Technical review of shoreline accretion and storm erosion modelling implemented for NAMDEB Southern Coastal Mine

Abstract

The mining operation of Namdeb Diamond Corporation in the Southern Coastal Mine (Oranjemund, Namibia) relies on the continuous seaward advance of the shoreline, achieved by artificial placement of large volumes of sediment along the coast. In coastal engineering practice this is designated as a mega-nourishment, but with important distinctions to traditional nourishment schemes, as it is neither a permanent nor a feeder mega-nourishment. The approach taken by Namdeb in the Southern Coastal Mine (SCM) is more appropriately characterised as a continuously prograding mega-nourishment, which over the last decades created the largest sandy beach accretion hotspot in the world. The complexity of such unprecedented shoreline advance in the SCM is further compounded by the very energetic wave climate that characterises the coast of southern Namibia, the variable bathymetric configuration of the nearshore that is masked by an apparent large-scale uniformity along the coast, and the notable variation in sediment characteristics, which range from fine sand to very coarse gravel and boulders. Advancing the shoreline along the SCM is nowadays part of a complex mining operation that integrates the removal of overburden to access mining faces located at depths in excess of 20 metres below mean sea level, construction of protective seawalls using overburden sediment, and targeted placement of large volumes of sediment on the beach for accreting the shoreline (i.e. beach nourishment). Planning and management of the shoreline at operational (seasonal to yearly) and strategic (multi-annual to decadal) timescales in this dynamic coastal environment requires information from coastal modelling to support decision-making. In the context of shoreline accretion modelling, this involves the ability to skilfully predict shoreline position for different timeframes and under different sediment discharge scenarios, while accurate modelling of storm-induced erosion is required for the design of resilient sandy seawalls and provision of early warning to mitigate the risks of extreme coastal storms.