An Improved Groundwater Model Framework for Aquifer Structures of the Quaternary-Formed Sediment Body in the Southernmost Parts of the Mekong Delta, Vietnam

Abstract

The Ca Mau peninsula (CMP) is a key economic region in southern Vietnam. In recent decades, the high demand for water has increased the exploitation of groundwater, thus lowering the groundwater level and leading to risks of degradation, depletion, and land subsidence, as well as salinity intrusion in the groundwater of the whole Mekong Delta region. By using a finite element groundwater model with boundary expansion to the sea, we updated the latest data on hydrogeological profiles, groundwater levels, and exploitation. The basic model setup covers seven aquifers and seven aquitards. It is determined that the inflow along the coastline to the mainland is 39% of the total inflow. The exploitation of the study area in 2019 was 567,364 m3/day. The most exploited aquifers are the upper-middle Pleistocene (qp2–3) and the middle Pliocene (n22), accounting for 63.7% and 24.6%, respectively; the least exploited aquifers are the upper Pleistocene and the upper Miocene, accounting for 0.35% and 0.02%, respectively. In the deeper aquifers, qp2–3 and n22, the change in storage is negative due to the high exploitation rate, leading to a decline in the reserves of these aquifers. These groundwater model results are the calculations of groundwater reserves from the coast to the mainland in the entire system of aquifers in the CMP. This makes groundwater decision managers, stakeholders, and others more efficient in sustainable water resources planning in the CMP and Mekong Delta (MKD).

Applying an Analytic Hierarchy Process and a Geographic Information System for Assessment of Land Subsidence Risk Due to Drought: A Case Study in Ca Mau Peninsula, Vietnam

“…Previous studies have often focused on a single city or a relatively small part of a delta and selected some factors such as groundwater depletion, the slow consolidation of weak water-saturated soil layers, saltwater intrusion, geological tectonics, relative sea level rise, etc. [57][58][59][60][61]. This research applied the AHP method and GIS technology to determine the weights of factors affecting drought and the subsidence risk zones in the Ca Mau Peninsula area.…”

The Process of Groundwater Salinization on the Ca Mau Peninsula (Mekong Delta, Vietnam): Evaluation of Saltwater Intrusion Pathways via Scenario Calculations Applying a 3D Groundwater Model

“…The study area aligns with the study area employed in our previous study (Hoan et al, 2022). It is located in the southernmost region of the MKD, Vietnam, covering the provinces of Ca Mau, Bac Lieu, and the lower part of Kien Giang (see Figure 2).…”

“…No private household wells are included in the model, since household wells operate with very small flows. Instead, for the model the water consumption for each commune is derived based on the population and an average rural water demand of 34 L/person/ day (Hoan et al, 2022). This water consumption for each commune is implemented in the model by several wells with a total flow rate equivalent to the derived water demand.…”

“…Modeling approaches have primarily employed the MODFLOW software package and have mostly covered large areas. A local high-resolution groundwater model for the CMP was developed by Hoan et al (2022). The National Center for Water Resources Planning and Investigation (NAWAPI) also developed a model of saline groundwater intrusion in the Mekong Delta using the Groundwater Modeling System (GMS) based on a simplified two-zone evaluation: water resources with a salinity below 1.5 g/L were defined as freshwater, while water bodies with higher salinities were defined as brackish and saline waters (MONRE, 2015).…”

“…In this study, we evaluate this hypothesis by scenario calculations and sensitivity analysis using a density respecting saline groundwater transport model, which is based on the groundwater flow model presented in Hoan et al (2022).…”