Chapter 8: The Hydrologic Cycle

Question 1

Define ‘Aerated zone’.

Answer 1

Region above the water table where pore spaces are not completely filled with water, and where water is held by capillarity.

Question 2

Define ‘Alluvial fan’.

Answer 2

A fan-shaped body of alluvium typically built where a stream leaves a steep mountain valley.
An alluvial fan is a fan-shaped deposit at the base of an upland, where a stream emerges onto low- land and abruptly loses energy.

Question 3

Define ‘Alluvium’.

Answer 3

Sediment deposited by streams in nonmarine environments.

Question 4

Define ‘Aquiclude’.

Answer 4

A body of impermeable or distinctly less permeable rock adjacent to an aquifer.

Question 5

Define ‘Aquifer’.

Answer 5

A body of permeable rock or regolith saturated with water and through which groundwater moves.

Question 6

Define ‘Braided stream’.

Answer 6

A channel system consisting of a tangled network of two or more smaller branching and reuniting channels that are separated by islands or bars.

Question 7

Define ‘Cave’.

Answer 7

Natural underground open space, generally with an opening to the surface.

Question 8

Define ‘Channel’.

Answer 8

The passageway in which a stream flows.

Question 9

Define ‘Channelization’.

Answer 9

The engineering modification of a stream channel for the purposes of flood control and control of erosion.

Question 10

Define ‘Condensation’.

Answer 10

The formation of a more ordered liquid from a less ordered gas.

Question 11

Define ‘Continental divide’.

Answer 11

A line that separates streams flowing towards opposite sides of a continent, usually into different oceans.

Question 12

Define ‘Delta’.

Answer 12

A body of sediment deposited by a stream where it flows into standing water.

Question 13

Define ‘Discharge’.

Answer 13

The quantity of water that passes a given point in a stream channel per unit time.

Question 14

Define ‘Dissolution’.

Answer 14

The chemical weathering process whereby minerals and rock material pass directly into solution.

Question 15

Define ‘Divide’.

Answer 15

The line that separates adjacent drainage basins.

Question 16

Define ‘Drainage basin’.

Answer 16

The total area that contributes water to a stream.

Question 17

Define ‘Eutrophication’.

Answer 17

Bodies of water with a high level of plant nutrients plant nutrients and consequently high levels of algae growth.
Sewage and excess fertilizers are among the most common surface water contaminants; they can lead to eutrophication, among other problems.

Question 18

Define ‘Evaporation’.

Answer 18

The process by which a liquid is converted to its vapor.

Question 19

Define ‘Flood’.

Answer 19

When a stream’s discharge exceeds the capacity of the channel.

Question 20

Define ‘Floodplain’.

Answer 20

A wide valley. Floodplains result from the deposition of fine sediment as a stream overflows its banks during a flood.

Question 21

Define ‘Gradient’.

Answer 21

A measure of the vertical drop over a given horizontal distance.

Question 22

Define ‘Groundwater’.

Answer 22

All the water contained in the spaces within bedrock and regolith.

Question 23

Define ‘Hydrologic cycle’.

Answer 23

The movement of water between the various reservoirs of the hydrosphere.

Question 24

Define ‘Hydrosphere’.

Answer 24

The totality of the Earth’s water, including the oceans, lakes, streams, water underground, and all the snow and ice, including glaciers.

Question 25

Define ‘Infiltration’.

Answer 25

Water that falls as rain, then penetrates into the soil where it becomes part of the groundwater.

Question 26

Define ‘Karst’.

Answer 26

Topography formed on limestones due to solution by groundwater; characterized by sinkholes and caves.

Question 27

Define ‘Lake’.

Answer 27

Inland body of water in a depression on the Earth’s surface; the water may be fresh or saline.
The level and salinity of a lake reflect a balance between freshwater input from streams and direct precipitation, outflow, and evaporation. Lakes can disappear as a result of changes in freshwater inputs, climate, or topography.

Question 28

Define ‘Load’.

Answer 28

The material that is moved or carried by a natural transporting agent, such as a stream, the wind, a glacier, or waves, tides, and currents.

Question 29

Define ‘Meander’.

Answer 29

A looplike bend of a stream channel.

Question 30

Define ‘Percolation’.

Answer 30

The flow of groundwater, including the vertical flow down from the surface and the lateral flow of water in the saturated zone.

Question 31

Define ‘Permeability’.

Answer 31

A measure of how easily a solid allows a fluid to pass through it.

Question 32

Define ‘Porosity’.

Answer 32

The proportion (in percent) of the total volume of a given body of bed- rock or regolith that consists of pore spaces.

Question 33

Define ‘Precipitation (of rain or snow)’.

Answer 33

The process by which condensed water gathers into droplets or particles and falls under the pull of gravity.

Question 34

Define ‘Recharge’.

Answer 34

The addition of water to the saturated zone of a groundwater system.

Question 35

Define ‘Saturated zone’.

Answer 35

The groundwater zone in which all openings are filled with water.

Question 36

Define ‘Sinkhole’.

Answer 36

A large solution cavity open to the sky.

Question 37

Define ‘Spring’.

Answer 37

A flow of groundwater emerging naturally at the ground surface.

Question 38

Define ‘Stream’.

Answer 38

A body of water that carries detrital particles and dissolved substances and flows down a slope in a definite channel. Every stream is surrounded by its drainage basin, which is separated from adjacent drainage basins by topographic divides.

Question 39

Define ‘Streamflow’.

Answer 39

Overland flow that is concentrated into well-defined conduits. It consists of storm flow and base flow.

Question 40

Define ‘Surface runoff’.

Answer 40

Water that drains off the surface of the land after rain.

Question 41

Define ‘Transpiration’,

Answer 41

Water vapor released from the surface of a leaf.

Question 42

Define ‘Tributary’.

Answer 42

A stream that joins a larger stream.

Question 43

Define ‘Water table’.

Answer 43

The upper surface of the saturated zone of groundwater.

Question 44

Define ‘Wetland’.

Answer 44

An area that is either permanently or intermittently moist.

Question 45

The hydrologic cycle describes the fluxes of water among the reservoirs of the hydrosphere, which includes the ocean, lakes, streams, underground water, and snow and ice. What percentage of the hydrosphere is each?

Answer 45

Ocean: 97.5 % of all water (saline).
Polar ice sheets: 74 % of all fresh water.
Groundwater: 98.5% of remaining unfrozen fresh water.
Then, small fraction in surface freshwater bodies > small fraction in pore spaces in soils > small fraction in atmosphere and bodies of organisms.

Question 46

What are some of the unique properties of water?

Answer 46

Very high surface tension, capillarity, ability to act as a solvent, very high heat of vaporization, very high heat capacity, and decrease in density upon freezing.

Question 47

The hydrologic cycle is powered by the ___ ___, and flow within the cycle is controlled by ___.

Answer 47

Sun’s heat and gravity.

Question 48

Overland flow and streamflow (storm flow + base flow) constitute surface runoff. Describe them.

Answer 48

Overland flow: Precipitation causes flowing water on surface that often takes the form of a thin, broad sheet; also called sheet flow.
Stream flow: Flow that becomes concentrated into well-defined conduits. Storm flow + Base flow.
Storm flow: Overland flow into a channel as result of precipitation.
Base flow: Fed by groundwater directly into channel. No base flow = ephemeral (dry up seasonally) and have base flow = perennial (don’t dry up).

Question 49

Streams and their channels are part of a complex natural system, controlled by the interplay between the stream’s ___-___ ___, ___, ___ ___ ___, ___, and ___ ___ (5 factors). As discharge changes, the velocity or the channel cross-sectional area, or both, also change.

Answer 49

Cross-sectional area, gradient, average flow velocity, discharge, and sediment load.

Question 50

What increases and what decreases as you move downstream?

Answer 50

Channel width and depth increase, velocity increases and gradient decreases.

Question 51

Where is the maximum velocity of water in a straight channel? A meandering/bending one?

Answer 51

The maximum velocity of water flowing along a straight channel segment is midstream, away from the frictional resistance of the banks. Where the water rounds a bend, the zone of highest velocity swings toward the out- side of the channel, facilitating the formation of meanders and point bars.

Question 52

A braided pattern with numerous shallow, shifting channels and bars is typical of streams that have …?

Answer 52

Highly variable discharge and an abundant supply of sediment.

Question 53

A stream’s load includes the coarse bed load, which moves along the bottom by ___, and the finer suspended load; together these constitute the sediment load. The dissolved load consists of materials carried in solution.

Answer 53

Saltation.

Question 54

Stream deposits form wherever …?, leading to deposition of the sediment load.

Answer 54

The stream energy changes.

Question 55

Continental divides separate all continents except ___ into large regions from which major through- flowing rivers enter one of the world’s major oceans. They usually coincide with …?, although their location can be influenced by other factors that control erosion and topography. Major divides exert a strong influence on climate.

Answer 55

Antarctica,

The crests of great mountain ranges.

Question 56

Wetlands, including ___, ___, and ___, are permanently or intermittently moist areas; they host significant biodiversity and perform many ecologic services. Wetlands in coastal regions, such as ___, ___, and ___, are transitional between freshwater and salt- water environments.

Answer 56

Swamps, marshes, and bogs.

Estuaries, salt marshes, and mangroves.

Question 57

How are floods studied and prevented?

Answer 57

Scientists use flood-frequency curves to calculate statistical recurrence intervals, giving a basis for planning and preparation. Computer models and GIS are used during real-time monitoring of storms to forecast the peak of a flood. Channels can be engineered for flood control, but channelization can have unexpected negative side effects, including degradation of the aquatic environment.

Question 58

Less than ___ percent of the fresh water in the hydro- sphere is groundwater, which occupies pore spaces in rock and regolith, but this is still many times larger than the volume of surface fresh water.

Answer 58

<1%.

Question 59

What two factors influence the amount and flow of groundwater?

Answer 59

Porosity and permeability.

Question 60

How does groundwater flow?

Answer 60

From areas of high water table to areas of lower.

Question 61

An aquifer that can rise to its natural water table is called an ___ aquifer. In contrast, a ___ aquifer is bounded above and below by an aquiclude. ___ can occur in circumstances where the ground surface intersects the water table.

Answer 61

Unconfined and confined and springs.

Question 62

How do caves, sinkholes and karsts form?

Answer 62

Caves form when circulating groundwater slowly dissolves and carries away carbonate rock, leaving underground voids. The process begins with dissolution along interconnected joints and bedding planes, and continues with the passages being slowly enlarged by percolating groundwater. A sinkhole is a large dissolution cavity that is open to the sky. In some regions of exceptionally soluble rock, sinkholes and caves are so numerous that they form karst terrain, characterized by many small, closed basins and intervening ridges or pinnacles.