Chapter 13 (running water)- Geology
water content of earths hydrosphere
-1.36 billion cubic kilometers
wide and shallow channel
-has a lot of frictional drag because so it has greater wetted perimeter -causing stream to go slower
gullies
-rills meet and form
oxbow lake
-the abandoned bend
zone of sediment production
- where most of the sediment is derived -located along the headwaters region of river system -sediment is compromised by the bedrock that is broken down by weathering and moved downslope -scouring the channel bed deepens the channels and adds to sediment load
cross sectional shape
-a slice taken across the channel -determine the amount of flow in contact with the banks and bed of the channel
flow velocity
-ability of a streams ability to erode and transport material is directly based off of -as velocity increases the stream flow becomes more turbulent -can change from place to place on river -strength of the current increased as you move deeper in the channel because the the greater fictional resistance near the banks and bed of the channel -determined ar gaging stations
stream terraces
-after a river had been flowing on a floodplain has then adjusted to a base level drop -it will start again producing a floodplain at a level below the original one
evapotranspiration
-both evaporation and transpiration involve the transfer of water from the surface directly to the atmosphere -often considered together as one process
rough
-channel can have boulders, irregularities in the channel bed and woody debris that can create
factors affecting flow velocity
-channel slope or gradient -channel cross sectional shape -channel size and roughness -discharge which is the amount of water flowing in channel
bed load
-coarse materials including coarse sands, gravel and even boulders typically move along the bed of a channel as a -they move by rolling sliding and saltation -moves much slower than the suspended load
stream valley
-consist of a channel and the surrounding terrain that directs water to the stream -includes the valley floor and valley walls -can be narrow steep valleys or very flat broad valleys
floodplain
-continuous lateral erosion caused by shifting meanders gradually produces a broad flat valley floor covered in alluvium -it becomes inundated when the river overflows its banks during flood stage -overtime it will widen so much that the stream is now only eroding some parts of the valley walls
bedrock channels
-cut into underlying strata and typically form in the head waters of river systems where streams have steep gradients -streams actively cutting into solid rock -streams tend to exhibit winding or irregular patterns -often contain steps and pools -tend to be located in narrow v- shaped valleys
settling velocity
-defined as the speed at which a particle falls through a still fluid -the larger the particle the faster it will settle -flat grains sink slower than spherical grains
zone of sediment transport
-downstream from the zone of sediment production -sediment acquired by the stream in transported through the channel network called trunk streams
base level
-downward limit to stream erosion -defined as the lowest elevation to which a stream can erode its channel -the level where the mouth of the stream enters the ocean
divide
-each drainage basin is bounded by imaginary line -clearly visible sharp ridge in some areas -the ridge can separate small gullies or even huge continents
cut off
-eventually the river may erode threw a narrow neck of land forming a new shorter channel segment called
drainage basin (watershed)
-every stream drains an area of land called -
rectangular pattern
-exhibits many right angle bends -pattern develops when the bedrock is criss crossed by a series of joints and fractures
sorting
-explain why particles of similar size are deposited together -when the larger particles settle first
headward erosion
-extending the heads of their channels upslope -the surface flow at the head of the channel has enough power to cut the channel deeper -the valley extends into previously undirected terrain
potholes
-features common to some bedrock channel that are circular depressions -created by abrasion action particles swirling in fast moving eddies
alluvial channels
-form in sediment that was previously deposited in the valley -banks and beds are composed of alluvium, they can undergo significant change in shape because material is constantly being eroded, transported and deposited -often flow in valleys that have wide valley floors consisting of sand and gravel
alluvium
-general term for sediment deposited by streams
river
-general term for streams that carry substantial amounts of water and have numerous tributaries
US geological survey
-has 7500 stream gaging stations -collect data about flow velocity, discharge and river stage
narrow deep channel
-has less frictional drag and will flow more rapidly -most efficient channel
water moves along all 4 of earths spheres
-hydrosphere -biosphere -atmosphere -geosphere
storage of water in glaciers
-if precipitation falls in areas at high elevation or high latitudes -the water may not immediately soak in, run off or evaporate -the water may become part of a snowfield or glacier
local or temporary base level
-includes level of lakes, resistant layers of rocks, and rivers that act as base level for tributaries
river system
-includes network of stream channels and the drainage basin -can be divided into 3 zones 1-zone of sediment production 2-zone of sediment transport 3-zone of sediment depostion
most precipitation does one of two things
-infiltrate(sink in ground) -run off
point bars
-inside of meandering channel -since its on the inside of the meander channel the water is going slow and depositing material along
runoff vs. infiltrate depends on several things
-intensity and duration of rainfall -amount of water already in the soil -nature of surface material -slope of land -vegetation
drainage systems
-interconnected networks of streams that exhibit many patterns
quarrying
-involves removal of blocks from the bed of a stream channel -process is aided by fracturing and weathering the rocks of the bed so they can be moved
capacity
-maximum load of solid particles a stream can transport per unit time -the greater the discharge then the greater capacity
two types of alluvial channels
-meandering channels -braided channels
competence
-measure of a streams ability to transport particles based on size rather than quantity -flow velocity is key -fast streams carry larger particles
largest drainage basin in north America
-mississippi river -collecting and carrying 40 percent of flow in the US
dendritic pattern
-most common drainage pattern -ressembles the branching pattern of a deciduous tree -forms when the underlying material is relatively uniform in its resistance to erosion and hence doesn't control the the pattern of stream flow -determined by the direction of slope of land
turbulent flow
-most streams expiernce this type of flow -strong turbulent behavior occurs in whirl pools and rolling white water rapids -even streams that appear smooth on the surface, still expierence this flow at the bottom -the turbulence acts to erode the channel because it can lift sediment
graded stream
-observing streams that adjust their profiles to changes in base level -necessary slope other channel characteristics to maintain the minimum velocity required to transport the material supplied to it -on average usually just transporting material
deposition
-occurs when a stream slows down causing reduction in competence -when the flow of velocity is less than the settling velocity -largest particles settle first
where water is located on earth
-oceans -glaciers -rivers -lakes -air -soil -living tissue
stream channel
-open conduit consisting of the stream bed and banks that act to confine the flow except during floods
cut bank
-part of meandering channel -outside of meander zone is active erosion area because the water is traveling faster
sandy channel
-particles are easily dislodged from the bed and banks and then lifted into moving water -usually undercut dumping even more loose sediment into streams -usually wide channels because lots of erosion is happening
coarse gravel or clay channels
-particles tend to be resistant to erosion -generally narrow channels because not much erosion is happening
infiltration
-portion of the water soaks into the ground -slowly moving downward then moving laterally and then finally seeping into lakes, streams or oceans
abrasion
-process by which the bed and banks of bedrock channel are ceaselessly bombarded by particles carried into the flow -bumping scratching rubbing of the particles erodes a bedrock channel
corrosion
-process in which rock is gradually dissolved by the flowing water -bedrock channels formed in soluble rock such a limestone are susceptible to... -type of chemical weathering
streams cut channels into bedrock through 3 different processes
-quarrying -abrasion -corrosion
trellis pattern
-rectangular drainage pattern in which tributary streams are nearly parallel -develops in areas of alternating weak and resistant bedrock
slot canyons
-regions where weathering is slow and rock is resistant -narrow valleys having nearly vertical walls -formed by the wear of water rushing through rock. A slot canyon is significantly deeper than it is wide
ultimate base level
-sea level
saltation
-sediment that appears to jump or skip along the stream bed -the sediments get lifted by current and are carried downstream a little and then gravity pulls them back down -sediments that are to large for this usually roll or slide on the bottom
longitudinal profile
-simply a cross section view of the stream from its source area (head) to the mouth where it dumps into another body of water -useful way of studying a stream -
immense volume of moving water
-single most important agent sculpting earths land surfaces
incised meanders
-some rivers have meandering channels that flow in steep, narrow bedrock valleys -means to cut into -can occur when the river is originally on a floodplain but the land starts to uplift and the river starts to downcut -a river meander that has been cut abnormally deeply into the landscape because uplift of the land has led to renewed downward erosion by the river
braided channels
-some streams consist of complex network or channels that thread their way among numerous islands or gravel bars -these channels have interwoven appearance -very common to see form at the end of glaciers -when the channel flow slows down deposition occurs and bars form -the bars split the path of the water
transpiration
-some water that soaks into the ground is absorbed by plants -then the plants release the water back into the atmosphere
v shaped valley
-steep sided walls formed by downcutting -most prominent features include rapids and waterfalls
water gap
-steep walled notch followed by a river -a transverse gap in a mountain ridge through which a stream or river flows
superposed stream
-streams cut across structures, they dont flow around them -eroded its channel into an existing structure -rivers take their courses with out regard to structures below
meandering channels
-streams that transport much of their load in suspension generally move in sweeping bends called meanders -flow in deep smooth channels -primarily transport mud, silt, sand or clay - individual bends migrate across the floodplain
runoff is dominant process
-surface material is impermeable -becomes to saturates -high slopes are steep -if areas are cover in concrete
wetted perimeter
-take a cross sectional shape -look at the amount of contact the water has with the banks and bed
river stage
-the height of the water surface relative to a fixed point
downcutting
-the lowering of the stream bed toward base level
discharge
-the measure most often used to compare the size of streams -the volume of water flowing past a certain point given a unit of time -measured by multiplying the streams cross sectional area by the velocity -when this increases so does the width, depth, and flow
mouth
-the point down stream where it empties into another water body -the gradient becomes less steep as it gets closer to the mouth
evaporation
-the process by which liquid water changes into water vapor(gas) -how ater enters the atmosphere from the ocean
gradient
-the slope of the stream channel -expressed as the vertical drop of a stream over a distance -when the gradient is steeper the more gravitational energy is available to drive channel flow
hydrologic cycle
-the unending circulation of water -energy source comes from the sun
water balance
-the volume that passes through each part of the water cycle annually -the hydrologic cycle is balanced -the total amount of water vapor remains the same, the average annual precipitation must be equal to water evaporated
stream erosion
-they have the ability to down cut and widen channels and they can transport wide amounts of sediment -its ability to transport is aided by raindrops that know sediment loose -when the ground is saturated it cant infiltrate and there for the water runs off transporting material it carries with it
settling velocity and flow velocity
-type and amount of material carried in suspended load depend on
dissolved load
-type of stream transport -brought to a stream by groundwater and is dispersed throughout the flow -when water goes through the ground it percolates small soluble soil compounds and carries around the dissolved mineral matter -velocity of stream flow has no effect on the streams ability to carry dissolved load -(invisible)
radial pattern
-typically develops on isolated volcanic cones and uplifts -type of drainage pattern
capacity and competence
-used to describe a streams ability to carry solid particles
suspended load
-usually streams transport the greatest amount of sediment here -usually only carries very fine sand, silt and clay particles -causes water to become muddy and murky -but during flood stage larger particles can be carried by this load -moves at a fast rate
downstream
-usually the further downstream you get the more water you get because of tributaries feeding into the channel - channel size typically increases as well because of the growing amount of water -also sediment grain is relatively smaller making the channel smooth and efficient
laminar flow
-very slow moving streams -water moves in nearly straight line paths parallel to stream channel
hill slope erosion
-water erosion on the hill slides -water flows down the hill of the drainage basin into the stream -main source of fine clay and sand particles carried into stream channels
stream
-water that flows in a channel regardless of size
bankful
-when a stream is so full but not yet flooding the floodplain -the maximum flow velocity occurs when the stream is at this stage
sheet flow
-when run off water starts flowing -it flows in broad thin sheets
rills
-when runoff water flowing in a sheet flow forms a small current that forms tiny channels called
run off
-when the rate of rainfall exceeds the grounds ability to absorb it -the surplus water flows over the surface into lakes, streams -flows if broad, thin sheets
zone of sediment deposition
-when the river approaches an ocean it slows and the energy to transport is gradually reduced -most of the sediments accumulate at the mouth of the river to form a delta
precipitation
-when water falls out of the moist air (clouds) -the water that falls straight back in the ocean has completed its cycle and is ready to start again -the water that falls on continents must make its way back to the ocean
head or headwaters
-where the stream starts -the source area
start and finish of water
1-runoff 2-sheet flow 3-rills 4-gullies 5-streams 6-rivers
2%
percentage of water divided among lakes, streams and ground water
1.76%
percentage of water stored in glaciers and ice sheets
96.5%
percentage of water stored in the global oceans