Solution 2

Wider beaches and lower water tables

NZ now has many instances where beach + dune width have been contemporaneously increased, consequent to simple restoration and importantly the unconfined proliferation of indigenous C4 halophyte dune plants. This work has been substantiated over nearly 20 years of extensive implementation and repeated numerous times to seek increased veracity – on both east and west coasts, plus North and South Island sites. The response is always comparable – increased width of beach + dune in tandem with increasing resilience to storms + reversal of erosion effects. Currently, over 120km of formerly-degraded coastal dunes have been restored by the many community members involved in this ecosystem restoration programme.

These effects and the critical success pathways have now been quantified and therefore are considered viable for others to successsfully implement in their own nations. See the photos below to gain an appreciation of how this restoration increases both beach AND dune width naturally.

The site below had a long history of degradational practices – with the dune reportedly retreating at least “40–60 metres inland” due to the effects of farming these dunelands plus mining the beach-face. Classic human-induced erosion. There have been no unnatural inputs onto this beach – just a single and simple planting of indigenous and unconfined C4 halophyte dune species (e.g. Spinifex) to restore normal and natural dune function. All introduced species (e.g. Ammophila) are destroyed by salt water inundation. Look closely at the increasing width of the beach + dune in the last photo compared with the earlier 1997 photo.

Ensuring the unconfined proliferation of these colonising plants is just as critical as planting the most suitable species – as this action truly repairs the natural ecosystem function of dunes. Many failures have occurred where this non-confinement aspect is ignored. Suitably robust evidence is available if required.

The following image reveals the powerful accretionary advantages of this unconfined proliferation of plants. Contrary to simple expectations, such progressive action simply increases beach width and not loss of beach width through encouraging plant domination of the beach-face. See ‘lower water tables’ information below.

Normal and natural dune function has been restored at this formerly degraded and eroding site by using indigenous plants. The Surf Lifesaving club rooms on the dune crest in the 1995 photo (top, above) were in danger of being relocated inland due to the coastal erosion pressures here. This club house is now considered completely safe as the burgeoning dune and beach continue their mutual seaward advance.

The mechanism that encourages this advance has recently been described, and involves a significant lowering of the dune water table in response to restoring the indigenous plant species (de Lange & Jenks 2007, Müller 2011). This is a natural and an evolved specialisation that pertains only to indigenous C4 halophyte dune plants – and is absent in all plants introduced to NZ for ‘fixing’ the dunes in response to the earlier degradation impacts. The presence of introduced plants encourages higher dune water table levels; this increases the pore water pressure of beaches which consequently leads to increased backwash erosion when these beaches are exposed to short-period waves during storm surges. Natural storm surges also increase the pore water pressure of beach sand, so lower water tables therefore reduce erosion potential.

“The superior drainage capabilities of Spinifex dunes increase the potential for swash infiltration … and reduce the potential for sediment fluidisation ... Lower groundwater levels increase sediment availability for further onshore aeolian transport through widening of the unsaturated beach. These effects make Spinifex more adept than Ammophila at mitigating the effects of erosion … “ (Müller 2011).

Thus, subsequent to this restoration of the indigenous and functionally-evolved coastal plants, quantification of actual beach + dune width increases and dune volume changes become possible (i.e. sand accretion):

ASSIDUOUS DUNE RESTORATION – PAPAMOA BEACH ECOSYSTEM RESPONSE: 1996 to JUNE 2014

Data collected from the above and other associated sites around NZ has provided the following findings, and this information published for the ESRI Users Conference in San Diego 2015: