Author(s): S. H. Truong; K. L. Phan; M. J. F. Stive

Linked Author(s): S.H Truong

Keywords: Sand mining; Compound channel; Vegetation; Numerical model; Mixing layer

Abstract: Sediment entrainment, transport, and deposition induced by the motion of water govern the river morphology. However, due to human interventions, such as land use changes, i. e., the construction of aquacultures, urbanization, channelization, the construction of dams, and river barriers, as well as the over-extraction of water or sand and river from the system, river systems have experienced considerable channel adjustment. In the Mekong Delta, the extraction of instream sand often surpasses natural replenishment rates (about 80 to 200 million tons per year), leading to significant interest in studying the effects of sand mining on river hydro-morphodynamics. Despite extensive research, the impact of sand mining on the lateral momentum exchange in the mixing layer of vegetated and non-vegetated compound channels is poorly understood. To obtain more insight, a schematized model covering the 2000 m river length and 1100 m width of the estuary (half of the estuarine width) of the Ham Luong Estuary was constructed in Delft3D. The impacts of sand mining were studied by reducing the bed elevation. Two different bottom elevations associated with no sand mining and with sand mining were considered. Furthermore, two scenarios of vegetation density, representing estuarine mangroves (no vegetation and sparse density), were imposed for each case. The effects of sand mining on the shear layer dynamics at the floodplain edge were evaluated by analysing the mean velocity profiles in different vegetation densities and bed elevation scenarios. The results show that sand mining does not seem to affect the inner layer, as the penetration of the mixing layer into the floodplain remains unchanged but significantly modifies the shear layer's outer layer by decreasing the velocity difference. This alteration is believed to be detrimental to the conditions needed for nutrient or sediment deposition within forested areas.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P1834-cd

Year: 2025