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.
30-536: The Alameda Ridge is a large gravel bar located in Portland , Oregon , United States . It forms a ridgeline above much of north and southeast Portland, with views of downtown and west side neighborhoods. Alameda Ridge runs through the Madison South , Roseway , Rose City Park , Beaumont-Wilshire , Alameda , and Sabin neighborhoods. Alameda Ridge was formed between 15,000 and 13,000 years ago at
60-444: A strangler fig around a host tree, with tendrils fusing together to form a mesh, is called anastomosing. In geology , veins of quartz (or other) minerals can display anastomosis. Ductile shear zones frequently show anastomosing geometries of highly- strained rocks around lozenges of less-deformed material. Molten lava flows sometimes flow in anastomosed lava channels or lava tubes . In cave systems, anastomosis
90-437: A connection may be normal (such as the foramen ovale in a fetus' heart ) or abnormal (such as the patent foramen ovale in an adult's heart); it may be acquired (such as an arteriovenous fistula ) or innate (such as the arteriovenous shunt of a metarteriole ); and it may be natural (such as the aforementioned examples) or artificial (such as a surgical anastomosis ). The reestablishment of an anastomosis that had become blocked
120-937: A large blood supply, thus helping regulate systemic blood flow . Surgical anastomosis occurs when segments of intestine , blood vessel, or any other structure are connected together surgically (anastomosed). Examples include arterial anastomosis in bypass surgery , intestinal anastomosis after a piece of intestine has been resected, Roux-en-Y anastomosis and ureteroureterostomy . Surgical anastomosis techniques include linear stapled anastomosis, hand sewn anastomosis, end-to-end anastomosis (EEA). Anastomosis can be performed by hand or with an anastomosis assist device. Studies have been performed comparing various anastomosis approaches taking into account surgical "time and cost, postoperative anastomotic bleeding, leakage, and stricture". Pathological anastomosis results from trauma or disease and may involve veins , arteries , or intestines . These are usually referred to as fistulas . In
150-415: A morphologically similar mycelial wave front that continues to grow and explore. The significant difference is that each septated unit is binucleate, containing two unfused nuclei , i.e. one from each parent that eventually undergoes karyogamy and meiosis to complete the sexual cycle. Also the term "anastomosing" is used for mushroom gills which interlink and separate to form a network. The growth of
180-533: 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
210-399: Is called a reanastomosis. Anastomoses that are abnormal, whether congenital or acquired, are often called fistulas . The term is used in medicine , biology , mycology , geology , and geography . Anastomosis: medical or Modern Latin, from Greek ἀναστόμωσις, anastomosis, "outlet, opening", Greek ana- "up, on, upon", stoma "mouth", "to furnish with a mouth". Thus the -stom- syllable
240-425: Is cognate with that of stoma in botany or stoma in medicine . An anastomosis is the connection of two normally divergent structures. It refers to connections between blood vessels or between other tubular structures such as loops of intestine . In circulatory anastomoses , many arteries naturally anastomose with each other; for example, the inferior epigastric artery and superior epigastric artery , or
270-666: Is the splitting of cave passages that later reconnect. Anastomosing rivers , anastomosing streams consist of multiple channels that divide and reconnect and are separated by semi-permanent banks formed of cohesive material, such that they are unlikely to migrate from one channel position to another. They can be confused with braided rivers based on their planforms alone, but braided rivers are much shallower and more dynamic than anastomosing rivers. Some definitions require that an anastomosing river be made up of interconnected channels that enclose floodbasins, again in contrast with braided rivers. Rivers with anastomosed reaches include
300-420: 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
330-401: The liver in patients with portal hypertension , often resulting in hemorrhoids , esophageal varices , or caput medusae . In evolution , anastomosis is a recombination of evolutionary lineage. Conventional accounts of evolutionary lineage present themselves as the branching out of species into novel forms. Under anastomosis, species might recombine after initial branching out, such as in
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#1732776375815360-404: 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
390-522: The anterior and/or posterior communicating arteries in the Circle of Willis in the brain. The circulatory anastomosis is further divided into arterial and venous anastomosis. Arterial anastomosis includes actual arterial anastomosis (e.g., palmar arch , plantar arch ) and potential arterial anastomosis (e.g. coronary arteries and cortical branch of cerebral arteries ). Anastomoses also form alternative routes around capillary beds in areas that do not need
420-425: 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
450-436: 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
480-442: The bifurcating fungal hyphae can form true reticulating networks. By sharing materials in the form of dissolved ions , hormones , and nucleotides , the fungus maintains bidirectional communication with itself. The fungal network might begin from several origins; several spores (i.e. by means of conidial anastomosis tubes ), several points of penetration, each a spreading circumference of absorption and assimilation. Once encountering
510-415: The case of recent research that shows that ancestral populations along human and chimpanzee lineages may have interbred after an initial branching event. The concept of anastomosis also applies to the theory of symbiogenesis , in which new species emerge from the formation of novel symbiotic relationships. In mycology , anastomosis is the fusion between branches of the same or different hyphae . Hence
540-411: The cases of veins or arteries, traumatic fistulas usually occur between artery and vein. Traumatic intestinal fistulas usually occur between two loops of intestine (entero-enteric fistula) or intestine and skin (enterocutaneous fistula). Portacaval anastomosis , by contrast, is an anastomosis between a vein of the portal circulation and a vein of the systemic circulation , which allows blood to bypass
570-404: 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
600-753: The end of the last ice age when the ice dam containing Glacial Lake Missoula collapsed some 40 times, causing the Missoula Floods , some of the largest floods known on earth. The flood waters spilled across Idaho and eastern Washington , surged down the Columbia River and through the Gorge , flooding the Willamette Valley as far south as Eugene, Oregon . These floods covered the city of Portland, Oregon in approximately 400 feet (120 m) of water, carving out Sullivan's Gulch,
630-639: The large ravine that holds Interstate 84 , and depositing large volumes of unconsolidated silt, sand, gravel, and boulders. As the west-flowing waters rushed around Rocky Butte , a volcanic cinder cone in the Boring Lava Field , sediments were deposited on the west side of the butte forming an approximately 100 to 150-foot (46 m) high bar that became Alameda Ridge. The ridge extends west roughly 6 miles (9.7 km) from Rocky Butte to approximately 15th Avenue and Skidmore Street. Portland residents began building on Alameda Ridge around
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#1732776375815660-462: The mouth of the river, it builds up to eventually create a sand bar that has the potential to extend the entire length of the river mouth and block the flow. Anastomosis An anastomosis ( / ə ˌ n æ s t ə ˈ m oʊ s ɪ s / , pl. : anastomoses ) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels , leaf veins , or streams . Such
690-487: The ocean. River mouth bars stagnate, or cease to prograde when the water depth above the flow is shallow enough to create a pressure on the upstream side of the bar strong enough to force the flow around the deposit rather than over the top of the bar. This divergent channel flow around either side of the sediment deposit continuously transports sediment, which over time is deposited on either side of this original mid channel deposit. As more and more sediment accumulates across
720-416: 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,
750-417: The river widens at the mouth, the flow slows, and sediment settles out and is deposited. After initial formation of a river mouth bar, they have the tendency to prograde . This is caused by the pressure from the flow on the upstream face of the bar. This pressure creates erosion on that face of the bar, allowing the flow to transport this sediment over or around, and re-deposit it farther downstream, closer to
780-521: The southern hillside to allow easier travel between neighborhoods. These stairways are still present today and are maintained by the City of Portland. Alameda Ridge runs through the Madison South , Roseway , Rose City Park , Beaumont-Wilshire , Alameda , and Sabin Neighborhoods, with some of the most expensive homes (some being worth more than one million dollars) located along the upper edge of
810-501: The southern slope in the Rose City Park , Beaumont , Alameda Neighborhoods. A growing concern among locals is the present-day removal or renovation of long-existing structures due to the need to repair them as well as the pressure to conform to more modern styles of living. 45°32′42″N 122°33′58″W / 45.54500°N 122.56611°W / 45.54500; -122.56611 Gravel bar A mid-channel bar,
840-427: The tip of another expanding, exploring self, the tips press against each other in pheromonal recognition or by an unknown recognition system, fusing to form a genetic singular clonal colony that can cover hectares called a genet or just microscopical areas. For fungi, anastomosis is also a component of reproduction. In some fungi, two different haploid mating types – if compatible – merge. Somatically , they form
870-482: The turn of the 20th century, as electric streetcars allowed real estate development to grow away from the city core. The steep hillside on the south side of the ridge provides beautiful views of Northeast Portland and the downtown skyline. This allowed early developers to cater to wealthy individuals. Because the Ridge was developed before cars were the primary mode of transportation, many public stairways were built along
900-461: 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
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