Hydrogeology Flashcards
Area of Influence
The area within which the potentiometric surface is lowered by withdrawal or raised by injection of water through a well.
Aquifer
A geologic unit that is saturated and sufficiently permeable to transmit significant economic quantities of water to wells and springs.
Capillary Fringe
The lowest part of the vadose zone, immediately above the water table, where water is under pressure that is less than atmospheric pressure.
Confined Aquifer
An aquifer overlain by a confining layer of low permeability.
Connate Water
(Fossil Water) Water trapped in the pores of a sedimentary rock at the time of deposition.
Darcy
A unit of intrinsic permeability = 9.87x10-9cm2
Darcy’s Law
This equation describes groundwater flow.
Q=KiA.
Discharge Area
An area where subsurface water is discharged to land, bodies of water, or the atmosphere.
Effective Porosity
The percentage of the total volume of a soil or rock that consists of interconnected pore space.
Field Capacity
The quantity of water held by the soil or rock against the pull of gravity. It is dependent on the length of time the soil or rock has been undergoing gravity drainage.
Flow Net
Two-dimensional representation of flow lines and equipotentials
(equipotential lines are perpendicular to flow lines)
(Flow line traces path of water particle, visualizes groundwater flow direction)
Ghyben-Herzberg Principle
The principle that states that the depth to which fresh water extends below sea-level is approximately 40 times the height of the water table above sea level.
Head
A measure of the potential energy of a fluid at any given point with respect to a given datum.
Th elevation to which water rises at a given point as a result of reservoir pressure.
Hydraulic Conductivity (K)
The capacity of a porous medium to transmit water.
The rate at which fluid can move through a permeable medium depends on properties of the fluid (viscosity and specific weight) and properties of the medium (intrinsic permeability).
Hydraulic Gradient (I)
Rate of change in total head per unit of distance of flow in a given direction
Intrinsic Permeability (k_i)
A property of the porous medium that measures the relative ease with which a fluid can be transmitted through it under a hydraulic gradient.
It is dependent upon the pore size and is measured in Darcys.
Juvenile Water
Water that is derived directly from magma and is thought to have come to the Earth’s surface for the first time.
Meinzer
A unit of hydraulic conductivity in gpd/ft2.
The rate of flow in gallons per day through a cross section of 1 square foot under a hydraulic gradient at 60ºF.
Perched Groundwater
Unconfined groundwater separated from an underlying body of groundwater by an unsaturated zone.
Permeability
The property of a porous rock or soil for transmitting a fluid.
It measure the relative ease of flow under unequal pressure.
Porosity (n)
The percentage of the bulk volume of a rock or soil that is occupied by void space.
Potentiometric Surface
A surface that represents the total head of groundwater and is defined by the level to which water will rise in a well.
Recharge Area
An area where water infiltrates downward in to the saturated zone.
Runoff (R)
That part of precipitation appearing in surface streams.
Specific Retention (S_r)
Ration of the volume of water a soil or rock can retain against gravity drainage to the total volume of the soil or rock, usually a percentage.
Specific Storage (S-s)
Amount of water per unit volume of a saturated formation that is stored or expelled from storage due to compressibility of mineral skeleton and pore water per unit change in head.
Specific Yield (Sy)
Ratio of the volume of water that drains from a saturated soil or rock due to gravity to the total volume of soil or rock. A percentage.
Specific yield = effective porosity!
Storativity or Storage Coefficient (S)
Volume of water that a permeable unit releases from or takes into storage per unit surface area of the aquifer per unit change in head.
Transmissivity (T)
The capacity of an aquifer to transmit water of the prevailing kinematic viscosity. T=Kb. where b = saturated thickness of the aquifer.
Unconfined aquifer
An aquifer with a water table.
Underflow (U)
Groundwater that flows beneath the bed or alluvial plain of a surface stream, especially in arid regions.
Vadose Zone or Zone of Aeration
A subsurface zone containing water under pressure that is less than atmospheric pressure.
It is measured from ground surface to the water table.
Water Table
The depth where the fluid pressure in the pores of the rock or soil is exactly atmospheric pressure
Watershed
The region drained by a stream or body of water or a drainage divide.
Input Sources
- Deep percolation from precipitation
- Seepage from surface water
- Groundwater underflow into aquifer
- Artificial recharge from irrigation, recharge wells, etc.
- Leakage through confining beds
Losses of Groundwater (output sources)
- Evapotranspiration
- Seepage to surface water
- Groundwater underflow from aquifer
- Discharge to springs
- Artificial discharge from wells, infiltration galleries, and drainage systems
- Discharge through confining beds.
What is below the water table?
Groundwater
What is above the water table?
The capillary fringe
What units are used for change in storage (dS)?
acre-feet-per year (AFY) or gallons per year (GPY)
What is 1 square mile in acres?
640 acres
What is 1 mile in feet?
5280 feet
Where is hydraulic pressure greater than atmospheric pressure?
Below the water table
Why is the vadose zone important?
It supplies water and nutrients to plants, is a zone of human activity, and is the medium that transports water and contaminants and recharges aquifers.
Where is hydraulic pressure negative (less than atmospheric pressure)?
Above the water table in the capillary fringe.
3 types of Preferential Flow:
- Macro pore flow that occurs along worm holes, root holes, or fractures.
- Funneled or focused flow along lenses that may concentrate and deflect the direction of flow.
- Unstable flow. i.e flow that breaks through interfaces and creates fungers that become more conducive to water flow, as compared to adjacent areas that are dry,
What does the Soil Water Retention Curve show?
As the water content increases the metric potential decreases until it approaches zero.
The area within which the potentiometric surface is lowered by withdrawal or raised by injection of water through a well.
Area of Influence
A geologic unit that is saturated and sufficiently permeable to transmit significant economic quantities of water to wells and springs.
Aquifer
The lowest part of the vadose zone, immediately above the water table, where water is under pressure that is less than atmospheric pressure.
Capillary Fringe
An aquifer overlain by a confining layer of low permeability.
Confined Aquifer
(Fossil Water) Water trapped in the pores of a sedimentary rock at the time of deposition.
Connate Water
A unit of intrinsic permeability = 9.87x10-9cm2
Darcy
This equation describes groundwater flow.
Q=KiA.
Darcy’s Law
An area where subsurface water is discharged to land, bodies of water, or the atmosphere.
Discharge Area
The percentage of the total volume of a soil or rock that consists of interconnected pore space.
Effective Porosity
The quantity of water held by the soil or rock against the pull of gravity. It is dependent on the length of time the soil or rock has been undergoing gravity drainage.
Field Capacity
Two-dimensional representation of flow lines and equipotentials
Flow Net
The principle that states that the depth to which fresh water extends below sea-level is approximately 40 times the height of the water table above sea level.
Ghyben-Herzberg Principle
A measure of the potential energy of a fluid at any given point with respect to a given datum.
Th elevation to which water rises at a given point as a result of reservoir pressure.
Head
The capacity of a porous medium to transmit water.
The rate at which fluid can move through a permeable medium depends on properties of the fluid (viscosity and specific weight) and properties of the medium (intrinsic permeability).
Hydraulic Conductivity (K)
Rate of change in total head per unit of distance of flow in a given direction
Hydraulic Gradient (I)
A property of the porous medium that measures the relative ease with which a fluid can be transmitted through it under a hydraulic gradient.
It is dependent upon the pore size and is measured in Darcys.
Intrinsic Permeability (k_i)
Water that is derived directly from magma and is thought to have come to the Earth’s surface for the first time.
Juvenile Water
A unit of hydraulic conductivity in gpd/ft2.
The rate of flow in gallons per day through a cross section of 1 square foot under a hydraulic gradient at 60ºF.
Meinzer
Unconfined groundwater separated from an underlying body of groundwater by an unsaturated zone.
Perched Groundwater
The property of a porous rock or soil for transmitting a fluid.
It measure the relative ease of flow under unequal pressure.
Permeability
The percentage of the bulk volume of a rock or soil that is occupied by void space.
Porosity (n)
A surface that represents the total head of groundwater and is defined by the level to which water will rise in a well.
Potentiometric Surface
An area where water infiltrates downward in to the saturated zone.
Recharge Area
That part of precipitation appearing in surface streams.
Runoff (R)
Ration of the volume of water a soil or rock can retain against gravity drainage to the total volume of the soil or rock, usually a percentage.
Specific Retention (S_r)
Amount of water per unit volume of a saturated formation that is stored or expelled from storage due to compressibility of mineral skeleton and pore water per unit change in head.
Specific Storage (S-s)
Ratio of the volume of water that drains from a saturated soil or rock due to gravity to the total volume of soil or rock. A percentage.
Specific Yield (S_y)
Volume of water that a permeable unit releases from or takes into storage per unit surface area of the aquifer per unit change in head.
Storativity or Storage Coefficient (S)
The capacity of an aquifer to transmit water of the prevailing kinematic viscosity. T=Kb. where b = saturated thickness of the aquifer.
Transmissivity (T)
An aquifer with a water table.
Unconfined aquifer
Groundwater that flows beneath the bed or alluvial plain of a surface stream, especially in arid regions.
Underflow (U)
A subsurface zone containing water under pressure that is less than atmospheric pressure.
It is measured from ground surface to the water table.
Vadose Zone or Zone of Aeration
The depth where the fluid pressure in the pores of the rock or soil is exactly atmospheric pressure
Water Table
The region drained by a stream or body of water or a drainage divide.
Watershed
- Deep percolation from precipitation
- Seepage from surface water
- Groundwater underflow into aquifer
- Artificial recharge from irrigation, recharge wells, etc.
- Leakage through confining beds
Input Sources
- Evapotranspiration
- Seepage to surface water
- Groundwater underflow from aquifer
- Discharge to springs
- Artificial discharge from wells, infiltration galleries, and drainage systems
- Discharge through confining beds.
Losses of Groundwater (output sources)
Groundwater
What is below the water table?
The capillary fringe
What is above the water table?
acre-feet-per year (AFY) or gallons per year (GPY)
What units are used for change in storage (dS)?
640 acres
What is 1 square mile in acres?
5280 feet
What is 1 mile in feet?
Below the water table
Where is hydraulic pressure greater than atmospheric pressure?
It supplies water and nutrients to plants, is a zone of human activity, and is the medium that transports water and contaminants and recharges aquifers.
Why is the vadose zone important?
Above the water table in the capillary fringe.
Where is hydraulic pressure negative (less than atmospheric pressure)?
- Macro pore flow that occurs along worm holes, root holes, or fractures.
- Funneled or focused flow along lenses that may concentrate and deflect the direction of flow.
- Unstable flow. i.e flow that breaks through interfaces and creates fungers that become more conducive to water flow, as compared to adjacent areas that are dry,
3 types of Preferential Flow:
As the water content increases the metric potential decreases until it approaches zero.
What does the Soil Water Retention Curve show?
1 Meinzer equals:
1 darcy equals:
Transmissivity Equation
Hydraulic Gradient Equation
i = dh/l = h1 - h2 / l
hydraulic gradient = change in head / distance between two points where heads are measured
Darcy’s Law:
vd = -K (h1 - h2 / l) = Q / A
Darcy’s Law in terms of Transmissivity:
Q = T * i * w
Flow rate equation
Q = vd *A
or
vd = K*i
Seepage velocity equation
vs = K*i/ne
Ghyben-Herzberg Principle equation
Z = 40*ht
Methods used to control and prevent salt water intrusion into a fresh water aquifer
- Controlled pumping to maintatin seaward hydraulic gradient in the fresh-water aquifer
- Artificial recharge at the ground surface to maintain seaward gradient.
- Placement of pumping trough between ocean and water-supply wells.
- Creation of an injection barrier ridge between ocean and water-supply wells.
- Construction of a man-made subsurface barrier.
Isotopes used to date young groundwater:
Tritium (Hydrogen-3)
Chlorofluorocarbons (CFC-11, CFC-12, CFC-113)
Krypton-85
Isotopes used to date Old Groundwater (60 - 50,000 years)
Radiocarbon (C-12, C-13, C-14)
Isotopes used to date Very Old Groundwater
Chlorine-36
Krypton-81 81Kr
Helium-4
