3.1.4. Deposition

The deposition of sediment can be seen in Figure 6: a dune formed behind the foundation. The dune moved slowly downstream with time. When C/*H* = 0.75, the axial scour hole edge along the centerline at the location of approximately x = 4.5D at 90 min. However the hole edge migrated to a location approximately x = 7.8 *D* downstream after 90min when *C*/*H* = 0.25. The migrating speed of dune is inverse proportional with the clearance between seabed and rotor. In each case, the highest sand dune is ~1 *D*. The axial location of the highest sand dune migrates with time. The upstream scour hole slope is much steeper than the downstream slope.

**Figure 6.** Temporal seabed profiles of di fferent times (t = 2 min, 15 min, 30 min, 60 min, and 90 min) with di fferent tip clearance at location y/*<sup>D</sup>* = 0. (**a**) Tip clearance =0.75 *H* and (**b**) tip clearance = 0.25 *H*.
