hydrologic cycle
movement of water through Earth’s four spheres
inflitration
precipitation soaks into the ground
runoff
precipitation runs over the surface
transpiration
water absorbed by plants and later transferred to the atmosphere
evapotranspiration
as evaporation and transpiration both move water from the surface to the atmosphere
Runoff starts as
sheet flow which develops into tiny channels called rills which forms gullies which form streams
streams
any water that flows in a channel, regardless of size
river
carries a substantial amount of water and has many tributaries
Drainage Basin
stream drains an area of land
Divide
the imaginary line separating one basin from another; sometimes visible as high ridge mountain region
3 zones of river systems
Sediment production, sediment transportation, sediment deposition
Sediment production
zone of a river where more sediment is derived
Located in the headwater region of a river system
Generated by: broken bedrock, bank erosion
Sediment transport
transported in trunk streams; amount of sediment being eroded equals amount being deposited
Sediment deposition
when a river reaches a large body of water, the energy decreases and river deposits sediments; usually only fine sediments are deposited in oceans
laminar flow
water flowing in a nearly straight path
turbulent flow
water moving quickly in an erratic fashion
Factors affecting flow velocity
the slope, channel shape, roughness, discharge,
The slope, or gradient of a stream
steeper gradient has more gravitational energy to drive channel flow
Channel shape
most effective channel has a small wetted perimeter (area where the rive is in contact with the channel) compared to its cross-sectional area
Channel size and roughness
increase in channel size will increase the cross-sectional area to wetted perimeter ration thus increasing efficiency; rough channels create turbulence and decreased velocity
Discharge
volume of water flowing past a certain point in a given unit of time
when discharge increases; the width, depth, flow, and velocity increase
longitudinal profile
cross-sectional view of a stream
most have a concave shape
head or headwater
source of the stream
mouth
the downstream point where the stream empties into a larger body of water
discharge, channel size, and velocity increases towards the mouth
Quarrying
involves removing large blocks from the channel bed
abrasion
scraping, bumping, and rubbing
erodes and polishes sediment s
Potholes
when fast moving, swirling sediment in eddies abrades a hole
Corrosion
rocks gradually dissolving in flowing water can occur in limestone bedrock channels
Transport of sediment by streams
Dissolved load (in solution) Suspended load (in suspension) Bed load (rolling along the bottom)
Dissolved load
most of the dissolved load is brought to a stream via groundwater
NOT affect by stream velocity
Suspended load
largest part of a stream is carried in suspension
amount carried is controlled by stream velocity and settling velocity (speed at which a particle falls through a liquid) of sediments
Bed load
Coarse sands, gravel, and boulders move along the stream bed by saltation (skipping or jumping)
Less rapid and more localized than transport via suspended load
Capacity
maximum load of solid particles a stream can carry
The greater the discharge the greater the capacity
Competence
the maximum particle size a stream can transport
Streams with a faster velocity have a higher competence
deposition of sediments by a stream
occurs when a stream’s velocity is less than the settling velocity
sorting
particles of the same size are deposited at the same time in this process
Larger particles are settled out first
alluvium
sediments deposited by streams
Bedrock Channels
cut into the underlying strata
meanders
streams transport suspended sediment in broad sweeping bends
Cutbank
outside of a meander
zone of active erosion
point bar
inside of a meander
zone of deposition
cutoff oxbow lake
a meander that has been cut off from joined bends
braided channel
is a network of converging and diverging channels that thread among numerous islands or gravel bars
stream valley
channel and surrounding terrain that directs water to the stream
alluvial channels have wide valley floors
bedrock channels have V-shapped valleys
base level
lowest point to which a stream can erode
Ultimate base level
sea level
Local or temporary base level
includes lakes, resistant layers of rock, and large rivers
changing conditions causes readjustment of stream activities
raising base level= deposition
lowering base level= erosion
graded stream
only transports sediment
Deltas
when sediment-filled streams enter a large body of water
water gap
notch where a river cuts through a ridge that lies in its path
Antecedent stream
stream existed before the ridge was formed
Superposed stream
Stream eroded into a preexisting structure
headward erosion
stream that lengthen its coarse by extending the head of the valley upslope ; can result in stream piracy where the diversion of the drainage of one stream into another
flood
occurs when the stream exceeds the capacity of its channel; most common and most destructive geological hazard
Regional flood
seasonal flood that typically result from spring rains or rapid melting of snow
Flash floods
occur with little or no warning in mountainous areas
Ice-jam floods
ice forms in rivers creating dams that will break when temperatures rise
Dam-Failure floods
Dams fail and release large amounts of water
Flood Control
Artificial levees
Channelization
flood control dams
non-structural approach