Assessment of synthetic series to design the capacity of flow regulation reservoirs

Abstract

Freshwater scarcity is perceived as a global systemic risk. Intending to reach water secutiry, flow regulation reservoirs are alternatives to improve streamflow and water storage, especially in places where demand exceeds water availability during periods of drought. However, the unavailability of historical series of flows in watersheds makes the adequate design of reservoirs difficult. To overcome such difficulties, synthetic series of flows are currently being generated for the specific sections of the watercourses where these structures are to be designed. The present study aimed to evaluate two methods of generating synthetic series of flows applied to design the capacity of flow regulation reservoirs in conditions of limited data. A monitored hydrological region (Itapemirim River Basin, Espírito Santo, Brazil) and synthetic flow series generated according to the methodologies of Rodrigues (2017) and Cesconetto (2021) were used. The methodologies were tested by cross-validation, and the results were compared using graphs and statistical indicators to the results obtained with observed data, measured in fluviometric reference stations. After analyzing the statistical indicators, such as the coefficient of determination (R2), the Nash-Sutcliffe efficiency index (NSE), and the reservoir design quality index (IQD), it was concluded that the method proposed by Cesconetto (2021) showed a tendency to under-design the capacities of the reservoirs, mainly for lower flows to be regularized (β < 0.75). The method proposed by Rodrigues (2017) performed better than the method proposed by Cesconetto (2021) for the design of the capacity of flow regulation reservoirs under conditions of limited data in the Itapemirim River Basin.