
confined aquifers
1) when aquifer is confined by acquicludes above + below
2) tends to have a sloping/dipping layer where it absorbs infiltrating water
artesian wells
1) when you drill a well into a confined aquifer –> pressure forces water to rise
2) if water rises up to surface = called a artesian well
3) if water only partially rises upward = subartesian
piezometric surface
elevation to which water in artesian well rises
Groundwater pollution
1) if pollution seeps into aquifer = may remain indefinitely
waterless zone
low limit of zone of saturation lacks pore spaces –> has no water
Groundwater mining problems
1) groundwater accumulates very slowly (.5 cm/year) but humans tap water very quickly (75 cm/year)
2) can cause subsidence (sinking of land)
Fossil water
1) groundwater considered nonrenewable resource
Dissolution
removal of bedrock through chemical weathering + action of water
