Effects of environmental flows on hydrological alteration and reliability of water demands

This paper presents a methodology to assess the effects of management strategies of environmental flows on the hydrological alteration of river basins on a daily scale. It comprises the collection and analysis of data, the implementation and calibration of a water allocation model; the computation of the natural flow regime; and the estimation, normalization, and aggregation of hydrological alteration indicators to obtain a global indicator of the hydrological alteration. The methodology was applied to a case study in the Iberian Peninsula: The Orbigo River basin, which belongs to the Duero River basin district. For that, three management scenarios were defined: the current scenario, a scenario without any environmental flow and the scenario with the environmental flows initially projected for the period 2022-2027. These scenarios were modelled with the SIMGES water allocation model, which is calibrated in the study site, and the hydrological alterations in four river stretches with different locations and characteristics were assessed. The implications of each environmental flow scenario on the demand reliabilities were also analysed. The global indicator of hydrological alteration obtained in the projected scenario was greater (better) than those of the other two scenarios, but the reliabilities of the water demands were worse. The methodology proposed in this work can be helpful to design environmental flow regimes considering both the effects on the hydrological alteration and the implication on the water demand reliabilities.