Conceptual approach for a holistic low-flow risk analysis

Abstract

Low-flow events, characterized by a significant water deficiency in river systems, have profound impacts on various water users and river ecology. Recent low-flow events in Europe have had severe economic and ecological consequences such as disruptions to hydropower production, irrigation bans, constraints on navigation and complete river drying. These events highlight the urgent need for effective low-flow risk management and demand a holistic risk analysis as a basis. The existing approaches to low-flow analysis often focus on hydrological aspects, utilizing indices such as the Standardized Runoff Index (SRI) or Low-flow Index. However, these indices lack information regarding consequences and impacts. Other approaches consider parts of a risk approach but often focus on special aspects, such as the economy; in general, no holistic assessment is made. This study introduces a conceptual approach to a holistic low-flow risk analysis. The approach provides a continuous long-term simulation to capture the special long-term behaviour of low-flow events and therefore avoids the complex definition of scenarios. In this conceptual approach, the low-flow risk is analysed using a combination of various analyses that cover all aspects from occurrence to consequences. Meteorological analysis is used to generate synthetic long-term weather data time series, which are transformed into runoff time series in hydrological analysis. Based on these results, hydrodynamic analysis quantifies the water levels, water temperatures, and flow velocities along the river. The consequences are analysed in terms of socio-economic and ecological consequences. The results represent a long-term series of damage values. Finally, the damage values are summed in the risk analysis and divided by the number of years considered in the analysis. For testing and demonstration purposes, the presented conceptual risk approach is partly applied to a proof-of-concept at the Selke catchment, a small river catchment in Germany. Finally, the results are presented, evaluated, and discussed.