Sand mining far outpaces natural supply in a large alluvial river

The world's large rivers are facing reduced sediment loads due to anthropogenic activities such as hydropower development and sediment extraction. Globally, estimates of sand extraction from large river systems are lacking, in part due to the pervasive and distributed nature of extraction processes. For the Mekong River, the widely assumed estimate of basin-wide sand extraction is 50 Mt per year. This figure is based on 2013 estimates and is likely to be outdated. Here, we demonstrate the ability of high-resolution satellite imagery to map, monitor, and estimate volumes of sand extraction on the Lower Mekong River in Cambodia. We use monthly composite images from PlanetScope imagery (5 m resolution) to estimate sand extraction volumes over the period 2016–2020 through tracking sand barges. We show that rates of extraction have increased on a yearly basis from 24 Mt (17 to 32 Mt) in 2016 to 59 Mt (41 to 75 Mt) in 2020 at a rate of ∼8 Mt yr−1 (6 to 10 Mt yr−1), where values in parentheses relate to lower and upper error bounds, respectively. Our revised estimates for 2020 (59 Mt) are nearly 2 times greater than previous best estimates for sand extraction for Cambodia (32 Mt) and greater than current best estimates for the entire Mekong Basin (50 Mt). We show that over the 5-year period, only 2 months have seen positive (supply exceeds extraction) sand budgets under mean scenarios (5 months under the scenarios with the greatest natural sand supply). We demonstrate that this net negative sand budget is driving major reach-wide bed incision with a median rate of −0.26 m a−1 over the period 2013 to 2019. The use of satellite imagery to monitor sand mining activities provides a low-cost means to generate up-to-date, robust estimates of sand extraction in the world's large rivers that are needed to underpin sustainable management plans of the global sand commons.

Cartographie De La Dynamique Historique Du Trait De Côte Des Plages De Guédiawaye Et Malika (Dakar, Sénégal)

L’érosion côtière est une des causes de la disparition des plages, du recul des falaises et de la perte de terrains à valeur socio-économique et écologique. La compréhension de la dynamique côtière est donc primordiale avant d’entreprendre toute politique d’aménagement du littoral. Cette étude se propose de retracer la dynamique historique du trait de côte de la zone de Malibu à Malika au Nord de Dakar qui subit actuellement une forte pression humaine avec l’extension de la Voie de Dégagement Nord. Elle est basée sur l’analyse de données de télédétection au moyen du logiciel ArcGIS 10.4 et de l’extension DSAS 4.3 (Digital Shoreline Analysis System). Les résultats obtenus laissent apparaitre, entre 1942 et 2011, une évolution du trait de côte en faveur d’une érosion avec une vitesse moyenne de -0,15 m/an. Cette évolution, qui n’est pas uniforme d’un secteur à un autre mais aussi d’une période à une autre, serait essentiellement due à l’action des agents hydrodynamiques qui gouvernent les mouvements sédimentaires. Néanmoins, la pression humaine commence à se faire sentir avec l’extension de la Voie de Dégagement Nord, les extractions de sables et la coupe des filaos au profit des constructions humaines dont les conséquences sur la dynamique côtière peuvent être alarmantes. Coastal erosion is one of the causes of the disappearance of beaches, retreat of cliffs and loss of land with socio-economic and ecological value. Understanding coastal dynamics is therefore essential before undertaking any coastal development policy. This study aims to retrace the historical dynamics of the coastline from the Malibu to Malika area located in the north of Dakar which is currently under strong human pressure with the extension of the Northern Clearance Way. It is based on the analysis of remote sensing data using ArcGis 10.4 and the DSAS 4.3 extension (Digital Shoreline Analysis System). The results obtained show, between 1942 and 2011, an evolution of the coastline in favor of erosion with an average speed of -0.15 m/year. This evolution, which is not uniform from a sector to another, but also from one period to another, is essentially due to the hydrodynamic agents which govern sediment movements. However, human pressure is starting to be felt with the extension of the Northern Clearance Way, sand extraction and the cutting of casuarinas for human constructions benefit. The consequences of such practices on coastal dynamics can be alarming.

Local scale interventions dominate over catchment scale controls to accelerate the recovery of a degraded stream

A premise of stream restoration theory and practice is that it is often futile to attempt to restore a stream at the reach scale (101–103 metres) until catchment scale problems have been addressed. This study considers reach scale restoration actions undertaken in Bryan Creek, a sand bed river in south east Australia impacted by a sediment pulse, after catchment sediment sources have been addressed. Local scale interventions, which were in-stream sand extraction, fencing to exclude stock and riparian revegetation, were evaluated by quantifying cross-section and thalweg variability, mapping in-stream and riparian vegetation and by classifying the morphology that emerged following each intervention. Following intervention channel reaches moved to one of three distinct states: simple clay bed, eroding reaches dominated by Juncus acutus, and reaches with deep pools and Phragmites australis. Boundaries between the intervention reaches were sharp, suggesting local scale interventions dominate over catchment scale processes. The magnitude and spread of variability metrics were similar between all reaches and differences in variability bore no relation to intervention type, despite the stark difference in post-intervention morphology. These findings suggest that cross-section and thalweg variability metrics are an inadequate proxy for the effectiveness of local scale interventions in accelerating the recovery of sand bed reaches from a bedload pulse. The most important implications for river managers is that local scale interventions can lead to substantial and rapid improvements in condition, and the change in condition of these reaches is almost independent of other reaches. In this case, the key to the pattern of reach scale geomorphic recovery is excluding stock from waterways so that a specific macrophyte can establish, trap sediment and develop pools.

Persistent effects of sand extraction on habitats and associated benthic communities in the German Bight

Sea-level rise demands for protection measures of endangered coastlines crucial for the local population. At the island of Sylt in the SE North Sea, shoreline erosion is compensated by replenishment with sand dredged from an offshore extraction site. We studied the long-term effects of sand extraction on bathymetry, geomorphology, habitats and benthic fauna. Sand extraction created dredging holes about 1 km in diameter and up to 20 m below the ambient seafloor level. Directly after dredging the superficial sediment layer, inside the pits was dominated by coarse sand and stones. Hydroacoustic surveys revealed only minor changes of bathymetry > 35 years after sand extraction. Obviously, backfill of the dredging pits was very slow, at a rate of a few millimeters per year, presumably resulting from low ambient sediment availability and relatively calm hydrodynamic conditions despite high wave energy during storms. Thus, a complete backfill of the deep extraction sites is likely to take centuries in this area. Hydroacoustic surveys and ground truthing showed that the backfilled material is mainly very fine sand and mud, turning the previously coarse sand surface into a muddy habitat. Accordingly, grab samples revealed significant differences in macrozoobenthos community composition, abundance and species density between recently dredged areas (< 10 years ago), recovery sites (dredging activity > 10 years ago) and undisturbed sites (control sites). Overall, dredging turned the original association of sand-dwelling species into a muddy sediment association. Since re-establishment of disturbed benthic communities depends on previous re-establishment of habitat characteristics, the low sedimentation rates indicate that a return to a pre-dredging habitat type with its former benthic community and habitat characteristics is unlikely. Since coarse sand is virtually immobile in this area, a regeneration towards pre-dredging conditions is also unlikely without human interference (e.g., mitigation measures like depositing coarse material on the seafloor to restore the sessile epifauna).

Developing an Ecological Risk Assessment to Effectively Manage Marine Resources in Data-Limited Locations: A Case Study for St Helena Sand Extraction

Maritime states are faced with the challenge of effectively managing their marine spaces to use resources sustainably, maximise economic potential and simultaneously protect their marine environments. Anthropogenic activities, whether in isolation or combination, all have effects on the natural environment. Each of these effects has a footprint in time and space. Assessing the distribution and intensity of human activities and their effects on marine biodiversity, and all other human uses and users is necessary for effective spatial planning, as well as to harmonise conservation with sustainable development. Assessing and managing combined pressures from human activities can be achieved using risk assessment and risk management processes. There are multiple examples of environmental risk assessments which propose a similar formula. However, standardised approaches to ecological risk assessment in data-limited locations that relate to sand extraction are limited. Also most assessments require a certain level of information to produce meaningful outcomes, that enable subsequent management action to appropriately reflect the identified level of risk. Here we outline an approach to assess the risk to the marine environment of sand extraction activity within the Exclusive Economic Zone and Marine Protected Area of St Helena Island in the Atlantic. The proposed risk assessment tool has supported the development of a sand extraction management strategy on St Helena, and will be used to inform future management plans and policies that allow anthropogenic activities to take place in a way that balances local management, monitoring and enforcement capability, in line with the International Union for Conservation of Nature (IUCN) Category VI designation. Both the tool and strategy promote sustainable use of resources and protection of the marine environment, which are key objectives stated in the St Helena Marine Management Plan.

Can smart policies solve the sand mining problem?

While sand has become a scarce essential resource for construction and land reclamation worldwide, its extraction causes severe ecological damage and high social costs. To derive policy solutions to this paramount global challenge with broad applicability, this model-based analysis exemplarily studies sand trade from Southeast Asia to Singapore. Accordingly, a coordinated transboundary sand output tax reduces sand mining to a large extent, while the economic costs are small for the sand importer and slightly positive for the exporters. As a novel policy implementation approach, a “Sand Extraction Allowances Trading Scheme” is proposed, which helps sustainably balance the importer’s economic growth with the exporters’ economic development.

Multiplicities of sandscapes and granular geographies

This commentary on William Jamieson’s article, ‘For Granular Geography’, which illuminates the granular relations of sand as it is transformed by capitalist urbanism, suggests that understanding what might constitute granular geographies requires further consideration of the multiplicities of granular material. It considers the manifold values of sand beyond its worth as an economic resource and explores the temporalities associated with the movement and fixity of sand. It goes on to argue that there is a need for renewed focus on the impacts of sand extraction for local communities and landscapes as well as for more substantive accounts of the myriad mobile choreographies of sand in processes of place-making.

The Unsustainable Use of Sand: Reporting on a Global Problem

Sand is considered one of the most consumed natural resource, being essential to many industries, including building construction, electronics, plastics, and water filtration. This paper assesses the environmental impact of sand extraction and the problems associated with its illegal exploitation. The analysis indicates that extracting sand at a greater rate than that at which it is naturally replenished has adverse consequences for fauna and flora. Further, illicit mining activities compound environmental damages and result in conflict, the loss of taxes/royalties, illegal work, and losses in the tourism industry. As sea-level rise associated with climate change threatens coastal areas, sand in coastal areas will play an increasingly greater role in determining the amount of damage from floods and erosion. The present analysis points to the need for swift action to regulate sand mining, monitoring, law enforcement, and international cooperation.

JUSTIFICATION OF RECLAMATION MEASURES IN THE DEVELOPMENT OF SAND DEPOSITS IN THE EASTERN CRIMEA

The results of the analysis of disturbed lands on the territory of the Republic of Crimea are presented. The justification of the developed scheme of restoration works on recultivation is considered on the example of the Karamskoye field for sand extraction in the Leninsky district of the Republic of Crimea. The choice of restoration work taking account of the series of benchmarks, regional and natural patterns, the set performance career, accepted the order and Deposit development, capacity mineral and overburden, technology and mechanization of production work, etc.