Week 8: Rivers

Question 1

What is a stream?

Answer 1

Any flowing body of water, regardless of size

Question 2

What is a river?

Answer 2

A major branch of a large stream system

Question 3

What is a channel?

Answer 3

The stream passageway

Question 4

What is a load?

Answer 4

The sediment carried by the stream

Question 5

What is discharge?

Answer 5

The quantity of water passing a given point

Question 6

Name and describe the two processes by which water in a stream moves.

Answer 6

Laminar Flow:
Straight or gently curved streamlines that run parallel to one another without mixing or crossing

Turbulent Flow:
A complex pattern of movement with streamlines crossing and forming swirls and eddies

Question 7

What is a suspended load?

Answer 7

All the material temporarily or permanently suspended in the flow

Question 8

What is a bed load?

Answer 8

The material carried by the stream along its bottom by sliding and rolling

Question 9

What is saltation?

Answer 9

The intermittent jumping of sand grains as they are lifted off the bottom, carried a short distance and then settle out

Question 10

What is abrasion?

Answer 10

A sandblasting action from sediments in the suspended and bed load that cause erosion on rocks the stream runs over or alongside.

Question 11

What is a stream valley?

Answer 11

The entire area between tops of the slopes on both sides of a river

Question 12

What is a stream channel?

Answer 12

A channel that carries all the water during normal, nonflood times.

Question 13

What is a flood plain?

Answer 13

A flat area about level with the top of the stream valley

Question 14

List the 2 common stream channel patterns.

Answer 14

• Meanders
• Braided Streams

Question 15

What are Meanders?

Answer 15

• Curved and bent river channels that wind across a floodplain
• Common in streams with a low gradient that typically cut through unconsolidated material
• Migrate over years, eroding the outside banks of the stream where current is strongest

Question 16

What are point bars?

Answer 16

Curved sandbars that deposit on the inside bank where current is slower in a meandering stream channel.

Question 17

What is an oxbow lake?

Answer 17

The crescent-shaped, water filled loop that is created when the meander loop neck becomes so narrow that the loop is bypassed by the river

Question 18

What are braided streams?

Answer 18

• High energy streams that have many channels instead of one single channel
• Channels split apart and then rejoin in a patter resembling braids of hair

Question 19

What is the gradient of a stream?

Answer 19

The distance the stream falls between two points

Question 20

What is a stream’s Long Profile?

Answer 20

• A line drawn along the surface of the stream from its source to its mouth
• It is a concave upward curve due to decreases in gradient downstream

Question 21

What is the base level?

Answer 21

It occurs where a river enters a body of standing water

Question 22

What is the discharge?

Answer 22

The amount of water in m3/s that passes down the river

Question 23

Why does the velocity of streams increase downstream?

Answer 23

Because the streams are deeper downstream and have less resistance from the stream bed, even though the gradient has decreased

Question 24

When does a flood occur?

Answer 24

When a stream’s discharge exceeds the capacity of the channel and the stream overflows its banks.

Question 25

Why are floods of significance and cause a large impact?

Answer 25

Because they increase both the discharge of the stream and its velocity. This means that a much greater amount of load is carried by the stream as well as the size of material. It results in a large amount of erosion and redeposition.

Large impact also because many communities are built on floodplains.

Question 26

What is a Recurrence Interval?

Answer 26

Commonly expressed as 10 year or 100 year flood events. Found by plotting the occurrence of past maximum discharges, including floods of different sizes on a probability graph.

Question 27

What is alluvium?

Answer 27

Sediment material deposited out of a stream

Question 28

Why does the size of sediment carried by a stream decrease in the downstream direction?

Answer 28

Because, although the velocity increases downstream, sorting leaves the larger particles upstream and abrasion reduces particles in size.

Question 29

What is a floodplain?

Answer 29

The part of the stream valley inundated with flood waters

Question 30

What is a levee?

Answer 30

A broad low ridge of sediment built along the side of the river channel

Question 31

What is a terrace?

Answer 31

The remains of an abandoned flood plain that is no longer used due to down-cutting of the river.

Question 32

What is an alluvial fan?

Answer 32

A fan shaped body of alluvium built where a stream leaves a steep mountain valley and the sudden decrease in gradient and velocity causes it to deposit its load on the valley floor.

Question 33

What is a Delta?

Answer 33

A sedimentary deposit that forms where a stream flows into a standing body of water and the velocity decreases rapidly causing the sediment loads to drop out.

Question 34

What is a drainage basin?

Answer 34

The total area that drains into the stream

Question 35

What are first order streams?

Answer 35

The smallest streams that lack tributaries

Question 36

What are second order streams?

Answer 36

Where two first order streams join and form a second-order stream

Question 37

What are third order streams?

Answer 37

Where two second order streams join. They can have first and second-order tributaries

Question 38

What is a Dendritic stream pattern?

Answer 38

Where branching channels are treelike

It reflects massive and/or flat-like rock strata where the rock imposes little control on stream patterns

Question 39

What is a Radial stream pattern?

Answer 39

Where channels radiate out - forms around a topographic high, such as a dome or volcanic cone

Question 40

What is a Rectangular stream pattern?

Answer 40

A rectangular arrangement of channels marked by right-angled bends.

It forms in areas where rocks are heavily jointed and fractured

Question 41

What is a Trellis stream pattern?

Answer 41

A rectangular arrangement of channels in which principle tributaries are parallel and very long.

It reflects dipping or folded strata in which the edges of rock units are exposed on the surface

Question 42

What are Placer Deposits?

Answer 42

Deposits of heavy minerals that have been concentrated mechanically (e.g. gold deposits).

For example, gold is of higher density and does not get removed by a lower stream flow which will remove most other minerals. The gold is then left behind and becomes concentrated.