Groundwater Hydraulics: Introduction to groundwater Flashcards
True or False
Groundwater only occurs above a water table in soils and geological formations.
False
Groundwater that is at or greater than atmospheric pressure occurs _______ the water table.
beneath
What is an aquifer?
A) A dry geological unit
B) A saturated permeable geological unit that transmits water
C) A non-permeable geological unit
B) A saturated permeable geological unit that transmits water
What is the difference between an aquitard and an aquiclude?
An aquitard is less permeable and may transmit some water, acting as a barrier to groundwater flow, whereas an aquiclude is incapable of transmitting significant quantities of water and acts as a complete barrier.
True or False
The Chalk Aquifer has very large pores which allow water to flow freely through the material.
False (It has very small pores, and water flows mainly through cracks in the rock.)
The Sandstone Aquifer has grain sizes that are generally _______ than those in the Chalk Aquifer.
larger
Which of the following is NOT a type of superficial deposit?
A) River alluvium
B) Limestone
C) Beach deposits
B) Limestone
True or False
An unconfined aquifer has water under pressure that is greater than atmospheric pressure.
False (It has atmospheric pressure)
In a confined aquifer, the water is confined by two _______ or _______.
aquitards, aquicludes
What is the base flow index in the context of valley aquifers?
It indicates that most of the water in the stream has come from groundwater.
True or False
The groundwater divide is the point at which the water table is at its lowest and water flows away from it.
False (It is where the water table is at a maximum, and water flows in different directions either side of it.)
True or False
In arid zones, valley aquifers are primarily recharged through regular rainfall events.
False
Where are valley aquifers found?
Temperate climates where the soil is porous and
permeable.
How do valley aquifers get recharged?
Rainfall infiltrates and saturates the rock up to a level called the phreatic
surface or water table.
In arid areas, the only significant recharge mechanism for valley aquifers is through _______ from mountainous areas or flash floods.
water flow
Where is the WT the highest in valley aquifers in arid zones?
Beneath the actual valley.
What characterizes an alluvial aquifer?
A) It is confined and isolated from surface water
B) It is found along the course of a stream or river and interacts with it
C) It contains mostly impermeable rock
B) It is found along the course of a stream or river and interacts with it
What is a perched aquifer?
A perched aquifer is a saturated lens of relatively low permeability, bounded by a perched water table, sitting on top of a main aquifer.
True or False
Perched aquifers typically provide large, stable water supplies.
False - storage involved relatively small
Baseflow is important because it allows rivers to _______ during dry periods.
flow
Why is baseflow important?
- Maintains
conservation
wetland habitats - Source of surface
water supply during
drought
Which catchment type reacts quickly to rainfall events with flashy river flow?
A) Groundwater dominated
B) Surface-water dominated
C) None of the above
B) Surface-water dominated
True or False
The River Kennet is an example of a surface-water dominated catchment.
False (It is groundwater dominated)
Groundwater in groundwater dominated catchments typically maintains baseflow even when it is not _______.
raining
What is the primary source of baseflow in groundwater dominated catchments?
Groundwater through springs and upwelling from the river.
True or False
Groundwater systems require high capital investment initially compared to surface water systems.
False (They usually require relatively low capital investment)
Field data for groundwater modelling are often sparse and require extensive _______ and inference.
interpolation
True or False
Groundwater is the most extracted raw material in the world, with annual extraction volumes between 800 and 1000 km³.
True
Groundwater is stored in the _______ or pore spaces within rock, which can be between grains or within cracks and fractures.
voids
What does the term “porosity” in the context of groundwater refer to?
A) The total amount of water in the ground
B) The measure of the void spaces in rock, expressed as a percentage
C) The depth at which groundwater is found
B) The measure of the void spaces in rock, expressed as a percentage
What are the four types of porosity mentioned?
Total porosity, effective porosity, drainable porosity, and kinematic porosity.
True or False
Drainable porosity refers to the volume of voids filled with water that cannot be drained by gravity.
False (It refers to the volume of voids that can be drained by gravity)
Effective porosity is the volume of voids that _______.
accept water
What is the Representative Elementary Volume (REV) in the context of porosity?
A) The smallest volume at which groundwater can be stored
B) A specified volume over which porosity is averaged to minimize local variations
C) A large volume that includes significant structural changes in rock
B) A specified volume over which porosity is averaged to minimize local variations
True or False
The resistivity method for measuring porosity depends on the conductivity of rock minerals.
True
Kinematic porosity depends on _______.
pore size distribution
How do you calculate the formation factor?
F = resistivity if the rock/resistivity if water contained in the rock
Why might groundwater be considered a critical resource for food production and safe drinking water?
Because it is a key source of water for these purposes, supporting agriculture and providing potable water where surface water might be unavailable or contaminated.
What is the order of magnitude of the different types of porosity?
n > n_e > n_d ≈ n_k
How do you calculate effective porosity?
V_(voids accepting water)/V_T
How do you calculate drainable porosity?
V_(voids drained by gravity)/V_T
How do you calculate kinematic porosity?
V_(flowing water)/V_T
What is Archies’s empirical equation?
F = C/n^m
Where m varies from 1.3 ~ 2
