China
Africa
Explore chapters and articles related to this topic
The Geosphere and Geochemistry
Published in Stanley E. Manahan, Environmental Chemistry, 2022
Streams mobilize sedimentary materials through erosion, transport materials along with stream flow, and release them in a solid form during deposition. Deposits of stream-borne sediments are called alluvium. As conditions such as lowered stream velocity begin to favor deposition, larger, more settleable particles are released first. This results in sorting such that particles of a similar size and type tend to occur together in alluvial deposits. Much sediment is deposited in floodplains where streams overflow their banks.
Hydraulics of alluvial channels
Published in Amithirigala Widhanelage Jayawardena, Fluid Mechanics, Hydraulics, Hydrology and Water Resources for Civil Engineers, 2021
Amithirigala Widhanelage Jayawardena
The topics on open channel flows discussed so far assume that the channel geometry is invariant. Such channels are usually artificially made by lining the bed and the banks with non-erodible materials such as concrete and/or masonry. In nature, however, rivers and canals are formed in loose sedimentary material, which allows the shape and the alignment to shift and adjust. The loose sedimentary material is known as alluvium, which consists of gravel, sand, silt and debris. The flow in the channel can erode the bed and banks, and the eroded materials which are usually known as sediments are carried downstream. Some of the sediments carried by the flow get deposited on the bed and banks as the flow energy becomes weaker. The two complementary processes of erosion and deposition take place until sediment equilibrium is attained, or until the sediments are transported to a reservoir or to the sea as in some rivers. Such rivers and channels formed on loose sedimentary material are called alluvial channels. They have the ability to change their geometry and alignment.
The Geosphere and Geochemistry
Published in Stanley Manahan, Environmental Chemistry, 2017
Streams mobilize sedimentary materials through erosion, transport materials along with stream flow, and release them in a solid form during deposition. Deposits of stream-borne sediments are called alluvium. As conditions such as lowered stream velocity begin to favor deposition, larger, more settleable particles are released first. This results in sorting such that particles of a similar size and type tend to occur together in alluvial deposits. Much sediment is deposited in floodplains where streams overflow their banks.
Geomorphic mapping and analysis of neotectonic structures in the piedmont alluvial zone of Haryana state, NW-India: a remote-sensing and GPR based approach
Published in Geomatics, Natural Hazards and Risk, 2023
Harsh Kumar, R. S. Chatterjee, R. C. Patel, Abhishek Rawat, Somalin Nath
The study area is a part of the tectonically formed Himalayan foreland basin. It is bounded by the Ghaggar River in the west and the Yamuna River in the east (Figure 2). It is covered by the recent Quaternary sediments brought down by the rivers from the Himalayan belts and from the peninsular India. The maximum thickness of the Quaternary sediments deposited is about ∼ 4.5 km (Goswami and Deopa 2013). The piedmont plains are composed of coarse textured, poorly sorted sediments brought down by the streams. The alluvial deposits are made up of sand, silt and clay intermixed with calcareous concretions (kankar) and pebbles in varying proportions. The Quaternary alluvium deposits can be divided into two chronostratigraphic units: (i) Older alluvium and (ii) Newer alluvium (Patel and Thakur 2000). The Older alluvium is formed by the depositional processes of the pre-existing palaeo-drainage of Middle to Upper Pleistocene period, comprising admixture of reddish clay, silt, sand with kankar, grey medium to coarse calcareous sand with kankar and sub-rounded to sub-angular unsorted pebble, gravel and cobble beds. The Newer alluvium is formed of present day streams, representing Holocene/Recent period. It is chiefly composed of blue to white-grey micaceous sand with alluvium inter-bands of purple and red clay.
Groundwater suitability zonation with synchronized GIS and MCDM approach for urban and peri-urban phreatic aquifer ensemble of southern India
Published in Urban Water Journal, 2018
The study area is situated on the southern part of the peninsular shield having gently sloping terrain, from the Wayanad plateau to the east to the coastal plain in the west. It constitutes rolling midland and coastal terrain (Geological Survey of India, 2005). The area can be divided into three geological belts viz. a linear NW-SE trending gneissic belt, along with the middle extending from north to south, a Charnockite belt occupying large areas in the south and a narrow coastal belt. Dominant hydrogeology of the area include laterite followed by coastal alluvium, the Weathered, Fissured and Fractured crystalline rocks. The alluvium consists of unconsolidated materials such as sand, silt and clay with a thickness varying between 2 m and 8 m, and the groundwater occurs under phreatic conditions.
Assessing social vulnerability to riverbank erosion across the Vietnamese Mekong Delta
Published in International Journal of River Basin Management, 2023
Van Pham Dang Tri, Phan Ky Trung, Thai Minh Trong, Daniel R. Parsons, Stephen E. Darby
The provinces of An Giang and Dong Thap experienced a wide range of effects as a result of riverbank erosion. Those findings massively aligned with previous study focusing on the physical changes of the river system (Bravard et al., 2013; Darby et al., 2016) as well as the fluctuation of water flows and sedimentation seasonally and temporally(Darby et al., 2016; Hackney et al., 2020). The VMD was formed by the alluvial deposition, thus the sediment from the Mekong River played the survival role for the delta's living ecosystems. The degradation of sediment, especially the alluvium, has resulted in a great deal of negative impacts, which riverbank erosion is notably highlighted (Anthony et al., 2015; Jordan et al., 2020). The surveyed communities were characterized by low-income, a high elderly population, low-educated, and ‘highly economic dependent’ households with family members under 15 or over 65 years old without sufficient qualifications to contribute to household income. These groups are commonly recognized as marginal groups by previous studies of Mavhura et al. (2017); Mustafa et al. (2011); Pham et al. (2018); and Tran et al. (2018). This study discovered a strong link between marginal groups and vulnerability, with the majority of them falling into the highly vulnerable (5th) and relatively vulnerable (4th) categories. This implies that these groups are already facing already complex vulnerability relevant challenges for survival. Additionally, regarding the reliability of the data obtained from the elderly and low-educated, the research considered this aspect right at the beginning of developing the study's structure, the questionnaire, the progress of household survey and data analysis. Specifically, at the survey phase, questions were asked based on the ‘normal conversation’ approach by interviewers, which allowed respondents to understand all questions without academic or professional knowledge prerequisites. A wide range of qualifications of interviewees was taken into account, from their capacity of communication, their Vietnamese understanding (as it might be difficult for the ethnic minority, then the local language translator needed). Furthermore, the study tested all obtained data to investigate whether there were any confounding values and variables. These steps were taken to assure that the obtained data were reliable and suitable for analysis.