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Geomorphology and Flooding
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
Giovanni Barrocu, Saeid Eslamian
Among various factors involved, there is the downslope gravity component tangent to the riverbed, the attrition due to the roughness of the bed, and the water turbulence caused by the irregular paths of the load elements of a different type, so that flow lines continuously deviate from one side of the channel to the other. In the flood plain, the bends, rapidly modified in any direction, tend to assume the shape of loops similar to the capital Ω, typical of the classic river Meander, the present-day Menderes in southwestern Turkey, characterized by a very convoluted and winding path along the lower reach, for which reason they are named meanders. The lateral flood erosion of two opposite banks may eventually cut off the narrow neck of a meander, which so becomes a crescent-shaped lake, named oxbow lake, separated from the river (Figure 2.12B). The stream short-circuits its course with increased momentum so that the flood enhances its erosion power.
Soils, rocks, and groundwater
Published in Rodrigo Salgado, The Engineering of Foundations, Slopes and Retaining Structures, 2022
Alluvial soils are deposits of interlayered gravel, sand, silt, and clay. They form as rivers carry and deposit particles of varying sizes, depending on the water velocity, which changes across time and space. Locally, at a river cross section, water velocity drops with distance from the center of the river. It also varies seasonally, as the river expands laterally to occupy its flood plain during rainy seasons and shrinks during drier periods (Figure 3.8). As a result, the river tends to deposit soils on the inside of a bend and to remove soil from the outside. This, over time, increases the sharpness of the bend (Figure 3.9b); this process may go so far that eventually it becomes easier for the river to cut across the soil, leaving the bend behind as an abandoned oxbow lake (Figure 3.9c). The water velocity also varies along the axis of the river. Closer to its source, it tends to be steeper, and water velocities, higher. As the river approaches its delta, velocities drop substantially, and the river deposits larger volumes of soil (which tends to be made up of finer particles).
Geologic Principles
Published in Stephen M. Testa, Geological Aspects of Hazardous Waste Management, 2020
Meandering streams can also be subdivided into three subenvironments: floodplain subfacies, channel subfacies, and abandoned channel subfacies. Floodplain subfacies is comprised of very fine sand, silt, and clay deposited on the overbank portion of the floodplain, out of suspension during flooding events. Usually laminated, these deposits are characterized by sand-filled shrinkage cracks (subaerial exposure), carbonate caliches, laterites, and root holes. The channel subfacies is formed as a result of the lateral migration of the meandering channel which erodes the outer concave bank, scours the riverbed, and deposits sediment on the inner bank referred to as the point bar. Very characteristic sequences of grain size and sedimentary structures are developed. The basal portion of this subfacies is lithologically characterized by an erosional surface overlain by extraformation pebbles and intraformational mud pellets. Sand sequences with upward fining and massive, horizontally stratified and trough cross-bedded sands overlie these basal deposits. Overlying the sand sequences are tabular, planar, cross-bedded sands which grade into microcross-laminated and flat-bedded fine sands, grading into silts of the floodplain subfacies. The abandoned channel subfacies are curved finegrained deposits of infilled abandoned channels referred to as oxbow lakes. Oxbow lakes form when the river meanders back, short-circuiting the flow. Although lithologically similar to floodplain deposits, geometry and absence of intervening point-bar sequences distinguishes it from the abandoned channel subfacies.
Nitrate pollution and expansion of free-floating plants in 3 lower Wisconsin River oxbow lakes
Published in Lake and Reservoir Management, 2023
David W. Marshall, Kenneth Wade, Jean L. Unmuth
Prior to the implementation of the federal Clean Water Act, from about the mid 20th century to the late 1970s, the Wisconsin River was severely polluted from the pulp and papermill industry (Ball and Marshall 1978). The LWSR oxbows were likely refugia during worst periods of industrial water pollution. Oxbow lake ecological services include habitat for lateral fish migrations, fish reproduction, and refugia from riverine environmental stressors (Bayley 1995, Killgore and Baker 1996, Amoros 2001, Slipke et al. 2005, Roach et al. 2009). Oxbow lakes near the Pleistocene sand terrace are greatly influenced by upland aquifer discharges (Pfeiffer et al. 2006). Some of the oxbows are spring lakes by definition since their water budgets are strongly influenced by groundwater discharges, with perennial outlets to the river but no inlets.