UNIT11 Groundwater Flashcards
what is groundwater
the liquid water that resides in sediment or rock under the surface of the earth
what percent of water is saltwater in ocean
97.2%
what percent of of water is in ice caps and glaciers
2.14%
what percent of water is groundwater
0.61%
what percent of water is surface water (not salty)
0.009%
what is a pore
a pore is any open space within a volume of sediment or a body of rock
the total volume of open space in a body or rock or volume of sediment is termed
porosity %
What is the porosity of vesicular basalt
20%
what is the porosity of non vesicular basalt
<1%
What is the porosity of limestone
25%
What is the porosity of Shale
5%
What is the porosity of Well sorted elian sandstone
30%
What is the Porosity of Poorly sorted Sandstone
15%
What is the Porosity of conglomerate unconformity
30%
What is the porosity of granite and marble
<1%
What is primary porosity
Open space or porosity that originally formed with the rock
Primary porosity decreases with
burial compaction and cementation
crystalline rocks have ____ porosity
very little
What is secondary porosity
New pore space formed after the rock first formed
When rocks fracture what kind of porosity can occur
Secondary porosity
What is permeability
Permeability refers to the ease with which fluids can pass through a material via an interconnected network of pores
Is permeability the same as porosity
NO
Permeability depends on
The number of available conduits
The size of the conduits
The straightness of the Conduits
Can rocks with high porosity have low permeability
Yes, Vesicular basalt is an example
How might a rock have high porosity yet low permeability
Rock surrounds each pore meaning there are no conduits connecting the vesicles
What is an aquifer
An aquifer is a high-porosity, High permeability rock that transmits water easily
What is an aquitard
an aquitard is a low permeability rock that hinders water flow
what are the two types of aquifers
confined aquifers and unconfined aquifers
The Ogallala Formation is an example of
an Unconfined aquifer
The Dakota sandstone is an example of
a confined aquifer
What makes an unconfined aquifer
The aquifer reaches the ground surface
What makes a confined aquifer
A confined aquifer lies beneath an aquitard
What is the Water Table
The water table is the top of the groundwater reservoir in the subsurface
The water table separates….
the unsaturated zone from the saturated zone
The unsaturated zone of the subsurface is known as the _____, and is characterized by
The Vadose zone is above the water table
The saturated zone of the subsurface is known as the ____, and is characterized by
The phreatic zone lies below the water table
Why do ponds dry out in droughts
The water table falls below the Pond
The water table changes due to
Seasonal variations in rainfall and infiltration and can also rise and fall with the tides in coastal areas
Topography can be used to estimate groundwater…..
Head and flow direction
Groundwater flows ____ Hills
down
A perched water table
Sits above a larger water table but cannot join it as it is “perched” on a small local aquitard
The water table discharges by flowing into
Local or regional Discharge areas, which are surface water deposits
The water table recharges via
rainfall via infiltration
Local discharge areas are more specific than
Regional Discharge areas
Deeper groundwater flow paths usually
Take longer to reach the discharge
about how fast do ocean currents move
3km/h
About how fast do steep river channels flow
30km/h
About how fast does groundwater flow
0.00002km/h or 2cm/h
Groundwater can be source of
Clean Water
Describe Hydraulic Head
The potential energy in higher elevation water and pressure exerted by the weight of overlying water causes an energy balance in the system and causes flow
Water deeper below the water table feels ___ pressure than at a lesser depth
More
Darcy’s Law States
That discharge volume is proportional to the hydraulic gradient multiplied by the permeability K or k - hydraulic conductivity for water
Darcy’s Law is
Q=K(h1-h2)/j)A
What kind of unconsolidated deposit has particularly high hydraulic conductivity
Gravel
High permeability will
increase flow rate
Steeper Gradient will
Increase flow rate
Low permeability will
Decrease flow rate
Shallower Gradient will
Decrease flow rate
Darcy’s Law is measured using a ____ or a _____
Piezometer or monitoring well
Wells are
Hole that are excavated or drilled to obtain water
Springs are
Natural Groundwater Outlet
A spring develops where
The water table intersects the surface
How do Wells work
The base of the well penetrates the aquifer below the water table
Water from the pore spaces migrate to the well and fill it to the depth of the water table
You need to monitor the rate of pumping and rate of recharge or drawdown might occur
What is Drawdown
When the water table is lowered due to Well water collection
What is a cone of depression
the cone shape of the water table created by the drawdown of wells
How do Artesian Wells work
the well punctures an aquitard into an aquifer and water rises to the potentiometric surface
What is the potentiometric surface
The imaginary water table that would occur if the aquifer was not contained by an aquitard
What is groundwater depletion
When so much water is pumped away the water level drops significantly and can even dry out rivers and swamps
A poorly planned septic tank and well can potentially result
in conical depressions causing a change in flow direction, and the release of contaminants into the groundwater
Saltwater intrusion comes from
Pumping using a well along the coast until eventually the removal of fresh groundwater causes salty groundwater to be pulled into your well
Vertical Saltwater Intrusion can be caused by ___ and causes ___
cause by breached dikes and flooding and causes root zone salinity,food scarcity, and water scarcity by contaminating aquifers
In land subsidence
the removal of groundwater causes pores to collapse and causes fissures and scarps
Natural contamination is when
Naturally occurring groundwater contains unwanted substances including iron ,manganese ,hydrogen ,, arsenic and other mineral deposits
Natural Contamination makes water ____
Hard and can cause pipe and faucet damage
Human cause contamination can come from
Septic tanks, Mines, salt, landfill, surface tanks, fertilizers, animal sewage, and injection wells
A contaminant Plume is
when groundwater transports pollutants away from a source of input and creates a contaminant plume.
Contaminant cleanup uses
Steam injection beneath the contaminated plume to drive the water upward in extraction wells
Contaminant cleanup is
Very expensive
Groundwater Overabundance is
An unwanted effect of a rising water table
Groundwater Overabundance can cause
Basement flooding
Catastrophic slop failure (vajont dam)
Why do caves form
Co2 reacts with water to form carbonic acid, this happens particularly to limestone. the more soluble beds are reacted away and form conduits or caves
When caves form in limestone bedrock, the region is at risk of
Sinkholes
The water table is important to monitor because it change the properties of
underlying rock and sediment
the largest reservoir of fresh water on earth is
Groundwater
Porosity and permeability determine…
how much groundwater there is and its ability to flow
Two types if permeability
Primary and Secondary
Water is stored underground in permeable ______ and unpermeable ____
Aquifers and Aquitards
The water table is the point at which all underling rock is
saturated
Groundwater flows along a similar path to
the overlying topography
Wells and springs are locations where
Groundwater comes to the surface
Sinkholes can form when
groundwater eats away underlying rock
Some human issues regarding groundwater include
Groundwater depletion, groundwater polution, groundwater overabundance
