Case study:Experimental flood in the Cardener river

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Location: 42° 7' 10.36" N, 1° 36' 13.87" E

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Project overview

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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
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Parent multi-site project
This is a parent project encompassing the following projects	No

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Project summary

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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

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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

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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 Select a catchment/subcatchment Site Edit site Name WFD water body codes WFD (national) typology WFD water body name Pre-project morphology Reference morphology Desired post project morphology Heavily modified water body National/international site designation Local/regional site designations Protected species present Invasive species present Species of interest Dominant hydrology Dominant substrate River corridor land use Average bankfull channel width category Average bankfull channel width (m) Average bankfull channel depth category Average bankfull channel depth (m) Mean discharge category Mean annual discharge (m3/s) Average channel gradient category Average channel gradient Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) Project started Works started Works completed Project completed Total cost category Total cost (k€) Benefit to cost ratio Funding sources Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design Stakeholder engagement and communication Works and works supervision Post-project management and maintenance Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Hydropower Hydromorphology Continuity of sediment transport, Structure & condition of riparian/lake shore zones Biology Physico-chemical Other reasons for the project To protect or improve the “dynamic equilibrium of the river.” Measures Edit Measures Structural measures Bank/bed modifications Floodplain / River corridor Planform / Channel pattern Other Non-structural measures Management interventions Experimental flood Social measures (incl. engagement) Other Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Physico-chemical quality elements Edit Physico-chemical quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Any other monitoring, e.g. social, economic Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit links and references Link Description http://www.sciencedirect.com/science/article/pii/S1462901117301545 All information on this page is copied from this article written by Fernando Magdaleno. Supplementary Information Edit 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.