The co-incidence of storm surges and extreme discharges within the Rhine–Meuse Delta

Abstract

The Netherlands is a low-lying coastal area and therefore threatened by both extreme river discharges from the Meuse and Rhine rivers and storm surges along the North Sea coastline. To date, in most flood risk analyses these two hazardous phenomena are considered independent. However, if there were a dependence between high sea water levels and extreme discharges this might result in higher design water levels, which might consequently have implications for flood protection policy in the Netherlands. In this study we explore the relation between high sea water levels at Hoek van Holland and high river discharges at Lobith. Different from previous studies, we use physical models forced by the same atmospheric forcing leading to concomitant and consistent time series of storm surge conditions and river discharge. These time series were generated for present day conditions as well as future climate projections and analysed for dependence within the upper tails of their distribution. In this study, dependence between the discharge at Lobith and storm surge at Hoek van Holland was found, and the dependence was highest for a lag of six days between the two processes. As no significant dependence of the threats was found for cases without time lag, there is no need for considering dependence in flood protection and policy making. Although future climate change is expected to lead to more extreme conditions in river discharges, we cannot conclude from this study that it will change the magnitude of the dependence for extreme conditions.

Investigating compound flooding in an estuary using hydrodynamic modelling: a case study from the Shoalhaven River, Australia

“…We recommend considering storm-tide and riverine flooding drivers jointly when assessing coastal flood risk in estuaries. This is particularly important for Australian estuaries with large catchment areas (> 10 000 km 2 ) which are known to have a quick response time to extreme rainfall but may be different in considerably larger estuarine systems, as the time lag between peak storm-tide levels and extreme discharge increases (Klerk et al, 2015). Classification schemes (e.g.…”

Storm surge and extreme river discharge: a compound event analysis using ensemble impact modelling

“…with a water level event at HvH occurring three days before the discharge 15 peak at Lobith. This is a shorter time lag than applied by Klerk et al (2015), who presented the dependence in the tail for a lag of six days. Despite this shorter time lag we find a similar relation between the two variables as Klerk et al (2015) (Fig.…”

“…Proxies for storm surge and river runoff were used, namely north-westerly winds and multi-day precipitation sums. In an attempt to use more realistic data to assess the statistical relationship between surge and river discharge, Klerk et al (2015) subsequently used variables diagnosed from hydrological, hydraulic and storm surge models. In their coarseresolution dataset covering the relatively short historical period from 1981-2010 they found a clear correlation between the two variables, but only when a substantial time lag of six days was taken into account.…”

River flood risk in Jakarta under scenarios of future change

“…The former has been assessed for Jakarta in Ward et al (2011b), and Muis et al (2015) have assessed both river and coastal flood risk at the scale of Indonesia using globally available data sets and models. Nevertheless, the impacts of river and coastal flooding can interact with each other -for example when high tides occur at the same time as extreme discharges -and this interaction should be a priority for future flood risk research, not just in Jakarta, but elsewhere (see, e.g., Keef et al, 2009;Klerk et al, 2015;Svensson and Jones, 2004). To enable an assessment of these interactions, one would need to develop time series of both high river discharge and high sea levels, in order to examine the temporal interactions and joint probabilities between these two variables.…”