Lessons learned from two coastal dune reconstruction experiments in Taiwan

Coastal dunes represent a natural barrier and play a vital role in the coastal defense against the waves and tides. Dune enhancement or reconstruction is considered to be a solution to avoid the negative effects on the ecological and aesthetic values of the coast by those engineering structures. Two field experiments were conducted for dune building at the Tainan coast in Taiwan. Experimental sets, including artificial vegetation, sand fence deployment and the bulldozed dunes with different surface pavements, were set up to re-build the foredune that have been previously damaged. A small natural remnant dune was chosen as the comparison set for evaluating the effectiveness of the sand accumulation and vegetation growth. The dune reconstruction processes were observed by monitoring the changes of dune profiles, surface sand grain size, and the vegetation density. The experiment results are used to suggest an appropriate dune rehabilitation procedure for this area. The results reveal that a bulldozed dune can raise the height immediately, and putting oyster racks on the bare surface can help the accumulation of sand and the colonization of vegetation that will quickly stabilize the artificial foredune. Sand surface covered with oyster shells may avoid wind erosion at the beginning, but it also hampered the vegetation colonization. Muddy sand surface formed a hard crust to reduce the wind erosion, but it also hindered the infiltration process that two gullies were found on the dune after a heavy rain. Sand fence should have an appropriate fence porosity to be effective.