![]() ![]() Les résultats indiquent que cela est dû à une réduction marquée dans l'ampleur et la fréquence des inondations, les taux de sédimentation et la migration des méandres. Au Montana, sur le lit majeur et sur 25 km en aval du Barrage de Fresno, construit en 1939, la densité des liards recrutés depuis 1939 est, de façon significative, moindre que sur les sites du lit majeur en amont, en Alberta. De tels événements d'inondation pendant la période de disséminatin des graines se font en moyenne une fois tous les 5 ans. En Alberta, le recrutement du liard qui amène la survie à long terme sur les barres de la rivière est en corrélation avec les années où les courants maximum quotidiens pendant la période de dissémentation des graines (1 juin – 10 juillet) atteignent un stade égal ou supérieur à l'inondation récurrente de 2 ans, basée sur la série d'inondations annuelles. ![]() occidentalis Rydb.) sur le lit majeur du Milk River, au sud de l'Alberta et au nord du Montana, ont été étudiés en relation avec l'hydrologie fluviale historique et les régimes de sédimentation. L'âge, la distribution et la densité de deux populations du liard des prairies ( Populus deltoides var. Based on this study, the prospects for cottonwood survival on floodplains downriver from dams in this and other prairie river valleys are not encouraging unless management measures are taken to reverse the trend. Results suggest that this is due to a marked reduction in flood magnitude and frequency, rates of sedimentation and meander migration. In Montana, on the floodplain for 25 km downstream of Fresno Dam, built in 1939, the densities of cottonwoods recruited since 1939 are significantly lower than on floodplain sites upstream, in Alberta. Such flood events during the seed dispersal period recur an average of once in 5 years. In Alberta, cottonwood recruitment leading to long-term survival on river meander lobes (point bars) correlates with years when daily maximum flows during the period of seed dispersal (June 1 to July 10) attain a stage equal to or greater than the 2-year return flood, based on the annual flood series. ![]() occidentalis Rydb.) on the floodplain of the Milk River, southern Alberta and northern Montana, were studied in relation to historical river hydrology and sedimentation regimes. Or, you can e-mail photos to us at and we may share them on this page or on social media.Age, distribution, and density of two populations of plains cottonwood ( Populus deltoides var. Please see the USGS social media sharing policy at. If you tag us with you are giving us permission to use your image. ![]() Here at USGS, we study how meanders are formed and can even model them to predict how the river may continue to change in the future, to better understand flooding hazards.Ĭan you find a meander in your area? If you don't see a river, see if you can spot a sidewalk or path that meanders, or watch how a drop of rainwater flows down a slightly sloped surface - does it make a straight or curvy path? Take a photo of a meander and tag us #findafeature or send it to us at be watching Instagram and Twitter for some great #findafeature examples and may share them here with the first name or initials of the contributor, and a general location. Due to erosion on the outside of a bend and deposition on the inside, the shape of a meander changes over time. This is why you often see sand bars and beaches on the inside of the curve. Why is this? Water is pushed to the outside of a bend, and erodes the curve further, while water on the inside is slower and deposits sediment. Once a meander starts, it often becomes more and more exaggerated. As a river makes its way through an area that is relatively flat, it often develops bends as it erodes its way through the path of least resistance. A meander is when water flows in a curvy, bendy path, like a snake. ![]()
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