Morphodynamic response of sand waves in the Taiwan Shoal to a passing tropical storm

Abstract

Data from three repeated multi-beam echo-sounder surveys of pre-storm, post-storm, and one year after the storm were used to study the response of sand waves in the Taiwan Shoal to the tropical storm, Talim. The measurements showed significant decreases in wave height of giant sand waves between post-storm and pre-storm, and moderate increases in one year period after the storm. The maximum decrease in wave height is more than 2 m and the averaged decrease is 1.2 m along the measured profile. The linear regression analysis shows an increasing trend of wave height changes from northwest to southeast along the profile. The uneven evolution pattern was possibly caused by the asymmetry of the currents induced by the cyclone winds. The analysis based on the Morlet wavelet function showed that the storm smeared out small-scale sand waves and eroded the giant sand wave crests, and recovery of bedforms after the storm. Two-dimensional features of storm effects were analyzed using the imagery of a Digital Terrain Model processed in a 2D survey area for pre-storm, post-storm and one year after the storm. The analysis revealed sand wave migration processes during the storm and the growing-back feature of the eroded wave crests after the storm.