Sand and gravel mining, transport, and consumption in the global construction industry is arguably the
world’s largest “source-to-sink” (S2S) sediment dispersal system. Construction aggregates are the world’s
most extracted solid material resource (OECD, 2019) with 30–50 billion tons currently mined annually,
largely used in concrete (UNEP, 2019). Total global sediment flux to oceans is around 19 billion tons
annually, of which ~1.5 billion tons is bedload material (Syvitski et al., 2005). While crushed rock is
increasingly important in construction aggregates (Torres et al., 2021), natural sand and gravel deposits
are still the primary mining targets globally (Torres et al., 2021; UNEP, 2019). Given the fact that
construction aggregates are generally coarser than fine sand, the most direct comparison between these two
global S2S systems is bedload estimates versus construction aggregates. This makes the global construction
S2S system an order of magnitude larger than all the world’s natural coarse-grained S2S systems combined.
Because coarse sediment is something that many geoscientists think about daily, this fact presents new
opportunities for societally relevant research directions.
Defining the Components and Drivers of the New Source-to-Sink System
Construction S2S systems (Fig. 1A) begin at the mining site (source; Fig. 1B); continue through transport
via trucks, trains, or barges and subsequent processing, usually mixing into concrete (transfer zones;
Fig. 1C); and final use, generally pouring concrete at a construction site (sink). This S2S system has
quantifiable drivers that control its evolution (Torres et al., 2021). Whereas climate and tectonics drive
natural systems, economic and social forces drive the construction S2S system (Gavriletea, 2017; Torres et
al., 2021). Any time a city, region, or country wants to expand infrastructure, given current
concrete-centric building practices, there must be a resultant increase in sand and gravel extraction,
transport, and consumption.
(A) Cartoon schematic of the new construction sand source-to-sink system. (B) Example of a river sand mine
in Malaysia. (C) Example of a typical concrete batch plant. Note stockpiles of sand in upper left awaiting
mixing into concrete. (D) Summary of global consumption of construction aggregates. Uncertainty envelope
is estimated using the conventional proxy of 6.5–10× cement consumption (Peduzzi, 2014; UNEP, 2019).
Implications and Opportunities
Understanding the Resource and Implications of Extraction
Natural sand and gravel can be extracted from one of two sources: old deposits or active systems (UNEP,
2019). Mining from older deposits represents a self-contained system with largely localized environmental
impacts. From an S2S perspective, such networks are important to understand in terms of available
resources, particularly to replace supply from more environmentally deleterious active sources. “Resource
exploration” is relatively simple for sand and gravel because most economic deposits are evident at the
surface. However, detailed surface mapping is not available in many places around the world. Moreover,
even where surface deposits are mapped in detail, subsurface architecture and grain size distributions may
be poorly known. This provides opportunity to help define the most sand- and gravel-rich locations to
target to minimize even local environmental impacts.
Most sand and gravel pits are in unconsolidated Quaternary deposits, meaning an improved understanding of
the history of recent coarse sediment flux through any given system is useful in predicting the best pit
locations. Developing relationships with mining companies motivated by such resource evaluation can lead
to access to sedimentary records that would otherwise be lost to science. Marine extraction is also
increasingly considered as an economic source for construction sand and gravel (Torres et al.,
2021)—motivating new efforts to better characterize seafloor sand deposits and understand marine coarse
sediment transport. While resource evaluation in older deposits is important, in many places, studying
extraction from active systems is a more pressing sustainability concern.
Although known to be unsustainable, and often illegal, mining from active systems is generally the
quickest and cheapest way to meet local demand. Such deposits are usually clean, unvegetated, and can even
be mined by hand. In terms of research contributions, while accurate natural bedload fluxes are
notoriously difficult to estimate, they are often the biggest hurdle in evaluating mining impacts in
active systems (Bendixen et al., 2019). Extracted volume/tonnage is also often difficult to estimate.
Reporting systems are not common globally, and mining activity is often informal. More innovative
solutions like using machine learning analysis of satellite images to track sand barges (Hackney et al.,
2020) are needed to address this problem. Beyond quantifying natural supply and human extraction, we also
need a better understanding of how natural systems respond to the removal of large volumes of coarse
The root cause of geomorphic change due to sand mining is an induced deficit in sediment supply that the
system re-equilibrates by cannibalizing older deposits. As summarized by Koehnken et al. (2020) in their
review of recent case studies, this can cause channel widening or deepening in fluvial systems, even
leading to alluvial streams stripped to bedrock, and increased beach erosion and retreat in littoral
systems. Other ecological impacts include destruction of aquatic habitats, increased suspended sediment,
and bed coarsening (Koehnken et al., 2020). Improving our understanding of how individual local
perturbations might integrate at the system scale remains an open opportunity to aid resource management
and guide environmental recovery.
Traceable Supply Networks: From Where, to Where?
Construction S2S systems can be surprisingly opaque. While most consumption occurs near extraction sites
(<100 km), there are often multiple options for mining within that radius. Moreover, increasing demand
in areas without their own domestic supply, like Singapore and Hong Kong, leads to longer transport, with
some supply chains operated by full-fledged illicit networks (Magliocca et al., 2021). Traceable sourcing
is the cornerstone of sustainability policy, yet in sand and gravel mining there are currently no
reliable, scalable monitoring methods beyond self-reporting and direct observation. My research group is
working on novel approaches to employ sand provenance analysis in tracing supply networks (Sickmann et
al., 2022), but more innovation is required in this area.
Understanding Drivers and Predicting Areas of Concern
Without alternative building materials and methods, demand for construction aggregates is projected to
double by 2060 (OECD, 2019). Identifying existing areas of environmental impact and predicting future
areas of concern are crucial for understanding long-term sand and gravel exploitation sustainability. This
offers the opportunity for geoscientists to work with economists, urban planners, and policymakers to
evaluate the best deposits for meeting demand. Sand in the concrete of a new skyscraper will never end up
back in the river from which it was taken. If we, as geoscientists, can proactively help predict areas
that need to be protected and better identify acceptable resource targets, we can further demonstrate
direct applications of our knowledge and skillsets to the sustainability challenges of the present and
Increasing awareness of sand and gravel mining in geoscience research and curriculum is a way to expand
the influence of geoscientists in planning a more sustainable future and for motivating new ways to
advance fundamental earth-systems science.
Thank you to R. Stern for constructive comments on an early version of this manuscript and to science
editor J. Schmitt and managing editor K. Giles for reviews that improved the work.
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Manuscript received 11 Nov. 2022.
Revised manuscript received 7 Dec. 2022.
Manuscript accepted 12 Dec. 2022.
Posted 12 Jan. 2023.
© 2023, The Geological Society of America. CC-BY-NC.