Monitored changes to foredunes on the Rangitikei-Wanganui coast

Abstract

As part of a survey of coastal change on the Rangitikei-Wanganui coast, foredunes at Himatangi Beach (Leisure Sands Subdivision) and the site of the Fusilier Wreck (Figure 1), 10km south and 15km north of the Rangitikei River mouth respectively, have been regularly monitored for up to six years. The foredunes occur on a section of sandy coastline which has been prograding at mean rates of between 0.6 and 1.0m/year for the last century (Gibb, 1978; Johnston, 1985). In contrast to this general trend of prograding coastline, the sand country of the coastal margin (including the foredunes) has historically been subject to severe wind erosion. The area is distinc- tive for its high, predominantly onshore winds (mean wind speed: 3.0m/s). Shepherd (1979) has calculated that wind speeds here are above the threshold velocity for sand for one-third of the time. At both monitoring sites stabilisation !!1 programmes have been used to counter the effects of wind erosion on the foredunes. Himatangi mechanical reshaping of the dune was followed by intensive marram planting and later by emplacement of an artificial barrier, while at the Fusilier Wreck site, stabilisation has been by intensive marram planting.