Search

Vietnam Mekong Delta (VMD), the country’s most important food basket, is constantly threatened by drought-infused salinity intrusion (SI). The SI disaster of 2020 is recognized as the worst in recent decades, hence inspiring this perspective article. The authors’ viewpoints on the disaster’s impacts and causes are presented. The arguments presented are mainly drawn from (i) up-to-date publications that report on the recent SI intensification in the VMD and (ii) the power spectral analysis results using water level data. We verified the intensifying SI in the VMD both in its frequency and magnitude and remarked on four of the key SI drivers: (i) upstream hydropower dams, (ii) land subsidence, (iii) the relative sea-level rise, and (iv) riverbed sand mining. Also, a non-exhaustive yet list of recommendable management implications to mitigate the negative effects of the SI is contributed. The mitigation measures must be realized at multiple scales, ranging from pursuing transboundary water diplomacy efforts to managing internal pressures via developing early warnings, restricting illegal sand mining activities, alleviating pressures on groundwater resources, and diversifying agriculture.

Kerala state in the southwestern coast of India is blessed with 41 west flowing rivers that debouch into the Arabian Sea. These rivers are small with limited river bed resources. Among the various human interventions that are threatening rivers, indiscriminate river sand mining is of paramount importance as the activity irreparably degrades rivers and its adjoining aquatic environments. Studies reveal that the river bed in their storage zones is lowering at a rate of 5–20 cm per year. In the present chapter, two case studies have been examined to disclose the severity of environmental problems of sand mining from the rivers draining the Western Ghats—an ecologically sensitive area in the Peninsular India.

Mining of sand and gravel with little regard to natural replenishment processes have imposed marked changes on the biophysical environment of the small rivers of Kerala in the southwest India. Considering the importance of management of river bed resources, the Government of Kerala enacted the legislation “The Kerala Protection of Riverbanks and Removal of Sand Act, 2001” to protect the rivers from large scale sand mining. This act also envisages provisions for periodic sand auditing in order to evaluate the sand mining process and to protect the rivers from unscientific human interventions. This chapter deals with the various procedures employed in sand auditing of the small rivers of Kerala (southwest India), taking the case of Periyar river an example.

Large-scale sand extraction from river environment for building constructions is a global phenomenon. Indiscriminate sand mining imposes a series of physical, ecological, and socio-environmental impacts on the river basins. Furthermore, the extraction of this granular material is unavoidable as the sustainability of construction industry depends heavily on it. In rivers, construction grade sand occurs in different sources—active channels, floodplains, and river terraces. Different mining methods (mechanical or manual) are adopted for the extraction of sand from these sources under dry (above water table) and/or wet (below water table) conditions. This chapter describes briefly the different sources, methods and hydrogeological bearings of sand and gravel extraction processes in river ecosystems.

River sand mining is widespread in most of the developing and developed countries. Of the different types of fluvial systems, small rivers (catchment area

Depending on the geological and geomorphological setting, the magnitude of the environmental impacts of river sand mining also varies. The activity imposes marked environmental impacts on land, water, atmosphere, and socioeconomic conditions of a river basin. Environmental impact Assessment (EIA) is an important tool to assess the positive (beneficial) and negative (adverse) impacts of the sand mining. Two different methods—Matrix method and Rapid Impact Assessment Matrix method are used here to assess the environmental impact of sand mining in the longest river of Kerala—the Periyar river. The study reveals that the activity is a major threat to the very existence of the Periyar river in particular and the small rivers of tropics in general. The rivers are reported to be degraded considerably due to uncontrolled sand mining over the past few decades. The impact assessment reveals that the adverse environmental impacts of sand mining dominate over the marginal and short-term benefits.

Mining of sand manifold higher than natural replenishments leads to severe damages to river systems. The mining process not only intercepts movement of sediments along the river channels, but disturbs the sediment balance established in the system over the geological time periods. Indiscriminate sand mining imposes several adverse impacts on the various environmental subcomponents of river ecosystems like bed forms, sediment milieu, water quality and quantity, flora and fauna, and socio-economic conditions of the people in the long run. The magnitude of these impacts depends on several factors such as type and scale of sand extraction, channel morphology, sediment transport processes and induced alterations in watershed characteristics. A better understanding of these impacts is very essential for formulating appropriate strategies for ameliorating and negating the impacts of river sand mining.

A key issue worldwide is the extent to which the beach/foredune is migrating (moving landward). This situation (Physical States 1 and 2) is the most frequently encountered, seaward progradation (Physical State 3) much less so. This chapter considers the ecosystem services and values of the three states identified in Chap. 4 and the trends and trade-offs associated with different management options. It provides an explanation of the way the values of each state change in response to both spatial and temporal driving forces. It reviews the influence of human activities on these values, providing a basis for assessing the need for intervention. The chapter includes a simple ‘State Evaluation Model’, designed to help decision-making for nature conservation purposes at the beach/foredune interface. The next Chap. 7 considers the trends and trade-offs associated with inland, more stable vegetated dune forms.

Occupation of sand dunes dates back many thousand years. This chapter provides a summary of the history of human occupation from Mesolithic Times to the present. It considers the way human activities have modified or destroyed the surface of the, sometimes extensive dune fields (Sects. 2.1 and 2.5). It describes the indirect impact these may have on the beach/foredune together with the implications of sediment depletion (Sect. 2.6). The cumulative nature of these developments helps identify a ‘sand dune squeeze’ (Sects. 2.7 and 2.8).

Beach erosion induced by sea level rise is a critical problem in Sri Lanka. Because accelerated sea level rise can be expected in the near future as a result of global warming, the country’s beaches may be further eroded, putting pressure on its coastal settlements, commercial activities, and land use systems. Rising sea levels would inundate adjacent areas of wetlands and lowlands, pushing them farther inland. The southwestern coast, the most densely populated part of the island, may be among the areas most severely affected by rising sea levels, even though many parts of the coastline are already protected by groin fields and revetments. This chapter assesses the degree of vulnerability expected in the coming decades, in terms of the loss of land, the loss of sand spits and river mouth barriers, and the inundation of land adjacent to wetlands and lowlands under scenarios of 0.3 m, 1.0 m, and 2.0 m sea level rise. The results show that the beaches of southwestern Sri Lanka would be lost under current protection levels. The endangered areas could include wetlands, where cultivated paddies would be destroyed by inundation and saltwater intrusion. The existing policies on coastal protection are reviewed in light of the findings of the vulnerability assessment, and further recommendations are made.