Velocity profile and turbulence characteristics over coral reefs in Derawan Island, East Kalimantan
Ayi Tarya, Faisal H. Muhammad and Nining Sari Ningsih

Department of Oceanography
Faculty of Earth Sciences and Technology
Bandung Institute of Technology

Abstract

Turbulent boundary layer dynamics over coral reef communities control many biologically important processes, including food capture by benthic organisms, mass transfer of dissolved nutrients, larval dispersal, waste removal, and sediment transport. All of these processes are controlled by hydrodynamic mechanism are directly related to the shear and turbulent mixing. Motivated by the importance of boundary layer dynamics to both large and small scale ecological processes on coral reefs, this study aims to investigate velocity profiles, the turbulence parameters and boundary layer flow over a coral reef. Moored measurements on currents and turbulence were conducted at the three coral reef sites in Derawan Island, East Kalimantan. Velocity profiles were inferred from Acoustic Doppler Current Profilers (ADCP). The velocity data showed logarithmic profile up to ca. 3 meter from the bed, sometimes even up to nearby the surface (14 meter). Reynolds shear stresses and turbulent viscosities were derived from ADCP data by using the beam variance method. The data profiles showed fairly well with theoretical of previous study for the coral reef boundary layer. Boundary layer parameters, such as the friction velocity and roughness length, were determined by fitting a logarithmic profile to the velocity data. The time scale analysis showed that mesoscale fluctuations were present and the characteristic turbulence time scale varies an order of magnitude in time.

Keywords: Velocity profiles, Boundary layer, Turbulence

Topic: Ocean-Atmosphere Dynamics