The effect of operational discharge capacity of pumps and sluices on flood hazards – A case study on discharging the Rhine and Meuse under sea level rise

Abstract. Future sea level rise will likely hamper the discharge of excess water from low-lying water systems all around the world. One example of such a water system is the Rhine-Meuse delta in the Netherlands, which discharges to the North Sea. A possible mitigation strategy involves closing off the delta from the North Sea with large dams and to discharge the incoming river discharge with large pumping stations. In this study, we determine the required amount of pump capacity by including the new concept of operational discharge capacity. This way we can account for the variations in the available pump and sluice discharge capacity due to variations in the head difference between the sea and water system and possible technical malfunctions. The effect of variations in the operational discharge capacity on return periods of extreme water levels in the water system is assessed within a probabilistic and hydraulic model framework.

We find that variations in operational discharge capacity substantially increase maximum water levels in the water system and increase flood frequencies compared to simulations with the assumption of a constant and fully available discharge capacity. In one scenario of our case study, including the effect of operational discharge capacity leads to an increase in flood frequency from 1/10,000 years to 1/75 years. In our case study, most of the increase can be attributed to including sluice reliability. Including pump reliability increases the frequency of higher water levels in the reservoir, until a water level is reached at which the sluices are available. However, available sluices can prevent a further increase of reservoir water levels. The precise effect of operational discharge capacity will vary per water system and design set-up. Yet, the examples in this paper show a clear effect for most design scenarios. Therefore, the operational discharge capacity is a crucial parameter that should be taken into account in the design of pumping stations.