As a river flows, rocks are weathered and eroded over time to form grains of sand and mud, which are deposit on the riverbed as sediments. Along the lower reaches in particular, the riverbed may be filled with sand. River sand may seem an inexhaustible resource. However, with the widespread use of river sand in construction in this age of rapid urban and infrastructure development, the global supply of river sand is already tight. Over-exploitation of river sand is wreaking havoc on the environment worldwide.
According to an estimation by the United Nations, in 2017 alone, global consumption of sand reached 28.7 to 32.8 billion tonnes. By 2030, the annual worldwide demand may increase to 50 billion tonnes. Sand is indeed in high demand!
River sand is the major component of concrete, which is a mixture of sand and cement. Cement binds the sand and gravel together like a glue, to give the concrete strength to support giant buildings. Apart from river sand, there is also marine sand. Taking into account the chemical constituents, however, marine sand is generally used only in marine reclamations, while it is the river sand that is appropriate for construction.
Sand is naturally common. In a river channel, sand is continuously formed. Unfortunately, the global construction craze has escalated demand for concrete. Extraction of river sand on a large scale has brought about pervasive damage to the natural environment. Dredging of river channels makes the water murky and stirs up pollutants deposited on the riverbed, causing pollution in the water source. Sand mining also directly ruins plant habitats along the riverbanks. As vegetation declines in area, the self-purification capacity of a river system is lowered, further affecting the water quality.
Ecological studies have shown that sand mining in rivers alters the composition of aquatic invertebrate communities and upsets the whole upper food chain. Dredging also kills many fish, damages the breeding and nursery grounds of juvenile fish, and affects migratory fishes. The impacts are profound—even after the work is completed, the original river environment has changed forever. Native fish populations can hardly be restored, but instead will be taken over by other invasive fish species with higher adaptability.
Furthermore, sand mining risks the river embankments and their flood control capacity. The embankments may easily collapse during heavy rainstorms, leading to floods and disasters. Massive extraction of river sand lowers the water table and affects underground water. In the long term, potable water supply and farmland irrigation will be affected, and the river may dry up in extreme circumstances. Irreversible adverse impacts affect people as well as the environment.
Owing to the high transportation costs of river sand, long-distance transport is not preferred in most cases. Rivers near rapidly developing cities and townships suffer most from excessive sand mining and the accompanying environmental problems.
Hong Kong consumes large amounts of river sand
In the past, river sand used in Hong Kong was largely imported from Guangdong province. In recent years, however, domestic demand for river sand in mainland China has been rising. In 2007, the mainland China government started implementing a quota system for river sand supplies, leading to escalating prices as competition for the quotas intensifies. Hong Kong began importing river sand from other South East Asian countries.
In fact, it is not only in China but worldwide that river sand supplies are stressed. River sand is even developing into a “currency”. In some places, such as Singapore, there is military force guarding stored sand. It is not surprising that the highly valuable resource attracts illegal sand mining. It is challenging to regulate sand mining and its resulting environmental problems.
Hong Kong, without many large rivers, produces no river sand. Yet it is among the top consumers of river sand. Hong Kong should adopt a more active role in tackling the environmental issues of river sand. For example, we should aim at reducing the use of concrete in building design, reusing sand and concrete from demolition, and researching concrete substitutes to minimise consumption of river sand.
Sand is a renewable resource that regrettably decreases given the pace of heedless development of human societies. It is urgent for us to rethink how to adjust our development model and make better use of the limited resources in nature for a sustainable future for all people on Earth.