GEOLOGY NOTES 1
What is permeability?
Ability to transmit water
What is base level?
The downward limit of erosion.
How does the water table change around a pumping water well?
The water table elevation decreases.
Which environmental issue most commonly affects groundwater aquifers in coastal or island areas?
saltwater contamination
As stream velocity slows, the smallest particles get deposited first.
f
Point bars are locations where erosion occurs whereas cutbanks are locations where deposition occurs.
f
The following photo shows a typical cut bank on the Missouri River (iPhone for scale). Note the steep profile with fine-grained sediments above coarser sands and gravels. which is true?
A cut bank is located on the outside of a meander bend.
Which of the following accounts for the largest usage of groundwater in the United States?
Agriculture and irrigation
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As water is withdrawn, the water pressure drops, and the sediment is left to support the weight on top of it.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.
What is the difference between capacity and competence?
Capacity is the maximum load of solid particles a stream can transport per unit of time, whereas competence is a measure of a stream's ability to transport particles based on size rather than quantity.
What localized lowering of the water table is present in this figure?
Cone of depression
_________ Load - ions in solution that are dispersed throughout the flow. _________load - larger sediments that bounce, roll, or slide along the bottom. _________ Load - fine sediments that are held up by the water and carried throughout the water column.
Dissolved, bed, suspended
Why does the Mississippi delta consist of seven coalescing subdeltas?
Each subdelta formed in sequence when the main flow of the river was diverted from one channel to a shorter, more direct path to the Gulf of Mexico. After each channel was abandoned, coastal erosion modified the newly formed subdelta.
Groundwater migrates from areas of low pressure to areas of high pressure.
F
The water table undulates with the ground surface. It is low where the ground surface is high and high where the ground surface is low.
F
Which 19th-century scientist developed the following equation that determines the discharge of an aquifer?Q=KA(h1−h2)d
Henri Darcy
Examine the groundwater flow patterns around Point X. Into which bodies of water (if any) will water that infiltrates at Point X eventually discharge?
LEFT LAKE
A __________ is separated from the groundwater system by the unsaturated zone.
Losing stream (disconnected)
Give It Some Thought: Aquifers - Suitable Rocks/Geologic Units for an AquiferPermeable rock strata that allow for the easy flow of groundwater through pores are called an aquifer. Groundwater moves by twisting and turning through small, interconnected openings. The smaller the pore spaces, the slower the groundwater flow. Porosity, the amount of pore spaces in a rock, and permeability, the ability of a material to transmit fluid, are two important concepts in groundwater movement and the formation of aquifers. Most sedimentary rocks, such as cavernous limestone, have a lot more pore spaces than igneous and metamorphic rocks, and in the case of igneous and metamorphic rocks, fractures must be present to provide voids or pores for an aquifer to develop.Porosity alone cannot measure a rock's capacity to yield groundwater, because rocks or sediments may be very porous, yet still not allow water to easily move through them. For example, clay has a high water storage capacity (porous), but its pore spaces are too small to make it a good aquifer. Hence, a rock or material has to have a high level of porosity and permeability to have the likelihood of being a good aquifer.
Low:-granite (igneous rock) with very few to no cracks-gneiss (metamorphic rock that used to be granite and underwent intense pressure)High:-unconsolidated gravel and sand-sandstone (sedimentary rock composed of sand grains)-conglomerate (sedimentary rock composed of various sizes of sediment such as pebbles and sand grains)
Where is the zone of sediment production in a stream?
Near the headwaters
How does water get from the oceans onto land?
Ocean water evaporates to form gaseous water and moves into the atmosphere, where it condenses into liquid water and falls out of the atmosphere to land as rain.
If gravity pulls infiltrating water downward, what force allows water to be pulled upward at the capillary fringe?
Surface tension
What would happen to atmospheric water if Earth were mostly covered with land?
The atmosphere would contain less water.
An agricultural company purchased a large tract of land adjacent to your property and built a group of large commercial greenhouses on it. This company uses a lot of water to keep the plants green and healthy. During a particularly dry summer, the amount of water available to your well starts to decrease. Since you are utilizing the same aquifer, what has this company done to the water supply?
The company has compromised the aquifer and is essentially mining the water from it.
What does the hydrologic cycle describe?
The hydrologic cycle describes how liquid and gaseous water move between the ocean, atmosphere, and land.
What would happen to the oceans if surface runoff and groundwater flow did NOT occur?
The oceans would become smaller.
What are the differences between laminar flow and turbulent flow?
Unlike a laminar flow, a turbulent flow erodes by lifting sediment from the streambed. Unlike laminar flow, a turbulent flow occurs where the flow resistance in the channel is the greatest. A laminar flow moves in nearly straight-line paths parallel to the stream channel; a turbulent flow moves in an erratic fashion with horizontal and vertical swirling motions.
How will channel velocity change along the longitudinal profile of a stream?
Velocity will start low and gradually increase toward the mouth due to increasing discharge downstream
What is porosity?
Volume of pore space in a material
Which of the following is a true statement about groundwater?
Water in a groundwater system is stored in subsurface pore spaces and fractures.
What is infiltration?
Water soaking into the ground
What is a flood?
When discharge in a river exceeds the river's capacity
Rock, such as shale or clay, or other unlithified sediment can produce layers that are well sorted, but do not allow water to move through them. Which of the following terms is most accurate for this type of layer?
an aquitard
People want to build their houses where they will have the right amount of groundwater. If the aquifer is shallow, then it will be less costly to drill a well than if the aquifer is deep. But if the aquifer is limited in size and is not recharged with water, a well might run dry eventually. Running out of water because a shallow well runs dry is a better option than having to dig deeply to find a new water source. It is actually cheaper to run piping from one source to another than to dig very deeply for a well and pump it to the surface. While it is flowing underground, water may encounter zones of weak or easily dissolved rock, usually limestone. Water can dissolve rock and cut underground streams and lakes. This is how caves form in limestone rocks. On the surface, the ground may cave in, forming sinkholes, or streams may disappear underground and then reappear. This type of landscape is called karst topography. While the land surface in areas with karst topography might be unsteady and ill-suited for building, freshwater just below the surface is an abundant resource. Below is an image of different sites for houses: a shallow aquifer, a deep aquifer, and a karst area with lots of caves near the surface. Sort the sites in terms of the best to worst places to build a house considering both the availability of water resources cost and how water affects the land surface.
best to worst
What are the three types of beds that comprise a delta from bottom to top?
bottomset beds, foreset beds, topset beds
The ________ is an elevational point that divides an entire continent into large drainage basins.
continental divide
_________− form where streams enter large lakes or oceans. _________− formed by floodwaters on either side of a stream. _________−− formed by mountain streams emerging onto a flat plain. _________−− small deposits that form in the stream channel.
dELTA, levee, alluvial fan, bar
If the velocity of a stream decreases, competence __________ and sediment is _____.
decreases, deposited
The geographical area where all surface water converges to one location is called its__________. 2. A delta forms at the __________ of a river, where the velocity of the water flow decreases and deposition is highest. 3. The volume of water flowing past a certain point in a given amount of time is a river's __________. 4. The __________ of a river have a steep gradient, high channel roughness, and low water volume. 5. A stream with a low to moderate gradient, carrying most of its load in suspension, should be characterized by many curves and bends called __________. 6. A river with a well-developed __________ has a flat low-lying channel and experiences flooding during periods of high discharge.
drainage basin, Mouth, discharge, headwaters, meanders, flood plain.
What is the cone of depression?
he shape that the water table takes on near a pumping well
When will a cone of depression stop enlarging?
hen the amount of water flowing toward the well equals the amount of water being pumped out of the well
As a hydrogeologist looking for a source of water for a housing development, which of the following attributes would you look for in a layer of sediment or sedimentary rock?
high porosity and permeability
Where is most of Earth's freshwater found?
ice at earths surface
Which of the following particle sizes is most likely to make up a stream's suspended load?
silt
The water table __________.
surface is a subdued version of the surface topography
Transpiration moves water from _______.
the biosphere to the atmosphere
The quantity of groundwater that can be stored within sedimentary material is most directly controlled by which of the following parameters?
the porosity of the material
What is evapotranspiration?
the transfer of water directly from the land's surface into the atmosphere
The ________ is the point in the subsurface where 100% of the pore spaces are filled with water.
zone of Saturation
In the __________, groundwater fills the pore space
zone of sat
What are the three main zones of a river system from highest to lowest?
zone of sediment production, zone of transportation, and zone of deposition
