Computational analysis of water shortage mitigation measures in the IJsselmeer region

Abstract

The increased frequency of droughts due to climate change has prompted national initiatives in the Netherlands to enhance resilience against water-related challenges, with the IJsselmeer region being crucial. To address drought-induced water shortages in the IJsselmeer region, this thesis examined two measures: (1) raising the summer target water level to increase buffer capacity and (2) increasing water supply by connecting the Amsterdam-Rhine Canal (ARK). This thesis evaluated the benefits and drawbacks of these measures, alongside the restoration of the 1980 Rhine riverbed position, which increases water flow to the IJsselmeer region via the IJssel. The IJsselmeer region, including IJsselmeer and Markermeer, serves key functions: safety (flood prevention), water supply, and nature, which often conflict, particularly between nature and other functions. The ARK supports navigation, discharges excess water, and contributes to water supply. Furthermore, these measures needed to be implemented in a manner that maintained the existing functions of both the IJsselmeer region and the ARK. This thesis used data on supply and demand for the IJsselmeer region from Delta scenarios Ref 2017 and Steam 2050. Ref 2017 represents current climate and socio-economic situation, while Steam 2050 assumes strong climate change and socio-economic growth. These scenarios were analyzed for two riverbed positions: 1980 and 2018, with the latter reflecting the current state. The maximum summer target water level increase determined was -0.05 m NAP (from -0.20 m NAP) starting in March, applicable only to the IJsselmeer due to higher flood risks in the Markermeer. Additionally, up to 51 m³/s of water could be supplied from the ARK to the IJsselmeer region. The current buffer capacity was sufficient for the Ref 2017 scenario under both riverbed positions. However, for Steam 2050, additional measures were required. With the 1980 riverbed position, either raising the summer water level to -0.05 m NAP or supplying 51 m³/s from the ARK was sufficient. With the 2018 riverbed position, both measures were necessary. The thesis’s assumptions significantly influenced results. Unchanged dike profiles in the IJsselmeer region limited the ability to increase water levels. Moreover, supplying 51 m³/s from the ARK was based on a Lobith discharge of 1200 m³/s; lower discharges would reduce the volume available for diversion. In conclusion, mitigating water shortages for Steam 2050 with the 2018 riverbed position requires both raising the summer water level to -0.05 m NAP and supplying 51 m³/s from the ARK.