mastering geology chapter 17 groundwater
How do a gaining stream and a losing stream differ?
A gaining stream exists when the elevation of the water table is higher than the surface of the stream. in contrast, a losing stream exists when the elevation of the water table is lower than the surface of the stream. A gaining stream gains an influx of groundwater through the streamed, whereas a losing stream loses water to the groundwater through the streamed.
In the late twentieth century, Hidden River Cave had suffered from significant pollution and bad odor. Although various chemical pollutants had been dumped or spilled nearby, none had intentionally been disposed of in Hidden River Cave. How did they end up there?
Hidden River Cave and the dump sites are connected via various sinkholes and subterranean passages.
The Mammoth Plateau near Mammoth Cave National Park is higher in elevation than the surrounding landscape and separates the Sinkhole Plain from the Green River. As the Mammoth Plateau is a major topographical barrier, how does precipitation that falls on the Sinkhole Plain make it into the Green River Valley?
Precipitation infiltrates into the subsurface via sinkholes and flows through subterranean passages to the Green River Valley.
What problem is caused by pumping groundwater for irrigation in the Southern High Plain?
a low precipitation rate and a high evaporation rate allow little water to recharge the aquifer.
The presence of the Green River has a significant impact on the water table in the area around Mammoth Cave National Park in Kentucky. How does the relationship between the Green River and the water table affect cave passage formation?
as the Green River erodes downward, the water table will lower as the groundwater flow toward the stream, carving new cave passages further from the surface.
Why might the ground subside after groundwater is pumped to the surface?
as water is withdrawn, the water pressure drops, and the sediment is left to support the weight on top of it. as a result, the sediment packs more closely together, causing the ground to subside.
Low porosity and permeability
granite gneiss
What geologic roles does groundwater play?
groundwater erodes bedrock through dissolution groundwater sustains streams during periods of no rainfall
What is groundwater, and how does it relate to the water table?
groundwater is water that occupies the zone of saturation within the ground. the water table is the upper limit of the groundwater.
How does the movement of groundwater relate to hydraulic gradient and hydraulic conductivity?
groundwater moves more quickly down steeper slopes than down shallow slopes. for this reason, the water table is known as the hydraulic gradient. groundwater flows more rapidly through sediments having greater permeability than through materials having lower permeability. this factor is known as hydraulic conductivity.
In order for an aquifer to be useful for reliable water extraction, what kind of porosity and permeability should it have?
high porosity, high permeability
What significant problem might arise when groundwater is heavily pumped at a coastal site?
if the groundwater withdrawal exceeds recharge, the saltwater will become high enough to be drawn into the wells
Which aquifer listed below would be the most effective in purifying polluted groundwater, and why?
permeable sandstone; the pores between grains are large enough to let water through but small enough to block contaminants.
Worldwide, the largest percentage of freshwater readily available to humans is stored in ______.
pore spaces between rocks and sediments
The depth below groundwater is the water table. Also, the structure and arrangement of rocks can affect the way groundwater flows. Which of the following can control groundwater's ability to flow?
pores/fractures in the rock change of water table elevation
Please contrast porosity and permeability.
porosity is the percentage of the total volume of rock or sediment that consists of pore spaces, whereas permeability.
List the features layered in the cross section of a flowing artesian well from top to bottom.
pressure surface, flowing artesian well, aquitard, aquifer, aquidtard
Where is the majority of liquid freshwater found?
rocks and sediments
What warms the waters that flow at Hot Springs National Park, Arkansas, and at Warm Springs, Georgia?
the geothermal gradient
What is the source of heat for most hot springs and geysers, and how is this reflected in the distribution of these features?
the heat sources for most hot springs and geysers are magma bodies and igneous rocks. thus, hot springs and geysers are often located where igneous activity occurs.
When rain falls on land, what factors influence the amount of water that soaks in?
the nature of the surface material the steepness of the slope the intensity of rainfall the amount of vegetation on the surface
Why do some artesian wells not flow at Earth's surface?
the pressure surface is below ground level
What is the cone of depression?
the shape that the water table takes on near a pumping well
How does the water table change around a pumping water well?
the water table elevation decreases
High porosity and permeability
unconsolidated gravel and sand sandstone conglomerate
Is the water table usually flat like the surface of a kitchen table, and why or why not?
underground, the water table is shaped like a subdued replica of the land surface. additionally, the water surfaces of rivers and lakes are the level of the water table.
What is infiltration?
water soaking into the ground
When will a cone of depression stop enlarging?
when the amount of water flowing toward the well equals the amount of water being pumped out of the well.
When might a well, Well A, go dry?
when the cone of depression of a second well intersects the deepest part of Well A.