ESC1000 Chapter 3 HW
what factors cause water to follow the paths shown in the above diagram?
Water that enters the groundwater at the recharge areas moves downwards due to gravity, and then loops upwards to the discharge areas due to water pressure.
What is a stream's longitudinal profile?
What is a stream's longitudinal profile?
Where is the largest liquid freshwater reservoir in the hydrosphere?
in groundwater
Where within streams are pebbles transported by currents?
in the bed load
How do stalactites and stalagmites form?
Stalagmites form when calcite-rich water falls to the floor from the ceiling, splattering minute amounts of calcite on the floor. After many such depositions, a stalagmite begins to take shape. Stalactites form on the ceiling when water seeps through the ceiling and deposits calcite. Eventually a soda straw develops, which develops into a stalactite after many more depositions of calcite.
If a stream flows over a layer of resistant rock that serves as a temporary base level, what will occur as the stream adjusts to the true base level?
The distance between the resistant rock and the headwaters will decrease through time, as resistant rock is eventually eroded.
In the above diagram, two wells are drilled to the same depth. Why was one well successful but the other not?
The left well is unsuccessful because it reaches into the unsaturated zone, whereas the well on the right is successful because it reaches into water on a perched aquifer.
How do the formations of incised meanders relate to stream terraces and base level?
When the base level drops, the incised meander erodes both downwards and back and forth across the flood plain. After several reoccurrences of base level drops, stream terraces are left as evidence of past base level drops.
What kind of aquifer might produce a flowing artesian well?
a confined aquifer
What feature may form where a stream enters the relatively still waters of a lake, an inland sea, or an ocean?
a delta
What is alluvium?
any sediment that is deposited by a stream
List the features layered in the cross-section of a flowing artesian well from top to bottom.
aquitard, aquifer (containing well base), aquitard, flowing artesian well, pressure surface
In what ways does a stream transport its load, and which part of the load moves most slowly?
as a bed load, which is the slowest mode of particle transport in streams as a dissolved load as a suspended load
Describe the problem associated with pumping groundwater for irrigation in parts of the High Plains.
A low precipitation rate and a high evaporation rate allow little water to recharge the aquifer.
Which choice describes how an erosional floodplain develops?
A stream approaches a level orientation, stops eroding, and starts meandering. As the stream meanders, it widens the valley by continuously eroding the banks on both sides. This widened valley is an erosional floodplain.
how was the spring in the above graphic created?
An aquitard blocked the downward movement of groundwater, causing it to move laterally. Where the permeable layer crops out at the surface, a spring resulted
Which of the choices below correctly defines base level and differentiates between ultimate base level and local (temporary) base level?
Base level is generally defined as the lowest elevation to which a stream can erode its channel. The ultimate base level is sea level, whereas local base levels are lakes, resistant layers of rock, and rivers that act as base levels for their tributaries.
Where are bedrock channels more likely to be found?
Bedrock channels are typically found in the headwaters of river systems where streams have steep slopes.
What is the difference between capacity and competence?
Capacity is the maximum load of solid particles a stream can transport per unit time, whereas competence is a measure of a stream's ability to transport particles based on size rather than quantity
How does groundwater create caverns?
Caverns are created when acidic groundwater dissolves and carries away limestone over time.
What are distributaries, and why do they form?
Distributaries are channels that are shorter and have higher gradients than the original stream channel. They form when the original channel becomes choked with sediment, and carry water away from this channel.
How does drawdown relate to the cone of depression? View Available Hint(s)
Drawdown is when the water table around a well is lowered due to water discharge. This depression in the water table is conical, and is called a cone of depression.
Which of the following choices correctly describes two processes that cut channels into bedrock?
During abrasion, the bed and the banks of the river are constantly bombarded by the particles carried in the water. During corrosion, soluble bedrock such as limestone is gradually dissolved by the flowing water.
What happened in the San Joaquin Valley as a result of excessive groundwater pumping?
Excessive groundwater discharge caused the water pressure to drop within the sediment, resulting in land subsidence.
Describe basic flood-control strategies.
Flood-control dams are built to store floodwater and then let it out slowly. Channelization involves altering a stream channel to speed the flow of water to prevent it from reaching flood height. Artificial levees are earthen mounds built on the banks of a river to increase the volume of water the channel can hold.
Is flow velocity usually greater at the head or at the mouth of a stream? Explain.
Flow velocity is usually greater at the mouth of the stream than the head of the stream due to an increase in channel size, an increase in channel discharge, and a decrease in channel roughness near the mouth.
How do gradient, discharge, channel size, and channel roughness typically change from the head to the mouth of a stream?
From the head of a stream to its mouth, the gradient and channel roughness decrease while the discharge and channel size increase.
About what percentage of freshwater is groundwater? How does this change if glacial ice is excluded?
Groundwater comprises 30.1 percent of Earth's total freshwater and 96 percent of Earth's liquid freshwater.
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.
What geological roles does groundwater play?
Groundwater sustains streams during periods of no rainfall. Groundwater erodes bedrock through dissolution.
How might a stream channel become braided?
If a large portion of a stream's sediment load consists of coarse material and the stream has a highly variable discharge, a stream channel can become braided.
How do regional floods and flash floods differ?
In contrast with regional floods that can usually be predicted, flash floods occur so suddenly that they cannot be predicted. Flash floods are more limited in geographical extent than regional floods. Flash floods generally cause more loss of human life.
Why do V-shaped valleys often contain rapids and waterfalls?
In many V-shaped valleys, resistant bedrock upstream creates rapids by acting as a local base level while downcutting occurs in less resistant bedrock downstream.
How do natural levees form?
Levees form as the result of the repeated flooding of a river within a floodplain. Each time the floodwaters recede, the suspended load that had been carried by the water is deposited, building up levees along the banks of the river.
In which ways do sinkholes form? PLEASE SELECT ALL THAT APPLY.
Limestone is dissolved by rain water, the bedrock surface lowers, and groundwater that is flowing in the passages below washes away the soil. A roof of an already formed cavern collapses under its own weight.
How does an oxbow lake form?
On oxbow lake forms when the bend of a meandering river is isolated from the river due to erosion forces creating a cutoff in the main river channel. This isolated bend becomes the oxbow lake.
Please contrast porosity and permeability.
Porosity is the percentage of the total volume of rock or sediment that consists of pore spaces, whereas permeability is the ability of a rock or sediment to transmit fluid.
What is the primary energy source that drives the hydrologic cycle?
the Sun
When rain falls on land, what factors influence the amount of water that soaks in?
the intensity of rainfall the steepness of the slope the amount of vegetation on the surface the nature of the surface material
Which of the following are considered triggers for mass-wasting events? Choose all that apply.
earthquakes oversteepening of the slope oversaturation of the material
The water table _______.
is at the surface in swamps
Which of the following might occur after excessive groundwater withdrawal?
land subsidence
What is meant by a nonstructural approach to flood control?
limiting certain activities or land uses, and implementing appropriate zoning regulations in high-risk flood areas
Which of the following methods of flood control is the cheapest and most effective?
nonstructural floodplain management
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
Which of the choices below is an erosional karst feature?
sinkhole
