Case study:Experimental flood in the Pisuerga river

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Location: 42° 54' 23", -4° 31' 45"
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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
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Project summary

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The release of the experimental flood was performed in May 2014 in order to improve river processes downstream of the dam (the Requejada Dam), and to increase geomorphic and ecologic dynamics—nowadays impoverished by dam operation. The release was conducted under a number of constraints: (i.) ensuring the security of people and property (the flooding protocol had to be activated in the river); (ii.) accommodating an existing fishing preserve (Quintanaluengos), whose managers requested a specific day of the week for the discharge; (iii.) the hydraulic characteristics of the open-channel spillways in the dam (bottomwithdrawal was not used during the discharge).

The flood was approximately calculated to fill the ordinary channel, with a peak discharge of 96 m3 /s (associated with a recurrence interval of 2.4 years), duration of 10.5 h, and total volume of 0.82 hm3 . The ramping rates were adjusted via logistic functions, and modified in the hydrograph every 10 min (Fig. 2). In some river sections, the flow slightly overtopped the bank and created minor flooding in adjacent fields.

Monitoring surveys and results

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Analyses of the ecomorphological effects of the controlled flood were based on monitored changes in river morphology, suspended load transport, and bedload transport. River morphology was analysed in terms of variation in the geometry of two channel sections (one in a riffle, one in a pool) along the study sub-reach, variation in the granulometric composition in those two sections, and assessments of the refuge index for fishes (García de Jalón et al., 1993) and the river habitat index (IHF – Pardo et al., 2002). Suspended load was measured in 10 different water samples. Bedload transport was analysed in four different locations by measuring the size of pre-coloured coarse sediments over 1 × 1 m2 , and their relative motion along the channel (Leopold, 2006).

Monitoring showed that changes in the river micro- and mesohabitats were highly limited (Cebrián et al., 2015) (Table 1). The variables analysed were only slightly modified and the values of habitat indices were consistent with pre-flooding conditions. The value of the suspended load transport was low and in direct response to flow changes, which could indicate that the origin of the suspended sediments was in the channel downstream of the dam. For bedload transport, most removed particles were smaller than 64 mm and were concentrated in the pool area, likely due to the high increment of water velocity. Larger particles were occasionally removed or flipped.

Lessons learnt

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Thus, the experimental flood release showed limited geomorphic benefit, despite reaching (or even overtopping) the channel banks. Most changes were related to the transport of fine sediments, but they did not enhance habitat variation, or create new fluvial forms. Cebrián et al. (2015) suggested that the results may have been associated with extensive modification of the channel after six decades of dam management. Bed incision or unbalanced river morphology could be hampering the geomorphic influence of ordinary flows, requiring higher flows than theorised to enhance sound morphological and ecological changes.


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Catchment and subcatchment



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Project background

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Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
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Monitoring



Reasons for river 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 Increase geomorphic and ecologic dynamics


Measures

Structural measures
Bank/bed modifications
Floodplain / River corridor
Planform / Channel pattern
Other
Non-structural measures
Management interventions Experimental flood
Social measures (incl. engagement)
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Monitoring

Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

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Any other monitoring, e.g. social, economic

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Monitoring documents



Additional documents and videos


Additional links and references

Link Description
http://https://www.sciencedirect.com/science/article/pii/S1462901117301545 All information on this page is copied from this article written by Fernando Magdaleno.

Supplementary Information

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References

Cebrián, M., Minaya, R., Prieto, L., Rodríguez, J., Rodríguez, I., 2015. Primer ensayo de evaluación de caudal generador en la cuenca del Duero aguas abajo de la presa de Requejada (río Pisuerga, Palencia). In: Actas del II Congreso Ibérico de Restauración de Ríos (Restauraríos). Pamplona. pp. 54–64.

García de Jalón, D., Casado, C., Mayo, M., Gallego, B., García, J., Brotons, P., Hervella, F., Mingo, A., 1993. Fijación de caudales mínimos ecológicos para los ríos Esla, Pisuerga, Duero y Duratón. C.G.S. S.A.

Leopold, L.B., 2006. A View of the River. Harvard University Press, Cambridge Massachusetts (298 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 link to the article above.