Sand mining far outpaces natural supply in a large alluvial river

Abstract

Abstract. 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 is lacking, in part due to the pervasive and distributed nature of extraction processes. In the Mekong River, current basin wide estimates of sand extraction are 50 Mt, and based on estimates from 2013. 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 and show that rates of extraction have increased year on year from 24 Mt (17 Mt to 32) in 2016, to 59 Mt (41 Mt to 75 Mt) in 2020 at a rate of ~8 Mt yr−1 (6 Mt yr−1 to 10 Mt yr−1); where values in parenthesis relate to lower and upper error bounds, respectively. Our revised estimates for 2020 (59 Mt) are nearly two 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 five year period, only two months have seen positive (supply exceeds extraction) sand budgets under mean and upper bound scenarios (five months under the lower bound estimates). We demonstrate that this net negative sand budget to the river is driving major 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 provide a low-cost means to generate up-to-date, robust estimates of sand extraction in the worlds large rivers that are needed to underpin sustainable management plans of the global sand commons.

Significant Human Modification of the Lower Arkansas River Sediment Budget

“…Even though sediment transport rates in the LAR indicate multi‐year timescale flood disturbance‐recovery processes still influence the riverine sediment discharge, results of the sediment mass balance analysis suggest that navigation dredging and S&G mining significantly reduced riverine sediment loads and contributed to lowering river resilience. A similar conclusion was also achieved in the Lower Mekong River where sand mining far outpaces the natural supply (Hackney et al., 2021). Thus, it is certain that management of dredging and sand mining is needed worldwide, especially in developing countries, to improve the sustainability of the ecosystem in large rivers (e.g., Best & Darby, 2020; Hackney et al., 2020).…”

“…(2022), while that in the Mekong River is much higher. This finding is in part due to the Mekong River flowing through developing countries where most people's subsistence tend to rely disproportionately on the natural resources in large rivers (e.g., Bendixen et al., 2021; Best & Darby, 2020; Bravard et al., 2013; Da & Le Billon, 2022), resulting in a ∼8 Mtyr −1 increase of sand mining rate from 2016 to 2020 (Hackney et al., 2021). Whereas the S&G mining rate in the LAR remains relatively constant between 1971 and 2019 (Figure 3b).…”

“…Rivers respond to the flood disturbances by natural erosion and sedimentation and thus impart some resilience to absorb a degree of changes (e.g., Best & Darby, 2020; Hackney et al., 2021). The need for increased barge transportation capacity has spurred proposals to deepen the MKARNS navigation channel from 2.7 to 3.7 m (9–12 feet), which would surely increase the amount of dredged sediments (USACE, 2005).…”

“…Estimates of sediment extraction from large river systems are lacking relative to those that document the influence of dams on sediment flux, in part due to the pervasive and distributed nature of extraction processes (e.g., Best & Darby, 2020; Hackney et al., 2021). Existing detailed sediment extraction research mostly focus on large rivers (i.e., Mekong, Ganges, and the Nile) in low‐ and middle‐income countries where unregulated and unmonitored sand mining constitutes an important source of livelihood and revenues (e.g., Bendixen et al., 2021; Gruel & Latrubesse, 2021).…”

“…14 Btyr −1 to ca. 12.6 Btyr −1 (e.g., Syvitski & Milliman, 2007; Syvitski et al., 2005), and significantly increased channel incision and river bank instability (e.g., Bendixen et al., 2021; Best & Darby, 2020; Hackney et al., 2021). Barge transport on rivers is a low‐cost and low‐emission shipping mode used globally (Best, 2019).…”