| 23 Dec 2025
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.
This manuscript reported a study on the flooding frequency in Rhine-Meuse delta in the Netherlands under sea level rise and considering the failure of pumps and sluice. The topic fulfills with the journal and is quite interesting. However, the study was very technical and the manuscript read like a technical report and was far from an academic journal paper. I would not support its publication in the present version. Below are suggestions for further revision.
(1) The introduction was long but most was related to the background of the problem. Discussion on the related academic topics was not enough. Besides, most of the cited references were published many years ago, not recent.
(2) The writing, formulas, and figures should be improved to reach the standard of an academic journal paper. For example,
(2.1) Figure 4 showed three sketches of the variation of pump head with flow rate. It read so confusing that how the authors obtained this relations and which situation they were used for. In the main text, for Figure 4(a), it was claimed that “The amount of energy loss varies with the flow velocity. Higher velocities cause higher friction losses, while eddies are more prominent at lower velocities. This results in a practical pump curve (Figure 4.a)”. Were there any references to support this sketch? “Eddies are more prominent at lower velocities” read strange, as the a faster velocity corresponds to a higher turbulent flow and more eddies. For what the eddies were ‘more prominent’?
(2.2) Besides, in Figure 4, the mathematical symbols were not standard, like Hdyn and Hstat.
(2.3) Similarly, in Figure 5, H_crit was also not a standard mathematical symbol.
(2.4) Figure 5, it is suggested to use subfigures to separate the figure into three subfigures and clarify what the subfigure shows. For example, the authors have not mentioned what the below-right part of the figure mean and used for.
(2.5) There were many errors related to mathematical expressions. For example, Line 236, “A peak discharge with a 2 year frequency”. Frequency has a unit of year?
(2.6) Moreover, line 240, “Both experiments correspond to 30,000 years (our return period of interest being 10,000 years x 3)”. It is hard to understand the meaning of the sentence in the bracket, especially “10,000 years x 3”.
(2.7) More, lines 316-317, “f(Fail)(= 7.2) is the frequency” and “f(Qex)(= 0.5)”? What were their meaning of these two mathematical expression?
(2.8) Figure 7 is a typical figure of this manuscript. There was no explanation of each subfigure. Even in the subfigure, there was not x and y titles of the plot like in Figure 7(a).
(3) The description of the method was not straightforward. There were a lot of wordy and useless descriptions. However, critical information should be provided but the authors did not. For example, Line 125, “for 2 meter and 5.4 sea level rise. In this study we only consider 2 meter sea level rise”. The authors should at least mention what scenario the “2 meter” and “5.4 meter” cases were used for? Why the authors only considered 2 meter in this study.
(4) Typos or grammar errors. For example,
(4.1) Line 42, “Haringvlietsluices” should be “Haringvliet sluices”.
(4.2) Line 116, “The northern outlet is the Nieuwe Waterweg is”. Delete one of the two “is”.
(4.3) Line 155, it should be Figure 4(a), not 4(c).
(4.4) Line 136, “buffer (Vbuffer) with a an incoming river discharge”. Delete “a”;
(4.5) Lines 125, “for 2 meter and 5.4 sea level rise” changed to be “2- and 5.4-meter sea level rise”