Sediment budget of a cuspate shoreline and its influence on spit development—Lagoa dos Patos, Brazil

The coastal sediment budget is an essential tool to understand erosion/accretion patterns along coastlines and to predict future changes. This work is one of the first approaches of a coastal sediment budget study in a cuspate shoreline covering the whole embayment-spit system. Taking this into consideration, this study aims to estimate the main longshore sediment transport patterns and propose a conceptual model of the regional sediment budget of the lagoon cuspate shoreline (Lagoa dos Patos-Brazil), while also analyzing its influence on the spit development. To do so, representative wind conditions (direction and speed) were used to force a validated lagoon wave model utilizing the process-based modeling suite Delft3D. The potential longshore sediment transport was computed along widely distributed cross-sections, based on representative wave cases, and the annual sediment budget was estimated. The results showed a pattern of inter-related source and storage areas along the bay beaches and the occurrence of short-term nodal zones (convergent and divergent), which have an important control on the regional sediment budget of the coast. The central littoral cells of the embayments behave as temporary sediment storage areas, while the southern littoral cells act as sources of sediments to the spits. The findings of this study demonstrate the important control that short-term nodal zones have on the annual coastal sediment budget of complex coastline shapes and, the importance of the budget of the adjacent updrift cell to the sediment supply for the spits.