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Geology 108 Final > Final Study Guide 8 > Flashcards

Final Study Guide 8 Flashcards

Hydrology

1
Q

Sketch the hydrologic cycle. What factors determine whether rainfall will run off or infiltrate?

A

Whether the water runs off or infiltrates is controlled by a number of mechanisms including precipitation rate (how hard it’s raining), soil water content (is it already saturated?), slope (steeper = more run-off) and vegetation (more veg. holds water).

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2
Q

Draw a graph showing the equilibrium water content of a parcel of air vs. temperature. Use this graph to explain why it rains (2 different causes).

A
  1. Two air masses near saturation, but with different temperatures, are mixed
  2. Air rises, causing it to cool, so cant hold as much water, so precipitates
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3
Q

Draw a cross-section across a river channel in an area of gentle topography. Label the following: bank, levee, flood plain, channel.

A
  • Alter hydrologic budget through changes in vegetation, impermeable area, construction, dams, flood control basins
  • Channelization = straighten (and shorten) channels to improve drainage. This increases gradient in channel, leading to higher velocity and more erosion
  • Impact on sediment delivery to deltas, beaches. Reduction in flow cuts sediment delivery. Debris basins intercept sand.
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4
Q

Which portion of a stream meander will be eroded? Why? What is the most critical factor for determining whether erosion or deposition will occur?

A
  • the outer side of the curve, because the velocity is faster on the outer side than on the inner curve. The speed/velocity of the river in relation to the curve.
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5
Q

Why are dams constructed?

A
  • Millions of people depend on dams to help provide the right amount of water in the right place at the right time. Lots of dams provide water for growing crops and for farm animals to drink. They also store water for fighting fires and can help control floods. Dams also give us hydroelectric power.
  • Renewable energy that does not pollute. A dam can cause floods and thus kill people.
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6
Q

What problems can each solve or cause?

A

Solve:

  • Flood control
  • Hydroelectric power
  • Water storage for dry times

Cause:

  • Loss of water through evaporation and infiltration
  • Loss of land and some recreational opportunities
  • Seismicity
  • Downstream impacts: less water, salinization and erosion
  • Siltation in reservoirs
  • Barrier to fish migration for spawning
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7
Q

What is the meaning of recurrence interval? How are event frequency and recurrence interval related?

A
  • An estimate of the interval of time between events like an earthquake, flood or a river discharge flow of certain intensity or size
  • When geologic events are random or quasi-random, it is helpful to represent their frequency as an average time between past events, a “recurrence interval” also known as a “return time.”
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8
Q

Do you expect floods to occur at regularly spaced intervals? Explain why or why not. How can we predict the size of a “100 year flood” on the basis of 20 years of stream gauging?

A
  • We cannot expected them to be at regularly spaced intervals. Certain environmental, natural phenomena can occur, disrupting interval times
  • human activities can also cause floods
  • In the 1960’s, the United States government decided to use the 1-percent annual exceedance probability (AEP) flood as the basis for the National Flood Insurance Program. The 1-percent AEP flood was thought to be a fair balance between protecting the public and overly stringent regulation. Because the 1-percent AEP flood has a 1 in 100 chance of being equaled or exceeded in any 1 year, and it has an average recurrence interval of 100 years, it often is referred to as the “100-year flood”.
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9
Q

What is residence time? How can it be calculated, and what assumption is involved? What are the major reservoirs of water in the earth’s crust, and approximately what is the residence time of water in each?

A
  • If a dynamic system is gaining and losing material at equal rates, the mass of the system is in a steady state, meaning that it doesn’t change over time.
  • dM/dt=Input - Output=0 (Input is equal to output)
  • Residence Time=System Mass/Input or Output
  • Reservoirs of Water:
    > Atmospheres can accumulate water quickly to produce a new storm with a residence time of 2 weeks.
    > Groundwater has long residence times and is not quickly replaced, with a residence time of 10-10,000 y.
    > Oceans have the longest residence times at 4,000 y. (10,000 y > 4,000 y)
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10
Q

What factors can lead to flooding?

A
  • Heavy rain
  • Snowmelt
  • Dam failure
  • Modification of flood plains and levees
  • Coastal floods from storm surge
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11
Q

How can we try to mitigate the impact of floods? Can upstream flood control increase downstream flooding? Briefly explain. What is channelization?

A
  • Channelization = Straighten (and shorten) channels to improve drainage–modify the channel so that it more efficiently transports water–thus decreasing the chance of flooding
  • This increases gradient in channel, leading to higher velocity and more erosion
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12
Q

Write Darcy’s Law and identify terms.

A
  • Q(volume of water)=A(cross sectional area flow) x (K(permeability)x H(vertical drop)/ L(flow distance))
  • A law in geology describing the rate at which a fluid flows through a permeable medium. Darcy’s law states that this rate is directly proportional to the drop in vertical elevation between two places in the medium and indirectly proportional to the distance between them. The law is used to describe the flow of water from one part of an aquifer to another and the flow of petroleum through sandstone and gravel.
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13
Q

Which rock types have the greatest hydraulic conductivity? Why?

A
  • Gravel, because they have a high intrinsic permeability
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14
Q

What geologic characteristics make a formation a good aquifer? Why?

A

An aquifer is a rock material with high permeability that acts as a transport system.

  • Sands and gravels
  • Jointed Units
  • Water occupies pours
  • Sandstones and limestones
  • Low permeability layers
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15
Q

How is hydraulic head (liquid pressure) measured?

A

It is usually measured as a liquid surface elevation, expressed in units of length, at the entrance (or bottom) of a piezometer

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16
Q

Flood Plain

A
  • an area of low-lying ground adjacent to a river, formed mainly of river sediments and subject to flooding
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17
Q

Erosion

A

wearing away, abrasion, attrition; weathering; dissolution, corrosion, decay; deterioration, disintegration, destruction. the process of wearing off or being eroded by wind, water, or other natural agents the gradual destruction or diminution of something

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18
Q

Delta

A

a landform that is formed at the mouth of a river, where the river flows into an ocean, sea, estuary, lake, or reservoir, Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river.

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19
Q

Ogallala Aquifer

A

Giant aquifer in Midwest, whose water level changes since 1940 have appeared to be between a decrease in 15 meters and an increase in 3 meters

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20
Q

Drainage basin

A

catchment area; area of land where surface water from rain converges to a single point at a lower elevation, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean

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21
Q

Natural levee

A

An elongated embankment compounded of sand and silt and deposited along both banks of a river channel during times of flood.

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22
Q

Saltation

A

Transport of a sediment in which the particles are moved forward in a series of short intermittent bounces from a bottom surface.

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23
Q

Antecedent Stream

A

A stream that has retained its early course in spite of geologic changes since its course was assumed.

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24
Q

River Terrace

A
  • a step like landform. A terrace consists of a flat or gently sloping geomorphic surface, called a tread that is typically bounded one side by a steeper ascending slope
  • throughout time there are different levels of floodplains and forms terraces
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25
Q

Stream Gradient

A

the grade measured by the ratio of drop in elevation of a stream per unit horizontal distance, usually expressed as feet per mile or meters per kilometer

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26
Q

Rain Shadow

A

An area having relatively little precipitation due to the effect of a barrier, such as a mountain range, that causes the prevailing winds to lose their moisture before reaching it.

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27
Q

Laminar Flow

A

also known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers

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28
Q

Permeability

A

How easy to move water through rock

29
Q

Meanders

A

a winding curve or bend of a river or road

30
Q

Hydraulic Conductivity

A

a property of vascular plants, soils and rocks, that describes the ease with which a fluid (usually water) can move through pore spaces or fractures

31
Q

Competence

A

the ability to carry a load of a given size; faster rivers have a high competence.

32
Q

Spring

A

the source of the river usually at high elevations, where the water starts to collect, arises from a perched water table/aquifer.

33
Q

Recurrence interval

A
  • RI = (N + 1)/ M
    > N=number of years on record
    > M=number of recorded occurrences of the event being considered
  • the time between events such as floods or earthquakes or other natural processes. Often we are interested in the average recurrence interval, which is determined by finding the mean of a series of recurrence intervals between events
34
Q

Divide

A

waters on each side of the divide never meet, but flow into the same ocean

35
Q

Gradient

A
  • the grade measured by the ratio of drop in elevation of a stream per unit horizontal distance
  • high gradient means steep slope and rapid flow of water
36
Q

Surface runoff

A

the water flow that occurs when the soil is infiltrated to full capacity and excess water from rain, melt water, or other sources flows over the land

37
Q

Aquitard

A
  • a zone within the earth that restricts the flow of groundwater from one aquifer to another. An aquitard can sometimes, if completely impermeable, be called an aquiclude or aquifuge. Aquitards comprise layers of either clay or non-porous rock with low hydraulic conductivity
  • same as a confining layer
38
Q

Floodplain

A
  • an area of land adjacent to a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge
39
Q

Alluvial fan

A
  • sediments deposited as the river widens dramatically (and the velocity of the river decreases) upon going from mountainous valley to plain.
40
Q

Turbulent Flow

A
  • the motion of a fluid having local velocities and pressures that fluctuate randomly
41
Q

Aquifer

A
  • a body of water that is held under ground and is created by the fact that the rocks that surround it are impermeable by water
42
Q

Longitudinal Profile

A

Streamflow everywhere balances input and output (besides during floods); longer term dynamic equilibrium between erosion and sedimentation.

43
Q

Braided stream

A

multiple “braids” (paths) to a stream, formed before meandering streams and occur when the river has a high velocity and sediment content.

44
Q

Base level

A

the theoretical lowest elevation, to which a river may erode, generally is at sea level

45
Q

Bed Load

A

particles in a flowing fluid (usually water) that are transported along the bed. Bed load moves by rolling, sliding, and/or saltating (hopping)

46
Q

Oxbow lake

A

formed when a river creates a meander, due to the river’s eroding the bank through hydraulic action, abrasion, and corrosion. over time, the meander becomes very curved, and eventually the neck of the meander will become narrower and the river will cut through the neck at a time of flood, cutting off the meander and forming the oxbow lake

47
Q

Water table

A

the ground water table is the boundary between the saturated and non-saturated zones of the Earth.

48
Q

Infiltration

A

?

49
Q

Porosity

A

the water storage capability in rocks. For example, non-cemented sandstone has more porosity than cemented sandstone.

50
Q

point bar

A

a depositional feature made of sand and gravel that accumulates on the inside bend of streams and rivers below the slip-off slope

51
Q

recharge

A
  • groundwater recharge, a hydrologic process where water moves to groundwater
  • surface water recharge, a hydrologic process where water runs off to surface watercourses
52
Q

Hydraulic Head

A

a specific measurement of liquid pressure above a geodetic datum

53
Q

Darcy’s Law

A

Q(volume of water)=A(cross sectional area flow) x (K(permeability)x H(vertical drop)/ L(flow distance))

54
Q

Terrace

A

a step-like landform that borders a shoreline or river floodplain

55
Q

Vadose Zone

A
  • the part of Earth between the land surface and the top of the phreatric zone, the position at which groundwater is atmospheric pressure
  • aka: the ground between the surface and the groundwater
56
Q

Saturated Zone

A

the zone in rock layers where all the pores are filled with water

57
Q

Perched Aquifer

A

an aquifer that rests on a layer of impermeable rock at a higher elevation.

58
Q

Settling Velocity

A
  • The fastest settling particles are huge, heavy, spherical molecules. The slowest settling particles, which sometimes cannot be settled accurately or properly, are tiny, light, irregularly shaped molecules. And for anything in between, here is a general guide as to what characteristics increase the rate of thickening
59
Q

Artesian Aquifer

A

an artesian aquifer contains very high pressure, so when a well taps into it, the water squirts out without being pumped

60
Q

Confined Aquifer

A

those in which an impermeable dirt/rock layer exists that prevents water from seeping into the aquifer from the ground surface located directly above; instead, water seeps into confined aquifers from farther away where the impermeable layer doesn’t exist

61
Q

Unconfined Aquifer

A

those into which water seeps from the ground surface directly above the aquifer

62
Q

Capacity

A

the total sediment carried by the river.

63
Q

Groundwater Overdraft

A

the process of extracting groundwater beyond the safe yield or equilibrium yield of the aquifer

64
Q

Cone of depression

A
  • occurs in an aquifer when groundwater is pumped from a well
  • In an unconfined aquifer (water table), this is an actual depression of the water levels
  • xIn confined aquifers (artesian), the cone of depression is a reduction in the pressure head surrounding the pumped well
65
Q

Tributary

A

stream/river that flows into a main stream, river or lake but not into the ocean. Deals with mountain divides and drainage networks that eventually lead to oceans.

66
Q

Dendritic

A

tree-like, most common form of drainage system. Twigs of the tree are the contributing streams that join together into a river.

67
Q

Drainage

A

system where smaller and larger rivers merge into streams, leads to the formation of a divide.

68
Q

Trellis drainage

A

characteristic of folded mountains, where smaller tributaries feed into a river valley from steep slopes of the mountains, usually at 90 degrees

69
Q

Grade

A

measures steepness of river.

Geology 108 Final (9 decks)

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