Landforms of Fluvial Erosion and Deposition
A pothole is a circular depression on the river bed carved out of solid rock. It is formed by a kind of drilling action as pebbles are caught in eddy currents and whisked around within a small natural crack or hollow. As time passes, the drilling action enlarges the hollow to form a pothole. Potholes are commonly found below waterfalls or rapids where hydraulic action is a significant process.
A waterfall is a sudden step in a rivers long profile. It is often the result of a tougher more resistant band of rock cutting across the valley. Unable to erode the rock at the same rate as the neighbouring rocks, a step is formed and a waterfall results. Over time, the river cuts backwards into the resistant rock causing the waterfall to retreat backwards forming a narrow, steep-sided gorge.
Rapid s are a series of small waterfalls associated with very disturbed turbulent water. Rapids are formed when rocks of varying resistances cut across a valley and erosive processes create a series of steps.
Meanders are sudden bends in the course of a river. Meanders form when areas of alternating pools (deep water) and riffles (shallow water) develop at equally spaced intervals along a stretch of river. The distance between pools is usually 5-6 times the width of the river bed. Because water is deeper in pools, the river is more efficient when passing over them. The energy and erosive power is therefore increased when passing over these areas. On the other hand, the river is less efficient when passing over riffles as there is more friction causing the river to lose energy.
This combination of the river gaining and losing efficiency at different intervals causes the river’s flow to become uneven, and maximum flow is concentrated on one side of the river. As the water speeds up, turbulence increases in and around pools. This leads to corkscrew-like currents in the river called helicoidal flow. These helicoidal currents spiral from bank to bank, causing more lateral erosion (abrasion and hydraulic action) and deepening of the pools – river cliff. This leads to the increased amount of eroded material being deposited on the inside of the next bend where the river loses energy – slip off slope. Combination of erosion and deposition exaggerates bend until large meanders are formed. These combined processes also give the meander’s asymmetric cross-section.
Oxbow lakes form because in meanders erosion is concentrated on the outer bend while deposition is predominant on the inner bend leading to the formation of point bars. The alternating zones of erosion and deposition cause meanders to migrate both across and down the valley. In addition meanders become more exaggerated and sinous.
As opposite bends erode towards each other, the neck of a meander will get progressively narrower until, during a period of high discharge, the river will cut through forming an oxbow lake.
Braiding is when a river subdivides into smaller streams. In between these channels small islands of deposited sediment will form. Braiding occurs where there is a sudden decrease in energy causing deposition of large amounts of sediments making the main channel to subdivide.
A floodplain is a flat area of land bordering a river that is subjected to periodic flooding. It is made up of silts and sands which have been deposited over many years. As a river floods its velocity is dramatically decreased causing energy to be reduced and a bulk of sediment to be floating in a thin sheet of water on the floodplain. Once the water has evaporated a fresh layer of alluvium is left behind.
Levees are natural embankments of sediment formed when the river floods.
Deltas
A delta is formed when a river enters a sea or lake loosing velocity and energy causing a large amount of sediment

to be deposited as a delta. Rivers flowing over deltas tend to break into many smaller channels called distributaries.
They are found in most areas of the world except the poles and have several characteristics in common. They
 drain large areas
 carry large quantities of sediment
 empty at coasts that are geologically quiet.
The Ganges is the largest covering roughly 128,000 sq km.
Types
1. Arcuate (fan-shaped) delta - e.g., Nile River, Indus, Rhone. Has many active, short distributaries taking sediment to their mouths. The shore line is smooth and waves push sediments against the edge forming a fanshaped delta with the wider portion facing the water. River and wind activity is well balanced. The receiving
(ambient) waters are rather shallow and have relatively even wave action arriving perpendicular to the shore with minimal longshore current. These are the most common type of delta.
Arcuate Source: Strahler.
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Bird-foot (shaped like a bird foot) delta - e.g., Mississippi River Ural River, Saskatchewan River. These are river dominated deltas. Tend to have one or a very few major distributaries near their mouths. The receiving basin has currents that carry the sediment away as it exits the distributary mouth. Wave action is low. The Mississippi is an excellent example. It displays multiple lobes caused by changing channels from time to time ( avulsion) . When one channel is stable for a long time it extends the delta far off shore producing its one main toe. Periodically, the levees are breached and a new channel take a shorter, more efficient route to the sea, forming a new lobe. So a series of lobes are formed as a result of channel

switching , giving the delta its characteristic bird’s foot shape. It is believed that the Mississippi has undergone this process at least five times.
Bird foot; Source: Strahler.
Cuspate (tooth-shaped) delta - e.g., Tiber River of Italy. These are wave dominated deltas. Usually has one distributary emptying into a flat coastline with strong waves hitting it head-on. This tends to push the sediment back on both sides of the mouth, with a "tooth" growing out onto the shelf.

Cuspate: Source: Strahler.
4. Estuarine delta - e.g., Seine River of France. These are tide dominated. Strong tides migrate up the river widening its mouth to form estuaries. In combination with wave action the river load is swept into the shallow sea or transported to areas of low energy where it settles into tidal flats insidethe coastline.
Estuarine: Source: Strahler.

Delta terms
Progradation - The river deposits sediments faster than the sea is able to remove them, so the delta grows outward into the sea (=progrades).
Aggradation - The river deposits build up (elevation) via overbank flooding, accumulation of biotic remains, etc., so the delta grows upward.
Transgression - The retreat of the delta, usually by the loss of sediment caused by continued wave attack or the reduction of nourishment soils.
It follows that deltas have four options:
1. They stagnate, i.e., remain in equilibrium.
2. They prograde.
3. They aggrade.
4. They transgress.
7) Process and Impact of Rejuvenation
Rejuvenation causes the river to increase its down cutting activity.
Rejuvenation is caused by tectonic activity causing dynamic rejuvenation, an increase in the volume of water in the drainage system, changes in base level either sea level falls or land rises due to eustatic fall in sea level (global fall in the level of the sea) or an isostatic change in the level of the land (local uplift of land).
Knick points are breaks in gradient along the profile of a river usually marked by rapids or waterfalls.
River terraces are the remnants of the former floodplain prior to rejuvenation. Terraces create steps in the valley cross profile.
Incised Entrenched meanders
Incised Meanders
If a rejuvenated river occupies a valley with well-developed meanders, renewed energy results in them becoming incised or deepened. The nature of the landforms created is largely a result of the rate at which vertical erosion has taken place. When incision is slow and lateral erosion is occurring, an ingrown meander may be produced. The valley becomes asymmetrical, with steep cliffs on the outer bends and gentler slip-off slopes on the inner bends. E.g. The River
Meuse, French Ardennes.
Entrenched Meanders
With rapid incision, where down-cutting or vertical erosion dominates, the valley is more symmetrical, with steep sides and a gorge-like appearance. These are described as entrenched meanders.
E.g. San Juan River , Utah.