![]() No general theory of meanders is as yet satisfactory, however in fact, present evidence suggests that no single theory will explain the formation and characteristics of all meanders and that few of the physical principles involved have yet been clearly identified. Evidence on flow resistance in curved channels suggests that a basic aspect of meander mechanics may be related to the distribution of energy loss provided by a particular configuration or curvature. Velocity distributions along river curves provide a generalized picture of flow characteristics. Because such meanders carry no sediment, the shapes of curves in rivers are evidently determined primarily by the dynamics of flow rather than by relation to debris load. Meanders formed by meltwater on the surface of glaciers, and by the main current of the Gulf Stream, have a relation of meander length to channel width similar to rivers. ![]() 3 The entrances to the abandoned meander eventually silt up. The river then follows a shorter course that bypasses the meander. This takes place because meanders tend to grow and become more curved over time. i The device comes in a variety of forms. An oxbow lake forms when a meandering river erodes through the neck of one of its meanders. The terms Greek key, fret, and meander are all names for a decorative device employed on buildings and objects beginning in ancient Greece and continuing to modern times. When coupled with stormwater wetlands or basins, oxbows can lead to significant reductions in flooding.Most river curves have nearly the same value of the ratio of curvature radius to channel width, in the range of 2 to 3. Figure 1: The Complex Greek Meander: Abraham Swan, The British Architect, (1758), Plate LV (detail). As precipitation events become more extreme due to climate change, this role for oxbow wetlands will become more important. ![]() When stream flows increase during and after precipitation events, oxbows can intercept some of the flood water and slowly release it back into the stream, helping to reduce the peak flows. Oxbows store up to one million gallons of water per acre of oxbow and can slow stormwater before it enters rivers and streams. Urban oxbows also capture and treat a variety of urban contaminants when linked to stormwater discharge. In many Iowa streams, a significant percentage of water flow is from tile drainage. Under international law, a thalweg is taken to be the middle of the primary navigable channel of a waterway that defines the boundary line between entities such as states. I If a river, stream, or road meanders, it follows a route that is not straight or direct. the location of the river channel at some point in the future, is. Meander migration consists of bank erosion on the outside bank of curved channels and point bar and floodplain building on the inside bank. We know from the relationships between Reynolds number and bed shear stress that higher flow. In geography and fluvial geomorphology, a thalweg or talweg (/ t l v /) is the line of lowest elevation within a valley or watercourse. us / miæn.d / uk / miæn.d r/ meander verb (RIVER/ROAD) Add to word list. The MeanderJP model is a meander migration model for predicting large-scale channel migration patterns. ![]() Water has to travel faster on the outside of bends than on the insides of bends. Meander Belt Width (Bw) defined by the lateral extent of meanders when the channel slope is in equilibrium with the sediment transport requirements of the river. The flow speed in the channel varies with the geometry of the meanders. Tile drainage is a type of drainage system that removes excess water in soil from below its surface. A meandering river channel has curves that meander back and forth on a gently sloping floodplain. Oxbows that intercept agricultural tile drainage can filter nearly 100 percent of nitrates from the water, if given enough time. Studies have shown that, on average, oxbows filter 42 percent of excess nutrients from water that flows into them. Restored oxbows remove nitrate from flood waters. As the river gains more velocity, the water is pushed to the outside of the river causing more erosion. Nitrates are a common nutrient necessary for agricultural production but are detrimental to water quality when introduced at high levels. Meanders are formed in the middle course of a river. The ability of an oxbow wetland to process and filter out excess nutrients depends on how long the oxbow can store water before it flows into the nearby stream.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |