Water Hyacinth Geotextiles as a Nature-Based Solution for Riverbank Protection in the Vietnamese Mekong Delta

Deltas are among the most productive and diverse global ecosystems. However, these regions are highly vulnerable to natural disasters and climate change. Nature-based solutions (Nbs) have been increasingly adopted in many deltas to improve their resilience. Among decision support tools, assessment of ecosystem services (ES) through spatially explicit modelling plays an important role in advocating for Nbs. This study explores the use of the Land Utilisation and Capability Indicator (LUCI) model, a high-resolution model originally developed in temperate hill country regions, to map changes in multiple ecosystem services (ES), along with their synergies and trade-offs, between 2010 and 2018 in the Vietnamese Mekong Delta (VMD). In so doing, this study contributes to the current knowledge in at least two aspects: high-resolution ES modelling in the VMD, and the combination of ES biophysical and economic values within the VMD to support Nbs implementation. To date, this is the highest resolution (5 by 5 m) ES modelling study ever conducted in the VMD, with ~1500 million elements generated per ES. In the process of trialling implementations of LUCI within the VMD’s unique environmental conditions and data contexts, we identify and suggest potential model enhancements to make the LUCI model more applicable to the VMD as well as other tropical deltaic regions. LUCI generated informative results in much of the VMD for the selected ES (flood mitigation, agriculture/aquaculture productivity, and climate regulation), but challenges arose around its application to a new agro-hydrological regime. To address these challenges, parameterising LUCI and reconceptualising some of the model’s mechanisms to specifically account for the productivity and flood mitigation capability of water-tolerant crops as well as flooding processes of deltaic regions will improve future ES modelling in tropical deltaic areas. The ES maps showed the spatial heterogeneity of ES across the VMD. Next, to at least somewhat account for the economic drivers which need to be considered alongside biophysical valuations for practical implementations of ES maps for nature-based solutions (Nbs) in the upstream VMD, economic values were assigned to different parcels using a benefit transfer approach. The spatially explicit ES economic value maps can inform the design of financing incentives for Nbs. The results and related work can be used to support the establishment of Nbs that ultimately contribute to the security of local farmers’ livelihoods and the sustainability of the VMD.

River bank (RB) erosion is a global issue affecting livelihoods and properties of millions of people. However, it has not received enough attention in the Vietnamese Mekong Delta (VMD), i.e., the world’s third largest delta, compared to salinity intrusion and flooding. There have been several studies examining RB and coastal erosion in the VMD using remotely sensed satellite data, but the applied methodology was not adequately validated. Therefore, we developed a novel SRBED (Spectral RB Erosion Detection) method, in which the M-AMERL (Modified Automated Method for Extracting Rivers and Lakes) is proposed, and a new RB change detection algorithm using Landsat data. The results show that NDWI (Normalized Difference Water Index) and MNDWI (Modified Normalized Difference Water Index) using the M-AMERL algorithm (i.e., NDWIM-AMERL, MNDWIM-AMERL) perform better than other indices. Furthermore, the NDWIM-AMERL; SMA (i.e., NDWIM-AMERL using the SMA (Spectral Mixture Analysis) algorithm) is the best RB extraction method in the VMD. The NDWIM-AMERL; SMA performs better than the MNDWI, NDVI (Normalized Difference Vegetation Index), and WNDWI (Weighted Normalized Difference Water Index) indices by 35–41%, 70% and 30%, respectively. Moreover, the NDVI index is not recommended for assessing RB changes in the delta. Applying the developed SRBED method and RB change detection algorithm, we estimated a net erosion area of the RB of –1.5 km2 from 2008 to 2014 in the Tien River from Tan Chau to My Thuan, with a mean erosion width of –2.64 m and maximum erosion widths exceeding 60 m in places. Our advanced method can be applied in other river deltas having similar characteristics, and the results from our study are helpful in future studies in the VMD.

Environmental pressures on livelihood transformation in the Vietnamese Mekong Delta: Implications and adaptive pathways.

The evolution of delta and riverbank erosion within the river basin can significantly impact the environment, ecosystems, and lives of those residing along rivers. The Vietnamese Mekong Delta (VMD), counted among the world’s largest deltas, has undergone significant morphological alterations via natural processes and human activities. This research aims to examine these morphological alterations and their impacts on local economic and social conditions in the VMD. This study utilized satellite data from 1988 to 2020, coupled with population density and land use/land cover (LULC) maps from 2002, 2008, and 2015. The findings reveal that the VMD experienced widespread erosion over the past three decades, covering an area of 66.8 km2 and affecting 48% of the riverbank length (682 km). In contrast to riverbanks, islets showed an accretion trend with an additional area of 13.3 km2, resulting in a decrease in river width over the years. Riverbank and islet erosion has had a profound impact on the LULC, population, and economy of the provinces along the VMD. From 2002 to 2020, eight different land use types were affected, with agricultural land being the most severely eroded, constituting over 86% of the total lost land area (3235.47 ha). The consequences of land loss due to erosion affected 31,273 people and resulted in substantial economic damages estimated at VND 19,409.90 billion (USD 799.50 million) across nine provinces along the VMD. Notably, even though built-up land represented a relatively small portion of the affected area (6.58%), it accounted for the majority of the economic damage at 70.6% (USD 564.45 million). This study underscores the crucial role of satellite imagery and GIS in monitoring long-term morphological changes and assessing their primary impacts. Such analysis is essential for formulating effective plans and strategies for the sustainable management of river environments.

Abstract. Regarding to the important environmental issues, eco-balance and eco-system should be discussed using long period data analysing and visible result of study. These visible results will be materials for construction of geo-design of the river basin. Both hydrological changes and surface changes of the Mekong delta was analysed with new data using hydrologic model with visible mapping in this study. The Mekong River delta, the third largest delta in the world, is presently shifting from growing to shrinking with its ecosystem and environment seriously degraded. These environmental changes are due to several factors such as 1)ill-planned water management schemes including hydropower dams in the river basin, 2) sediment starvation, 3) increased nutrient inflows, in combination with other human activities including infrastructural extension, riverbed mining, delta subsidence, degradation of coastal mangrove belt, and gaps in governance in the whole Mekong basin under the climate change and sea level rise. Both scientific and management communities have suggested that the rate of Mekong delta shrinking will increase markedly this century. The paper compiled new data and mapping together with recent key studies implying that much of the degradation in the Vietnamese Mekong delta is due to recent human activities, particularly hydropower dams in the entire Mekong river basin.By comparison with period before 1990s when there were no large dams, the natural regime here has changed with the annual sediment load to the delta having decreased by 50–60%, the flood discharges have also decreased, the hydrological seasonal regime has shifted as most of the Mekong River water is now trapped in these large dams, and the salinity intrusion into the delta now occurs earlier by 20–30 days. Further, the river bed is on the average deeper by 0.14 m, to which riverbed mining also contributes. There has been a recent increase of erosion of river banks at 400 locations and coasts. The 66% of all of foreshore is now eroding, and the rate of these events is accelerating with time. If all the proposed mainstream hydropower dams in the Lower Mekong Basin have been built, then the Vietnamese Mekong delta with its ecosystems and about 18 million people face critical issues of sustainability. This presentation also focused on some remedial conceptual solutions that may decrease, but not eliminate, the negative impacts of these dams for the Vietnamese Mekong delta. Non-engineering solutions have the highest propriety, but engineering solutions are needed for protecting eroded coastal foreshore, river bank erosion and the fragile mangrove belt. Toward to realization of SDG’s in this study region, the integrated management system of the river basin would be desired.

Deltas are often densely populated and support much of the world’s fishes, forest products and agriculture. Protecting livelihoods and ecosystem services in deltas is therefore of global importance. The environmental degradation and the climate change are one of the multiple pressures experienced by deltas affecting the ecosystem services that pose risk in the livelihoods of the locals as well as the global population living in these areas. There is a need for new strategies for sustainable development to help deltas mitigate the effects of climate change as well as adapt to the changing conditions in a context of increasing uncertainty of hazards. Coastal areas of the Vietnamese Mekong Delta (VMD) are highly vulnerable due to land use changes and extreme climate hazards. This study will explore the specific aspects of deltas from a complexity-based approach, and analyse Nature-based Solutions as alternatives towards sustainable development in these areas. This examines Nature-based solutions (NbS) as a complementary or alternative approach to managing hazards in the Vietnamese Mekong Delta. We investigated the potential NbS as a complementary and sustainable method for mitigating the impacts of coastal disaster risks, mainly cyclones and floods. Finally, we address this gap by conducting a systematic literature review to assess the existence of policy instruments such as the Law on Natural Disaster Prevention and Mitigation (2009), Flood and Storm Prevention and Control (2000), Law on Dykes (2006), that adopt NbS and to evaluate the existence of specific examples of NbS.

Global sand demand due to infrastructure construction has intensified sand mining activities in many rivers, with current rates of sand extraction exceeding natural replenishment. This has created many environmental problems, particularly concerning riverbank stability, which adversely affects the livelihoods of people in the Vietnamese Mekong Delta (VMD). However, sand mining’s social impacts in the region remain inadequately understood. Here we assess locals’ perception of sand mining activities in the VMD and its impacts on riverbank erosion. Residents living along the Bassac River, a hotspot of sand mining, were interviewed. Our results showed that while sand mining is perceived as destructive to the environment, few were aware of its role in worsening riverbank erosion. Only residents directly affected by riverbank collapse were aware of the implications of sand mining and its negative effect on bank stability, as they seem to have actively sought clarification. Our findings highlight the need for greater awareness and understanding among the locals regarding sand mining’s impact on riverbank stability.

This paper outlines the prerequisites and process of establishing of a community-based energy centre for sustainable agriculture practices in a rural village in the Vietnamese Mekong Delta. The centre was constructed by community consensus building and consisted of two main components including a community house and a community-biogas production system. The community house acts as a place where local people organize community activities such as traditional festivals and the production local products for local markets as well as community tourism. The community-biogas production system consists of a 41,6 m3 large biogas digester. The digester utilizes collected bio-degraded organic wastes from the local households and waste from animal husbandry as well as additional available green biomass such as water hyacinth. Methane produced will be used for cooking activities at the centre and delivered to the households in the community. Local people have contributed their own labours to build and manage the community-energy centre. Capacity building for the community is supported by experts of universities in both Vietnam and Japan. The community further intents to self-organize themselves to earn benefits through sustainable agricultural production such as planting organic vegetable and fruit trees, animal and fish raising, etc. This model is the first step in promoting the village as the “the most beautiful village” to clean up and promote environmental and sustainable technologies in the village. Furthermore, it is also a good option for inclusion in upgrading criteria for new rural development issued by Vietnamese government.

Chapter 15 - Erosion of mangrove-mud coasts, resilience of coastal protection, and outlook on nature-based solutions in the Vietnamese Mekong Delta

<p>Nature Based solutions (NBS) have been presented in the recent past as a potential solution to natural and climate change adverse effects on human well-being and socio-economic activities.  In this study, we present a simulation design methodology for NBS that can mitigate the effect of storm surges and coastal erosion. The chosen NBS is marine seagrass and it will be applied to the coastal strip of the Emilia-Romagna coasts. Within the framework of the OPEn-air laboRAtories for Nature baseD solUtions to Manage environmental risks (OPERANDUM) project, the seagrass NBS is presented within a simulation design methodology consisting of the comparison between validated wave numerical simulations for the present climate and modified wave simulations with marine seagrass. In this context, the unstructured version of WAVEWATCH III (WW3) model has been implemented for simulating the wave characteristics across the Emilia-Romagna coastal strip with and without seagrass.</p><p>The calibration/validation of WW3 was carried out and sensitivity experiments using the various wind-input dissipation source packages and bottom friction formulations were also attempted to evaluate the model performances (validation results presented here are for the entire 2017 year). The ST6 physics along with SHOWEX bottom friction formulations were chosen ideal for the study area. To evaluate the model results a directional wave rider buoy data was utilized. The model simulated significant wave parameters namely Hs (significant wave height), Tm (mean wave period) were compared with buoy observations and high correlations (0.93) were found with Hs comparison. Further the WW3 model was modified by including the modified bottom dissipation stress due to submerged vegetation, thereby incorporating the NBS as a potential mechanism for wave amplitude reduction. The seagrass species ‘Zostera marina’ was chosen in this study and comparisons showed that seagrass is capable to reduce the wave energy in the study area. Furthermore, the dependence on seagrass plant high-density and low-density scenarios, together with seagrass parameters (height and width of the seagrass) and species show the sensitivity of the results even on reduction of wave energy as obtained with different degrees by all NBS scenarios.    </p><p><strong>Keywords</strong>: Nature-based solutions, WW3, marine seagrass, storm surge, Zostera marina.</p>

Climate change and trans-boundary development in the major deltas of the world, including the Vietnamese Mekong Delta have exacerbated environmental risks. Land subsidence, riverbed sand mining, and intensive groundwater extraction have all contributed to lower channel bed levels, resulting in riverbank erosion and the loss of assets and livelihoods for local residents. This study investigated the drivers, and classified the social vulnerability of local communities affected by riverbank erosion along two main branches in the Vietnamese Mekong. Direct interviews were conducted with 218 erosion-affected households along the Mekong and Bassac rivers in Dong Thap and An Giang provinces in order to create a social vulnerability index. More than 70% of the total surveyed households belonged to the highly, moderately, or low vulnerability groups, suggesting a range of affected communities within the sample, some of whom had the ability to cope with its short-term impacts. However, the estimated social vulnerability index revealed significant geographical heterogeneity, with communities along the Mekong branch being more vulnerable than those along the Bassac. The recommendations from our investigations include the establishment of community awareness programmes, as well as policy changes that ensure and support local residents’ livelihoods adaptation. Stakeholder participation and enhanced community engagement was found to be the most important tools available in terms of aiding local people cope with the complex impacts of riverbank erosion.

Riverbank erosion, once considered an inevitable process, has emerged as a severe and unpredictable issue, exacerbated by climate change and human activities. The Vietnamese Mekong Delta (VMD) has faced significant erosion, leading to considerable infrastructural damage and economic losses. This study aims to predict riverbank erosion susceptibility along the Ham Luong River using a logistic regression (LR) model for 100 riverbank locations, classified as eroded or stable, with twelve conditioning variables. The LR model achieved an overall accuracy (ACC) of 0.83 and an area under the receiver operating characteristic curve (AUC) of 0.86 through 15-fold cross-validation. Sensitivity analysis identified the bank slope, soil moisture, and bank height as key factors influencing erosion susceptibility. Probability analysis revealed that an increased bank slope may cause greater riverbank instability, whereas higher soil moisture levels may reduce erosion susceptibility. These findings highlight the importance of stabilizing bank slopes and maintaining soil moisture to mitigate the riverbank erosion susceptibility effectively, emphasizing the need for managing water levels in rivers and canals during the dry season as part of disaster risk management in the VMD.

The Vietnamese Mekong Delta is dissected by a dense system of natural rivers and manmade canals which are connected to the sea, and has a coastline of more than 700 km in length. In recent years, coastal erosion, river bank erosion and landslides have become more serious, and are considered as disasters because they have such severe impacts on the livelihoods of residents in the region. Flooding, heavy rainfall in the wet season, soft alluvial soils, extraction of sand from the Mekong River, and increasing river traffic are all factors contributing to riverbank erosion and landslides. Whereas, rising tides, strong waves, deforestation of coastal areas, and reduced sediment transport from upstream in the Mekong River (due to upstream dam construction) are the main factors contributing to coastal erosion. This paper will discuss causes, property damage and impacts on livelihoods caused by these disasters as well as the government’s solutions and people’s attitude to cope with them.

In recent years Nature-based Solutions (NbS) have received increasing attention in coastal areas due to their ability to counteract Hydro-Meteorological Hazards (HMHs) and adverse climate change effects through habitat restoration and the re-establishment of Ecosystem Services (ES). Regardless of the wide adoption of NbS, there remain gaps and barriers in the effective uptake and implementation. There is an urgent need to define the specifics of NbS outcomes, measures of success and appropriate evaluation metrics. To bridge this knowledge gap this review focuses on: i) the terminology of NbS applied in coastal archetypes; ii) the ecosystem services delivered; iii) the HMHs targeted by NbS; and iv) the effectiveness indicators and metrics applied to monitor the impact of NbS implementation, including the tools and technologies employed. The NbS terminology applied addresses a range of different approaches included under the umbrella term NbS, e.g., building with nature, nature-based adaptation, or mitigation, and ecosystem-based management. Yet most of the included approaches mention the provisioning of ES as part of the main objective, relying on habitats and ecosystems to provide these services. In the scope of this paper 87.1% of the included ES can be attributed to regulating services such as reduction of erosion rates, coastal protection, carbon sequestration and water quality improvement.  The ES also clearly align with the climate change hazards addressed by NbS which include, e.g., flood and erosion risk, sea level rise, eutrophication, and extreme weather. These hazards are addressed through the implementation of NbS which aim to, e.g., reduce wave energy, anticipate storm surges, achieve good ecological/environmental status of water, re-establish carbon sinks and mitigate storm risk. To evaluate the effectiveness of NbS in counteracting these hazards and mitigate the impact of climate change this work identified 28 indicators. The indicators reflect mainly habitat characteristics and ES, e.g., geomorphology, vegetation cover and composition, risk reduction, carbon sequestration, and storm surge attenuation, complemented by socio-economic indicators such as willingness to pay and stakeholder perception. They are supported by multitude of metrics, evaluated through a variety of monitoring methods encompassing historical records (to create a baseline using, e.g.,  salinity records, seagrasses, vegetation status, or habitat size), questionnaires (to evaluate stakeholder values), in-situ measurements and remote sensing (to assess change in, e.g., bed level dynamics, vegetation presence, carbon stock, bird species, and marsh surface following NbS interventions) and modelling (the impact of NbS through, e.g., UVVR, morphology, vegetated leading edge, and habitat distribution). The results of this review will support the upcoming monitoring activity of saltmarsh restoration in the Venice lagoon (Italy) as part of the REST-COAST project and will pave the way for the creation of a methodological framework to systematically evaluate NbS effectiveness under current and future climate change scenarios. The project leading to these results has received funding from the European Union’s Horizon2020 research and innovation programme under grant agreement No 101037097.

Coastal erosion, caused by extreme weather events such as storms, poses a major risk to the sustainability of estuarine and coastal shorelines. Storm surges, driven by intense winds and low atmospheric pressure, can rapidly raise sea levels, leading to severe inundation and increased erosion along vulnerable coastlines. Addressing these challenges requires innovative and sustainable approaches that go beyond traditional engineered defenses.Nature-Based Solutions (NBS) for coastal protection are strategies that utilize natural ecosystems to protect coastal environments from erosion, flooding, and other environmental challenges. These solutions act as natural barriers, reduce wave energy and stabilize shorelines. In contrast to traditional engineered coastal defense systems, NBS provide sustainable, cost-effective, and resilient alternatives. Furthermore, they provide additional benefits such as new habitat creation for coastal organisms, carbon sequestration, and improved water quality. Seagrass meadows, in particular, act as natural wave dampers, interfering with coastal wave processes and significantly lowering wave heights, which reduces the impact of wave-induced stress on shorelines.This study employs an integrated modeling framework to conduct "What-If" Scenarios (WiS) for evaluating the effectiveness of seagrass meadows as a coastal protection measure. The framework combines a regional hydrodynamic model with the morphodynamic model XBeach to simulate storm impacts and nearshore morphological changes. This framework further integrates artificial intelligence (AI) with hydro-morphodynamic numerical simulations to enhance the efficiency on predicting bed level changes as indicators of erosion and deposition dynamics. Using different coastal areas (e.g. within the German Bight or Black Sea), the scenarios explore different configurations of seagrass meadows to determine optimal strategies for erosion reduction.The analysis highlights the importance of selecting appropriate planting depths, meadow density, and stem height to maximize the protective benefits of seagrass. Results indicate that the placement of meadows, rather than simply maximizing their size, plays a critical role in mitigating erosion. Strategic adjustments in planting design, based on storm characteristics and local bathymetry, can significantly enhance the efficiency of sediment stabilization, reducing erosion risks across varying conditions. This work demonstrates the value of Digital Twin-based What-If Scenarios for guiding the design and implementation of NBS. By simulating different configurations and environmental conditions, the approach fosters data-driven decision-making and collaborative planning among stakeholders. The findings provide actionable insights for coastal managers and policymakers, supporting the broader adoption of NBS as a viable strategy for enhancing coastal resilience and adapting to the growing impacts of climate change.