RiversRivers

Where Do Rivers Get Their Where Do Rivers Get Their Water? 466Water? 466

Drainage Basin – provides Drainage Basin – provides water for the river. water for the river.

Where Do Rivers Get Their Where Do Rivers Get Their Water? 466Water? 466

Basin Slope – Basin Slope – Runoff from a Runoff from a steep slope is steep slope is higher than a higher than a gentle slope. gentle slope.

Tributaries – Tributaries – Small channels Small channels that carry water that carry water to rivers. to rivers.

Drainage Patterns 467Drainage Patterns 467 Dendritic Drainage Dendritic Drainage

Pattern – Where Pattern – Where rocks have about rocks have about the same resistance the same resistance to erosion.to erosion.

Radial Drainage – Radial Drainage – Occurs on a Occurs on a mountain, drainage mountain, drainage flows downhill in all flows downhill in all directions directions

Drainage Patterns 467Drainage Patterns 467

Structurally Structurally Controlled Controlled Pattern – Pattern – Erosion along Erosion along faults or faults or fractures. fractures. TrellisTrellis Rectangular Rectangular

Trellis

Rectangular

How is Material How is Material Transported and Transported and

Deposited?Deposited?Soluble ions are Soluble ions are dissolveddissolved in and carried in and carried by moving waterby moving water

Fine particles can be carried in Fine particles can be carried in suspension (floating) in watersuspension (floating) in water

Sand grains Sand grains can roll and can roll and bounce alongbounce along Cobbles and Cobbles and

boulders mostly boulders mostly roll and slide roll and slide during high flowsduring high flows

Material moving on Material moving on river bed is river bed is bed loadbed load

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How Is Material How Is Material Transported and Deposited Transported and Deposited

in Streambeds? 468in Streambeds? 468 Suspended Material - Particles - Particles

that are small enough to be that are small enough to be carried along with a slow carried along with a slow current, such as clay (AKA mud) current, such as clay (AKA mud) or silt or silt

SaltationSaltation – (from the latin word – (from the latin word saltus – to leap) the process of saltus – to leap) the process of larger particles (sand) bouncing larger particles (sand) bouncing off the bottom of the streambed.off the bottom of the streambed.

Transfer of Materials Transfer of Materials Continued 468Continued 468

Larger cobbles and boulders – Larger cobbles and boulders – generally slide but ONLY if there is a generally slide but ONLY if there is a high flowhigh flow

Bed LoadBed Load – Material that is pushed, – Material that is pushed, bounced, rolled, and slid along the bounced, rolled, and slid along the bottom. This sediment exceeds the bottom. This sediment exceeds the carrying capacity of the river carrying capacity of the river

Chemicals – dissolve in water and Chemicals – dissolve in water and are transported (Calcium and are transported (Calcium and sodium)sodium)

Transport vs. Deposit Transport vs. Deposit 468468

Materials are transported when Materials are transported when the river moves quickly. The the river moves quickly. The river then has a high carrying river then has a high carrying capacity. capacity.

When the velocity slows, more When the velocity slows, more material is deposited because material is deposited because the carrying capacity is the carrying capacity is reduced.reduced.

TurbulenceTurbulenceViscosity (resistance to flow) and Viscosity (resistance to flow) and

surface tension act to keepsurface tension act to keep water smooth, as in water smooth, as in

slow-moving waterslow-moving water

Moving water Moving water has inertia has inertia (tries to keep (tries to keep moving with moving with same speed same speed and direction)and direction)

At higher velocities or near At higher velocities or near obstacles, flow becomes obstacles, flow becomes more chaotic (turbulent), more chaotic (turbulent), forming a swirl called an forming a swirl called an eddyeddy

Upward-Upward-flowing flowing

eddies can eddies can pick up pick up

loose loose materialmaterial

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Turbulence in Flowing Turbulence in Flowing water 469water 469

ViscosityViscosity - resistance to flow - resistance to flow Slow rivers = high viscosity and calm waterSlow rivers = high viscosity and calm water Fast rivers = low viscosity and Fast rivers = low viscosity and chaotic chaotic

waterwater or turbulent water. or turbulent water. Turbulent rivers have Turbulent rivers have eddieseddies which are which are

horizontal or vertical swirls in the horizontal or vertical swirls in the water. water.

Turbulent water usually increases the Turbulent water usually increases the amount of grains to be picked up and amount of grains to be picked up and carried making the water cloudycarried making the water cloudy

Erosion in streams 468Erosion in streams 468

Sand and larger clasts lift because of low Sand and larger clasts lift because of low pressure created by water flowing over pressure created by water flowing over the grain tops or are pushed up by the grain tops or are pushed up by turbulent water.turbulent water.

Once lifted, the clasts collide with Once lifted, the clasts collide with obstacles and break off. obstacles and break off.

AbrasionAbrasion – when pieces of rock are – when pieces of rock are sandblasted off as a result of material sandblasted off as a result of material flowing by. flowing by. Only happens on upstream side of rock. Only happens on upstream side of rock.

Erosion in streams 468Erosion in streams 468

Also occurs when water and Also occurs when water and sediments swirl in a small area. sediments swirl in a small area. Creates bowl-shaped pots called, Creates bowl-shaped pots called, potholespotholes

Turbulent flow loosens and lifts Turbulent flow loosens and lifts material from the streambed. material from the streambed.

DissolutionDissolution removes soluble removes soluble material material

Erosion, Rivers, and Erosion, Rivers, and Bedrock 469Bedrock 469

Many rivers are carved into Many rivers are carved into bedrock. If the bedrock is hard, the bedrock. If the bedrock is hard, the shape of the river is controlled by shape of the river is controlled by the geology. the geology.

Waterfalls – The steep gradient Waterfalls – The steep gradient (vertical change/horizontal (vertical change/horizontal distance) and fast velocity does not distance) and fast velocity does not allow for erosion on the sides of the allow for erosion on the sides of the river.river.

Erosion, Rivers, and Erosion, Rivers, and Bedrock 469Bedrock 469

Canyons – originally started Canyons – originally started where bedrock was softer. where bedrock was softer. Once formed, hard to change Once formed, hard to change the direction of the river.the direction of the river.

Channel Size, Water Channel Size, Water Velocity, Discharge, and Velocity, Discharge, and

Sediment Load 470Sediment Load 470 As the gradient decreases, sediment As the gradient decreases, sediment

size decreases.size decreases. Channel size (width x depth) increasesChannel size (width x depth) increases Velocity increases because there are Velocity increases because there are

feeder streams adding additional waterfeeder streams adding additional water Discharge (amount of water flowing Discharge (amount of water flowing

through a specific part of the river) through a specific part of the river) increasesincreases

Sediment load – increases until it can Sediment load – increases until it can be deposited at the mouth of the river. be deposited at the mouth of the river.

River Behavior Through the River Behavior Through the Year 471Year 471

Peak Discharge - when discharge is Peak Discharge - when discharge is the highest. Its usually spring the highest. Its usually spring because of the snowmelt. because of the snowmelt.

Water Budget – the amount of Water Budget – the amount of water evapotransporated and water evapotransporated and regenerated (in the form of regenerated (in the form of precipitation) during the year. precipitation) during the year. Surplus – more precipitation than Surplus – more precipitation than

evapotransporationevapotransporation Deficit – more evapotransporation Deficit – more evapotransporation

than precipitation than precipitation

Rivers Through the YearRivers Through the Year

Perennial Stream – flows all year Perennial Stream – flows all year long. Needs to be fed by long. Needs to be fed by groundwater because it doesn’t rain groundwater because it doesn’t rain all year. all year.

Curves in Rivers and Curves in Rivers and StreamsStreams

Low sinuosityLow sinuosity: : gently curvedgently curved

BraidedBraided: network : network of interweaving of interweaving channelschannels

MeanderingMeandering: very : very curved; high sinuositycurved; high sinuosity

16.05.a2-4Observe the channels in three riversObserve the channels in three rivers

Why do rivers have Why do rivers have curves? 474curves? 474

Sinuosity – Sinuosity – The amount of curves The amount of curves for a given length. for a given length.

Inside of a curve is shallow so the Inside of a curve is shallow so the velocity is slower. Sediment is velocity is slower. Sediment is deposited here, known as the deposited here, known as the point point barbar. .

Outside of a curve is deeper so the Outside of a curve is deeper so the velocity is faster causing erosion on velocity is faster causing erosion on the outer bank or the outer bank or cut bankcut bank

Landforms in the Landforms in the headwaters of Rivers 476headwaters of Rivers 476

HeadwatersHeadwaters – The beginning of a – The beginning of a stream or riverstream or river

Waterfalls – A steep gradient formed Waterfalls – A steep gradient formed when hard rock impedes downcutting when hard rock impedes downcutting by the stream. by the stream.

Rapids – rough, turbulent water along Rapids – rough, turbulent water along a stream. Form when the gradient a stream. Form when the gradient steepens and the river is constricted steepens and the river is constricted by bedrock or large rocks.by bedrock or large rocks.

Braided Rivers 478Braided Rivers 478 Braided river – a Braided river – a

network of channels network of channels that split and rejoin. that split and rejoin. Usually have a lot of Usually have a lot of sediment and a steep sediment and a steep gradient. gradient.

When glaciers melt, When glaciers melt, there is an abundance there is an abundance of water and sediment of water and sediment and the braided river and the braided river systems flood and form systems flood and form new rivers. new rivers. This allows sediment to This allows sediment to

redistribute redistribute

When Rivers Reach Base When Rivers Reach Base Level 482Level 482

Base Level – the oceanBase Level – the ocean Delta – When currents slow, Delta – When currents slow,

deposit is dropped along the deposit is dropped along the shoreline. shoreline. Silt and clay are carried Silt and clay are carried

farther out into sea.farther out into sea.