Cumulated dam impact in France, Spain and Portugal (SUDOANG project)

1. SUDOANG PROJECT

The SUDOANG project has provided common tools and assessment methods to managers to support the eel conservation in the SUDOE zone (Southern France, Spain and Portugal). One of the goals of the project was to develop an eel abundance and distribution atlas in the three countries, based on the results of the implementation of Eel Density Analysis (EDA). This model extrapolates eel abundance from a range of river segments sampled by electrofishing, to the whole river and lake network, by considering how eel abundance, size and sex vary according to different parameters related to eel habitat. To do this, we have created a dataset of "cumulated dam impact" which compiles different ways of calculating cumulated height from the sea.

2. SUDOANG DATABASE

The dataset on cumulated impact was first derived from information on obstacles collected by the SUDOANG project. Obstacles data for the three countries were imported in the SUDOANG database (deliverable 2.2.1), whose structure is inherited from the DataBase for EEl (DBEEL), developed during a European research project (POSE - Pilot projects to estimate potential and actual escapement of silver eel, Walker et al., 2011). This database is designed to contain all data relative to eel biology and anthropogenic pressures applying to eel. During the course of SUDOANG, this database was used and ameliorated. 

In France the obstacles were compiled from three pre-existing different databases:

• the Referential of flow obstacles (ROE) ,
• the Information of Ecological Continuity (ICE) and
• the Flow Obstruction Database (Base de Données des Obstacles à l'Ecoulement, (BDOE).

The data we have integrated into the SUDOANG 1.0.4. database came from a database dump of the 12th September 2019. The inventory includes bridges that have a significant impact on river continuity.

In Spain, data came from:

• the MITECO Ministry,
• the Basque Water Agency (URA),
• the Catalan Water Agency (ACA),
• the University of Girona,
• the University of Córdoba,
• the Xunta of Galicia and
• the AMBER project.

In Portugal the data came from:

• the Portuguese Water Agency (APA),
• the University of Lisbon,
• the University of Porto and
• the AMBER project.

3. DATA DESCRIPTION

• Data collected on artificial obstacles

Artificial obstacles were classified into 10 types according to the Adaptive Management of Barriers in European Rivers (AMBER) project. Some additional types (e.g., penstock pipes) were added to identify other obstacles in national databases that did not fit the AMBER classification (Table 1). Sometimes dams from different branches are connected, creating a dam-network. In those cases, we have only kept the dam(s) in the main course and use a hierarchical classification of the dams to only consider the cumulated height from the sea to the reference dam. We included only obstacles that are presently standing, i.e., not planned, under construction, or destroyed. Dikes, longitudinal control structures and grates were excluded.

We have projected obstacles on the SUDOANG river network at the nearest point within 300 m. To avoid projecting large obstacles in the wrong location in the southwestern France, SUDOANG experts have reviewed and corrected this information. We have also used an algorithm that extracts the best obstacle height data from the three existing databases in France. In the Iberian Peninsula, data providers validated and corrected obstacle location and height using a Shiny application developed by the project, in which they could directly correct the height of obstacles.

Table below shows the attributes associated with the obstacles table (csv delimiter ",").

• Modeling missing data and estimating the cumulative impact on obstacles

For those obstacles missing height information, we have calculated height using a Generalized Linear Models (GLM of log transformed height, family = gaussian, link = identity. In France the model was based on river segment slope, river segment median flow and hydrographic basin. In the Iberian Peninsula, we have implemented a simpler model based on obstacle type, as information about flow or slope was not available for all river segments.

The cumulated impact of obstacles was assessed by creating a table joining each river segment with all the dams located in the downstream course. Using this, various metrics were computed using different assumptions concerning the effect of obstacles. The heights were power transformed to test for a different effect of obstacle’s height (the cumulated effect of two obstacles of 1 m might be different than the cumulated effect of a single obstacle of 2 m), and functions were developed to calculate cumulated obstacle transformed variables. Other variables were also tested. In fact, tests in France have shown that factors such as presence of a fish pass, and eel passability did not improve the model performance. For this reason, but also because in the Iberian Peninsula this type of information was too limited, we used dam height to model the cumulative height of obstacles at a given river segment. 

Table below shows the attributes associated with the cumulated_dam_impact_SUDOANG table (format Rdata - to be read with the R software, this will load as a data.frame called datadam).

* Project co-financed by the INTERREG SUDOE Programme through the European Regional Development Fund (ERDF).

4. READ MORE

• Eel data (Anguilla anguilla) and associated environment variables used to fit the EDA model in the SUDOE area (SUDOANG project) (10.5281/zenodo.7964967)
• Atlas of European Eel Distribution (Anguilla anguilla) in Portugal, Spain and France (10.5281/zenodo.7546419)
• Electrofishing data for eel in Spain and Portugal (SUDOANG project) (10.5281/zenodo.8207785)