The conincidence of severe storm tides and weather conditions affecting the closure reliability of storm surge barriers

The efficacy of the flood protection of the Netherlands critically depends on the reliable functioning of six Dutch storm surge barriers. Usually, these barriers are open and they only close in case of severe storm tides. The storm surge barrier performance (i.e. the amount of risk reduction due to their presence) depends roughly on the height, the structural reliability, and the closure reliability. Obviously, hydraulic overload and the probability of structural failure increase with storm severity and tide levels. Yet, it is also likely that a storm tide coincides with meteorological conditions that may harm the closure reliability. This compound event is typically not accounted for in current flood risk assessments, potentially leading to underestimation of the flood risk. This study explores what meteorological conditions may affect the closure reliability and how these conditions may coincide with storm tides that require a closure. We found that storm tides can both coincide with reliability reducing and reliability increasing meteorological conditions. Yet, in general it has a negative impact on the closure reliability. This implies that the actual flood risk may be somewhat higher than usually perceived.