Reservoir impacts downstream in highly regulated river basins: the Ebro delta and the Guadalquivir estuary in Spain

Abstract

Abstract. Regulation by reservoirs affects both the freshwater regime and the sediment delivery at the area downstream, and may have a significant impact on water quality in the final transitional water bodies. Spain is one the countries with more water storage capacity by reservoirs in the world. Dense reservoir networks can be found in most of the hydrographic basins, especially in the central and southern regions. The spatial redistribution of the seasonal and annual water storage in reservoirs for irrigation and urban supply, mainly, has resulted in significant changes of water flow and sediment load regimes, together with a fostered development of soil and water uses, with environmental impacts downstream and higher vulnerability of these areas to the sea level rise and drought occurrence. This work shows these effects in the Guadalquivir and the Ebro River basins, two of the largest regulated areas in Spain. The results show a 71 % decrease of the annual freshwater input to the Guadalquivir River estuary during 1930-2014, an increase of 420 % of the irrigated area upstream the estuary, and suspended sediment loads up to 1000 % the initial levels. In the Ebro River delta, the annual water yield has decreased over a 30 % but, on the contrary, the big reservoirs are located in the main stream, and the sediment load has decreased a 99 %, resulting in a delta coastal regression up to 10 m per year and the massive presence of macrophytes in the lower river. Adaptive actions proposed to face these impacts in a sea level rise scenario are also analyzed.

High-Resolution Interannual Evolution of the Dune Toe at a Mesotidal Barrier (Camposoto Beach, SW Spain)

“…From the analysis of washover dimensions and morphologies, and based on the proposal by Matias et al [8], it can be concluded that the main cause of washover generation is structural erosion [39]. This, together with a lack of sediment derived in large part from heavy dam constructions in the rivers that nourish the SW coast of the Iberian Peninsula [54,55], can hinder dune recovery, and it is linked to a long-term erosion trend. Evidence of this sediment shortage includes the nourishment works performed at Camposoto over recent decades [35], as well as the outcropping of the fossil salt marsh layers of the foreshore (Figure 12), like the episodes described by Burningham [18] and Davis and Fitzgerald [19] in similar spit-barrier systems.…”

The role of the Gulf of Cadiz circulation in the redistribution of trace metals between the Atlantic Ocean and the Mediterranean Sea

“…The estuary is tidal, with the behaviour of the river discharge and the renewal of the estuarine water jointly determined by the tidal and neighbouring coastal currents (Ojeda et al, 1995). Finally, the GD river has a length of 657 km and a drainage area of about 57,400 km 2 (Polo et al, 2016). Its current mean discharge rate is 90 m 3 s À1 , with a marked interannual variability (see Fig.…”

Implications of water management representations for watershed hydrologic modeling in the Yakima River basin

“…Since the 1990s, increasing demands for irrigation, municipal water consumption, and critical environmental flow for conserving wildlife habitats in the context of climate change have challenged water resource management in the basin. Thus, there is an urgent need to reliably simulate water cycling in the basin to provide a solid basis for policy formulation and management actions which strive to achieve a balance among water demands for different purposes (Poff et al, 2003).…”