Quantifying turbulence from field measurements at a mixed low tidal energy site

This study explores typical characteristics of the mean and turbulent profiles at a mixed low tidal energy site (40 m mean water depth) where the waves have limited effects on the currents. The turbulence profiles were derived from secondary current data using a 5-beam ADCP which was optimised for wave measurements. The tidal currents have peak flows of ~1 m/s during spring tide. The turbulence intensity is no less than 10% at peak flows and compares well with values at other tidal channels (at ~5 m from seabed). The Reynolds stresses show symmetry at the neap tide but less so for the spring tide. Although the qualitative profiles of TKE are similar between the neap and spring tides, the values of TKE for flood flow are the largest throughout the deployment. The integral length scales are in good agreement with theory, and with estimates based on the mixing length concept. The measured turbulence parameters are sensitive to flow inhomogeneity, Doppler noise, and ADCP tilt. The findings demonstrate the practical benefits of exploiting secondary current data at a mixed low tidal energy site for estimating typical turbulence characteristics; such information can be used to define design standards and protocols for marine energy devices.