2 research outputs found
Undamning the Douro river catchment: a stepwise approach for prioritizing dam removal
Dams provide water supply, flood protection, and hydropower generation benefits, but
also harm native species by altering the natural flow regime, and degrading the aquatic and riparian
habitats. In the present study, which comprised the Douro River basin located in the North of
Portugal, the cost-benefit assessment of dams was based upon a balance between the touristic
benefits of a dammed Douro, and the ecological benefits of less fragmented Douro sub-catchments.
Focused on four sub-catchments (Sabor, Tâmega, Côa and Corgo), a probabilistic stream connectivity
model was developed and implemented to recommend priorities for dam removal, where this action
could significantly improve the movement of potadromous fish species along the local streams.
The proposed model accounts for fish movement across the dam or weir (permeability), which
is a novel issue in connectivity models. However, before any final recommendation on the fate
of a dam or weir, the connectivity results will be balanced with other important socio-economic
interests. While implementing the connectivity model, an inventory of barriers (dams and weirs)
was accomplished through an observation of satellite images. Besides identification and location of
any obstacles, the inventory comprised the compilation of data on surrounding land use, reservoir
water use, characteristics of the riparian gallery, and permeability conditions for fish, among others.
All this information was stored in a geospatial dataset that also included geographical information
on the sub-catchment drainage network. The linear (drainage network) and point (barriers) source
data were processed in a computer program that provided or returned numbers for inter-barrier
stream lengths (habitat), and the barrier permeability. These numbers were finally used in the
same computer program to calculate a habitat connector index, and a link improvement index,
used to prioritize dam removal based upon structural connectivity criteria. The results showed
that habitat patch connectivity in the Sabor, Tâmega and Côa sub-catchments is not dramatically
affected by the installed obstacles, because most link improvement values were generally low. For the
opposite reason, in the Corgo sub-catchment, obstacles may constitute a relatively higher limitation
to connectivity, and in this case the removal of eight obstacles could significantly improve this
connectivity. Using the probabilistic model of structural connectivity, it was possible to elaborate
a preliminary selection of dams/weirs that critically limit stream connectivity, and that will be the
focus of field hydraulic characterization to precisely determine fish movement along the associated
river stretches. Future work will also include the implementation of a multi-criteria decision support
system for dam removal or mitigation of the critical structures, as well to define exclusion areas for
additional obstaclesinfo:eu-repo/semantics/publishedVersio