Author(s): Marco Lompi; Luis Mediero; Enrique Soriano; Enrica Caporali

Linked Author(s): Marco Lompi, Luis Mediero, Enrica Caporali

Keywords: Floods; Climate change; Hydrological dam safety; Dam overtopping; Hydrological model

Abstract: Climate change will likely increase frequency and magnitude of precipitation extremes and floods. Increasing design peak flows in the future could lead to underestimations in the design capacity of current spillways, increasing the probability of exceedance of dam overtopping. Therefore, new methodologies are required for hydrological dam safety assessment considering climate change. This study presents a methodology for including the impact of climate change on floods and reservoir water levels to assess hydrological dam safety. The methodology is applied to the Eugui Dam in the River Arga catchment (Spain). The impact of climate change on floods in the River Arga catchment is quantified by using the delta changes in precipitation quantiles extracted from climate projections at the national scale in Spain (Garijo & Mediero, 2019). The RIBS distributed hydrological model has been used to quantify the expected changes in flood quantiles at the Eugui Dam for three time windows (2011-2040, 2041-2070, and 2071-2100), two Representative Concentration Pathways (RCP 4.5 and RCP 8.5) and seven return periods (2, 5, 10, 50, 100, 500 and 1000 years) (Lompi et al, 2021). The HBV continuous hydrological model is used with a daily time step to simulate inflow discharges in the Eugui reservoir using rainfall and temperature climate change projections as input data. The HBV model is calibrated with 13 years of observations of precipitation, temperature, as well as inflow discharges in the reservoir. A reservoir simulation model is developed to obtain reservoir water levels by using inflow discharges as input data and considering reservoir operation rules. The calibrated HBV model is forced with rainfall and temperature climate change projections for an ensemble of 12 climate models to assess the changes in the expected reservoir water levels at the Eugui dam for each time window and emission scenario, comparing the results between the future periods and the control period. A set of 10 000 peak inflow discharge values are randomly generated from GEV distribution functions fitted to the outputs of the RIBS model. A hydrograph shape and an initial reservoir water level is assigned to each peak flow. The Volumetric Evaluation Method (VEM) is used to simulate flow routing processes in the reservoir, as the Eugui Dam has a gated spillway. The frequency curve of maximum reservoir water levels is obtained for each scenario, assessing the expected changes in the probability of exceedance of dam overtopping. Moreover, a stochastic procedure gives a confidence level to the results analyzing all the uncertainty chain of the methodology. The methodology proposed in this study can assess hydrological dam safety considering the impact of climate change on floods and expected reservoir water levels, fulfilling the requirements of recent regulations to consider the impact of climate change on dams.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022904

Year: 2022