running water (16) Flashcards
What are the four spheres of the earth?
Hydrosphere
Atmosphere
Geosphere
Biosphere
Hydrologic cycle
The unending circulation of Earth’s water supply. The cycle is powered by energy from the Sun and is characterized by continuous exchange of water among the oceans, the atmosphere, and the continents
What is the distribution of total global water?
Oceans (96.5%)
Freshwater (2.5%)
Saline lakes and groundwater (1%)
What is the freshwater distribution?
Glaciers and ice sheets (68.6%)
Groundwater (30.1%)
Surface water and other freshwater (1.3%)
What is the surface water distribution?
Snow and ice (73.1%)
Lakes (20.1%)
Soil moisture (3.52%)
Swamps (2.53%)
Evaporation
The process by which liquid water changes into water vapor (gas)
Infiltration
The movement of surface water into rock or soil through cracks and pore spaces
Runoff
Water that flows over land rather than infiltrating into the ground
Transpiration
The release of water vapor to the atmosphere by plants
Evapotranspiration
The combined effect of evaporation and transpiration
Water balance
The volume that passes through each part of the cycle annually
What is the absolute quantity that is cycled through the atmosphere over a 1-year period?
380,000 cubic kilometers
Explain the idea that the hydrologic cycle is balanced.
Annual precipitation worldwide must equal the quantity of water evaporated
What is the most important force sculpting the Earth?
Water
What factors determine the amount of runoff?
The intensity and duration of rainfall The amount of water already in the soil The nature of the surface material The slope of the land The extent and type of vegetation
Why is runoff high in urban areas?
Many features are impermeable (buildings, roads, parking lots, etc.)
Sheet flow
Initial runoff flows in broad, thin sheets across slopes
Rills
Threads of current that form tiny channels
Gullies
Rills joined to form streams, and eventually, rivers
Stream
A general term to denote the flow of water within any natural channel. Thus, a small creek and a large river are both streams
River
A general term for a stream that carries a substantial amount of water and has numerous tributaries
What are the two sources that support streamflow in humid regions?
Overland flow that sporadically enters the stream and groundwater that enters the channel
How do streams lose water in arid regions?
The water table may be below the level of the stream channel. The stream loses water to the groundwater system by outflow percolating through the streambed
Drainage basin/watershed
The land area that contributes to a stream
Divide
An imaginary line that separates the drainage of two streams, often found along a ride
What river has the larges drainage basin in North America?
Mississippi River; 40% of the flow of the United States
What is the main source of fine particles (clays and fine sand) carried in stream channels?
Hillslope erosion
Headward erosion
The extension upslope of the head of a valley due to erosion
What causes downcutting?
Headward erosion
Three zones of a river system
Zones of sediment production (erosion)
Zone of sediment transport
Zone of sediment deposition
Zone of sediment production
Where most of the sediment is derived
Located in the headwaters
Zone of sediment transport
Trunk systems are how sediment travels
Zone of sediment deposition
Fine sediments and dissolved ions are typically the sediment that actually reaches the ocean
Dendritic pattern
A stream system that resembles the pattern of a branching tree
Radial pattern
A system of streams running in all directions, away from a central elevated structure, such as a volcano
Rectangular pattern
A drainage pattern characterized by numerous right angle bends that develops on jointed or fractured bedrock
Trellis pattern
A system of streams in which nearly parallel tributaries occupy valleys cut in folded strata
When does a dendritic pattern develop?
When the surface material is essentially uniform in its resistance to erosion (pattern is determined chiefly by the direction of slope of the land)
When does a radial pattern develop?
On isolated volcanic cones and domal uplifts
When does a rectangular pattern develop?
When bedrock is crisscrossed by a series of joints and/or faults
When does a trellis pattern develop?
In areas underlain by alternating bands of resistant and less-resistant rocks and is particularly well displayed in the folded Appalachian Mountains, where both weak and strong strata outcrop in nearly parallel belts
Water gap
A pass through a ridge or mountain in which a stream flows
Antecedent stream
A stream that continued to downcut and maintain its original course as an area along its course was uplifted by faulting or folding
Superposed stream
A stream that cuts through a ridge lying across its path. The stream established its course on uniform layers at a higher level without regard to underlying structures and subsequently downcut
Luminar flow
The movement of water particles in straight-line paths that are parallel to the channel. The water particles move downstream without mixing.
Turbulent flow
Erratic movement of water often characterized by swirling, whirlpool-like eddies. Most streamflow is of this type
How does turbulence contribute to a stream’s ability to erode its channel?
It acts to life sediment from the streamed
Flow becomes more turbulent as the velocity of a stream _____.
Increases
Gradient
The slope of a stream, generally expressed as the vertical drop over a fixed distance
What happens when gradient is steeper?
More gravitational energy is available to drive channel flow
Wetted perimeter
The total distance in a linear cross-section of a stream that is in contact with water
What is the most efficient channel?
The one with the least wetted perimeter for its cross-sectional area
Flow velocities are higher where?
In small channels
Bankfull
When maximum flow velocity occurs, before water starts to inundate the floodplain
What is the effect of rough channels on flow velocity?
Boulders, irregularities in channel bed, and woody debris significantly reduces flow velocity
Discharge
The quantity of water in a stream that passes a given point in a period of time
What is the discharge of the Mississippi River?
16,800 cubic meters
Stage
The height of water surface relative to a fixed reference pint
Longitudinal profile
A cross section of a stream channel along its descending course from the head to the mouth
Mouth
The point downstream where a river empties into another stream or water body
Quarrying
Removing loosened blocks from the bed of a channel during times of high flow rates
Abrasion
The grinding and scraping of a rock surface by the friction and impact of rock particles carried by water, wind, and ice
Potholes
A depression formed in a stream channel by the abrasive action of the water’s sediment load
Corrosion
A process by which soluble rock is gradually dissolved by flowing water
Dissolved load
The portion of a stream’s load that is carried in solution
Suspended load
Fine sediment carried within the body of flowing water or air
Bed load
Sediment moved along the bottom of a stream by moving water, or particles moved along the ground surface by wind
What particles are typically carried in suspended loads?
Silt, sand, and clay particles
Settling velocity
The speed at which a particle falls through a still fluid. The size, shape, and specific gravity of particles influence settling velocity
Saltation
Transportation of sediment through a series of leaps or bounces
Capacity
The total amount of sediment that a stream is able to transport
What kind of capacity do large rivers with high flow velocities have?
High capacities
Competence
A measure of the larges particle a stream can transport; a factor dependent on velocity
The greatest erosion and transportation of sediment occurs during floods…
Increased velocity
Greater competence
More turbulence
Larger particles are set in motion
Which particles settle first?
The largest
Sorting
The degree of similarity in particle size in sediment or sedimentary rock
Alluvium
Unconsolidated sediment deposited by a stream
Bedrock channel
A channel in which a stream is cutting into solid rock. Such channels typically form in the headwaters or river systems where gradients are high
Steps
Steep segments where bedrock is exposed (rapids, or waterfalls)
Pools
Relatively flat segments where alluvium tends to accumulate
Alluvial channel
A stream channel in which the bed and banks are composed largely of unconsolidated sediment (alluvium) that was previously deposited in the valley
What are two common types of alluvial channels?
Meandering channels and braided channels
Meander
A loop like bend in the course of a stream
What are characteristics of meanders?
Streams that flow in relatively deep, smooth channels and primarily transport mud (silt and clay), sand, and occasionally fine gravel
What is an example of a meander?
The lower Mississippi River
Cut bank
The area of active erosion on the outside of a meaner
Point bar
A crescent-shaped accumulation of sand and gravel deposited on the inside of a meander
Cutoff
A short channel segment created when a river erodes through the narrow neck of land between meanders
Oxbow lake
A curved lake that is created when a stream cuts off a meander
Braided channel
A stream channel that is interwoven with other stream channels. Such channels form where a large portion of a stream’s sediment load consists of coarse material (sand and gravel) and the stream has a highly variable discharge
Stream valley
The channel, valley floor, and sloping valley walls of a stream
Slot canyons
In arid regions, where weathering is slow and rock is particularly resistant, narrow valleys develop with nearly vertical walls
Base level
The level below which a stream cannot erode
Ultimate base level
Sea level; the lowest level to which stream erosion could lower the land
Local/Temporary base level
The level of a lake, resistant rock layer, or any other base level that stands above sea level
