Author(s): Francesca Di Concilio; Luis Garrote; Giacomo Viccione

Linked Author(s): Giacomo Viccione

Keywords: Environmental Flow; EFMs; Water needs; Reliability index; Eco-deficit

Abstract: Recently, the management of environmental flow (EF) has become a key issue in water policy due to the ongoing climate change, with longer, more frequent drought periods, and competing water uses stressing the resource. Therefore, the issue of balancing ecosystem needs and human demands has become an important matter to be tackled, when allocating EF and managing water resources. In this framework, this study aims to analyse the trade-off between water requirements in terms of multiple anthropic demands and environmental needs. The study case concerns the Santa Teresa Reservoir in the Tormes river, in the Castilla y Leon region of Spain. The reservoir supplies water for the irrigation demand and the urban demand of Salamanca district. The urban demand and the EF represent constraints to be absolutely fulfilled. Trade-off optimization is carried out by comparing three different scenarios in which multiple water needs and the EF follow a prioritisation. Scenario #1 is defined as the reference basis, in which existing conditions, consisting in the water supply to the Salamanca urban district, Tormes, La Maya, Villagonzalo irrigation systems, are implemented. User defined thresholds at the Santa Teresa Reservoir alone are implemented in Scenario #2, whereas the inflow of Rio Almar, tributary of Tormes, is considered in conjunction with the reservoir thresholds in Scenario #3. Among the considered environmental flow methods (EFMs), four allowed the definition of the EF with minimum deficits at the users. Trade-off between multiple water needs and the EF was assessed with the eco-deficit EFd, defined as the difference between the specified ecological flow and the actual flow released. For the Tormes River, EFd ranged from 0.04 hm3/y, for the 20% of average summer flow (20%ASF), to 56,14 hm3/y, for 40% of mean monthly flow (40%MMF). Demand satisfaction in the analyzed was evaluated using the supply reliability index Ir defined as the ratio between the yearly averaged supply to the users and the water demand. The obtained mean at the network nodes of the maximum Ir, are 81,7 %; 95,8%; 96,5%; for scenarios 1,2 and 3 respectively. Results highlighted that no single action, even if operated on a simple system, is decisive in isolation. Only the combination of actions can generate a good compromise between water demand for irrigation and urban supply and environmental needs.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022675

Year: 2022