Fluvial Landforms

Rill

Tiny hillside channels a few centimeters wide and deep that are cut by ephemeral rivulets. Grades into gullies.

Gully

Intermediate between rills and arroyos, which are larger incised stream beds. They tend to be deep and long and narrow, and continuous or discontinuous. Dongas, vocarocas, ramps, lavakas.

Arroyo

Ephemeral stream channels in arid and semiarid regions. They often have steep or vertical walls and flat, sandy floors. Wadi, washes, dry washes, coulees, donga, nullah.

Bedrock channel

Eroded into rock. Characterized by pools and steps. Have winding irregular patterns.

Meandering channel

Stream channel with broadly sinuous banks that curve back and forth in sweeping bends. Deep and smooth.

Knickpoint

A sharp irregularity (such as a waterfall, rapid, or cascade) in a stream-channel profile. Made of resistant rock.

Entrenched meander

Symmetrical forms and evolve where downcutting is fast enough to curtail lateral meander migration, a situation that would arise when a large fall of base level induced a knickpoint to migrate upstream.

Ingrown meander

Asymmetrical forms and result from meanders moving sideways at the same time as they slowly incise owing to regional warping.

Alluvial channel

A stream channel in which the bed and banks are composed largely of unconsolidated sediment (alluvium) that was previously deposited in the valley.

Straight channel

Uncommon, restricted to V-shaped valleys that are themselves straight owing to structural control exerted by faults or joints.

Braided channel

A network of converging and diverging channels that thread among numerous islands or gravel bars. Mainly bed load. Common on ends of glaciers.

Anastomosing channel

Have a set of distributaries that branch and rejoin. Set of interconnected channels separated by bedrock or by stable alluvium.

Anabranching channel

Consist of multiple channels separated by vegetated and semi-permanent alluvial islands or alluvial ridges.

Base level

Lowest elevation to which downcutting by a stream is possible.

True valley

Linear depressions on the land surface that are almost invariably longer than they are wide with floors that slope downwards.

Floodplain

Broad, flat, valley floor covered with alluvium. Carved by a meandering stream.

Erosional floodplain

Forms when a river erodes laterally and creates a floodplain.

Depositional floodplain

Produced by major fluctuations in base level or climate conditions.

Pool

A deep, slow-moving part of a stream, usually wider than elsewhere on the stream.

Riffle

A rocky or shallow part of a stream or river with rough water.

Alluvial fan

Fan-shaped deposits. Accumulate along steep mountain-fronts. Common in arid and humid regions. Fan-shaped due to main flow swinging back and forth between tributaries.

Playa

Flattest and smoothest landform on Earth. They occur in closed basins of continental interiors.

Bolson

The slope and basin area between the crests of two adjacent ridges in a dry region.

Bajada

An apron of sediment along a mountain front created by the coalescence of alluvial fans.

River terrace

A flat, step-like surface standing above the floodplain of a stream and representing an erosional remnant of an older floodplain. Roughly flat area that is limited by sloping surfaces on the upslope and downslope sides.

Structural bench

Resistant beds in horizontally lying strata producing flat areas on valley sides.

Paired river terrace

Form where the vertical downcutting by the river is faster that the lateral migration of the river channel.

Unpaired river terrace

Form where the lateral migration of the river channel is faster than the vertical downcutting.

Bedrock terrace

Strath. Start in valleys where a river cuts down through bedrock to produce a V-shaped valley, the floor of which then widens by lateral erosion.

Alluvial terrace

A level, step-like landform that forms when a stream erodes its bed so that a horizontal surface is raised relative to the channel.

Divide

A ridge that divide each drainage basin. An imaginary line.

Pothole

Holes carved into rock at the base of river with a whirlpool action.

Steps

Exposed bedrock in bedrock channels.

Stream valley

The channel and the surrounding terrain that directs water to the stream.

Valley wall

Sloping walls that rise above the valley floor.

Distributaries

The fan of small streams formed where a river spreads out over its delta.

Back swamp

A poorly drained area on a flood-plain resulting when natural levees are present.

Yazoo tributary

A tributary that flows parallel to the main stream because a natural levee is present.

Outlet

Where streams exit drainage basin. Has lower elevation compared to the rest of the basin.

Trunk stream

Where sediment acquired is transported through the channel along streams.

Effluent stream

Type of stream where flow is maintained during the dry season by groundwater seepage into the channel.

Influent stream

Type of stream that is everywhere above the groundwater table and flows in direct response to precipitation. Water from the channel moves down to the water table, forming a recharge mound. Loses water.

Point bar

A crescent-shaped accumulation of sand and gravel deposited on the inside of a meander.

Cut bank

The steep bank feature that forms on the outside of a river bank due to erosion.

Oxbow lake

A crescent-shaped lake (often temporary) that is formed when a meander of a river is cut off from the main channel.

Bars

Segments of braided channels that are composed of coarse sediments and causes the flow to split.

Graded stream

A stream that has the correct channel characteristics to maintain exactly the velocity required to transport the material supplied to it. Neither erode nor deposit.

U-shaped valleys

Common distinguishing parameter of alluvial channels.

V-shaped valleys

Common distinguishing parameter of bedrock channels.

Incised meander

Meandering channels that flow in steep, narrow, valleys. May initially form in a floodplain then change in base level occurred (base level drop or uplift).

Delta

Sediment-choked stream. Grows outward at entry of lakes, inland sea, or ocean. Triangular in shape. Sediment supply > erosion.

Natural levee

A deposit of sand or mud built by floods up along, and sloping away from, either side of the flood plain of a river or stream. By meandering rivers with broad floodplains