Geomorphological aspects of the problem of protecting the shores of the Sakhalin Island

Abstract

The presence of the frozen grounds on the coasts including the barrier lagoon ones, thermo-abrasion observed on some sites, the presence of shore ice and icings lasting up to the end of May, allow to consider the shores of the north-western and eastern Sakhalin as subarctic type. It was determined that during last 50 years more than 15 км 2 of accumulated plain was lost as a result of shore erosion only in the north and south-east of Sakhalin Island. The spatial structure of erosion has existed in its general outline since the 1930s. Since 1940 the extension of eroded shores has enlarged nearly two times. The spatial rhythms of erosion with wave length about 30 and 60 km determine the main regularities of shore erosion pattern. The formation of non-uniformity of beach structure and accordingly the irregular distribution of its wave-decreasing properties along the shore were considered. On the seashore of Sakhalin more than thirty sites were found, where quasi-rhythmic forms of shore relief were observed. But all the deformations of underwater relief were observed only in the frames of rated close depth. The special attention was devoted to the changes of wave-suppression characteristics of the beach during beach deposits freezing and under the open sea influence. The freezing of the 40-50 cm of the upper parts of shore profile and decrease of wave-suppression characteristics (mainly drainage and roughness), caused by this, occurred during this period before the formation of the shore ice and icings (1.5–2 months). According to the observations the height of swash zone increases by 30–45%. The calculations showed that the height of wave run-up for bank slope of storm bar may increase owing to freezing by 2–2.5 times.