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Abstract. Underwater dunes are found in various environments with strong hydrodynamics and sandy, movable sediment such as rivers, estuaries and continental shelves. They have a diversity of morphology, ranging from low to high-angle lee sides, and sharp or rounded crests. Here, we investigate the influence of lee side morphology on flow properties (time-averaged velocities and turbulence). To do so, we carried out a large number of numerical simulations of flows over dunes with a variety of morphologies using Delft3D. Our results show that the value of the mean lee side angle, as well as the value and position of the maximum lee side angle, have an influence on the flow properties investigated. We propose a classification with 3 types of dunes: (1) low-angle dunes (mean lee side < 10°), over which there is no permanent flow separation, except if the maximum slope is steeper than 20° and situated close to the trough, and over which only little turbulence is created; (2) intermediate-angle dunes (mean lee side 10–20°) over which there is generally no permanent but likely an intermittent flow separation, situated over the trough; and (3) high-angle dunes (mean lee side > 20°) over which the flow separates at the brink point and reattaches shortly after the trough, and over which turbulence is high. We discuss the implications of this classification on the interaction between dune morphology and flow.

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