Quantification of changes in the beach volume by the application of an inverse of the Bruun Rule and laser scanning technology

Abstract

© 2015, Estonian Academy Publishers. All rights reserved. We address the possibilities of combining terrestrial (TLS) and airborne laser scanning (ALS) techniques with the classical concept of equilibrium beach profile to quantify the changes in the total sand volume of slowly evolving sandy beaches. The changes in the subaerial beach are determined from a succession of ALS surveys that were reduced to the same absolute height using a TLS survey of a large horizontal surface of constant elevation. The changes in the underwater sand volume from the waterline down to the closure depth are evaluated using an inverse of the Bruun Rule. The relocation of the waterline is extracted from the ALS scanning of elevation isolines of 0.4–0.7 m. The method is applied to an about 200 m long test area in the central part of Pirita Beach (Tallinn Bay, north-eastern Baltic Sea). The sand volume in this area exhibits extensive interannual variations. The annual gain of sand in the entire beach was about 2000 m3/y in 2008–2010 and the annual loss was about 1100 m3/y in 2010–2014. The changes in the underwater part of the beach are by a factor of 2–2.5 larger than the changes in the subaerial part.