page_title: Bar (river morphology)
hierarchical_section_title: Bar (river morphology)
caption_attribution_description: Le cirque de la Madeleine, Gorges de l'ardèche
context_page_description: A bar in a river is an elevated region of sediment that has been deposited by the flow. Types of bars include mid-channel bars, point bars, and mouth bars. The locations of bars are determined by the geometry of the river and the flow through it. Bars reflect sediment supply conditions, and can show where sediment supply rate is greater than the transport capacity.
  A mid-channel bar, is also often referred to as a braid bar because they are often found in braided river channels. Braided river channels are broad and shallow and found in areas where sediment is easily eroded like at a glacial outwash, or at a mountain front with high sediment loads. These types of river systems are associated with high slope, sediment supply, stream power, shear stress, and bed load transport rates. Braided rivers have complex and unpredictable channel patterns, and sediment size tends to vary among streams. It is these features that are responsible for the formations of braid bars. Braided streams are often overfed with massive amounts of sediment which creates multiple stream channels within one dominant pair of flood bank plains. These channels are separated by mid-channel or braid bars.
context_section_description: 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 bars, and common in braided rivers), point bars (common in meandering rivers), and mouth bars (common in river deltas). The locations of bars are determined by the geometry of the river and the flow through it. Bars reflect sediment supply conditions, and can show where sediment supply rate is greater than the transport capacity.
  A mid-channel bar, is also often referred to as a braid bar because they are often found in braided river channels. Braided river channels are broad and shallow and found in areas where sediment is easily eroded like at a glacial outwash, or at a mountain front with high sediment loads. These types of river systems are associated with high slope, sediment supply, stream power, shear stress, and bed load transport rates. Braided rivers have complex and unpredictable channel patterns, and sediment size tends to vary among streams.  It is these features that are responsible for the formations of braid bars. Braided streams are often overfed with massive amounts of sediment which creates multiple stream channels within one dominant pair of flood bank plains. These channels are separated by mid-channel or braid bars. Anastomosing river channels also create mid-channel bars, however they are typically vegetated bars, making them more permanent than the bars found in a braided river channel which have high rates of change because of the large amounts of non-cohesive sediment, lack of vegetation, and high stream powers found in braided river channels.
  Bars can also form mid-channel due to snags or logjams. For example, if a stable log is deposited mid-channel in a stream, this obstructs the flow and creates local flow convergence and divergence. This causes erosion on the upstream side of the obstruction and deposition on the downstream side. The deposition that occurs on the downstream side can create a central bar, and an arcuate bar can be formed as flow diverges upstream of the obstruction. Continuous deposition downstream can build up the central bar to form an island. Eventually the logjam can become partially buried, which protects the island from erosion, allowing for vegetation to begin to grow, and stabilize the area even further. Over time, the bar can eventually attach to one side of the channel bank and merge into the flood plain.
  A point bar is an area of deposition typically found in meandering rivers. Point bars form on the inside of meander bends in meandering rivers. As the flow moves around the inside of the bend in the river, the water slows down because of the shallow flow and low shear stresses there reduce the amount of material that can be carried there. Point bars are usually crescent shaped and located on the inside curve of the river bend. The excess material falls out of transport and, over time, forms a point bar. Point 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, on the outside curve of the river bend in a meandering river. Here, at the deepest and fastest part of the stream is the cut bank, the area of a meandering river channel that continuously undergoes erosion. The faster the water in a river channel, the better it is able to pick up greater amounts of sediment, and larger pieces of sediment, which increases the river's bed load. Over a long enough period of time, the combination of deposition along point bars, and erosion along cut banks can lead to the formation of an oxbow lake.
  A mouth bar is an elevated region of sediment typically found at a river delta which is located at the mouth of a river where the river flows out to the ocean. Sediment is transported by the river and deposited, mid channel, at the mouth of the river. This occurs because, as the river widens at the mouth, the flow slows, and sediment settles out and is deposited. After initial formation of a river mo
caption: Point bar at a river meander: the Cirque de la Madeleine in the Gorges de l'Ardèche, France.
exif: {"Image ImageDescription": "Minolta DSC", "Image Make": "Minolta Co., Ltd.", "Image Model": "DiMAGE 7Hi", "Image Orientation": "Horizontal (normal)", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop 7.0", "Image DateTime": "2003:08:16 16:47:40", "Image YCbCrPositioning": "Centered", "Image PrintIM": "[80, 114, 105, 110, 116, 73, 77, 0, 48, 50, 53, 48, 0, 0, 0, 5, 0, 1, 0, 22, ... ]", "Image ExifOffset": "376", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "954", "Thumbnail JPEGInterchangeFormatLength": "4774", "EXIF ExposureTime": "1/350", "EXIF FNumber": "28/5", "EXIF ExposureProgram": "Program Normal", "EXIF ISOSpeedRatings": "100", "EXIF ExifVersion": "0220", "EXIF DateTimeOriginal": "2003:08:08 12:42:30", "EXIF DateTimeDigitized": "2003:08:08 12:42:30", "EXIF ComponentsConfiguration": "YCbCr", "EXIF BrightnessValue": "83/10", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "3", "EXIF MeteringMode": "Pattern", "EXIF LightSource": "Unknown", "EXIF Flash": "Flash did not fire, compulsory flash mode", "EXIF FocalLength": "1847/256", "EXIF SubjectArea": "[1280, 960, 320, 192]", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "Uncalibrated", "EXIF ExifImageWidth": "2560", "EXIF ExifImageLength": "1920", "EXIF CustomRendered": "Custom", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF DigitalZoomRatio": "0", "EXIF FocalLengthIn35mmFilm": "28", "EXIF SceneCaptureType": "Standard", "EXIF GainControl": "None", "EXIF Contrast": "Normal", "EXIF Saturation": "Normal", "EXIF Sharpness": "Normal", "EXIF SubjectDistanceRange": "3"}