We model the impact of rock roughness parameterisation on tidal stream power extraction.

The site of application is the Fromveur Strait, a tidal stream location off western Brittany.

Numerical results are compared with field data of currents amplitude and direction.

Tidal currents are strongly impacted in the north-eastern and southward edges of the Strait.

Noticeable differences in bottom shear stress are identified over the sand bank of the Four.