Case study:Fish pass on the Najerilla River

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Location: 42° 27' 55", -2° 42' 21"
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Project overview

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Status Complete
Project web site
Themes Habitat and biodiversity
Country Spain
Main contact forename Rincón Sanz
Main contact surname Gonzalo
Main contact user ID
Contact organisation
Contact organisation web site
Partner organisations
Parent multi-site project
This is a parent project
encompassing the following
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Project summary

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The concerning weir was small and it served to supply irrigation communities in the area. In origin, the weir was of an approximate height of 40 cm. However, over time, an erosion was generated downstream the obstacle so its height increased to 1.5 meters and the weir became impassable. This was a problem since the community of fish in the river is very varied and this obstacle became a serious problem for its movement through the river.

Among the variety of existing fishways, in this particular case the chosen option was the installation of a rock ramp. This type of device mimics the natural conditions of the river. Usually have an inclined plane with a slope always ≤ 10%, in which blocks of stone of considerable size are inserted.

The advantages of this kind of devices are:

- It offers better conditions of passage (both upstream and downstream).

- Its appearance is better integrated with the environment.

- It allows the evacuation of flows (including ecological flows).

- It does not alter the structure of the obstacle.

- Low maintenance cost.

On the other hand the disadvantages are:

- It requires more space to be built.

- It needs more flow to ensure their functionality.

- It is only applicable to obstacles with small-medium heights (less than 2.5 m).

In this case, the Najerilla River presents marked contrasts of flow between high and low waters, so that it was proposed to make two sections of the fishway: a deeper central ramp of about 10 m wide and two shallower lateral ones of 4 m wide each. Stone blocks of about 1 meter diameter were placed so that no channels were formed where the water reaches a high speed and impedes the ascent of the fish. Finally, gravels have been embedded in the surface of the ramp in order to increase the roughness of the ramp bottom. The slope of the ramp was 5%

Monitoring surveys and results

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The implementation of monitoring programs is essential to evaluate the correct functioning of the fishways. In this regard, there is a lack of information about this action.

Lessons learnt

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Image gallery

Rock ramp in the Najerilla River with a low flow (left) and with a higher flow (right). Photo credits: Pedro Boné.

Catchment and subcatchment


WFD water body codes
WFD (national) typology
WFD water body name
Pre-project morphology
Reference morphology
Desired post project morphology
Heavily modified water body No
National/international site designation
Local/regional site designations
Protected species present No
Invasive species present No
Species of interest Brown trout (Salmo trutta), Luciobarbus graellsii, Barbus meridionalis, Parachondrostoma miegii, Gobio lozanoi
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 10 - 100 m³/s
Mean annual discharge (m3/s) 16.5
16.5 m³/s
16,500 l/s
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)

Project background

Reach length directly affected (m)
Project started
Works started
Works completed
Project completed
Total cost category 50 - 100 k€
Total cost (k€) 61.8
61.8 k€
61,800 €
Benefit to cost ratio
Funding sources Part of this work was supported through FEADER funding (European funding to improve the rural development).

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

Reasons for river restoration

Mitigation of a pressure Barriers to fish migration
Hydromorphology Continuity for organisms
Biology Fish: Abundance, Fish: Species composition
Other reasons for the project It generates a profit in the agricultural communities of the zone.


Structural measures
Bank/bed modifications Creation of fish passes
Floodplain / River corridor
Planform / Channel pattern
Non-structural measures
Management interventions
Social measures (incl. engagement)


Hydromorphological quality elements

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

Biological quality elements

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

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

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

Monitoring documents

Additional documents and videos

Additional links and references

Link Description A link on the Wetlands International website to a document that describes the project.
http:// All information on this page is copied from the document mentioned above which is written by Ecohidráulica, S.L.

Supplementary Information

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Boné P. (2015) Rampa para peces en el Río Najerilla (Torremontalbo, La Rioja). Buena práctica para recuperar la continuidad del curso fluvial.

Confederación Hidrográfica del Ebro (2009). Pasos de peces para permeabilizar estructuras transversales en la cuenca del Ebro. Tecnoma.

Sanz-Ronda, J. et al. (2015) Sistemas de adaptación de pasos de agua a la migración de los peces. Ejemplos realizados en España. Seminario técnico LIFE-Miera: Gestión de un corredor ecológico.