Assessment of Water Quality During 2018-2022 in the Vam Co River Basin, Vietnam

Water pollution in the Vam Co River basin is becoming more complicated due to untreated wastewater being directly discharged into rivers and canals from agricultural, industrial, and domestic activities. To assess the water quality in this area, this study conducted monitoring at ten sampling locations (S1-S10) from 2018 to 2022, calculated the Water Quality Index (WQI) for each parameter, and simulated water quality in 2022 using the 1D- MIKE 11 model developed by DHI with two main modules including HD and AD. The findings showed that most parameters did not surpass the allowable limits per QCVN 08-MT:2015/BTNMT on Vietnam National Technical Regulation on Surface Water Quality. However, organic and microbial pollution led to certain parameters, such as BOD5, COD, and Coliform, exceeding the limits. The lowest water quality was recorded in Long An province, especially at sampling locations S3, S4, and S6, with the average WQI for nine water quality parameters from February to July 2022 being 58.4, 67.8, and 21.1, respectively. Additionally, the simulation outcomes of the MIKE 11 model salinity, BOD5, DO, and NH4 aligned with the real measurements taken. It has been observed that the southern area of the Vam Co River Basin possesses poorer water quality than the northern part, with Long An province located downstream of the Vam Co River basin being the primary source of pollution. The development of this hydraulic model signifies a crucial milestone in comprehending and regulating the effects of pollution in monitoring and managing water management systems, controlling saline intrusion, and ensuring water supply for agricultural production and daily use in the Vam Co River basin

Predicting Future Salinity Variability in the Ca Mau Peninsula due to Climate Change

The Ca Mau Peninsula (CMP) in Vietnam's Lower Mekong Delta faces pressing challenges, including sea-level rise, land subsidence, flooding, and saltwater intrusion. Recent years have witnessed an earlier and more severe dry season, leading to heightened saltwater intrusion. As many CMP provinces rely on the Mekong River for their watersupply, they are highly susceptible to prolonged drought and salinization. This study employs the MIKE 11 hydraulic model to project saltwater intrusion scenarios in the CMP up to 2050, based on Vietnam's 2016 Ministry of Natural Resources and Environment (MONRE) sea-level rise projections, considering water regulation from the Cai Lon-Cai Be sluice system. The model was calibrated and validated successfully, with salinity concentrations also validated at four stations. The projections indicate that saltwater intrusion during the dry season could start 1 to 1.5 months earlier by 2050, with salinity levels exceeding 30g/l in February. This salinity increase reduced upstream river flow, and sea-level rise will impact the region's agriculture and domestic water supply

Holistic coastal protection strategies with nature-based solution for climate change adaptation in deltaic coast

River deltas are the most dynamic landforms on earth and have become more prone to disasters due to climate change and rising sea levels. Sea level rise and other coastal hazards, such as coastal erosion, salinity intrusion, and storm surges, affect delta ecosystems and the livelihoods of people depending on them. Many people live in deltas, with several of them experiencing a growing population, which requires a sustainable and integrated approach to balance various and often competing interests, notably ecosystem conservation, biological and cultural diversity, agricultural productivity and other social and economic benefits to support livelihoods. This study proposed coastal protection strategies for the Mekong delta, including nature-based solutions and permeable breakwaters. Although single coastal protection defences are currently the prevailing practices in the region, their success is limited to slowing down the erosion rate. Due to the complexity of the hydrodynamic and morphological regimes and the characteristic of the mangrove mud coast, one single line of defence is neither sustainable nor successful. Accordingly, this study proposes holistic coastal protection strategies for mangrove muddy coasts under climate change, namely multiple lines of defences incorporating first nature-based solutions and green infrastructure. Second, advanced perforated hollow triangle breakwaters are introduced based on principles of environmental exchange and conservation, such as previously applied to the coastline of Tien Giang province. These breakwaters have shown benefits for wave reduction, as well as for stimulating sedimentation and for restoring mangrove ecosystems. Lastly, holistic coastal protection strategies are proposed for the entire coast of the Mekong delta, with comprehensive coastal protection solutions presented for Ben Tre province

Experimental modeling of bed morphological changes and toe erosion of emerged breakwaters due to wave-structure interactions in a deltaic coast

Large-scale coastal erosion in the Mekong Delta has been dramatically increasing in severity in recent decades. Several effective hard engineering solutions have been implemented in this delta to efficiently prevent coastal erosion and stimulate sedimentation while supporting local ecosystem conservation. These measures include Pile-Rock Breakwaters (PRBW), Hollow Triangle Breakwaters (HTB) and Semicircular Breakwaters (SBW). However, research on sediment transport, morphological changes and toe erosion for these offshore breakwaters is very limited and is currently in the initial stages of understanding the specific conditions of sediment characteristics and foundations. The objective of this study was to reproduce the morphological changes and toe erosion of three breakwaters due to wave-structure interactions. This was investigated using 2D physical models with 3000 irregular waves during 8 experimental hours (equal to 15,000*Tp). To extract the bed morphological changes and toe erosion, specialized laser measurements (SW50M laser ruler) and analysis of high-speed video recording by image digitalization were applied. The experimental results show that the shape and structural design of offshore breakwaters can have a significant influence on the bed morphology on both the seaside and the leeside. We found that generally, the toe of the construction on the seaside was eroded due to the occurrence of reflected waves and that the flow is narrowed while passing through the construction, increasing the flow velocity and causing toe erosion. Additionally, the accretion of sediment at the leeside of the breakwaters was found to be mainly driven by the transport of sediment through the construction. Comparing the breakwater designs, the experimental results showed that the HTB has the maximum and fastest accretion rates behind the breakwater. The SBW has high wave energy dissipation efficiency, although the toe erosion rate is faster than the other classes of breakwaters. The PRBW shows the fastest toe erosion rate in front of the structure and causes accretion at the leeside of the construction but at a lower rate than the HTB. The findings from this study will help practical designers to reinforce the foot of construction when designing breakwaters and inform stability calculations. We recommend applying these three classes of breakwaters, especially the HTB and SBW, for stimulating sedimentation for mangrove restoration in the mud-coast delta