Case study:Experimental flood in the Cardener 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
The Sectorial Plan of Environmental Flows (ACA, 2005) requires the
annual release of one effective discharge from the dam (the Llosa del Cavall Dam), in order to
protect or improve the “dynamic equilibrium of the river.” This
controlled release lasts 24 h, and its seasonality is linked to the natural
period of occurrence of ordinary floods in the river. Presently, the Plan
defines a peak discharge of 8.4 m3
/s for the controlled flood. Ramping
rates are defined as follows (t indicates 1-h time gaps):
• Rising limb: Qt+1 (maximum) = 1.8Qt
• Recession limb: Qt+1 (minimum) = 0.7Qt
To study the adequacy of this value, the Catalan Water Agency (with support from the Technical University of Catalonia) decided to comparatively monitor in 2015 the effects of three different peak flows that were lower than the 2-year recurrence flood (i.e., 4, 8, and 12 m3 /s; Pallarés and Martín-Vide, 2015; Fig. 3). The first and smaller flood was released between March 3 and 4, the second was released between April 13 and 15, and the third and larger was released between June 15 and 16. The base environmental flow released from the dam is commonly around 1.5 m3 /s.
Monitoring surveys and results
Analyses of the ecomorphological
effects of the controlled flood in the Cardener River were based on
monitored changes in river morphology, suspended load transport, and
bedload transport (Pallarés and Martín-Vide, 2015). Changes in rivermorphology were quantified by determining geomorphic variation at a
number of channel sections along the study sub-reach. Suspended
sediments were sampled pre- and post-event at different channel
locations. Bedload changes were analysed by (i.) colouring portions
of gravel bars with spray and tracing the modifications, and (ii.)
measuring shifts in the granulometric curves of selected channel sites
after flood occurrence. Other observations made included a visible
assessment of the changes in trophic conditions, riverbed armoring, and
an assessment of the IHF index (Pardo et al., 2002).
Main morphologic changes found under post-event conditions occurred in the river sub-reach closer to the dam toe. During the managed floods with higher flows (i.e., 8 and 12 m3 /s), erosion rates reached 1.16 m3 per linear meter at the upper sampled station (width = 16.5 m). Changes were especially pronounced in the riffle areas. By contrast, lower stations did not show any major morphological changes, and the 4 m3 /s event did not result in significant morphological activity in the channel.
Suspended transport was relatively pronounced during the 8 and 12 m3 /s events; suspended sediment concentrations reached 0.22–0.37 g/l at some sampling sites. This fine load was generated inside the study reach, mostly from the immediacy of the dam, and did not stem from the upper basin. With respect to bedload, significant transport of particles occurred during the three flood events. The extent of transport was greater (and the size of the transported particles bigger) for the higher-flow flood events. Granulometric analyses showed an increase in grain size in the riverbed, and a reduction (or elimination) of clogging conditions by fine sediments.
Lessons learnt
In summary and according to Pallarés and Martín-Vide (2015), ecogeomorphic activation of the 7-km long study reach may
be optimised by the release of 12 m3
/s flooding events; a peak rate
higher than the present legally defined rate of 8.4 m3
/s. Suspended and
bedload transports are particularly relevant at rates of 8 m3
/s and
higher; especially in the sampling sites closer to the dam toe. However,
both types of transport could be primarily associated with in-thechannel
sources, which could be progressively hampered by the existing
lack of upstream inputs. Habitat conditions exhibited a limited positive
trend with increasing discharge. On the basis of these findings, the authors suggested that larger peak discharges could be desirable, but
would also require the implementation of measures for increasing
sediment discharge from the dam in order to avoid progressive incision
and further sediment shortages along the study reach.
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Catchment and subcatchment
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Project background
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Measures
MonitoringHydromorphological quality elements
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Any other monitoring, e.g. social, economic
Monitoring documents
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Additional links and references
Supplementary InformationEdit Supplementary Information References Agència Catalana de l’Aigua (ACA), 2005. Pla Sectorial de Cabals de Manteniment de les conques internes de Catalunya. Generalitat de Catalunya; Departament de Medi ambient i Habitatge Pallarés, A., Martín-Vide, J.P., 2015. Efectes de l'alliberament de cabal generador a preses de Catalunya. Treball Final de Grau. Marítima i Ambiental, Escola Técnica Superior d́ Enginyeria de Camins, Canals y Ports. Departament d’Enginyera Hidràulica, Universitat Politècnica de Catalunya (UPC), Barcelona (83 p.). Pardo, I., Álvarez, M., Casas, J., Moreno, J.L., Vivas, S., Bonada, N., Alba-Tercedor, J., Jáimez-Cuéllar, P., Moyà, G., Prat, N., Robles, S., Suárez, M.L., Toro, M., VidalAbarca, M.R., 2002. El hábitat de los ríos mediterráneos: Diseño de un índice de diversidad de hábitat. Limnetica 21 (3-4), 115–133 For more references, please check the article link above.
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