Flash flood early-warning system in a Mediterranean reservoir at operational scales for hydropower production

The operation of hydropower systems relies on the hydraulic conditions of the water system and their management is carried out based on certain operation rules (e.g., turbine minimum and maximum discharge) and environmental flows requirements. The effects of global change in hydropower systems are varied as expected changes in the meteorological forcing agents determine considerable modifications in the water flows that affect the amount of available water and thus, the production and profitability from hydropower plants. In this context, flash-flood events are especially relevant as quick management decisions need to be applied to minimize not only the potential damages downstream, but also the energy production losses connected to a conservative approach. The optimization of the decision-making process under flash flood events has two main challenges in these areas. On the one hand, there are several meteorological forecasting systems at different spatiotemporal scales currently available. However, the greater uncertainty linked to the rapid response time of these headwater catchments limits their use. On the other hand, the insufficient number of control points with available real time measurements (i.e., precipitation gauges and water level controls) makes it difficult to create early warning systems with an appropriate uncertainty quantification.

This study presents the definition of an early warning system that forecasts the inflow into a headwater Mediterranean catchment with a fast hydrological response. The Cala dam (59 hm³) was selected as the pilot reservoir with hydroelectric production as its main use, but also with irrigation and leisure demands. The contributing catchment (535 km²) is a good example of Mediterranean conditions in southern Spain, with agroforestry uses and a quick response to intense precipitation events due to steep slopes, shallow soils and groundwater redistribution, which does not favor the modulation of the hydrological response. The warning system was built based on the current operational rules of the reservoir. Once the flood event starts, the use of real time information about the water volume stored in the reservoir and the inflow in the next hour estimated using a Bayesian approach based on antecedent precipitation and other water flows states in the catchment, constitute the hydrological indicators to base the decision on, together with the generation of thresholds and requirements of the hydropower system. This methodological scheme could be easily transferable into other Mediterranean catchments with similar characteristics. Moreover, the development of these tools as decision support systems in the decision-making process is essential and allows the incorporation of advanced plans to adapt to global warming.

 

This work has been funded by the project FEDER UCO-1381239 Herramienta de pronóstico estocástico de caudal para gestión de centrales hidroeléctricas en cuencas mediterráneas a distintas escalas temporales, with the economic collaboration of the European Funding for Rural Development (FEDER) and the Office for Economy, Knowledge, Enterprises and University of the Andalusian Regional Government.