Types of Rivers

Question 1

Types of Rivers

Answer 1

BRAIDED

MEANDERING

Question 2

Braided Channel

Answer 2

1. Number of channels:more than 1
2. Size of channel:smaller
3. Shape of Channel (w/d ratio):wide and shallow
4. Discharge:variable
5. Sediment Load:coarse, poorly sorted sediment sometimes moving as bed-load
6. Gradient:Steep

Question 3

Meandering

Answer 3

1. Number of channels:1
2. Size of channel:larger
3. Shape of Channel (w/d ratio)wide and Deep
4. Discharge:consistent and stable
5. Sediment loadfiner, better sorted sediment constantly moving in suspension
6. Gradient

shallower, lower

Question 4

Bedload

Answer 4

Includes sediment that moves by:

SALTATION

TRACTION

Question 5

Saltation

Answer 5

Sediment bounces along the bottom.

Question 6

Traction

Answer 6

Sediment rolls or slides along the bottom.

Question 7

Sediment load in a Braided River

Answer 7

coarse, poorly sorted sediment sometimes moving as bedload.

Question 8

Sediment load in a Meandering River

Answer 8

finer, better sorted sediment constantly moving in suspension.

Question 9

Braided Rivers start…

Answer 9

Higher up in the drainage basin

Question 10

Definition of a braided river

Answer 10

Braided rivers are defined by the presence of multiple channels separated by piles of sediment called channel bars.

Question 11

Channel bars found in braided rivers

Answer 11

• Temporary piles of sediment that form during brief periods of increased dischargee.
• large quantities of coarse, poorly sorted sediment is eroded, transported and deposited over short distances and times.
• These bars often have a massive structure because deposition was rapid.
• may be within the channel or attached to the channel sides.

Question 12

PICTURE —> O A

Answer 12

At A, water turbulence increases in the down-current or lee side of the channel bar which causes water velocity to drop

As a result, finer grains are sometimes deposited as a tail on the lee side of the bar.

The bar can also be reworked to some degree as water level drops and during low flow conditions.

Question 13

Permeability

Answer 13

Measure of how well connected the pores are in sediment

Question 14

Anastomosing Rivers

Answer 14

Very much like the braided river in that it has multiple channels. However the channel bars that separate flow are more permanent. because they have been stabilized by vegetation growth.

Question 15

Thalweg

Answer 15

the line that defines where the deepest, fastest moving water is.

Question 16

Cut bank

Answer 16

Erosion takes place at the outer bank to create a steeper cut bank because here is where the fastest water is.

Question 17

Secondary flow caused by the cut bank?

Answer 17

There is more water pressing up against the outer bank which raises the water level here.

The surface from the cut bank to the point bar is inclined.

As a result there is a weaker secondary

Question 18

Secondary flow caused by the cut bank?

Answer 18

There is more water pressing up against the outer bank which raises the water level here.

The surface from the cut bank to the point bar is inclined.

As a result there is a weaker secondary flow of water along the bottom from the cut bank to the point bar.

Question 19

Sediment layers in a point bar cross bed

Answer 19

As water moving from the cut bank to a point bar slows down deposition takes place, creating a layer of sediment .

1. (bottom) sediment at the base of the point bar is the coarsest sediment.
2. medium grain sediment
3. finer grain sediment.

Question 20

Cross bed

Answer 20

layer of sediment deposited on the point bar at an angle

Question 21

When does a river move most of its sediment?

Answer 21

During a flood when there is faster moving water in the channel. (not common)

Question 22

Internal structure of a point bar

Answer 22

• series of super-imposed cross beds.

- horizontal layers within (“fining upwards” sequence of coarse, medium, fine grain sizes)

Question 23

how does a meandering river migrate?

Answer 23

• Lateral Migration (deposition on the point par and erosion on the cut bank) , the channel migrates laterally (sideways).
• Downstream Migration (focusing of energy (the fastest water) further down stream at point E)

Question 24

Where does sediment eroded from the cut bank end up?

Answer 24

Sediment eroded at A does not end up at B (the point directly across from it). The cross channel flow is much weaker than the downstream flow, so it ends up at a point bar further downstream.

Question 25

Cross over point

Answer 25

The place between meander loops where the thalweg is in the center of the channel as it moves from one side to the other.

• more symmetrical because processes are more evenly distributed. flow converges at the surface.
• the channel is shallower here than at the point bar/cut bank. (here it is often called a pool.)

Question 26

flood plain

Answer 26

A flat, low-lying area along a stream channel, created by and subject to recurrent flooding

Question 27

Cross over point Vs. Point Bar/Cut Bank Pool

Answer 27

INSERT IMAGE

Question 28

This channel and its various shapes are the result of ….

Answer 28

periods of increased discharge