Impact: The construction of seawalls has significant effects on the marine environment. Seawalls are constructed to push the shoreline between 200 and 500m into the sea, permitting access to diamond deposits of the subtidal. The seawalls require constant maintenance as rough seas typical of this coast continually erode the walls. Overburden alone is often insufficient for the construction and maintenance of these dams, and as a result, other sources of material are used for building material including the coastal dunes (in itself an impact on the terrestrial environment). Following mining, maintenance of the seawalls ceases, the wall collapses, and the area is left to reform a new shoreline. Because the seawalls are constructed of a melee of fine sands to boulders not resembling the original beach material, the resulting shore is left physically altered. In some cases fine-grained beaches have been left as coarse-grained beaches while in other cases, rocky reefs have been converted to boulder fields. As discussed above, alterations to grain size can have profound effects on biological communities of sandy beach and rocky shore communities. Although such an impact has hitherto not been assessed in terms of field studies, the effects are roughly predictable. Pre-mining baseline data has been collected at one site, however, and the impact should be fully quantified once mining is underway in the next few years.
Mitigation: Mitigation action includes the use of materials for seawall construction that are roughly equivalent to the sandy beaches that are stripped.
6.5.3 Environmental Impacts of Shallow-Water Mining Operations (
Diver-assisted shallow-water mining activity targets gravel-filled gullies and potholes between reef ridges. Access to this gravel is either via the shore or through boat-based operations.
Access to Shore-based Mining Sites
Impact: Access to nearshore diamondiferous gravel by shore-based operators often requires the construction of new roads, blasting rock cuts, moving of boulders and the construction of work camps in order to move machinery sufficiently close to the seashore. The act of mining leaves tailing dumps, most often left above the high water mark. The aesthetic and terrestrial impacts of these activities, albeit at a larger scale, have been discussed above.
Mitigation: It has been suggested that impacts of this nature could be mitigated if nearshore diamond pumping were undertaken exclusively from boats. Although possible, start-up costs associated with such a policy may be prohibitive for new entrants.
Impact: Kelp (primarily Laminaria spp.) is often cut by divers to provide unencumbered access to the mining site. This activity causes a localised impact, the severity and duration of which depends on the extent and frequency of kelp cutting and the age of the plants. Kelp sporelings settle most successfully at or near the holdfasts of adult kelp plants, and recovery of kelp beds proceeds from the fringe of the cut area. Therefore, the greater the area cut the slower the recovery. By the same argument, a clear-cut area or repeatedly cut area will recover relatively more slowly than an area where only adults are cut and small kelp plants are left behind. In the best case scenario, recovery can take less than two years, although in some areas recovery has not occurred, especially where high densities of sea urchins (Parechinus angulosus) occur. Sea urchins feed preferentially on kelp sporelings, and in sufficient densities can keep an area entirely denuded of kelp. Many animals utilise the kelp bed habitats during the juvenile stage of their lives, and the loss of this habitat could have a small but important cascade effect.
Mitigation: Mitigation action includes restricting the width of the lane of kelp cut, discouraging clear-cutting, and discouraging repeated cutting.
Impact/Mitigation: Nearshore pumping of diamondiferous gravel by divers has a myriad of effects, such as the development of sediment plumes; uncovering of new reef where gravel is removed; the smothering of reef where tailings are discharged; the de-stabilising of reef where ‘cementing’ gravel is removed; physical disturbance of the suction pipe and diver abrading the reef; and the moving of boulders to access gravel beneath.
Concern has been expressed regarding the effect of sediment plumes on the primary productivity of phytoplankton and macroalgae. Compared with the naturally high levels of suspended sediment in this highly dynamic nearshore environment or the fine tailings deposited into the sea from land-based mining operations, this impact is thought to be negligible.
Nearshore mining putatively impacts the habitat of rock lobsters, rock lobsters themselves and their food source. A strong association of rock lobsters with reef- and boulder-dominated seabed has been established, as has the diversity of benthic organisms, most of which constitute the food source of the rock lobster. Diamond mining primarily targets sand and gravel areas, however, and the mining process does not directly threaten the reef and boulder communities. By removing gravel, mining may in fact expose expanses of previously embedded rock and boulders. Although these are initially uninhabited, recolonisation by benthic communities is rapid and the area becomes statistically indistinguishable from unmined areas within six months, despite the bottom topography being considerably altered. Mining activity therefore can effectively convert gravel gullies into boulder beds, which are potentially suitable for habitation by rock lobsters.
The converse can also occur, however, if tailings are dumped onto reef- and boulder-dominated seabed, thereby smothering rock lobster habitat and/or food. Some dumping inevitably occurs on adjacent reef, but if this is restricted the impact is thought to be limited, as small quantities of tailings will be dispersed during subsequent storms. If the impact is cumulative, however, this can have the effect of converting preferred rock lobster habitat into sub-optimal small boulder or unsuitable gravel areas. These areas may be stabilised in time, although further research is needed before conclusive answers can be given concerning the impact of rock piles and tailings dumps. Mitigation measures should, however, include keeping the shifting of boulders to a minimum and dumping of tailings further offshore on non-reef areas.
Although diamond divers admit to pumping rock lobsters ‘for the pot’, the quantities involved are insignificant compared to the annual quota landed by the commercial rock lobster industry. To discourage poaching, however, mining vessels should be inspected occasionally for illegal catches, and mining licenses be confiscated if found guilty.
Seabirds and Seals
Impact/Mitigation: Disturbance of seabirds and seals on the nearshore islands off the Namibian coast is a further issue of environmental concern. Nearshore subcontractors working the island concessions are forbidden to land on the islands except in emergency or if accompanied by personnel from the Ministry of Fisheries and Marine Resources (MFMR) in Lüderitz. All landings are recorded and reported to the MFMR.
Impact/Mitigation: Allegations have also been made that the activity of diamond boats within the Olifants River estuary, and mining operations near the estuary mouth, have led to a reduction in gillnet catches of harders by local subsistence fishermen. Problems associated with waste disposal and maintenance operations which potentially release contaminants (e.g. oil, antifouling paints, sewage) into the estuarine environment have also raised concerns. Although the conclusions of the EIA were speculative only, reduced catches were attributed to overfishing and possible recruitment failure rather than boat traffic. It was, however, recommended that mining near or within the mouth and increased use of the estuary as a harbour for diamond vessels be discouraged.