Learning objectives Processes of River Transportation River Profiles : Long Profile River Profiles : Cross Profile Fluvial Landforms River Abstraction / Stream Piracy. Learning objectives

Fluvial Landforms Waterfalls Forms when resistant layer of rock prevents vertical erosion Softer underlying layers are eroded Resistant layer is undermined and collapses. Waterfall retreats upstream. Forms a Gorge or Ravine.

High Force waterfall, R. Tees Waterfalls create a gorge upstream as they recede, This is a steep sided valley with no floodplain.

6 An overhang develops where the softer rock below is eroded. In time this will collapse. plunge pool relatively softer rock a band of hard rock interrupts the river’s course

Victoria Falls

Rapids in the Upper Tees Valley

FLOODPLAIN Flat areas next to rivers Lower course During flooding – velocity is slower due to friction Silt is deposited by the flood Increases fertility of floodplain

FLOOD PLAIN River Landforms

Fluvial Landforms Levees Form on the floodplain on the lower course Flooding causes overflowing of banks Heavier deposits occur repeatedly on the banks Deposits are built up to raised banks known as levees May be artificially raised and strengthened as flood protection Swamps may form on the floodplain

Formation

Fluvial Landforms Meanders / Ox-bow Lake River reaches flat land Begins to meander Velocity is highest on the outer bend - erosion – undercut bank – river cliff Velocity is lower on the inside bend - deposition – slip-off slope – gradual slope.

On the outside of the meander water is flowing more quickly On the outside of the meander water is flowing more quickly. This results in erosion and the formation of a undercut slope or river cliff. On the inside of the meander water is flowing more slowly. This results in deposition and the formation of the slip-off slope or river beach.

CROSS PROFILE ROUND A BEND Y X X Y Undercut Erosion Faster flow Deposition Slower flow Slipoff

McKenzie River meanders and glacial lakes

Ox Bow Lake Formation

Ox Bow lake on Mississippi

F L A T LOWER COURSE OF A RIVER BRAIDED STREAM M O U T H MARSH SANDBANKS MEANDERS

Braided stream The velocity of the river is reduced and this causes the river to split and rejoin many times The river flows over loose sandy alluvium An example of a Braided stream is the Orange river between Upington and Augrabies Falls. As a result of the wide channel, the river flows slowly and large deposits of alluvium form islands in the middle of the river.

Braided River

Braided River, Shyok River, India

The Aswan Dam and the Nile Delta Fluvial Landforms The Aswan Dam and the Nile Delta Deltas When a river enters the sea or a lake the gradient is gentle and the flow speed of the river is reduced resulting in the deposition of sediments causing the river channel to become blocked. Requirements for a Delta to form A large and constant supply of silt. A slow flowing river with water all year No strong tidal effect in the sea A calm, shallow sea with

Development of Delta