Xâm nhập mặn nước dưới đất trong tầng chứa nước Pleistocen phía nam đồng bằng Sông Hồng, Việt Nam

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Tác giả: Đức Nhận Đặng, Larsen Flemming, Văn Hoan Hoàng, Văn Lâm Nguyễn, Quý Nhân Phạm, Thị Lựu Trần

Ngôn ngữ: vie

Ký hiệu phân loại: 627.5 Reclamation, irrigation, related topics

Thông tin xuất bản: TC Khoa học trái đất và môi trường - ĐH Quốc gia Hà Nội, 2018

Mô tả vật lý: 45618

Bộ sưu tập: Metadata

ID: 492623

Thêm vào giỏ

Fresh groundwater was found in the Pleistocene aquifer in the southern part of the Red River Delta in 70‟s of last century. It is located mainly in the south of Nam Dinh province and small part in southeast of Ninh Binh province. The fresh-saline boundary seems to migrate southward recently and downsize the area of fresh groundwater. It is necessary to find out the mechanisms of salt intrusion into the zone of freshwater in order to mitigate the negative impacts to the quality of water supply. Based on the survey data of groundwater chemistry, transient electromagnetic sounding, borehole logging, drilling, and chemical analysis of pore water squeezed from the low permeable sediment in the study region, it was determined the current spatial distribution of saline water in the Pleistocene aquifer and in marine clay layers. By combining these data with the results from previous studies, this study has determined the mechanisms of the salt intrusion into the freshwater zone. It was found that salinity in the Pleistocene aquifer is generated from two main sources (1) Vertical salt intrusion from the upper marine clay layer which is controlled by the diffusion and density flow and (2) Horizontal saltwater incursion due to the high hydraulic gradient which is controlled by the convection and dispersion which was generated by over groundwater exploitation.Nước dưới đất nhạt đã được tìm thấy ở phía nam của đồng bằng sông Hồng, trong tầng chứa nước Pleistocen vào những năm 70 của thế kỷ trước, chủ yếu nằm ở phía nam của tỉnh Nam Định và một phần nhỏ phía đông nam tỉnh Ninh Bình. Trong những năm gần đây, ranh giới mặn nhạt di chuyển về phía nam và làm giảm diện tích nước phân bố nước nhạt. Việc xác định cơ chế xâm nhập mặn nhằm hạn chế tác động tiêu cực đến chất lượng cung cấp nước cho nhân dân địa phương là hết sức cần thiết và cấp bách. Trên cơ sở số liệu điều tra khảo sát thủy địa hóa, số liệu khảo sát địa vật lý (phương pháp trường chuyển và karota), kết quả phân tích thành phần hóa học nước lỗ rỗng được chiết ép từ lớp trầm tích thấm nước yếu trong vùng nghiên cứu, đã xác định sự phân bố không gian hiện tại của nước mặn trong tầng chứa nước Pleistocene và trong lớp thấm nước yếu nguồn gốc biển. Việc kết hợp những kết quả nghiên cứu trên với các kết quả nghiên cứu trước đây, đã xác định cơ chế xâm nhập mặn nước dưới đất trong tầng chứa nước Pleistocen trong vùng nghiên cứu. Kết quả nghiên cứu cho thấy, nước mặn xâm nhập vào thấu kính nước nhạt trong tầng chứa nước Pleistocen bởi hai nguồn chính: (1) nước mặn xâm nhập từ lớp sét nguồn gốc biển phủ bên trên tầng chứa nước Pleistocen qua quá trình khuếch tán và phân dị trọng lực và (2) nước mặn trong cùng tầng chứa nước Pleistocen do chênh lệch áp lực thủy tĩnh chi phối bởi quá trình đối lưu và phân tán gây ra bởi việc khai thác nước quá mức.

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