Bar (river morphology)
Encyclopedia
A bar in a river
is an elevated region of sediment
(such as sand
or gravel
) that has been deposited
by the flow. Types of bars include mid-channel bars (also called braid bar
s, and common in braided river
s), point bar
s (common in meandering rivers
), and mouth bar
s (common in river delta
s). Bars are typically found in the slowest moving, shallowest parts of rivers and streams
, and are often parallel to the shore and occupy the area farthest from the thalweg
.
The locations of bars are determined by the geometry of the river and the flow through it. Point bars form on the inside of meander bends in meandering river because the shallow flow and low shear stresses there reduce the amount of material that can be carried there. The excess material falls out of transport and forms the bar.
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
is an elevated region of sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
(such as sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
or gravel
Gravel
Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...
) that has been deposited
Deposition (geology)
Deposition is the geological process by which material is added to a landform or land mass. Fluids such as wind and water, as well as sediment flowing via gravity, transport previously eroded sediment, which, at the loss of enough kinetic energy in the fluid, is deposited, building up layers of...
by the flow. Types of bars include mid-channel bars (also called braid bar
Braid bar
Braid Bars, or mid-channel bars, are landforms in a river that begin to form when the discharge is low and the river is forced to take the route of less resistance by means of flowing in locations of lowest elevation. Over time, the river begins to erode the outer edges of the bar, causing it to...
s, and common in braided river
Braided river
A braided river is one of a number of channel types and has a channel that consists of a network of small channels separated by small and often temporary islands called braid bars or, in British usage, aits or eyots. Braided streams occur in rivers with high slope and/or large sediment load...
s), point bar
Point bar
A point bar is a depositional feature of streams. Point bars are found in abundance in mature or meandering streams. They are crescent-shaped and located on the inside of a stream bend, being very similar to, though often smaller than towheads, or river islands.Point bars are composed of sediment...
s (common in meandering rivers
Meander
A meander in general is a bend in a sinuous watercourse. A meander is formed when the moving water in a stream erodes the outer banks and widens its valley. A stream of any volume may assume a meandering course, alternately eroding sediments from the outside of a bend and depositing them on the...
), and mouth bar
Mouth bar
A mouth bar is a bar in a river that is typically created in the middle of a channel in a river delta. It is created by a positive feedback between mid-channel deposition and flow divergence. As the flow diverges near the ocean, sediment settles out in the channel and creates an incipient mouth bar...
s (common in river delta
River delta
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...
s). Bars are typically found in the slowest moving, shallowest parts of rivers and streams
STREAMS
In computer networking, STREAMS is the native framework in Unix System V for implementing character devices.STREAMS was designed as a modular architecture for implementing full-duplex I/O between kernel or user space processes and device drivers. Its most frequent uses have been in developing...
, and are often parallel to the shore and occupy the area farthest from the thalweg
Thalweg
Thalweg in geography and fluvial geomorphology signifies the deepest continuous inline within a valley or watercourse system.-Hydrology:In hydrological and fluvial landforms, the thalweg is a line drawn to join the lowest points along the entire length of a stream bed or valley in its downward...
.
The locations of bars are determined by the geometry of the river and the flow through it. Point bars form on the inside of meander bends in meandering river because the shallow flow and low shear stresses there reduce the amount of material that can be carried there. The excess material falls out of transport and forms the bar.