Chapter 13 Surface WaterChapter 13 Surface Water

Chapter 13.1Chapter 13.1

Streams and RiversStreams and Rivers

• Carry over half of all water that Carry over half of all water that falls on Earth’s surface to the falls on Earth’s surface to the ocean and almost all erosion.ocean and almost all erosion.

River SystemsRiver Systems

• Tributary – stream that runs into Tributary – stream that runs into a large streama large stream– Beaver is a tributary of the OhioBeaver is a tributary of the Ohio

• River System – a river and all of its River System – a river and all of its tributariestributaries

• Drainage Basin (watershed) – Drainage Basin (watershed) – includes all the land that drains into includes all the land that drains into the riverthe river

• Divide – highland that separates Divide – highland that separates one drainage basin from anotherone drainage basin from another– Rocky Mountains – the major Western Rocky Mountains – the major Western

divide for the Mississippi river. Rain divide for the Mississippi river. Rain falling on the Eastern side flows to the falling on the Eastern side flows to the Mississippi; on the Western side to the Mississippi; on the Western side to the PacificPacific

Characteristics of Characteristics of Streams and RiversStreams and Rivers

– Controlled by velocity, gradient and Controlled by velocity, gradient and shape of channelshape of channel

• Velocity – distance the water travels Velocity – distance the water travels in a given amount of timein a given amount of time– Faster it moves the more material it can Faster it moves the more material it can

carry and the larger the size of the carry and the larger the size of the materialmaterial

• Gradient – steepness of the slope of Gradient – steepness of the slope of a streama stream

• Discharge – the amount (volume) of Discharge – the amount (volume) of water that passes a certain point in water that passes a certain point in a given amount of timea given amount of time– The streams that feed the stream the higher The streams that feed the stream the higher

the discharge (downstream)the discharge (downstream)– Rain and melting snow may also add to Rain and melting snow may also add to

discharge increasing the streams velocitydischarge increasing the streams velocity

• Channel – the path the water Channel – the path the water flowsflows– A wide winding channel will slow the A wide winding channel will slow the

water down due to frictionwater down due to friction– A straighter deeper channel will have A straighter deeper channel will have

less friction therefore a higher velocityless friction therefore a higher velocity

Chapter 13.2Chapter 13.2

Stream Erosion and Stream Erosion and DepositionDeposition

• Running water is the most Running water is the most effective agent of erosion.effective agent of erosion.

How streams weather How streams weather and erode materialand erode material• Rapidly flowing water can lift, split off and move Rapidly flowing water can lift, split off and move

rockrock

• Abrasion is the most effective form of erosion. The Abrasion is the most effective form of erosion. The stream uses sand, pebbles and boulders as cutting stream uses sand, pebbles and boulders as cutting tools.tools.– The cut banks and beds of rivers and round The cut banks and beds of rivers and round

themselves in doing sothemselves in doing so– Potholes – sand pebbles and boulders swirl in Potholes – sand pebbles and boulders swirl in

whirlpools grinding out a hole in the streams bed.whirlpools grinding out a hole in the streams bed.

•Limestone and marble most easily eroded by Limestone and marble most easily eroded by rockrock

How streams transport How streams transport materialmaterial• Load – soil and rock material being Load – soil and rock material being

transported by the streamtransported by the stream– Solution (dissolved load) – most comes Solution (dissolved load) – most comes

from groundwater entering the streamfrom groundwater entering the stream– Suspension – turbulence keeps material Suspension – turbulence keeps material

supported in water – cause the water to supported in water – cause the water to look muddylook muddy

– Bed load – material that is too heavy to be Bed load – material that is too heavy to be carried in solution travels on the floor (bed)carried in solution travels on the floor (bed)

• Competence – is a measure that describes the Competence – is a measure that describes the maximum size of the particle a stream can maximum size of the particle a stream can carrycarry

• Capacity – is a measure of the total amount of Capacity – is a measure of the total amount of sediment a stream can carrysediment a stream can carry– Velocity controls both the higher the velocity Velocity controls both the higher the velocity

the larger the competency the larger the competency

• During floods sand and pebbles can be carried During floods sand and pebbles can be carried in suspension this when most of the streams in suspension this when most of the streams erosion is doneerosion is done

Stream Deposition Stream Deposition

• Deposition (dropping of load) Deposition (dropping of load) occurs in a stream when its occurs in a stream when its velocity or discharge is velocity or discharge is decreaseddecreased

• The greatest decrease in a rivers The greatest decrease in a rivers velocity occurs when it empties velocity occurs when it empties into a sea or lake. All sediment into a sea or lake. All sediment will depositedwill deposited

Depositional featuresDepositional features

• Delta fan shaped deposit that forms Delta fan shaped deposit that forms when a river flows into a quiet or when a river flows into a quiet or large body of waterlarge body of water– Small current and waves along with a large Small current and waves along with a large

amount of sediment helps deltas to formamount of sediment helps deltas to form– Distributaries – branches in the delta that Distributaries – branches in the delta that

distributes sedimentdistributes sediment

• Alluvial fan – form at the base of a steep Alluvial fan – form at the base of a steep hill in a dry regionhill in a dry region

Chapter 13.3Chapter 13.3

River ValleysRiver Valleys

• Begins as a gulley which grow in Begins as a gulley which grow in length, width and depth every length, width and depth every time it rainstime it rains

• When it cuts deep enough to hit When it cuts deep enough to hit the ground water it becomes a the ground water it becomes a streamstream

• Headward erosion – stream Headward erosion – stream lengthens above its headwaterlengthens above its headwater

Canyons and v-shaped Canyons and v-shaped valleysvalleys• Canyons form – when the river cuts Canyons form – when the river cuts

into its bed rapidly or when the rock into its bed rapidly or when the rock materials on the side of the canyon materials on the side of the canyon are resistant to erosion.are resistant to erosion.– Rock type will affect the speed of cutting alsoRock type will affect the speed of cutting also

• V-shaped valleys describe youthful valleysV-shaped valleys describe youthful valleys– No large bends will existNo large bends will exist– V-shaped comes from the exposed walls V-shaped comes from the exposed walls

being eroded by longer amount of timebeing eroded by longer amount of time

• Base level – lowest level a stream Base level – lowest level a stream can erode tocan erode to– Controlled by what the stream flows intoControlled by what the stream flows into– Closer to base level the lower the gradient Closer to base level the lower the gradient

and sideways erosion occursand sideways erosion occurs

• Stream Piracy – through headward Stream Piracy – through headward erosion, one river wears through the erosion, one river wears through the divide and captures the headwaters of divide and captures the headwaters of the other riverthe other river

Rapids and WaterfallsRapids and Waterfalls

• Rapids are formed by the Rapids are formed by the recession of waterfallsrecession of waterfalls

• Waterfalls are reduced by Waterfalls are reduced by underminingundermining– Undercut the waterfall which eventually Undercut the waterfall which eventually

fallsfalls

Chapter 13.4Chapter 13.4

Flood plains and FloodsFlood plains and Floods

• Flood – when a river overflows it Flood – when a river overflows it banks the part of the valley banks the part of the valley floor it covers is the flood plainfloor it covers is the flood plain

Features of a Flood plainFeatures of a Flood plain• Reasons why a river near base level meanders Reasons why a river near base level meanders

(bends)(bends)– River current is more easily deflected because of River current is more easily deflected because of

a lower velocitya lower velocity– Erosion is more dominate on the outside of the Erosion is more dominate on the outside of the

bendbend

• Oxbow lake – curved body of water formed when the Oxbow lake – curved body of water formed when the river cuts off a bendriver cuts off a bend

• Levees – build up of sediment along the river bank Levees – build up of sediment along the river bank formed floods when the slower water deposits formed floods when the slower water deposits materialmaterial

FloodsFloods

• Deposit minerals and nutrients on Deposit minerals and nutrients on flood plains, making the area flood plains, making the area fertile for agriculturefertile for agriculture

• Flash floods occur on small narrow Flash floods occur on small narrow streams during heavy downpoursstreams during heavy downpours

• Floods on large rivers occur due to Floods on large rivers occur due to large amounts of rain of long large amounts of rain of long periods of timeperiods of time

Flood Prevention and Flood Prevention and ControlControl

• Plant vegetation to control runoffPlant vegetation to control runoff

• DamsDams

• Artificial levees – walls built Artificial levees – walls built alongside a streamalongside a stream

• Spillways – channel built parallel Spillways – channel built parallel to the main channel in the back to the main channel in the back swamp to divert waterswamp to divert water