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Floodmark and Its Areas of Applications
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
Niranjan Bhattacharjee, Ratneswar Barman, Saeid Eslamian
The meandering and reticulated river channels characterized by frequent change have also been responsible both for causing and intensifying floods. Due to the high supply of water at the time of heavy rains, the rivers used to breach their banks and embankments and meet the neighboring streams to follow the reticulated network of streams. Heavy sedimentation along the channel beds has also made the channel shift laterally and make reticulated or anatomizing channels. Hence when flooding occurs along the Nanoi, the waters flow down to the neighboring river Barnoi. The aggravation in the channel network processes also happens due to the rising of river beds. For example, the earthquake of 1950 resulted in raising the river bed of the Brahmaputra by about three meters in some places. River parameters like channel length, width, and gradient, channel meander, along with the level and discharge of water have their integrated effect on the channel morphology and hydrologic flows of water and sediments. All these have been responsible for the occurrences and intensification and varying marks of floods.
Practical issues – roughness, conveyance and afflux
Published in Donald W. Knight, Caroline Hazlewood, Rob Lamb, Paul G. Samuels, Koji Shiono, Practical Channel Hydraulics, 2018
Donald W. Knight, Caroline Hazlewood, Rob Lamb, Paul G. Samuels, Koji Shiono
Channels provide an important habitat for plants, which in turn provide a range of useful functions such as creating sheltered areas with reduced velocities for fauna, altering the temperature, light penetration and oxygen concentration to promote a variety of species and encouraging siltation. These plants are a vital source of shelter and food for fish, invertebrates and some birds. Where water spills overbank, the drying and wetting of the berms promotes vegetation growth of wetland plants. Vegetation also plays an important role in preventing scour and protecting bed and banks through the binding action of the roots. Channel maintenance is, therefore, multifaceted, incorporating a range of requirements such as providing sufficient capacity to convey flood flows; reducing the seasonal cutting requirements (and hence expenses) where possible; utilising the bank and scour protection function of the vegetation and promoting the natural habitat.
Hydraulic Flows: Overview
Published in Marian (Editor-in-Chief) Muste, Dennis A. Lyn, David M. Admiraal, Robert Ettema, Vladimir Nikora, Marcelo H. Garcia, Experimental Hydraulics: Methods, Instrumentation, Data Processing and Management, 2017
Marian (Editor-in-Chief) Muste, Dennis A. Lyn, David M. Admiraal, Robert Ettema, Vladimir Nikora, Marcelo H. Garcia
In addition to the boundary-layer classifications described in section 2.2.1, Volume I, OCFs comprise a wide variety of channel and flow conditions, as this section outlines. Open channels can be either natural channels (e.g., rivers, streams, etc.) or artificial channels (e.g., manmade canals, drainage channels, non-pressurized culverts, laboratory flumes). Open channels are called prismatic channels when their cross-section and bed slope are constant, and non-prismatic channels when their cross section and/or slope change in the main flow direction. From a morphologic point of view, an open channel is rigid (strictly or practically speaking) if erosion or deposition processes do not alter its geometry (cross section, slope, alignment), or deformable if its geometry changes due to erosion or deposition. Most natural channels are non-prismatic, deformable-bed channels, and most prismatic channels, such as irrigations canals, are manmade.
Enhancing flood risk assessment through integration of ensemble learning approaches and physical-based hydrological modeling
Published in Geomatics, Natural Hazards and Risk, 2023
Mohamed Saber, Tayeb Boulmaiz, Mawloud Guermoui, Karim I. Abdrabo, Sameh A. Kantoush, Tetsuya Sumi, Hamouda Boutaghane, Tomoharu Hori, Doan Van Binh, Binh Quang Nguyen, Thao T. P. Bui, Ngoc Duong Vo, Emad Habib, Emad Mabrouk
Identifying flood governing parameters for flooding susceptibility mapping is critical and influences model accuracy (Kia et al. 2012). Runoff in a drainage system is influenced by the watershed features, terrain, catchment area, land use types, and land cover during floods (Hölting and Coldewey 2019). Generally, there are no uniform and standard selection criteria for FSM controlling factors. The selection of flood-controlling parameters depends on various factors such as the area’s location, topography, hydrology, and human activities. Here are some common parameters used for flood control, along with the justification behind their selection (Rahman, Chen, Elbeltagi, et al. 2021; Rahman, Chen, Islam, et al. 2021b): (1) Watershed characteristics: such as its size, shape, and slope, can affect the amount and speed of water runoff, which can, in turn, affect flood risk. (2) River channel characteristics: such as shape, width, depth, and roughness of a river channel can all affect how water flows through it. (3) Topography data: such as elevation maps and terrain models, can help identify areas more prone to flooding. (4) Land use and land cover: Human activities such as urbanization, deforestation, and agriculture can alter the natural landscape and affect flood risk. For example, urbanization can increase the number of impervious surfaces, leading to more runoff and higher flood risk. Land use and land cover analysis can help identify areas where land use changes can be made to reduce flood risk.
2D morphodynamic modelling as a predictive tool for gravel replenishment: the Saint-Sauveur Dam case study
Published in International Journal of River Basin Management, 2022
Guillaume Brousse, Nicolas Claude, Florian Cordier, Rémi Loire, Magali Jodeau
Many gravel-bed rivers are regulated by dams (Grant, 2012; Oud, 2002). It is acknowledged that dams may alter both water and sediment supply, and are considered first-order control factors of channel form (Lane, 1955). Channel response to dam- generated disturbances depends on the regulation of water flow and sediment supply (Brandt, 2000; Petts, 1984). For dammed gravel-bed rivers, a fraction of coarse sediments (gravels and coarser sediments) are trapped in the reservoir (Kondolf, 1997) and only the fine part of the suspended load (sand and finer sediments) can pass through the dam. Depending on dam characteristics and the capacity of the manager to operate flushing, more-or-less coarse sediment can pass through the dam in terms of volume, grain size and frequency (Melun, 2019). In cases where sediment transport is interrupted, the downstream alluvial material gradually disappears, to the benefit of armoured bed or bedrock outcrops. This leads to channel degradation and narrowing, bar fixing and bar vegetalization, as well as a dramatic loss of typical biological habitat (Brenna et al., 2020). Of course, mitigating the downstream environmental consequences of sediment trapping is not the only problem facing dam managers, who must also deal with decreasing storage reservoir capacity and increasing flood risk due to upstream channel aggradation (Sumi, 2006).
Sedimentation and erosion patterns within anabranching channels in a lowland river restoration project
Published in International Journal of River Basin Management, 2022
Ivan D. Medel, Andrew Phillip Stubblefield, Conor Shea
Deposited sediment within the Unit 1 secondary channel experiences the highest proportion of deposited sand (70.6%, Figure 6) within the middle section that coincides with the elevation of mean high tide lines. Low proportions of sand were found to be deposited at the entrance of the unit 2 secondary channel (4.9%, Figure 6) yet increase to 40.0% within the middle section suggesting that sand already present within the reach is being remobilized in addition to sediment coming from main channel. Furthermore, the uniform, high deposition recorded by the longitudinal profiles are composed primarily of silt-sized grains due to the low secondary channel entrance flow velocities (Figure 6). Unit 3 exhibits a strong longitudinal gradient in the proportion of deposited sand grains with 86.3% sand present the entrance declining to 15.3% within the downstream backwater section (Figure 6). Because secondary channel entrances are located 0.6 m to 0.9 m above the primary channel thalweg, the high sand proportions at the entrance provide evidence that main and entrance channel velocities are sufficient to transport sand particles in suspended load. Deposition occurs at the expansion of the secondary channels where flow depths and water velocities decrease in response to increases in channel width.