The role of reservoir operation in sediment contribution to water quality: an spatiotemporal scale analysis along the Guadalquivir river

In Mediterranean areas, where water scarcity is a common and recurrent problem, reservoirs play a key role in water resources management. Water allocation for different uses (e.g., urban, agricultural, hydroelectric, and ecological) can be affected by numerous external and internal factors limiting  their water quality condition in the reservoir and in the downstream areas. On the one hand, the loads of substances that alter water quality standards (e.g., sediments, nitrogen, phosphorus). On the other hand, the influence of the management and operation of the reservoir affects the streamflow natural regime. An example of these effects is found in the Guadalquivir river basin (Southern Spain), a highly regulated basin (113 reservoirs) with a relevant problem of sediment inputs throughout the river. The high sediment load is a consequence of the existence of high rates of erosion, favored by the complex orography, the high slopes, the extreme rainfall and the land uses, which partially or totally expose the surface of the land (e.g., olive groves). In this context, the objective in this work is to assess how water quality dynamics are affected by the management and operation of the Guadalquivir’ reservoirs system.

Historical information available for the study period 2011-2022 in 9 control points located in the Guadalquivir river and the main contributing subbasins was compiled,  including: 1) inflow, outflow, stored water volume and precipitation data in reservoirs on a monthly and daily basis, and 2) suspended solids concentration data on a monthly and hourly scale, all of them provided by public regional government data networks.

As result, the sediment loads received by the reservoirs located in the main axis of the Guadalquivir were estimated at daily, monthly, and annual time scales, showing direct relationships with water inputs. Two different scenarios depending on discharges and precipitation in the contributing subbasins were found to cause different effects in water quality: ordinary operation scenario and flood operation scenario. 

Therefore, the combined  understanding of the operational (discharges) and natural (rainfall events) drivers constitutes a relevant step for the effective, efficient, and sustainable management of water resources in reservoirs contributing to one of the challenges of society to comply with the Water Framework Directive in the current context of global warming.

Acknowledgements: This work has been funded by the project Integrated Management for the control of water inputs and sediments in reservoir systems in the Guadalquivir basin, with the economic collaboration of the European Funding for Rural Development (FEDER) and the Office for Economy, Knowledge, Enterprises and University of the Andalusian Regional Government.