Suspended sediment load at the lowermost Ebro River (Catalonia, Spain)

Abstract

a b s t r a c tSeveral attempts to estimate the suspended load and the sediment deficit caused by the reservoirs have been carried out in the lower Ebro River. However, existing data are scarce, scattered along time and space, and obtained under different hydrological conditions and methods. This study estimate the presently suspended sediment load of the lowermost Ebro River, using field data collected during three consecutive years at different verticals of a cross-section and covering a large range of discharges. In addition, the daily suspended load for the last 30 years has been reconstructed and validated. The suspended load for the period 2007e2010 has been estimated at 84,000 t/y (±9800 t) while 99,500 t/y (±18,000 t) accounted for 1981e2010 period. Approximately, 80% of the total suspended load (period 2007e2010) has been transferred as inorganic load. A significant seasonal variability in the total (organic and inorganic) suspended load is observed. Therefore, two distinct cycling phases in the suspended load production and transfer has been inferred: an initial phase in which the sediment was prepared into the basin followed by a second phase in which most of the load was transferred downstream. These two phases are governed by the relative temporal location of the natural floods and the river regulation from the reservoirs. Nowadays, less than 1% of suspended load is transferred compared to pre-dams construction. The current levels of suspended load are very low and not enough to supply the material needed to maintain the delta elevation and avoid coastal retreat. The sustainability of the lower Ebro River and its delta could only be guaranteed by the implementation of a new reservoir management concept with the allocation of an appropriate liquid and solid flow regime.

Suspended sediment transport dynamics in rivers: Multi-scale drivers of temporal variation

“…Continuous sediment data (as well as data on catchment-scale variables that drive SS transport) in time and space are often scarce and collected with a range of different methods, that may not be comparable or consistent (Kettner et al, 2007;Rovira et al, 2015;Vanmaercke et al, 2011). Furthermore, large datasets require the use of complex data management techniques and advanced computational skills.…”

“…Changes in vegetation cover (e.g. due to crop rotation or natural seasonal variations) can cause a shift in the dominant sediment source to the river (Belmont et al, 2011;Rovira et al, 2015;Sun et al, 2015). Furthermore, erosion hotspots such as gullies can form on fields during storm events, causing an increased contribution of sediment from from a specific source.…”

“…Over long timescales, discharge or water yield (i.e. amount of water per unit of time) is often a good predictor of mean sediment loads (Horowitz, 2008;Rovira et al, 2015). Changes in rainfall patterns and amounts (e.g.…”

“…Changes in rainfall patterns and amounts (e.g. as associated with climate change) can cause significant changes in long-term SS loads (Kettner et al, 2007;Rovira et al, 2015;Walling, 2009). Furthermore, a shift in sediment source(s) can cause variable sediment loads under similar (constant) hydro-meteorological conditions.…”

“…as a result of tectonic activity or mass movements) can cause a (permanent) shift in the sediment supply (Bracken et al, 2015;Foerster et al, 2014;Fryirs, 2013). In addition, human interventions along the river network such as dam construction, flood alleviation schemes and soil and water conservation techniques can cause long-term legacy effects on the sediment supply to the river and/or the sediment transport capacity of the river (Chen et al, 2016;Rovira et al, 2015;Sun et al, 2015;Verstraeten et al, 2002;Wohl, 2015).…”