rivers- middle course

what is a meander? what are its main characteristics?

large curve/ bend in a river mainly caused by lateral erosion

• inner bend: slip-off slope

• outer bend: river cliff

how do meanders form?

1. river channel is uneven-some parts more shallow, some more deep.

   • inside bend: shallow water on inside bend so water moves slower, resulting in more friction btwn. water bed and banks. this reduces speed, encouraging deposition and resulting in a slip-off slope.

   • outer bend: deep water on outside bend means water moves faster, resulting in les friction btwn. water and banks. this increases speed and encourages abrasion and hydraulic action, undercutting the bank and forming a river cliff

what is an ox bow lake?

small, horse-shoe shaped lake located several metres off a fairly straight stretch of river in its middle + lower courses

how are ox-bow lakes formed?

1. meander neck becomes narrower due to continued lateral erosion whereas meander loop becomes larger due to more deposition (inner bend) and more erosion (outer bend).

2. river floods so main flow of water cuts straight across meander neck, creating a shortcut and resulting in the meander loop becoming a redundant loop (as it stops being the used as the main flow)

3. redundant loop becomes increasingly separated from the main channel due to deposition and vegetation growth, leaving a semi-circular lake behind.

4. ox-bow lake eventually dries up and becomes a meander scar