Calibration procedure of regional flow duration curves evaluating water resource withdrawal from diversion dams

In the last decades, climatic changes in Mediterranean regions and frequent events of water resource scarcity in supply systems have required addressing the problem of increasing the inflows in storage reservoirs by connecting them to diversion dams. Usually, diversion dams do not have a large storage volume; consequently, these works are not able to regulate monthly flow, and they can divert to reservoirs only a part of river flow. In this field of research, this study aims to provide a procedure to evaluate water volumes withdrawn from diversion dams considering river flows and transfer flows. The procedure is founded by analysing 36 gauging stations in Sardinia (Italy), where a unique regional flow duration curve (FDC) can be defined. The effectiveness of regional evaluation of volume withdrawn, based on a monthly time scale analysis, has been investigated. The methodology allows finding optimal values of regional FDC parameters in order to better evaluate water resources withdrawn from diversion dams with respect to the current estimation used in the Sardinia Region Water Plan (SRWP). The current SRWP (RAS 2006) uses a fixed and extremely precautionary value of the FDC that underestimates withdrawal volumes. Moreover, a correlation analysis has been carried out in order to extend the evaluation of optimal FDC parameters for ungauged basins that allows to improve application of this procedure. Obtained results could allow to update the SRWP as highlighted in the final application to a real water system.