A one-dimensional hydraulic HEC-RAS model was developed to forecast the change in salinity in the tributaries of the Co Chien and Hau Rivers in Tra Vinh province, Vietnam. The boundary data includes river discharge at Can Tho and My Thuan, water levels, and salinity at coastal monitoring stations. Six monitoring stations along the Co Chien River and Hau River were selected to study salinity changes. Four scenarios for the period 2020–2050 were selected, including SLR17, SLR22, SLR26L, and SLR26H, corresponding to sea level rise (17, 22, and 26 cm) and upstream river discharge decrease (in the ranges of 100–128% and 80–117% at Can Tho and My Thuan, respectively) in the dry season based on new climate change scenarios in Vietnam and previous studies. The results highlight that when the average discharge at Can Tho and My Thuan reduces, the salinity increases more significantly than the impact of sea level rise. Salinity at the monitoring stations in Tra Vinh province is projected to increase within the ranges of 4–21% and 3–29% along the Co Chien River and Hau River, respectively. In addition, sea level rise is seen to affect the discharge distribution into the Co Chien River. It suggests an urgent need to raise farmers’ awareness of climate change adaptation, investment in production equipment, and appropriate regulation of riverbed mining and activities upstream in the Mekong River.

This study aimed to evaluate the subsurface drainage of a permeable friction course (PFC) via two-dimensional finite element analysis. To achieve the scope, PFCs with equivalent water flow paths of length values of 10, 15, 20, and 30 m and slope values of 0.5%, 2%, 4%, 6%, and 8% were modelled based on FEniCS and implemented entirely in Python programing language to extract the time for surface ponding according to a range of rainfall intensities. The results show that when the rainfall intensity and the length of equivalent water flow path of the PFC rose, the time for surface ponding decreased. For instance, with a rainfall intensity of 10 mm/h and a slope of 0.5%, when the length of equivalent water flow path increased by 20 m, the time for surface ponding dropped by 21 min. Moreover, when the slope of the equivalent water flow path and the thickness of the PFC increased, the time for surface ponding increased. For instance, with a rainfall intensity of 10 mm/h, and a PFC with an equivalent length of 10 m, when the slope increased by 16 times, the time for surface ponding increased more than two times. The current study highlights that the thickness of the PFC has the most influence on subsurface drainage. The findings of this study indicate that at high rainfall intensities, the subsurface drainage of a PFC is not sensitive to its geometric design. Further experimental investigations are needed to evaluate and validate the subsurface drainage of a PFC considering permeability, rutting, and environmental factors.

Nghiên cứu nguyên nhân sạt lở bờ sông: trường hợp nghiên cứu tỉnh Trà Vinh

Saltwater damage in the Vietnamese Mekong Delta: A case study of agricultural livelihoods in Hung My commune, Tra Vinh province

Bài báo trình bày nghiên cứu xử lý nền đất yếu bằng bấc thấm (PVD) kết hợp hút chân không và gia tải trước tại khu công nghiệp Long Thành, Đồng Nai. Hiệu quả xử lý được đánh giá thông qua số liệu quan trắc hiện trường kết hợp phân tích giải tích và mô phỏng số. Kết quả cho thấy các chỉ tiêu cơ lý của đất được cải thiện rõ rệt sau xử lý. Cụ thể, độ ẩm tự nhiên giảm 25,5% và hệ số rỗng giảm 29,2%, trong khi sức kháng cắt không thoát nước và áp lực tiền cố kết tăng lần lượt 20,1% và 26,0%, cho thấy nền đất trở nên chặt hơn và khả năng chịu tải được nâng cao. Số liệu quan trắc cho thấy nền đạt khoảng 90% độ cố kết sau khoảng 70 ngày khi áp dụng hệ số vượt tải thiết kế khoảng 1,2 lần tải khai thác. Kết quả nghiên cứu cũng cho thấy khi tăng hệ số vượt tải lên khoảng 1,4 lần, thời gian đạt độ cố kết mục tiêu có thể rút ngắn khoảng 15%, trong khi tổng độ lún thay đổi không đáng kể.