Case study:Experimental flood in the Ebro river
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Project overview
| Status | Complete |
|---|---|
| Project web site | |
| Themes | Environmental flows and water resources, Habitat and biodiversity, Hydromorphology |
| Country | Spain |
| Main contact forename | Fernando |
| Main contact surname | Magdaleno |
| Main contact user ID | |
| Contact organisation | |
| Contact organisation web site | |
| Partner organisations | |
| Parent multi-site project | |
| This is a parent project encompassing the following projects |
No |
Project summary
Flood releases from the dams were managed by the dam operator
(Endesa Generación S.A.) and controlled by the Ebro Basin authority.
After two consecutive dry years that led to substantial hydrological and
ecological concerns regarding river dynamics and the interaction with
human uses, an understanding was reached in 2002 among the hydropower
operator, the water authorities, and the scientific community to
promote the release of flushing flows. Except for in 2004 and 2005,
since then flushing flows have been performed on a regular basis, twice
a year (in autumn and spring). The discharged floods have normally
required the delivery of about 36 hm3 over 16 h, with peak flows of 900
to 1300 m3
/s (each).
Monitoring surveys and results
The design and downstream effects of
these floods have been monitored and discussed in several studies
(Batalla et al., 2006; Batalla and Vericat, 2009). In 2010, the flood
hydrograph was slightly modified because of progressive reductions in
the efficiencies of the 2002–2009 releases. Recently, Tena et al. (2013)
monitored flow and sediment transport, river bathymetry, and geomorphic
effects during the flushing flow of May 2008, and Tena et al.
(2014) focused on the spatial and temporal dynamics of suspended
sediment transport during the 2008–2011 flushing events. Those
experiments have made use of different sampling procedures (e.g.,
sonar backscatter for estimating macrophyte density, or a boardmounted
acoustic Doppler current profiler (ADCP) to measure discharge
and hydraulics). The sampling reach for many of those works
was a 12-km long reach located between the Flix Dam toe and the Ascó
gauging station.
Lessons learnt
The main overall effects on river geomorphology determined by
Tena et al. (2013, 2014) highlight the remarkable but irregular
effectiveness of flushing flows for macrophyte removal, which reaches
95% in the sub-reaches closer to the dam but decreases substantially
downstream. The released flood showed a significant ability to entrain
and transport sediment, but limited overall geomorphic impact. Mobilization
was primarily limited to fine-medium gravels, whereas bedload
rates remained low, likely due to the short duration of the events. The
seasonality of the releases was directly related to sediment availability,
with higher sediment peaks observed in autumn despite similar flushing
peaks. In parallel, different routing velocities were found for discharge
and sediments.
Some of these findings can be attributed to the fact that the rate of discharge increase per unit time during flushing flows is an order of magnitude higher than during natural events (Batalla and Vericat, 2009). Therefore, flushing flows show greater transport capacity than the natural floods, despite having a lower magnitude and shorter duration. The authors also concluded that the Lower Ebro River shows evidence of being under geomorphic adjustment 40 years after dam construction.
Most importantly, flushing flows in the Lower Ebro River have been shown to be compatible with hydropower operation. Gómez et al. (2014) calculated and compared the cost of the reduced power generation due to the release of flushing floods with the observed willingness to pay for river restoration programmes. They concluded that the provision of artificial floods had a cost equivalent to a small fraction of the energy delivered to the market and overall annual revenue (0.17% for the two annual flushing floods).
Image gallery
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Catchment and subcatchment
Site
Project background
Cost for project phases
Reasons for river restoration
Measures
MonitoringHydromorphological quality elements
Biological quality elements
Physico-chemical quality elements
Any other monitoring, e.g. social, economic
Monitoring documents
Additional documents and videos
Additional links and references
Supplementary InformationEdit Supplementary Information References Batalla, R.J., Vericat, D., 2009. Hydrological and sediment transport dynamics of flushing flows: implications for river management in large Mediterranean Rivers. River Res. Appl. 25 (3), 297–314. Batalla, R.J., Vericat, D., Palau, A., 2006. Sediment transport during a flushing flow in the lower Ebro River. In: In: Rowan, J.S., Duck, R.W., Werritty, A. (Eds.), Sediment Dynamics and the Hydromorphology of Fluvial Systems 306. IAHS Publication, Wallingford, UK, pp. 37–44. Tena, A., Książek, L., Vericat, D., Batalla, R.J., 2013. Assessing the geomorphic effects of a flushing flow in a large regulated river. River Res. Appl. 29 (7), 876–890. Tena, A., Vericat, D., Batalla, R.J., 2014. Suspended sediment dynamics during flushing flows in a large impounded river (the lower River Ebro). J. Soils Sediments 14 (12), 2057–2069. Gómez, C.M., Pérez-Blanco, C.D., Batalla, R.J., 2014. Tradeoffs in river restoration: flushing flows vs. hydropower generation in the Lower Ebro River, Spain. J. Hydrol. 518, 130–139. For more references, please check the link to the article above.
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