Lower Course Landforms

Question 1

Deltas

Answer 1

Occur where deposition exceed sediment removal so fallen out of dynamic equilibrium

Conditions: High suspended load/large sediment load; Low gradient; feeds into low energy sea/lake where small tidal range & weak currents so limited wave action to transport sediment away.

• Deposition occurs as the velocity decreases as enters sea/lake so energy decreases and competence decreases so deposition of bedload and suspended load occurs.
• Flocculation is the mixture of sea and fresh water where clay particles coagulate and become heavier so sink and are deposited.
• Turbidity current: current of rapidly moving, sediment-laden water down a slope.

Question 2

Delta Beds

Answer 2

Topset - larger, header materials deposited first
Foreset - Medium graded particles travel a little further before being deposited
Bottomset - finest materials travel furthest and are deposited last

Question 3

Delta Examples

Answer 3

Bird’s Foot - finger like depositions built out to sea along distributaries’ channels - looks like birds claw - Mississippi
Arcuate - Curving shoreline - dendritic pattern of drainage. Many distributaries break away from channel. LD keeps seaward edges smooth - Nile
Cuspate - Pointed like a cup/tooth and shaped by gentle but opposing, regular currents or LD - Ebro

Question 4

Levées

Answer 4

1. River tops banks and velocity decrease as friction increases due to shallow water
2. This reduces competence and energy of river so deposition occurs
3. Coarsest material deposited first closest to channel but finer particles can travel further as they require less energy to be transported
4. This forms depositions of sediment to create raised banks
5. Subsequent floods lead to more deposition and the levées increase in size
6. Further flooding leads to deposition of bed of channel so river flows at a higher level than the floodplain.

Question 5

Floodplain

Answer 5

Areas of flat land either side the river channel which forms the valley floor in the middle and lower course of a river.

Increase width = migration meanders eroding valley sides and removal interlocking spurs

Increase in sediment depth due to levees, and water remains after flood for days until being evaporated leaving behind a fresh layer of alluvium. Point bars and meander scars become incorporated into flood plain increasing alluvium build up. Also river terraces occur when the sea level changes and the river cuts down into bed so flood plain is at a lower level than old floodplain.

Uses: Fertile so good for farming and flat so good for building on.