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The Upper Cau river basin that plays an important role in socioeconomic developments the North of Vietnam is sensitive to changes of climate influencing flows, erosion, and water resources. The main objective of this study is to assess and simulate impacts of climate change on erosion and water flow in the basin. Using a GIS database, and Soil, and Water Assessment Tool (SWAT) model, the water flow, and soil loss assessed with data in period 1980-1999 called the base period, then simulated until 2100 considering the medium emission scenario (B2). The simulation results showed that the total annual runoff and soil loss tends to increase compared to the base period. For flow, the change rate of the simulation period is higher than the base period; the water flow rate will increase by 0.22% (2020-2039) and up to 1.37% (2080-2100). The total annual soil loss of the simulation period at Gia Bay station tends to increase steadily compared to the baseline, namely by 6.2% (2020-2039) and 25.5% (2080-2100). Overall, the result in this study shows that effects of climate changes on the basin are severe enough under the scenario B2 that is useful for authorities for basin management.

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Flooding caused by historically high flows, especially in Tra Khuc-Ve River basin in the Mid-Central region in Vietnam in November 2013, which caused widespread damage. The purpose of this paper was to establish the inundation maps in the downstream part of Tra Khuc-Ve rivers by using the coupling of the hydrological and hydraulic models (MIKE SHE/MIKE 11 and MIKE 11 GIS). Calibration and validation of the hydrological model were in good agreement in terms of the vibration amplitude, absolute value, and phases. The hydraulic model results showed good agreement between observed and simulated flood events in 2012 and 2013 after calibration and validation. The rainfall forecasting from the IFS model was also used to establish six flood warning scenarios based on the alarm level III (6.5 m) and the historical level (8.76 m). The inundation maps showed the extent of flooding and the water depth in the downstream part of the study area. The simulation results of historical data showed that Tu Nghia and Son Tinh Districts were the most affected areas by inundation with over 11% affected area while Quang Ngai Town inundated 8.1%. The study results will support decision makers in planning to reduce the impacts of natural disasters in Tra Khuc-Ve River basin in the future.

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Nghiên cứu đã ứng dụng được sản phẩm mưa dự báo IFS làm đầu vào cho mô hình MIKE SHE phục vụ tính toán và dự báo lưu lượng nước đến cho hai hồ chứa trên lưu vực sông Trà Khúc-Sông Vệ. Quá trình hiệu chỉnh và kiểm định mô hình thủy văn sử dụng số liệu của các trận lũ điển hình trên lưu vực từ năm 2013-2016. Kết quả hiệu chỉnh và kiểm định mô hình chỉ ra sự tương đồng về pha và biên độ dao động giữa lưu lượng tính toán và thực đo tại hai trạm Sơn Giang và An Chỉ. Kết quả đánh giá kiểm định và dự báo lưu lượng nước đến hai hồ ĐăkĐrinh và hồ Nước Trong cho kết quả rất tốt theo các chỉ tiêu đánh giá r, R 2 , NSE, RMSE, MAE, PBIAS. Kết quả dự báo thử nghiệm cho hai trận lũ điển hình năm 2017 cho thấy chất lượng dự báo lưu lượng đến hai hồ đã tăng lên đáng kể. Đây sẽ là một công cụ hiệu quả phục vụ tốt cho công tác dự báo nghiệp vụ trong tương lai.

Abstract:The origin and quality of groundwater in the Southeastern region (belongs to Southern Plain) were identified by using isotopic techniques and geochemical analysis. Groundwater samples were collected from 7 aquifers: the Holocene, upper Pleistocene, middle Pleistocene, lower Pleistocene, upper Pliocene, middle Pliocene and Miocene aquifers. The water isotopic compositions ( 2 H and  18 O) were determined to elucidate the origin and the interaction between surface water and groundwater studies. Transit time (age) of the groundwater samples was determined to explain the direction of groundwater flow. The dating techniques included 3 H and 14 C isotopes measurement, followed by a correction for the initial 14 C-activity by the 13 C-composition ( 13 C) in TDIC (Total Dissolved Inorganic Carbon). Geochemical parameters of the groundwater samples were measured either directly in the field or in the laboratory. The results showed that the groundwater from the Holocene and upper Pleistocene aquifers was most recharged from the local meteorological and hydrological systems, including local precipitation, river and reservoirs. Thus, it has short transit time and its stable isotopic composition is spread around the local meteoric waterline and lines for rivers or reservoirs water. The groundwater in the deeper aquifers: middle and lower Pleistocene, and Neogene aquifers has old age up to 22.5 ka BP. Its water seems to be recharged from the areas with an altitude from 600 to 700 m higher to the Neogene deposit layer altitude. The groundwater in the SE SP (South-Eastern Southern Plain) region has a high quality. The water type is Na-Ca-Mg-HCO 3 with low content of chloride and TDS (Total Dissolved Solids). Calcite/dolomite and gypsum dissolution, organic matter decomposition and sequence of red-ox reactions proceeding through different electron acceptors sediment were controlled the chemistry of the groundwater in the study region.