A view of Lake Tissø. © DHI
The industrial cluster of Kalundborg is one of the largest in Denmark. The water supply is vital, and the industries have for years developed water saving technologies using recirculation to reduce water usage. Today, Kalundborg Utility abstracts surface water from Lake Tissø to deliver high-quality water to local industries. To continue doing so, the water permit must be renewed, which has sparked the need to evaluate current environmental impacts and practices in a broader context. The new long-term water permit will be granted for several decades and since future climate changes will likely affect runoff and flows, the environmental conditions and water supply sustainability must be accounted for.
DHI was contracted by Kalundborg Utility to help investigate and develop a new operation strategy for the structure controlling water releases from Lake Tissø, but also take part in a series of stakeholder meetings. The objective of the meetings was to obtain a common understanding of pros and cons in order to reach an acceptance of a balanced solution for a new water permit application. Apart from water extraction, environmental impacts to birds, fish and vegetation were considered along with agricultural drainage requirements and recreational activities.
Analysis provided valuable insights
Taking changing climatic scenarios until 2050 into account, simulations of water levels in Lake Tissø showed increasing flood risks during winter periods and decreasing water supply security due to extended dry periods. The simulations also demonstrated the need for a backup water resource to maintain full supply security in the future. By increasing lake storage to meet dry season requirements, it was possible to increase the extraction and improve environmental flows with only minor adverse impacts on drainage conditions. Making relatively simple modifications to the structure and adopting a different control strategy, allowed for substantial improvements.
Overall, DHI’s analysis provided valuable insights into the current control strategy. Simulation results revealed that structure operation by current water level rule curves does not satisfy multi objective criteria. The performance of the current and new control strategies was measured by percent of time in which the strategy was in compliance with the individual water level and flow criteria over a 20-year period.
Based on the simulations performed by DHI, Kalundborg Utility has decided to secure additional backup capacity to reduce the risk of future production losses for the involved industries.