STREAMS & STREAMS & RIVERSRIVERS

Chapter 6Chapter 6

REVIEW…. The Water REVIEW…. The Water CycleCycle

6.1 Streams and Rivers6.1 Streams and Rivers

River SystemsRiver Systems

(structure)(structure)

TributaryTributary- a stream that - a stream that runs into another stream runs into another stream or riveror river

River system-River system- a river and all of its a river and all of its tributariestributaries

Drainage basin, Drainage basin, or watershed-or watershed- all the land all the land that drains into the that drains into the river river either directly or through either directly or through its its tributariestributaries

ex) Mississippi ex) Mississippi River systemRiver system

Divide-Divide- high land that high land that separates one drainage separates one drainage basin from anotherbasin from another

Ex) Continental Divide in Ex) Continental Divide in the Rocky Mountainsthe Rocky Mountains

CharacteristicsCharacteristics Velocity- distance that water travels in a Velocity- distance that water travels in a

given amount of timegiven amount of time Related to the amount of energy that the water hasRelated to the amount of energy that the water has Erosion occurs more quicklyErosion occurs more quickly Other characteristics affect the velocity: Other characteristics affect the velocity:

Gradient, Discharge, and Channel CharacteristicsGradient, Discharge, and Channel Characteristics Gradient- steepness of the slope of a Gradient- steepness of the slope of a

stream or riverstream or river Steep at its source; gradual at sea levelSteep at its source; gradual at sea level

Characteristics Characteristics continued…continued…

Discharge- the amount, or volume, of water that Discharge- the amount, or volume, of water that passes a certain point in a given amount of timepasses a certain point in a given amount of time Not constant over length of a riverNot constant over length of a river Increases downstream as tributaries add more waterIncreases downstream as tributaries add more water Not constant year-round- increased Not constant year-round- increased

precipitation/melting snowprecipitation/melting snow Channel- the path through which the water flows Channel- the path through which the water flows

in a stream or riverin a stream or river Shallow, winding stream with many boulders has Shallow, winding stream with many boulders has

contact with surface area that causes it to slow down by contact with surface area that causes it to slow down by friction friction

Straight channel that is wide and deep has less surface Straight channel that is wide and deep has less surface area in contact with water, so velocity is greaterarea in contact with water, so velocity is greater

Velocity is greatest at the top center of the streamVelocity is greatest at the top center of the stream When it curves, zone of max. speed shifts to the outer When it curves, zone of max. speed shifts to the outer

bankbankSEE FIGURE 3 (p.160)SEE FIGURE 3 (p.160)

Different types of Stream Different types of Stream ChannelsChannels

Base LevelBase Level Base Level = lowest point to which a stream Base Level = lowest point to which a stream

can erode its channel.can erode its channel. Base level is usually the level at which the Base level is usually the level at which the

mouth of a stream enters the ocean or the mouth of a stream enters the ocean or the next body of water.next body of water.

Temporary Base Level vs. Ultimate Base LevelTemporary Base Level vs. Ultimate Base LevelTemporary = lakeTemporary = lake Ultimate = sea levelUltimate = sea level

A stream in a broad, A stream in a broad,

flat-bottomed valley flat-bottomed valley

that is near its base level that is near its base level

often develops many meanders.often develops many meanders.

ErosionErosion Running water wears Running water wears

down Earth’s surface by down Earth’s surface by breaking up bedrock breaking up bedrock and by removing eroded and by removing eroded rock and soil materialsrock and soil materials

Breaks up materials by Breaks up materials by mechanical meansmechanical means Abrasion mainly; in time, Abrasion mainly; in time,

creates rounded boulders, creates rounded boulders, pebbles, and sand grains pebbles, and sand grains from the cutting toolsfrom the cutting tools

6.2 Stream Erosion and 6.2 Stream Erosion and DepositionDeposition

DepositionDeposition--

the process by the process by which materials which materials are depositedare deposited Occurs because the Occurs because the

river or stream no river or stream no longer has enough longer has enough energy to transport energy to transport themthem

Stream Flow & ErosionStream Flow & Erosion There is more stream There is more stream

velocity in the velocity in the middle/top of the streammiddle/top of the stream

Erosion will be greater Erosion will be greater in the middle of the in the middle of the straight stream straight stream (increase depth)(increase depth)

Deposition will occur on Deposition will occur on the stream/river banks the stream/river banks where the channel turns where the channel turns and the velocity of the and the velocity of the waterway dropswaterway drops

SEE FIGURE 3 SEE FIGURE 3 (p.160)(p.160)

Erosion & Deposition Erosion & Deposition Features in an Old Features in an Old

Stream/RiverStream/River

Erosion cont…Erosion cont…

Potholes- Potholes- deep oval or deep oval or

circular basins circular basins formed when formed when water in a river water in a river develops small develops small whirlpools, and whirlpools, and materials grind materials grind potholes in the potholes in the bedrockbedrock

Plunge pool-Plunge pool-

a basin that has been a basin that has been worn away at the base worn away at the base of a waterfall by the of a waterfall by the action of falling wateraction of falling water

Dunn River FallsDunn River Falls

Chemical weathering Chemical weathering consists of dissolving soluble consists of dissolving soluble

mineralsminerals Calcite is dissolved, which may form pits and holes in Calcite is dissolved, which may form pits and holes in

the riverbedthe riverbed Widens existing cracks and holesWidens existing cracks and holes

Depositional FeaturesDepositional Features Delta-Delta- a fan-shaped deposit that forms a fan-shaped deposit that forms

when a river flows into a quiet or large when a river flows into a quiet or large body of waterbody of water River water comes to almost a standstill at River water comes to almost a standstill at

a deltaa delta Distributaries-Distributaries- branches formed by rivers branches formed by rivers

flowing over its deltaflowing over its delta Responsible for Responsible for delta’s shapedelta’s shape

Formation is Formation is delicate balance delicate balance between deposition between deposition and erosionand erosion

Alluvial fan- fan-shaped depositAlluvial fan- fan-shaped deposit May form when a steep mountain May form when a steep mountain

stream meets dry, level land at the base stream meets dry, level land at the base of a mountainof a mountain

Differs from a deltaDiffers from a delta Deposit is formed on land, not in waterDeposit is formed on land, not in water Sediments are coarse sands and gravels Sediments are coarse sands and gravels

rather than fine silt and clayrather than fine silt and clay Surface is sloping, Surface is sloping,

not flat like that of a not flat like that of a

deltadelta

Transported MaterialTransported Material Load- the eroded rock and soil materials that Load- the eroded rock and soil materials that

are transported downstream by a riverare transported downstream by a river Suspension- a state in which rock materials Suspension- a state in which rock materials

carried by a river are stirred up and kept from carried by a river are stirred up and kept from sinking by the turbulence of stream flowsinking by the turbulence of stream flow Materials are heavier than water, but the Materials are heavier than water, but the

turbulence keeps them stirred upturbulence keeps them stirred up The faster a stream flows, the more turbulent and The faster a stream flows, the more turbulent and

muddy it becomesmuddy it becomes Bedload- sand, pebbles, and boulders that are Bedload- sand, pebbles, and boulders that are

moved along the bed of a stream and that are moved along the bed of a stream and that are too heavy to be carried in suspensiontoo heavy to be carried in suspension

Transporting MaterialsTransporting Materials Two measures are used to describe the ability of Two measures are used to describe the ability of

a stream to transport materialsa stream to transport materials Competence- a measure that describes the maximum Competence- a measure that describes the maximum

size of the particles a stream can carrysize of the particles a stream can carry Capacity- a measure of the total amount of sediment a Capacity- a measure of the total amount of sediment a

stream can carrystream can carry Depend on the velocity and dischargeDepend on the velocity and discharge Vary along a stream and change throughout the Vary along a stream and change throughout the

yearyear High velocity + High discharge = large amount High velocity + High discharge = large amount

of sediment and larger sizes of sediment of sediment and larger sizes of sediment particlesparticles

Stream DepositionStream Deposition River will deposit part of its load when River will deposit part of its load when

either velocity or discharge decreaseseither velocity or discharge decreases Velocity may decrease if channel widens Velocity may decrease if channel widens

or river meets an obstruction (curving or river meets an obstruction (curving bank/rock outcrop)bank/rock outcrop)

Speed decreases at the inside of the Speed decreases at the inside of the curve and when the river empties into curve and when the river empties into the sea- deposits the most materialthe sea- deposits the most material

Discharge and velocity increase during Discharge and velocity increase during a flood, then decrease as flood waters a flood, then decrease as flood waters subsidesubside

Meanders – write your Meanders – write your own notes!own notes! Erosion occurs Erosion occurs

along the along the OUTSIDE of a OUTSIDE of a meander…meander…

……because the because the water is FASTER water is FASTER there (more there (more velocity, more velocity, more energy to erode)energy to erode)

Deposition occurs Deposition occurs along INSIDE along INSIDE curves, (it’s slower curves, (it’s slower & water cannot & water cannot transport sediment transport sediment any longer)any longer)

Stream ValleysStream Valleys Narrow valleysNarrow valleys

narrow V-shaped valley shows narrow V-shaped valley shows that the stream’s primary work that the stream’s primary work has been down cutting toward has been down cutting toward base levelbase level

Rapids and waterfallsRapids and waterfalls Wide valleysWide valleys

Downward erosion is less dominantDownward erosion is less dominant More energy is directed side to sideMore energy is directed side to side FloodplainFloodplain- the flat, low-lying portion - the flat, low-lying portion of a stream valley subject to periodic of a stream valley subject to periodic

floodingflooding

Linville Linville GorgeGorge

Carved out of Carved out of the bedrock by the bedrock by

the river the river forming a river forming a river

valley.valley.

FloodplainsFloodplains

Streams that Streams that flow on flow on floodplains move floodplains move in meandersin meanders

Cutoffs- shorter Cutoffs- shorter channel channel segmentssegments

Oxbow lakes- Oxbow lakes- abandoned bend abandoned bend of a river/streamof a river/stream

Oxbow Lake FormationOxbow Lake Formation Meander forms (because the Meander forms (because the

stream is close to base level)stream is close to base level)

Far side of curves erode Far side of curves erode faster, inching closer & faster, inching closer & closer together.closer together.

Curves join, and water Curves join, and water moves past the bypass loopmoves past the bypass loop

Deposition occurs at the Deposition occurs at the ends of the loop (because ends of the loop (because velocity drops), cutting off velocity drops), cutting off the oxbow lake.the oxbow lake.

FloodsFloods

Most caused by rapid spring snow melt Most caused by rapid spring snow melt or storms that bring heavy rains over a or storms that bring heavy rains over a large regionlarge region Ex: Mississippi River in 1993Ex: Mississippi River in 1993

Measures to control floodingMeasures to control flooding Artificial Levees- earthen mounds built on Artificial Levees- earthen mounds built on

the banks of the riverthe banks of the river Flood-control dam- store floodwater and Flood-control dam- store floodwater and

then let it out slowlythen let it out slowly Limits on floodplain development- Limits on floodplain development-

minimizing the development on floodplainsminimizing the development on floodplains

Flood plains & LeveesFlood plains & Levees Developing in flood Developing in flood

plains causes great plains causes great economic loss.economic loss.

What can we do to What can we do to help this??help this??

• Build smaller levees farther apart…

• Less expensive to build…

• Improves habitat in the flood plain.