Suspended sediment dynamics during flushing flows in a large impounded river (the lower River Ebro)
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The aim of this work was to improve the understanding of the spatial and temporal dynamics of suspended sediment transport during flushing flows in a large regulated river, the lower River Ebro (NE Spain).
Materials and methods
Relationships between sediment and discharge (i.e. discharge (Q)–suspended sediment concentrations (SSC)) were examined during six flushing flows using continuous discharge and turbidity records obtained at six monitoring sections distributed along the lower Ebro River for the 2008–2011 period.
Results and discussion
Analyses revealed marked spatial and temporal patterns. At the spatial scale, the Q–SSC relationships were mostly influenced by the different routing velocity of discharge and sediment waves. At the upstream sections, the sediment peak usually preceded peak discharge (i.e. clockwise loop); however, flow routing through the 85-km channel length tends to increase the lag between them, modifying the hysteresis towards counter-clockwise patterns in the downstream direction. At the temporal scale, the season when the artificial releases were performed strongly influenced the sediment availability, with similar-magnitude flushing flows generating higher sediment peaks in autumn than in spring.
These results are of great interest in order to reinforce the flushing flows programme in the lower Ebro River, so as to help achieve the sustainability of the riverine and deltaic ecosystems.
KeywordsDams Flushing flows Hysteresis River Ebro Suspended sediment transport
This research has been carried out within the framework of a series of research projects funded by the Spanish Ministry of Education and Science 2002–2012 (REN2001-0840-C02-01/HID, CGL2005-06989-C02-02/HID, CGL2006-11679-C02-01/HID, CGL2009-09770/BTE); the Spanish Ministry of Economy and Competitiveness, through the project Consolider Ingenio 2010 CSD2009-00065; and by research contracts to (a) study the polluted sediments in the Flix Reservoir 2006–2008, funded by the Spanish Ministry of Environment and the Catalan Water Agency; (b) characterise riverbed conditions under macrophyte cover in the lower Ebro (2009–2011), funded by Ebro Water Authorities—CHE, through URS-España; and (c) to study hydraulic and sedimentary characteristics of selected flushing flows, funded by ENDESA Generación SA. The second author has a Ramon y Cajal Fellowship (RYC-2010-06264) funded by the Spanish Ministry of Science and Innovation. Special thanks are due to the Ebro Water Authorities and Endesa Generación SA for their collaborative support during the investigation, providing assistance, and useful data. The support of the members of the Fluvial Dynamics Research Group (RIUS) is greatly appreciated. We are grateful to Mark Smith for reviewing the first version of this manuscript and to Josep Carles Balasch for providing insights into the river–groundwater exchange processes that help us to assess the validity of the Q routing procedure.
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