What does a river discharge of 18,000 m3 a second mean?
At present, the Rhine is structured in such a way that a volume of water of 15,000 m3/s at Lobith can be discharged safely to the sea. The measures in Room for the River will increase this discharge capacity by a thousand cubic metres a second to 16,000 m3/s.
Where does the extra water come from?
Where does the extra water come from?
The most recent national and international studies and climate scenarios indicate that the discharge of water through the Rhine is increasing in winter. This is mainly due to the higher levels of precipitation and rising temperatures (higher temperatures mean that less water is retained in the form of snow). As a result, the Rhine will become more of a rain river in the future. If the climate scenarios are stated as discharges, we expect the volume of water passing through the Rhine towards the Netherlands in 2100 to vary from 17,000 to 22,000 m3/s or more. The Rheinblick 2050 study of the International Commission for the Hydrology of the Rhine Basin also calculated that the discharge at Lobith will increase. The commission therefore confirms the basic assumptions relating to Rhine discharges in the future that were presented in the National Water Plan (2009) and also used for the Rivers Delta Programme.
Whether the water discharges referred to here will actually reach the Netherlands is determined by flooding in the German part of the basin. If the dikes in Germany are breached, water is removed from the discharge wave, resulting in lower discharges downstream, including the Netherlands, in a process referred to as the “capping of the discharge wave”. Controlled floods also reduce downstream discharge levels. The degree of capping depends on the extent to which German measures for flood risk management (such as dikes or water storage) are actually implemented. In the Action Plan on Floods of the International Commission for the Protection of the Rhine, Germany stated its intention to complete its dike upgrade programme and to implement the planned river-widening projects in the not too distant future. In addition, it should be kept in mind that German government authorities will implement emergency measures (such as positioning sandbags) when river discharges are extreme to prevent or mitigate the threat of flooding.
Given these insights into increasing discharges, capping, and the impact of German measures in this regard, the Delta Programme has assumed that, in the longer term, the maximum discharge that can reach the Netherlands could increase by 2,000 m3/s to 18,000 m3/s. This maximum discharge is not necessarily the discharge level used when designing specific dike upgrade or river widening projects. This design discharge depends on the design horizon taken into consideration, the climate scenario, the applicable standard, and the failure mechanism considered. The Minister of Infrastructure and the Environment explained this to the House of Representatives on 30 November 2015 in an annex accompanying the “Water Memorandum”. You can find more information by downloading the PDF file.
Best available knowledge
The above insights were confirmed by an international expert panel and in the GRADE study (Generator of Rainfall and Discharge Extremes). According to the Flood Risk Management Expertise Network, the GRADE method currently represents the best available knowledge. The level of 18,000 m3/s has also been adopted in the Room for the River Key Planning Decision (2006) by the legislator as being normative for 2100. The Delta Commissioner therefore followed this line in DP2015. Should new research result in new understanding, the adaptive approach requires these measures to be adjusted accordingly.