Floods Countermeasures by Hybrid Appraches with Hard and Natural Engineering and Flooding events at Mediterranean Coasts
Abstract
Silvano Focardi and Milva Pepi
Floodings can seriously affect coastal regions, endangering human life and causing geomorphological changes, with important consequences for urban infrastructures, harbour facilities, coastal tourism infrastructures, agriculture of coastal areas, fishery acivities, and transports. Factors causing flood events include climate change as in the case of increases in the probability and intensity of precipitations, sea level rise, coastal erosion, land subsidence, increased river flow, deforestation, wildfires, and an intensive urbanization with important changes in the uses of coasts. The phenomenon of flood hazard is expected to increase in the next years. In order to protect coastal areas, hard engineering infrastructures as concrete seawalls, breakwaters, groins, or dikes, have often been used, although they are quite expensive to build and maintain, and can deteriorate coastal vegetation. Green infrastructures, although mostly present in zones at low density, provide nature-based coastal protection and can be represented by restored or conserved coastal wetlands to produce natural buffer from storms, such as wetlands, barrier islands, reefs, mangrove and marsh ecosystems. In the last years it has emerged that each of these two approaches has problems when used alone, thus suggesting the use of hybrid infrastructures combining hard and green engineered structures. Hybrid infrastructures combine both hard and soft engineering strategies, evidencing high ratio of benefits to costs with low residual risk. As an example of a hybrid infrastructure, coastal embankments as hard infrastructure have been combined with green infrastructures as shallow beaches, coastal forests, rice paddies and dunes. The combination of hard and green technologies in hybrid approaches has shown to be effective in preventing disasters derived from flooding in coastal areas. The Mediterranean Basin presents a high coastal vulnerability, with prevalence of low elevation zones as shallow sedimentary coasts, dunes, reefs, lagoons, estuaries and deltas. Mediterranean climate is characterized by unique morphological characteristics causing complex interactions between precipitation increases and lower antecedent soil moisture, leading to threshold effects in the catchments responses. Flooding can affect Mediterranean coastal areas with negative impacts on populations and ecosystems. Given the increasing coastal flood risk, there is an urgent need for measures to enhance the resilience of Mediterranean urban areas. Various measures for mitigating urban coastal flooding have been implemented in the european coasts of Mediterranea Sea, including coastal barriers, infrastructural drainage systems, wetlands, and mobile dams. Although various strategies to mitigate coastal flooding have been implemented in recent decades, further investigations are necessary in order to face with the increasing challenges posed by climate change, coupled with a rapid socioeconomic development. Innovative approaches are necessary that rely on local knowledge and request the intevention of stakeholders. In this mini-review, a description of innovative hybrid engineering approaches for protection of coasts from flooding effects has been reported, along with a description of sensitive areas of Mediterranean coasts, related engineering interventions and possible future countermeasures.