Short‐term monitoring of foredune formation on the east coast of South Africa

Abstract

Although dunes fronted by sandy beaches constitute approximately 80 per cent of South Africa's coastline, few studies have addressed the formation and life cycle of coastal foredunes, the small, ephemeral shore-parallel dune ridges typically less than 5 m high and 20 m wide, which form seaward of the storm line. This study used regular, detailed topographic surveys of embryo and foredunes at Tugela mouth, an aggrading stretch of shoreline on the subtropical east coast of South Africa, over a 32-month period, to gain insight into the formation and motion of these highly mobile landforms over the short term.Average wind drift potential at Tugela mouth during the study period, at 2·35 m s −1 , was an order of magnitude lower than that typical of most parts of the eastern South African coast. The dominant sand-moving wind for the region was from the southwest to west-southwest at 10·7 to 13·8 m s −1 , with a secondary vector from north to north-northeast at 10·8 to 13·8 m s −1 . Significant shoreline retreat, a result of the low sediment yield of the Tugela River during the study period, was one of the main results. This provided the context for redistribution of sand from the inland to the seaward side of the study area, a consequence of the dominant wind direction, and for frequent creation and destruction of short-lived embryo dunes. Those foredunes which survived the whole study period tended to increase in height, but there was no consistent directional trend in foredune crest movement throughout the 32 months.The study results generally supported Psuty's model of foredune development, but could not confirm his contention of landward retreat of dune forms under conditions of shoreline erosion. This may be due to the relatively short duration of the study, or possibly to low wind drift potential at the site.

The influence of coarse woody debris on gravel beach geomorphology

“…They develop as woody debris deposited during storms traps sand falling from the cliffed dune face (Carter, 1988). These dunes are generally seasonal and easily destroyed during storm events as they often lie on the seaward side of the main foredune, as noted in South Africa (Oliver and Garland, 2003). On wide beaches debris can form across broad areas trapping sand in a wide zone up to 200 m across which Carter (1988) termed embryo dunes.…”

Assessment of highly active dune mobility in the medium, short and very short term

“…Consequently, specific changes were identified on a smaller scale. As in the case studied by Olivier and Garland (2003), an examination of the cross-sections showed that the largest sand elevation changes usually occurred at or near the dune brink. According to Long and Sharp (1964), dunes with a distinctly separate brink and crest may behave differently from dunes where the two features are one and the same.…”

“…Nowadays, a great number of coastal dunes around the world are considered to experience inactivity due to climatic changes (dunes are often stabilised by vegetation because of a decrease in wind power), sand mining and other disturbances, as an increase in vegetation cover due to a decrease in the rabbit population (Ranwell, 1960;Thomas, 1960Thomas, , 1963. Some of them have been already researched in Brazil Martinho et al, 2010), USA and Canada (Nield and Baas, 2008;Girardi and Davis, 2010), South Africa (Olivier and Garland, 2003), Israel (Tsoar and Blumberg, 2002), Denmark (Clemmensen et al, 2009), the Netherlands (Arens et al, 2005) and other European countries (Pye, 2001;Buynevich et al, 2007). Although restoration activities are mainly focused on the reactivation of these ecosystems to increase biodiversity and avoid coastal erosion, in other cases, stabilization is the main purpose, especially when the original dune development conditions vary, reflecting differences in the vegetation cover, changing sand supply or increasing migration rates.…”

Quantification and implications of change in organic carbon bearing coastal dune cliffs: A multiscale analysis from the Northumberland coast, UK

“…Olivier and Garland (2003) monitored foredune development with total station topographic surveys and Esteves et al (2012) used differential global positioning system (DGPS) surveys to quantify thresholds for dune erosion beyond a measurement accuracy of 2 m, although both approaches achieve sparse spatial coverage. The generally smooth undulations of dune fields have proven suitable for the application of airborne light detection and ranging (lidar) survey data.…”