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Reservoir is an efficient way for flood control and improving all sectors related to water resources in the integrated water resources management. Moreover, multiobjective reservoir plays a significant role in the development of a country's economy especially in developing countries. All multi-objective reservoirs have conflicts and disputes in flood control and water use, which makes the operator a great challenge in the decision of reservoir operation. For improved multi-objective reservoir operation, an integrated modeling system has been developed by incorporating a global optimization system (SCE-UA) into a distributed biosphere hydrological model (WEB-DHM) coupled with the reservoir routing module. The new integrated modeling system has been tested in the Da River subbasin of the Red River and showed the capability of reproducing observed reservoir inflows and optimizing the multi-objective reservoir operation. First, the WEB-DHM was calibrated for the inflows to the Hoa Binh Reservoir in the Da River. Second, the WEB-DHM coupled with the reservoir routing module was tested by simulating the reservoir water level, when using the observed dam outflows as the reservoir release. Third, the new integrated modeling system was evaluated by optimizing the operation rule of the Hoa Binh Reservoir from 1 June to 28 July 2006, which covered the annual largest flood peak. By using the optimal rule for the reservoir operation, the annual largest flood peak at downstream control point (Ben Ngoc station) was successfully reduced (by about 2.4 m for water level and 2500 m 3 $s -1 for discharge); while after the simulation periods, the reservoir water level was increased by about 20 m that could supply future water use.

Landslides govern the evolution of landforms and pose a serious threat across the globe, especially in mountainous areas. In the northwestern area of Vietnam, a deep-seated landslide occurred near the new Mong Sen bridge in Trung Chai commune, Sapa town, Laocai province. In October 2020, some serious cracks were observed above a natural slope near a road, which was under construction to connect the Noi Bai-Laocai highway to Sapa town. The crack area was divided into two zones. Since this phenomenon could not only cause loss of life but also damage to the properties located downhill, the construction was stopped until the slope was rehabilitated. In this study, geological investigations, laboratory tests, and stability analysis were conducted to understand the failure mechanism. The analysis results showed that cutting activities during the construction of the road contributed to the sliding of the sloping soil mass. The following rehabilitation works at the failed area were conducted: (1) removing the soil above the natural slope; and (2) constructing the retaining system, including ground anchors and soil nails to retain the remaining slope. Results of stability analysis demonstrated that the retained slope would be stable after treatment.

No abstract

Currently, a mixture of bentonite and soil is widely used for the bottom liner of landfill; however, the landfill using this mixture for the liner in Vietnam is limited. Therefore, this paper focuses mainly on investigating the physical and mechanical properties of soil samples from Hanoi, Vietnam; then compared their hydraulic conductivity before and after mixing with bentonite and fly ash in order to assess the efficiency of these mixtures for the landfill in Vietnam. From the hydraulic conductivity results, it was found that a mixture that has 15% or greater than15% of soil replaced by fly ash combined with bentonite (with the ratio between fly ash and bentonite is 4:1) can have the value of hydraulic conductivity (less than 1x10 -9 m/s) satisfies Vietnamese standard for bottom liner. Thus, this mixture can be used for landfill in Vietnam. In addition, several X-ray diffraction (XRD) tests along with Energy Dispersive X-ray Spectroscopy (EDX) on Scanning Electronic Microscopy (SEM) were also conducted for better understanding mechanism of reduction in hydraulic conductivity of mixed samples when bentonite combined fly ash added.