Suggested mitigation and management of dunes and drift sands

• The golden rule for development on soft coasts is to avoid the littoral active zone, especially the frontal dunes and backbeach, which essentially represents the country’s coastal buffer. During planning, a comparative analysis should be made between the oldest and the most recent aerial photographs to determine the littoral active zone, and hence the setback line for development.

• Roads. Railways, bridges, powerlines, parking lots, houses and any other movable structures must not be placed within reach of the littoral active zone, and especially not within the coastal buffer zone and in estuaries. It is recommended that major roads, railways and powerlines are located four to five kilometres landward of the coastline. Bridges and traffic ways that have to cross through these areas should be built on piers as opposed to filled in causeways.

• Where bush covered coast dunes form a distinct series of ridges and troughs parallel to the beach, permit only camping and caravanning activities in the trough behind the first definite dune ridge. Confine permanent structures of any nature to landward-most third or fourth dune trough and ridge zone.

• Where multiple small dune barrier ridges occur on shorelines which are growing seawards, restrict the location of any permanent structure of any kind to beyond the oldest landward vegetated ridge. The younger ridges are colonised by dune pioneer plants and are still in an extremely unstable state.

• Where relatively small vegetated dunes occur as a single or double ridge only, all development should be confined to the landward base of the dunes. Dunes stabilised by indigenous forest or bush should not be removed to obtain a view.

Dunes covered by Rooikrans may be cleared, and even reformed, provided stabilisation is carried out. What may be expected to occur as a result of shaping is the recurring accumulation of sand, which will have to be removed on a regular basis and the dune re-stabilised.

• In high, steep, and broad vegetated dune cordons, all permanent development should be confined to the landward base of the dunes. On-site placement of structures should take advantage of natural gaps in the tree canopy. Footpaths must not result in donga erosion, or mass slumping may occur after downpours.

• Where dunes are poorly developed, or where only a gradual rise occurs landward from the backbeach zone, the closest any permanent development should be permitted is between 40 and 50m back from the seaward edge of the completely vegetated sands.

• All vehicle and footpath access onto beaches must be orientated away from the predominant and gale force wind directions. Where wind originates from two opposing quarters, then access should be at right angles to the two major opposing winds.

• Avoid the use of French drains or pit latrines in living areas serviced by fresh water from the dune aquifer. Avoid the disposal of waste in these areas as well.

• Prevent overgrazing or thinning out of dune vegetation by stock or game as this induces the formation of blow outs and donga slumping.

• Structures within dune areas must be protected against fire, and fire frequency within these areas must be controlled. In the south Western Cape, large areas of dunes are vegetated by highly flammable Fynbos. There are two main peaks of fire occurrence in these areas: in the summer dry season, and in winter during Berg Wind conditions. On the eastern seaboard where savannah abuts bush covered dunes, a similar fire risk exists during dry spells.

• In most cases, industry and municipal sized towns cannot be supported by local water supply from dune aquifers.

b) Reclamation

• Reclamation of dunes can only be justified where drift sands endanger resources or structures. Essentially, the dune feature represents the most effective method for controlling a drift sand problem.

• Bare dunes should not be stabilised simply because they are bare. Left alone, bare dunes (especially of the transverse type) may remain essentially the same for many decades.

• Where mobile dunes pose little or no threat either to natural resources, development, structures or infrastructure, then the best option is to leave them alone.

• Once it has been determined that reclamation is in fact required, determine the following features before initiating any programme:

o Identify the landscape and shoreline position of the mobile sand.

o Identify the reach of the active littoral zone.

o Identify the type of dune.

o Identify which processes are active.

o Identify the trend and direction of change.

o Determine an action priority of highest to lowest (i.e. complete or partial stabilisation, maintenance, or enhancement of existing conditions) based on a land use analysis of the area.

• Reclamation o dunes must be directed to two key sites, namely the sand source and along the landward encroaching front. Reclamation must be done so that the natural processes are harnessed into doing most of the dune building and stabilisation work.

• Dune stabilising methods must make use of flexible materials with open sieve-like characteristics, such as brush wood or cut reed mats, under or inter-planted with pioneer dune plants indigenous to the area.

• If stabilising materials are in short supply, then old fish nets may be used along the leading edge of the migrating dune, while planting up the backbeach with strand plants.

• Invasive or other problem plants such as Port Jackson and Rooikrans should be used for brushwood. Green or rip pods must be removed prior to placing.

• Ideally only locally indigenous strand plants should be used in dune reclamation.

These should be planted in mixed clumps and not as single species communities.

• A migrating parabolic dune may be contained by:

o Covering both the advancing crest zone and the sand source area near the beach with a one metre deep cover of densely packed brushwood, or a single layer of closely packed reed stems.

o Local dune pioneer plants should be planted during the rains, immediately ahead of the brushwood laying. Otherwise inter-planting with dune plants may be done after the rains.

o Wherever possible, use only problem plants as brushwood.

o Where a littoral dune is absent, an artificial one may be initiated along the driftline, either by planting dune pioneer plants, or by erecting a brushwood or reed slat fence.

o If a high water table is present, then the surface of sand at the seaward base of the parabolic dune may be skimmed off to expose the moist sand. This alone will stabilise the source area.

• Bare transverse dunes are, by virtue of their hyper-mobility, the most difficult type to reclaim:

o As all the dunes are reversing, it is possible to establish indigenous dune colonising pioneers in the slacks between dunes and in dune hollows against the compact semi-stable dune base.

o Attention must first be given to the landward encroaching margin and to the sand source area.