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72 Cards in this Set
- Front
- Back
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General parts of river system
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collecting system
transport system dispersing system |
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Collecting System
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-Headwaters region
-water flows into tributary streams -steeper gradient --> fast flowing -actively eroding banks, place sediment into transport -creates V shaped valley |
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Transport System
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-main (trunk) stream of river
-transporting water & sediment -discharge high --> substantial erosion -discharge low --> deposition |
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Dispersing System
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-end of stream, empties into body of water
-velocity drops to zero, water disperses to ocean -sediment deposited, creating distributary channels -delta created -located at streams ultimate base level |
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Drainage Basin
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area drained by stream system
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Drainage Divide
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ridge separating adjacent drainage basins
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Through-Flowing Stream
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reach ocean
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Intermontane Streams
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flow into adjacent basins, no outflow to sea
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pluvial lakes
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freshwater lakes occupying intermontane basin in glacial periods
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playa lakes
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smaller saltwater lakes occupying intermontane basin in interglacial periods
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Laminar flow
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no mixing, flow lines dont cross
not common in streams, happens in parking lot after rain |
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Turbulent flow
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flow lines cross, mixing of fluid
common in streams transports sediment and oxygen in water takes oxygen back into river system |
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velocity of water in straight streams
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velocity less and less near channel bed
fastest moving water in middle of stream slowest on sides |
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velocity of water in meandering streams
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fastest velocity on outside of curves
erosion of cutbank, deposition of point bar |
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sediment transport
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dissolved load
suspended load bed load |
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dissolved load
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ions in solution
top layer carried uniformly throughout water |
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suspended load
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generally clay and silt sized, small particles
turbulent flow keeps fragments in suspension |
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bed load
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fragments rolling, bouncing along stream bed
large particles |
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stream capacity vs. competency
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capacity - total volume of sediment that a stream can carry
competency - the ability of a stream to transport a particular size of particle (e.g., boulder, pebble, etc) |
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Agents of erosion in stream system
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abrasion
hydraulic action hydraulic implosion |
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Agent of Erosion - Abrasion
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turbulent water uses sediment to scour stream bed
bed load is abrasive tool downcutting into rock main tool of erosion |
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Agent of Erosion - Hydraulic Action
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velocity of water picks up and removes loose sediment from bed
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Agent of Erosion - Hydraulic Implosion
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shock waves erode bed of stream when gas bubbles collapse
example: waterfalls, white from gas bubbles. when they implode, they send out a shockwave can get into solid rock |
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How/why does manner and intensity of erosion vary along length of stream?
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due to changes in
-gradient (slope of stream bed) -velocity of water -discharge (amount of water moving in stream) |
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Streams - Downward Erosion
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common in the headwaters of stream
river system is eroding stream bed down into the rock, seeking ultimate base level deepens channel |
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Streams - Headward Erosion
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extension of drainage system towards drainage divide
stream becomes longer and wider erodes upslope |
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Stream Piracy
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headward erosion causes one stream to intersect the course of another
intersected stream starts to flow down channel of first stream |
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Streams - Lateral Erosion
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erosion of river banks rather than bed
results in undercutting of banks |
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Lateral Erosion in Steep to Moderate Gradients (Slope Retreat)
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lateral erosion typically in tributary systems of stream
creates overall V-shaped profile across stream drainage |
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Lateral Erosion in Gentle Gradients (meandering streams)
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lateral erosion typically in main trunk of stream system
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Intermontane Streams...
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arid to semi-arid climates
water/sediment accumulate in basin create landforms of Alluvial Fans, Bajadas, Playa Lakes |
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Alluvial Fan development
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fan shaped deposits of coarse gravel/sand
produced where intermittent streams/slurry flows deposit sediment at base of mountain front fine sediment carried further out |
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Playa Lake development
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saline lakes produced by evaporation of intermontane lakes
filled with fine silts and clays, evaporite "salts" |
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Bajada development
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coalescence of several alluvial fans into a broad apron of sediment
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Braided Streams
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tend to form in areas where streams have variable discharge and abudant sediment loads
occur in 2 common locations : 1. where river systems exit steep slopes, move into gentle gradients 2. along glacial melt water streams |
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Meandering Streams development
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lateral migration --> erosion of cutbank, deposition of point bar
meanders can be cut off to form cut-off meanders and eventually oxbow lakes |
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Delta development
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wedge of sediment formed at river mouth when running water enters standing water
current slows, stream loses competence and sediment settles out subdivided into delta plain, delta front, prodelta |
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Classification of Deltas
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River Dominated Deltas - bird foot, protrude into marine environment
Wave Dominated Deltas - waves redistribute sediment to give curvilinear shape Tide Dominated Deltas - numerous funnel shaped channels perpindicular to shoreline |
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Stream Terrace
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flat surface underlain by alluvium that borders a stream
form when streams carve downward into their floodplains step-like benches along side of valley |
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Stream Evolution - Early, Middle, Late in Humid Climate
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Early Stage - characterized by broad plateau being actively eroded by downcutting and headward erosion.
Middle Stage - headward erosion has converted the plateau region into rounded hills, dendritic drainage system is now well-developed , flood plains beginning to develop. Late Stage - erosion has stripped away surrounding hills and very broad floodplain with meandering stream. |
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Stream Evolution - Early, Middle, Late in Arid Climate
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Early - Alternating cliffs and slopes characterize angular topography. network of stream channels begins to develop, cliffs retreat laterally. original surface undissected
Middle - erosion continues to dissect the area into network of deep canyons. local relief reaches maximum, resistant rock layers form cap rock plateaus, mesas and buttes Late - erosion shrinks mesas/buttes and forms a peneplain near sea level. only a few resistant remnants punctuate nearly flat region |
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Dendritic Drainage Pattern
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rivers flow over uniform substrate with uniform initial slope, develop dendritic network
looks like pattern of branches connecting to the trunk of tree |
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Radial Drainage Pattern
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forming on surface of a cone-shaped mountain flow outward from mountain peak
looks like spokes on wheel |
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Rectangular Drainage Pattern
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in place where rectangular grid of fractures (vertical joints) breaks up the ground, channels form along preexisting fractures
streams join each other at right angles |
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Trellis Drainage Pattern
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in places where drainage network develops across landscape of parallel valleys and ridges
major tributaries flow down a valley and join trunk stream that cuts across ridges resembles garden trellis |
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Consequent Drainage
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stream flow is in accord with regional slope
stream flow is in consequence with slope |
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Subsequent Drainage
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geologic structure is controlling factor for stream flow;
flow is subsequent to underlying structure |
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Antecedant Drainage
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a transverse stream (flows across the trend of mountainous structure)
established before the mountainous structure was uplifted |
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Superposed Drainage
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transverse stream whose valley and direction of flows were developed in one set of structure and were later superposed upon deeper structure in rock
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Rejuvenated or Incised Drainage
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stream has an established river pattern, slow uplift of region allows for downcutting without a change in overal rivers pattern
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Groundwater Recharge
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area where water enters ground and infiltrates down to water table
amount of recharge determines the elevation for the water table |
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Groundwater Discharge
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location where groundwater flows back up to surface, may emerge at springs
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Aquifer
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areas of water saturated permeable rock/sediment
lava flow, sand, gravel |
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Aquiclude/aquitard
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impermeable rock and sediment
such as clay rich soil zones, soil |
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Water table
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upper surface of zone of saturation
flow directions -- along curved paths perpindicular to water table contour lnnes |
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Ground Water moves by....
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slow moving, along curved paths from areas of high water pressure to areas of low water pressue
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Sources of Porosity in groundwater
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1. size and shape of clast in silt-size and larger
2. sorting of clasts 3. compaction of clasts 4. cementation of sand 5. rock structures: cooling joints, flow breccia, tectonic joints |
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Permeability in groundwater
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measure of how easily regolith orbedrock allow fluids to pass through
pore spaces must be connected and large enough for water to freely pass through |
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Why do springs exist?
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-ground surface intersects water table in a discharge area, occurs in valley floors
-flowing groundwater collides with steep impermeable barrier, and pressure pushes it up to the ground along barried -perched water table intersects surface of hill -where downward-percolating water runs into impermeable layer and migrates along the top surface of layer to hillslope -network of interconnected fractures channels groundwater to surface of a hill |
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Artesian Systems
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needed to create : confined aquifer with recharge area located at higher elevation and discharge location at lower elevation
how they operate: hydraulic pressure on water at low elevation causes it to rise vertically until pressure is equalized |
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Dakota Aquifer
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confined aquifer associated with tilted Dakota sandstone
recharge along mountain fronts has filled the sandstone and limestone units with water. |
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Wells
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man made form of discharge
pumping of slow moving groundwater from well produces cone of depression because water can be removed faster that water can flow and recharge |
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High Plains Aquifer
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unconfined aquifer which extends across great plains
30% of groundwater used in irrigation in US comes from this aquifer tapped extensively after dust bowl recharge of aquifer cannot keep pace with discharge from wells |
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Cone of Depression
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the downward pointing, cone-shaped surface of water table in location where water table is experiencing drawdown because of well pumping water
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Erosion by Groundwater
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occurs in regions of soluble rock and humid climates
most common soluble rock is limestone & dolomite as water flows thorugh soil, acid is formed which can cause minerals to be dissolved |
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Carbonic Acid Dissolution
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reaction of CO2 and groundwater
dissolves limestone to form underground caves formed from top down |
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Sulfuric Acid Dissolution
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formed by reaction of of rising hydrogen sulfide gas with oxygenated groundwater.
8x more reactive to limestone than carbonic forms caves from bottom up |
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Development of Sinkholes
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dissolution of limestone in area created caverns.
as caverns enlarge, roofs of cave become thinner until roofs collapse, creating sinkhole |
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Solution Valleys
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sinkholes which have joined together
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Disappearing streams
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streams which flow into sinkholes
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Remnant knobs / erosional remnants
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limestone comprising hills on top of shale layer that is below limestone layer
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Deposition by Groundwater
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groundwater carrying dissolved minerals drips into caverns, leaving behind precipitate (travertine)
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