A Novel Approach to Assessing the Impacts of Dam Construction on Hydrologic and Ecosystem Alterations. Case Study: Castril River Basin, Spain

The hydrological situation of rivers, the fundamental driving force of river ecosystems, has continued to change due to the impact of human activities on water environments. Intra- and inter-annual variation also causes alterations in morphology, water quality, flora, and fauna in riparian zones. In this study, we present a novel approach to assessing the impacts of dam construction on flow river regimes and associated ecosystems in the Castril River (Spain). We compared the altered flows recorded from 2000 to 2018 with those of the natural regime of the river obtained from a previously calibrated hydrological model after the dam was put into operation in 2000. The Indicators of Hydrologic Alteration in RIverS (IAHRIS) method was used because it considers the inter- and intra-annual variabilities of Mediterranean climates. The results showed that the average differences in annual volumes between the natural and altered regimes were below 10% for normal and wet years but decreased to 20.49% in dry years. Thus, the alteration of usual values remained between excellent and good. In droughts and floods, values were from good to moderate, respectively. The flow rate control reduced flow peaks downstream from the dam, decreasing hydrological connectivity of river-riverine-flood plains. This decrease may reduce the transportation of sediment and organic resources, threatening habitat rejuvenation and floodplain biodiversity. This study provides a valuable tool to monitor the impacts of existing dams’ regulated regimens, allowing decision makers to develop flow management strategies and adaptation measures to meet ecological water requirements.