Case study:Experimental flood in the Pisuerga 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 release of the experimental flood was performed in May 2014 in
order to improve river processes downstream of the 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
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.
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.
Lessons learnt
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
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