ABSTRACT
The length of the 300-km-long mainland shore which receded at less than 0·3 m/yr increased from 151 km in the early period to 171 km in the late period. In addition, the length of shore fronted by wide (≥ 15 m) beaches decreased from 64 km in 1876–77 to 35 km in 1968, and the length of shore without a beach increased from 84 km in 1876–77 to 112 km in 1968.
These changes have been caused largely by man-made structures. Harbor structures – mostly jetties – have caused accelerated recession, whereas shore-protection structures – mostly groins and seawalls – which have increased in number from about 60 in 1876–77 to about 3600 in 1973, have caused decelerated recession. The effect of the shore-protection structures has more than offset the effect of the harbor structures. Seawalls, by directly armoring the shore from waves, and groins, by trapping sand and thus reducing the wave energy reaching the shore, have also led to many of the changes in the beaches by reducing the volume of sand supplied by shore erosion. Thus even though the best natural form of shore protection – a beach – is diminishing, the shore is receding less rapidly because of the shore-protection structures.
