Fluvial Landforms – Running water

• Two components of Running water
• Overland flow on general land surface as a sheet.
• Linear flow as stream and rivers in valleys.
• Overland flow causes sheet erosion. Depending upon irregularities of the land surface, the overland flow may concentrate into narrow to wide paths. Because of the sheer friction of the column of flowing water, minor or major quantities of materials from the surface of the land are removed in the direction of flow and gradually small and narrow rills will form. These rills will gradually develop into long and wide gullies; the gullies will further deepen, widen, lengthen and unite to give rise to a network of valleys. In the early stages, down-cutting dominates during which irregularities such as waterfalls and cascades will be removed. In the middle stages, streams cut their beds slower, and lateral erosion of valley sides becomes severe. Gradually, the valley sides are reduced to lower and lower slopes. The divides between drainage basins are likewise lowered until they are almost completely flattened leaving finally, a lowland of faint relief with some low resistant remnants called monadnocksstanding out here and there. This type of plain forming as a result of stream erosion is called a peneplain(an almost plain).

Life cycle of River.

• Youth - Streams are few during this stage with poor integration and flow over original slopes showing shallow V-shaped valleys with no floodplains or with very narrow floodplains along trunk streams. Waterfalls and rapids may exist where local hard rock bodies are exposed.
• Mature - Streams are plenty with good integration. Still V shaped valley but deep (Wider valley – U Shaped valleys). Waterfalls and rapids disappears.
• Old -  Smaller tributaries during old age are few with gentle gradients. Meander freely oxbow lake, etc.

Base level concept (Types)

• Grand level – Mean Sea Level (MSL)
• Temporary base level – Base level compare to near major Stream (Ex: R. Yamuna compare to R. Ganga)
• Local base level – Compare to near water source (Ex: River compare to near lake).

Erosional Landforms

Valleys

• The rills will gradually develop into long and wide gullies; the gullies will further deepen, widen and lengthen to give rise to valleys Potholes and Plunge Pools.
• Many types of valleys like
• V-Shaped Valley
• Gorger (I Shape) – gorge is a deep valley with very steep to straight sides.
• Canyons - Characterised by steep step like side slopes.
• Rapid & Catarats
• Rapid – undulating water (Reason – Presence of alternative hard and soft rock)
• More rapids are called cataracts.

Potholes and Plunge Pools (at base of waterfalls).

• Over the rocky beds of hill-streams more or less circular depressions called potholes.
• Large and deep holes at the base of waterfalls are called plunge pools.

Incised or Entrenched Meanders

• Very deep and wide meanders can also be found cut in hard rocks.

River Terraces

• Surfaces marking old valley floor or floodplain levels.
• Vertical erosion by the stream into its own depositional floodplain form paired and unpaired terraces.

Depositional Landforms

Alluvial Fans

• Load gets dumped and spread as a broad low to high cone shaped.
• Stream flow over fans are not confined to their original channels for long and shift their position across the fan forming many channels called distributaries.
• Humid areas – low cones with gently slope.
• Arid & Semi-arid Climate – High cone with Steep slope.

Delta

• Formed in Alluvium soil (Fertile).
• Load carried by the rivers is dumped and spread into the sea. Spread and accumulates as a low cone.
• Coarsest materials settle out first and the finer fractions like silts and clays are carried out into the sea.

Condition for delta formation

• Active erosion during the upper course of the river.
• Shallow sea court.
• Sheltered coast (Absence of Tides).
• Absence of ponds or the curves of river.

Types of Delta

• Arcurate – Dentrits pattern (Tree like).
• Bird foot – Shape of bird foot (Crow) – Mississippi.
• Cuspate or Estearise (Most delta is Estuarise) – Tooth like projection.
• Truncated delta – due to raise in sea level the cut off delta.
• Ganges Brahmaputra – Largest Delta (Sundarbans)

Floodplains, Natural Levees and Point Bars

• Deposition develops a floodplain. A river bed made of river deposits is the active floodplain. The floodplain above the bank is inactive floodplain (Contain Flood deposits and Channel deposite).
• The flood deposits of spilled waters carry relatively finer materials like silt and clay. The flood plains in a delta are called delta plains
• Natural levees are found along the banks of large rivers. They are low, linear and parallel ridges.
• Point bars are also known as meander bars found at concave side of meanders. sediments deposited in a linear fashion by flowing waters.

Meanders

• Loop-like channel patterns called meanders develop over flood and delta plains.
• Occur in Later mature or Early Old Stage of River.
• Meander is not a landform but is only a type of channel pattern.
• Propensity of water flowing over very gentle gradients to work laterally on the banks;
• Unconsolidated nature of alluvial deposits making up the banks with many irregularities which can be used by water exerting pressure laterally.
• Coriolis force acting on the fluid water deflecting it like it deflects the wind.
• Cut of Bank – Characterized of active erosion.
• Slip of Bank - Characterized of active deposition.

River Rejuvenation

• Due to fall of BL the youth & Mature Stages elongated and deposition started at long time.

Landforms associate with River Rejuvenation

• Polycyclic Landforms
• Paired & unpaired terraces.
• Knick point & Knick point Waterfall.
• Incised Meanders/ Entrenecenched Meanders/ Engrourm Meanders. (The Meandered river form paired or unpaired terraces due to fall of sea level (Negative impact)).
• Valley in Valley Topography.

River Capture/ Piracy