Morphodynamics of gravel beaches and their response to nourishment

Abstract

Modeling the long term beach morphology after nourishment provides a better understanding of the nature of the beach. In this thesis, the morphodynamics of a gravel beach at Kalemyel Bay after two nourishments in March 2020 and March 2021 are modeled. The model of each year focuses on four cross-sections and their profile evolution in one year after the nourishment. SWAN software is used to model the wave climate which has the most important factor for the profile evolution. 8 wave conditions that have the highest impact on the profile evolutions have been selected and used in the morphology model. The morphologic changes due to cross-shore sediment transport are simulated in XBeach-G. Longshore sediment transport is modeled with the diffusion equation. The results obtained from the longshore model are superposed on the XBeach-G outputs of the cross-sections. The results of the XBeach-G of the profiles after the nourishment in March 2020 remain less evolved compared to the site measurements. This may imply that an unconsidered storm occurred in Summer 2020 at Kalemyel Bay. The results of the XBeach-G for the nourishment in March 2021 are in line with the long-term estimations of the Bo˘gazi¸ci University Coastal Engineering Laboratory. However, for simulations of both years, longshore transport is overestimated especially on the west side of the beach. The irregular beach fill along the shore affects the longshore transport results. Still, there is a dominance of the cross-shore transport over the longshore transport. The average beach width loss due to cross-shore transport after second nourishment, where the average width gain was 5.90 m, is 3.65 m, while for longshore transport this amount is 1.64 m. It is deduced that the nourishment can be designed such that the fill is thicker in the middle of the beach than the sides since the material will move to the ends of the domain in time.