Coastal regions are more and more affected by changes in water levels, storm patterns etc. owing to climate change. Nourishments and other human interventions constitute common practice in order to maintain and secure these areas. However, many aspects, especially the hydrodynamics, are not yet fully understood due to the complexity of the acting processes. This study investigates the evolution of submerged sandmounds under wave, current, and combined flow conditions, and examines the relation between the observed morphodynamic response, and the imposed hydrodynamic forcing. It aims to provide insight towards a better understanding of the hydrodynamics and morphodynamics that will lead to more efficient design, and accurate behaviour prediction of the nourishments. A physical experiment (MODEX) provided a reference dataset of hydrodynamic and morphodynamic measurements (wave height, flow velocity, bathymetry). The extent to which the dataset covers the full spectrumof acting processes was examined via a literature study of the documented mechanisms under wave, current, and combined flow conditions. It was found that the data do not capture slope effects, flow separation, and ripple influence on flow velocity. The analysis of the data resulted in the quantification of the flow types effect on several geometrical aspects (mound height, footprint area and shape, ripple pattern), and the position of the mound. In order to examine the extent to which the measured velocities are responsible for the observed response, sediment transport rates were estimated using an energetics model that depends on total, and orbital velocity. The results provided evidence that the observed response can not be fully explained using mean and orbital velocities. For this reason the study suggests an interpretation of the sediment pathways under the various flow types. Nevertheless these are on based on reasoning, and thus are not considered to be proven. Moreover, the results revealed a relation between aspects of the morphological response and Umax2 (which relates to the instantaneous maximum flow energy). The mound height reduction rate (dHm/dt), and migration rate (dx/dt) scale linearly with Umax2 , while the mound footprint length/width ratio displays an inverse linear relation. Lastly, the relation betweenmound area change rate (dA/dt), and flow energy is linear for non-oscillatory, and combined flow, and a parabolic for oscillatory flow. Finally, despite the limitations and omissions, this study provides significant insight on the evolution of submerged mounds. It is first step in the direction of more accurate prediction of morphological change, and more efficient design of nourishments.

Since 2003 there is a cooperation between the Hydraulic Engineering department of Delft University of Technology and Bulgarian universities. The cooperation focusses on exchange of knowledge and the development of the coast in the area of Varna. Dutch and Bulgarian students get the possibility to gain experience in data collecting, processing and interpreting. Repeating this fieldwork every year in the same area will provide an overview of the coastal development in the Varna area. The students will act as consultants for local hotel owners at the Varna coast. Their work consists of measuring hydraulic aspects in the project area and making a rehabilitation plan for the St. Elias Marina. Data collection consist of inventory material near site, beach measurements, wave measurements, profile measurements, quarry analysis and a bathymetric survey. The rehabilitation plan contains the development of sub-areas in the St. Elias Marina like the peninsula, north beach, south beach and the breakwater.