Water Resources Planning Institute,
Water Resources Agency, Ministry of Economic Affairs
The main purpose of the riverbed material investigation is to obtain the grain size distribution of the armor layer and floodplain material in the riverbed. The results of the investigation can be used to judge and analyze river scouring and silting conditions, the roughness setting of the river channel, for hydraulic and sediment model simulation and used as a reference for river channel maintenance mainagement.
The methods of riverbed material investigation are generally divided into surface sampling and volumetric sampling. The surface sampling is to acquire the information on the pebbles on the surface layer which is more suitable for floodplain and near shallow water areas. The volumetric sampling is to acquire the vertical distribution of the materials in surface layer and armor layer below, which is usually opted in practice, as it is more objective and easier. The flow chart of riverbed material investigation is shown in Figure 1, and in-situ test is shown in Figure 2 and 3.
Figure.1 Flow chart of riverbed material investigation
Figure.2 In-situ volumetric sampling (excavation of test pit)
Figure.3 In-situ volumetric sampling (sieve analysis)
Riverbed materials change are sensitive to topography, geology or river development; different sites need different consideration requirements, it is necessary to gather and realise existed information (e.g., historical data of cross-section and riverbed material, geological features and orthophoto) to effectively choosethe best investigation methods.
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