WHY DO RIVERS MEANDER

Question 1

Where do rivers meander (1)

Answer 1

formation starts in the middle course of a river

reaches its greatest extent in the flatter lower course, where any excess energy is used to erode laterally rather than vertically

Question 2

Why does it meander? 2

Answer 2

never entirely uniform

• along relatively straight sections, irregularities in the bed + banks, caused by differing channel material + flow characteristics, –> regular patterns of POOLS and RIFFLES -

once started they are SELF PERPETUATING

Question 3

3

Answer 3

as water flows through path of least resistance the THALWEG diverts to one side of the riffle, CONCENTRATING turbulent flow on ONE SIDE of channel –> erosion –> embryonic river cliff

Question 4

4

Answer 4

in the same way, slower flow occurs on the opposite bank, increasing deposition –> embryonic point bar

Question 5

5

Answer 5

DOWNSTREAM of initial OUTSIDE bend, thalweg follow fall line back into river BUT its momentum is OFF CENTRE so flows downstream to THE OPPOSITE side of next riffle
REPEATING the process

thalweg therefore begins to move from SIDE TO SIDE

Question 6

6

Answer 6

pattern is repeated downstream - channel becomes increasingly SINUOUS as excess energy is diverted more LATERALLY than vertically the closer to BASE LEVEL

Question 7

7

Answer 7

HELICOIDAL FLOW plays a role whereby faster SURFACE WATER MOVES TO THE OUTSIDE BANK –> asymetric cross section

Question 8

8

Answer 8

DYNAMIC EQUILIBRIUM governs extent of meandering

DE caused by BALANCE BETWEEN CONDITIONS that r always changing and the move towards a steady state