An integrated physical and cost-benefit approach to assess groins as a coastal erosion mitigation strategy

Future investments required for the construction and maintenance of coastal defense interventions are expected to increase, due to increasing coastal erosion issues along social, environmental and economically valuable coastal areas. The high costs related with coastal defense interventions require improved knowledge on their performance, considering impacts, costs and benefits. Despite the existence of several cost-benefit approaches applied to coastal zones, in this study a well-defined, sequential and integrated methodology supported by already existent numerical models is developed and applied to assess the effectiveness (shoreline evolution impacts), costs and benefits of different coastal defense interventions. This methodology encompasses three integrated modules, including a shoreline evolution module (to estimate areas of territory maintained, gained or lost over time), a coastal structure pre-design module (to estimate material volumes of coastal works) and a cost-benefit evaluation module (to assess cost-benefit evaluation criteria). The approach allows for the physical and economic comparison of different coastal defense intervention scenarios, helping coastal management and planning entities to define strategies. In this study, the proposed methodology was applied to evaluate the performance of different groin scenarios, based on a hypothetical case study. The case study allowed highlighting the importance of the physical and economic analysis of different scenarios. Results show that the definition of coastal defense interventions is complex where, on the one hand, best physical solutions are sometimes related to very high costs and, on the other hand, best economic scenarios lead to high territory losses. Thus, the innovative approach presented in this study shows that an integrated analysis of shoreline evolution, coastal intervention design and subsequent costs and benefits allows to improve the physical and economic performances of coastal defense interventions.