EVSC10001 Lecture Notes - Lecture 27: Sinkhole, Capillary Fringe, Porosity
11 Jun 2018
School
Department
Course
Professor
Surface water and Runoff
Water cycle
Continuous movement of water on, above and below the surface of the Earth
-
Climate and ocean (Evaporation, precipitation)
Heat from sun causes evaporation
○
Oceans contain 97% of Earth's water
○
Water falls from clouds
○
-
Runoff and lakes
Water flow above ground as runoff, forming streams, rivers, swamps,
ponds, and lakes
○
-
Plant transpiration
-
Infiltration and groundwater
Water penetrates the Earth's crust and comes back out as geysers or
volcanic steam
○
-
25% of water on earth is groundwater!
-
1% is freshwater lakes and rivers
-
What is groundwater?
Water that has infiltrated the soil
-
Gravity leads to infiltration and percolation
-
Unsaturated zone
Contains air
○
Pore spaces filled with water and air
○
Adhesion and cohesion
○
Capillary fringe (moisture sticks to grains)
○
-
Groundwater surface (table)
-
Saturated zone
Pore spaces filled with water
○
-
Porosity = pore space - storage capacity
-
Depends on density of grain packing, size, shape and sorting
-
Permeability = inter-connectedness - depending on porosity + connection
b/w pores) - though flow (fast, slow, no flow)
-
Sand increases porosity
-
Limestone increase porosity (solution cavities)
-
Granite decreases porosity
-
Primary porosity: formed with material (pores), decreases over time due to
compaction, cementation, etc.
Secondary porosity: formed after material (joint, fissure, faults, dissolution etc.)
Groundwater table
Depth to table varies - depends on RECHARGE
-
Effluent: intersection -> water flows out onto surface
-
Influent: not intersecting -> recharge + stocking up
-
Larger distance in higher areas/elevations than in valleys
Valleys: groundwater intersects -> ponds, creeks
○
-
Aquifers: sediment or rock that transmits water easily
Unconfined aquifer: intersects the surface in contact with the atmosphere
Water seeps from ground surface directly above aquifer
○
-
Confined aquifer: isolated from surface, beneath and between aquitards
Impermeable rock layer prevents water from seeping into aquifer from
ground surface above
○
-
Aquiclude: sediment or rock that hinders water flow
Perched water table: accumulation of groundwater above the water
table in unsaturated zone - groundwater trapped above an
impermeable soil layer -> forms saturated material in unsaturated zone
○
Discontinuous aquicludes - prevent downward infiltration to water
table
○
-
Groundwater flow
Flow velocity depends on
Porosity and permeability1)
Hydraulic head (ie potential energy available to drive the flow)
3H = elevation + pressure
§
Hydraulic gradient = difference in hydraulic head / distance (L)
§
Smaller hydraulic head with distance
§
2)
Darcy's law: groundwater flow velocity (v) proportional to hydraulic
gradient
-
Upland recharge pressurizes the aquifer
-
Artesian aquifer: confined aquifer containing groundwater under positive
pressure - causes water level in well to rise to a point where hydrostatic
equilibrium has been reached
Artesian wells tap confined, tilted aquifers
○
Water rises to potentiometric surface
Wells below this surface will flow without pumping
§
○
-
Groundwater flows:
Slowly (friction)
-
In various directions
-
On various spatial scales
-
From RECHARGE ZONE to DISCHARGE ZONE
-
Extraction of groundwater
Depression in ground water table when ppl make wells
-
Water extraction -> lowers water table -> ground water depletion 1)
Subsidence: sinking of the ground because of ground water extraction
Water not in pores -> cities sink
○
Clays reshape -> cant store as much water as before
○
2)
Salt water intrusions - b/ of higher density in groundwater body3)
Groundwater discharge
SPRINGS
Natural groundwater discharge
○
Contact spring: Permeable layer and impermeable layer meet
Perched water table intersect
§
○
-
Overflow spring
○
Fault spring - fault has brought together 2 diff types of bedrock
○
Contact springs
○
Karst springs form where groundwater weathers through limestone
bedrock, and water in underground caverns emerges
○
OASES in desert
From spring flow
-
At fault trace
-
Hydrothermal activity
"hot springs" discharge of groundwater @ 30-140 degrees
-
2 settings for formation
Deep groundwater surfaces along faults
○
Geothermal regions (shallow magma)
○
-
Rich in dissolved minerals
-
Extends deep into lithosphere
-
Hot springs + geysers
-
Groundwater
Thursday, 7 June 2018
1:54 pm
Surface water and Runoff
Water cycle
Continuous movement of water on, above and below the surface of the Earth
-
Climate and ocean (Evaporation, precipitation)
Heat from sun causes evaporation
○
Oceans contain 97% of Earth's water
○
Water falls from clouds
○
-
Runoff and lakes
Water flow above ground as runoff, forming streams, rivers, swamps,
ponds, and lakes
○
-
Plant transpiration
-
Infiltration and groundwater
Water penetrates the Earth's crust and comes back out as geysers or
volcanic steam
○
-
25% of water on earth is groundwater!
-
1% is freshwater lakes and rivers
-
What is groundwater?
Water that has infiltrated the soil
-
Gravity leads to infiltration and percolation
-
Unsaturated zone
Contains air
○
Pore spaces filled with water and air
○
Adhesion and cohesion
○
Capillary fringe (moisture sticks to grains)
○
-
Groundwater surface (table)
-
Saturated zone
Pore spaces filled with water
○
-
Porosity = pore space - storage capacity
-
Depends on density of grain packing, size, shape and sorting
-
Permeability = inter-connectedness - depending on porosity + connection
b/w pores) - though flow (fast, slow, no flow)
-
Sand increases porosity
-
Limestone increase porosity (solution cavities)
-
Granite decreases porosity
-
Primary porosity: formed with material (pores), decreases over time due to
compaction, cementation, etc.
Secondary porosity: formed after material (joint, fissure, faults, dissolution etc.)
Groundwater table
Depth to table varies - depends on RECHARGE
-
Effluent: intersection -> water flows out onto surface
-
Influent: not intersecting -> recharge + stocking up
-
Larger distance in higher areas/elevations than in valleys
Valleys: groundwater intersects -> ponds, creeks
○
-
Aquifers: sediment or rock that transmits water easily
Unconfined aquifer: intersects the surface in contact with the atmosphere
Water seeps from ground surface directly above aquifer
○
-
Confined aquifer: isolated from surface, beneath and between aquitards
Impermeable rock layer prevents water from seeping into aquifer from
ground surface above
○
-
Aquiclude: sediment or rock that hinders water flow
Perched water table: accumulation of groundwater above the water
table in unsaturated zone - groundwater trapped above an
impermeable soil layer -> forms saturated material in unsaturated zone
○
Discontinuous aquicludes - prevent downward infiltration to water
table
○
-
Groundwater flow
Flow velocity depends on
Porosity and permeability1)
Hydraulic head (ie potential energy available to drive the flow)
3H = elevation + pressure
§
Hydraulic gradient = difference in hydraulic head / distance (L)
§
Smaller hydraulic head with distance
§
2)
Darcy's law: groundwater flow velocity (v) proportional to hydraulic
gradient
-
Upland recharge pressurizes the aquifer
-
Artesian aquifer: confined aquifer containing groundwater under positive
pressure - causes water level in well to rise to a point where hydrostatic
equilibrium has been reached
Artesian wells tap confined, tilted aquifers
○
Water rises to potentiometric surface
Wells below this surface will flow without pumping
§
○
-
Groundwater flows:
Slowly (friction)
-
In various directions
-
On various spatial scales
-
From RECHARGE ZONE to DISCHARGE ZONE
-
Extraction of groundwater
Depression in ground water table when ppl make wells
-
Water extraction -> lowers water table -> ground water depletion 1)
Subsidence: sinking of the ground because of ground water extraction
Water not in pores -> cities sink
○
Clays reshape -> cant store as much water as before
○
2)
Salt water intrusions - b/ of higher density in groundwater body3)
Groundwater discharge
SPRINGS
Natural groundwater discharge
○
Contact spring: Permeable layer and impermeable layer meet
Perched water table intersect
§
○
-
Overflow spring
○
Fault spring - fault has brought together 2 diff types of bedrock
○
Contact springs
○
Karst springs form where groundwater weathers through limestone
bedrock, and water in underground caverns emerges
○
OASES in desert
From spring flow
-
At fault trace
-
Hydrothermal activity
"hot springs" discharge of groundwater @ 30-140 degrees
-
2 settings for formation
Deep groundwater surfaces along faults
○
Geothermal regions (shallow magma)
○
-
Rich in dissolved minerals
-
Extends deep into lithosphere
-
Hot springs + geysers
-
Groundwater
Thursday, 7 June 2018 1:54 pm
Surface water and Runoff
Water cycle
Continuous movement of water on, above and below the surface of the Earth
-
Climate and ocean (Evaporation, precipitation)
Heat from sun causes evaporation
○
Oceans contain 97% of Earth's water
○
Water falls from clouds
○
-
Runoff and lakes
Water flow above ground as runoff, forming streams, rivers, swamps,
ponds, and lakes
○
-
Plant transpiration
-
Infiltration and groundwater
Water penetrates the Earth's crust and comes back out as geysers or
volcanic steam
○
-
25% of water on earth is groundwater!
-
1% is freshwater lakes and rivers
-
What is groundwater?
Water that has infiltrated the soil
-
Gravity leads to infiltration and percolation
-
Unsaturated zone
Contains air
○
Pore spaces filled with water and air
○
Adhesion and cohesion
○
Capillary fringe (moisture sticks to grains)
○
-
Groundwater surface (table)
-
Saturated zone
Pore spaces filled with water
○
-
Porosity = pore space - storage capacity
-
Depends on density of grain packing, size, shape and sorting
-
Permeability = inter-connectedness - depending on porosity + connection
b/w pores) - though flow (fast, slow, no flow)
-
Sand increases porosity
-
Limestone increase porosity (solution cavities)
-
Granite decreases porosity
-
Primary porosity: formed with material (pores), decreases over time due to
compaction, cementation, etc.
Secondary porosity: formed after material (joint, fissure, faults, dissolution etc.)
Groundwater table
Depth to table varies - depends on RECHARGE
-
Effluent: intersection -> water flows out onto surface
-
Influent: not intersecting -> recharge + stocking up
-
Larger distance in higher areas/elevations than in valleys
Valleys: groundwater intersects -> ponds, creeks
○
-
Aquifers: sediment or rock that transmits water easily
Unconfined aquifer: intersects the surface in contact with the atmosphere
Water seeps from ground surface directly above aquifer
○
-
Confined aquifer: isolated from surface, beneath and between aquitards
Impermeable rock layer prevents water from seeping into aquifer from
ground surface above
○
-
Aquiclude: sediment or rock that hinders water flow
Perched water table: accumulation of groundwater above the water
table in unsaturated zone - groundwater trapped above an
impermeable soil layer -> forms saturated material in unsaturated zone
○
Discontinuous aquicludes - prevent downward infiltration to water
table
○
-
Groundwater flow
Flow velocity depends on
Porosity and permeability1)
Hydraulic head (ie potential energy available to drive the flow)
3H = elevation + pressure
§
Hydraulic gradient = difference in hydraulic head / distance (L)
§
Smaller hydraulic head with distance
§
2)
Darcy's law: groundwater flow velocity (v) proportional to hydraulic
gradient
-
Upland recharge pressurizes the aquifer
-
Artesian aquifer: confined aquifer containing groundwater under positive
pressure - causes water level in well to rise to a point where hydrostatic
equilibrium has been reached
Artesian wells tap confined, tilted aquifers
○
Water rises to potentiometric surface
Wells below this surface will flow without pumping
§
○
-
Groundwater flows:
Slowly (friction)
-
In various directions
-
On various spatial scales
-
From RECHARGE ZONE to DISCHARGE ZONE
-
Extraction of groundwater
Depression in ground water table when ppl make wells
-
Water extraction -> lowers water table -> ground water depletion 1)
Subsidence: sinking of the ground because of ground water extraction
Water not in pores -> cities sink
○
Clays reshape -> cant store as much water as before
○
2)
Salt water intrusions - b/ of higher density in groundwater body3)
Groundwater discharge
SPRINGS
Natural groundwater discharge
○
Contact spring: Permeable layer and impermeable layer meet
Perched water table intersect
§
○
-
Overflow spring
○
Fault spring - fault has brought together 2 diff types of bedrock
○
Contact springs
○
Karst springs form where groundwater weathers through limestone
bedrock, and water in underground caverns emerges
○
OASES in desert
From spring flow
-
At fault trace
-
Hydrothermal activity
"hot springs" discharge of groundwater @ 30-140 degrees
-
2 settings for formation
Deep groundwater surfaces along faults
○
Geothermal regions (shallow magma)
○
-
Rich in dissolved minerals
-
Extends deep into lithosphere
-
Hot springs + geysers
-
Groundwater
Thursday, 7 June 2018 1:54 pm
Document Summary
Continuous movement of water on, above and below the surface of the earth. Water flow above ground as runoff, forming streams, rivers, swamps, ponds, and lakes. Water penetrates the earth"s crust and comes back out as geysers or volcanic steam. Depends on density of grain packing, size, shape and sorting. Permeability = inter-connectedness - depending on porosity + connection b/w pores) - though flow (fast, slow, no flow) Primary porosity: formed with material (pores), decreases over time due to compaction, cementation, etc. Secondary porosity: formed after material (joint, fissure, faults, dissolution etc. ) Depth to table varies - depends on recharge. Effluent: intersection -> water flows out onto surface. Influent: not intersecting -> recharge + stocking up. Larger distance in higher areas/elevations than in valleys. Aquifers: sediment or rock that transmits water easily. Unconfined aquifer: intersects the surface in contact with the atmosphere. Water seeps from ground surface directly above aquifer. Confined aquifer: isolated from surface, beneath and between aquitards.
