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Rivers are the lifeblood of ecosystems, weaving through landscapes to connect habitats, sustain biodiversity, and provide vital resources to communities. Yet, rivers around the world are disrupted by outdated dams, weirs, culverts, and other blockages that fragment habitats, block fish migration, and degrade ecological health. The consequences are far-reaching, threatening not only ecosystems but also the communities that depend on healthy rivers.
Research by the European Open Rivers Programme has highlighted both the urgent need for action and the immense potential of dam removal to restore ecosystems, improve biodiversity, and revive natural river connectivity.
Since 2022, Princeton Hydro President and Principal Geoffrey M. Goll, PE — an expert in water resources engineering — has been collaborating with organizations in Portugal to advance shared goals of river restoration and ecosystem revitalization. In October 2024, Mr. Goll traveled to Portugal, where he met with the organizations driving forward the country’s ecosystem restoration efforts and visited the sites of three key projects he has, or is currently collaborating on.
This blog explores those restoration efforts, highlighting how they address the challenges of river fragmentation while establishing a blueprint for future restoration efforts.
One of the most significant examples of these collaborative restoration efforts is the groundbreaking Galaxes Weir Removal project, which set the stage for future initiatives by addressing river fragmentation on Portugal’s Odeleite River.
Galaxes Weir Removal project in Portugal’s Algarve Region marked the country’s first civil removal of an obsolete river barrier to benefit migratory fish species. Associação Natureza Portugal in association with World Wildlife Fund Portugal (ANP/WWF), a non-profit NGO dedicated to the conservation of nature and the protection of the planet, reached out to Mr. Goll and Ms. Lisa Hollingsworth-Segedy of American Rivers, to undertake this pioneering effort.
Completed in March 2023, the removal of the 2-meter-high Galaxes Weir restored 7.7 kilometers of river connectivity, aiding in the preservation of critical fish species such as the Spanish minnowcarp (Anaecypris hispanica) and the critically endangered European eel (Anguilla anguilla). By improving river flow and ecological conditions, the project also bolstered economically vital fisheries, enhanced recreational opportunities, and supported local tourism, establishing a model for future restoration initiatives. Funding for the Galaxes Weir removal was provided by the European Open Rivers Programme (EORP), a grant-giving organization dedicated to restoring European rivers. The international partnership that brought Mr. Goll and Ms. Hollingsworh-Segedy into the fold was facilitated by connections made through the World Fish Migration Foundation. He and Ms. Hollingsworth-Segedy were asked to provide guidance on the de-construction of this concrete structure.
The success of the Galaxes Weir Removal project highlights the importance of both engineering knowledge and techniques, as well as community engagement. By involving local communities throughout the process, the project fostered a sense of shared responsibility and ensured that the ecological and cultural value of the river was preserved. It also underscored the benefits of dam removal as a swift and effective strategy to enhance biodiversity and promote sustainable river management.
The photos below, taken by ANP/WWF, depict the Galaxes Weir project site before, during, and after removal:
Click here to see more photos, watch videos of the removal process, and read more detailed information about this groundbreaking project.
Building on the success of the Galaxes Weir removal, the ANP/WWF team expanded its efforts to Santarém, Portugal, northeast of Lisbon, on the Perofilho Stream, a tributary of the Tejo River. The Perofilho Weir, a 2-meter-high concrete barrier, fragmented habitats and disrupted the natural flow of the stream. The National Authority for Nature and Forests Conservation (ICNF) identified the Galaxes Weir as one of the obsolete barriers to be removed to improve fish and overall biodiversity in the area and restore fluvial connectivity.
This restoration project, initiated in 2023, was led by ANP/WWF in collaboration with SOS Animal (weir owner) and the Santarém Municipal Council (local government). Mr. Goll was invited to design the removal of the concrete weir, including innovative solutions such as the use of live timber crib walls for stream bank stabilization. He also provided consultation to the onsite construction manager during the removal process and conducted a final site walkthrough following construction, offering recommendations to ensure long-term success.
The photos below, provided by EORP and by ANP/WWF, depict the Perofilho Weir project site before, during, and after removal:
The Perofilho Weir removal, completed in October 2024, restored 2.2 kilometers of the Perofilho Stream—nearly half its total length—reconnecting it with the Tejo River. This comprehensive restoration project addressed sediment management, habitat rehabilitation, and flood risk reduction, resulting in significant improvements to water quality and ecological health. Key species benefiting from these efforts include the Eurasian otter (Lutra lutra) and the Iberian painted frog (Discoglossus galganoi). Notably, it also enabled the first research into fish species inhabiting the stream.
This milestone project not only revitalized a critical aquatic ecosystem, it also established a blueprint for future river restoration efforts in Portugal and beyond.
During Mr. Goll’s visit to Portugal in October 2024, he toured the Perofilho Weir removal site alongside Maria João Costa, Water Coordinator of ANP/WWF. Together, they participated in a live video event hosted by the World Fish Migration Foundation, celebrating the project’s success. Broadcasted on the Dam Removal Europe YouTube channel, the event highlighted the restoration effort’s impact on biodiversity and river connectivity. If you missed the live broadcast, the recording is available online. Watch now:
The Oeiras River in western Algarve winds through rural landscapes, agricultural zones, and small towns before merging with the Arade River. This intermittent Mediterranean stream supports native and endangered species and serves as a habitat for some of Portugal’s most iconic mammals.
Recognizing the river’s ecological significance, the ICNF identified it as a high-priority conservation area with potential for impactful restoration. In collaboration with the company Somincor, ICNF contracted ANP/WWF to evaluate the removal of nine barriers along the river, beginning with the upstream Horta Fialho Weir.
To complete the proposed work, ANP/WWF is undertaking several activities, including feasibility assessments, local community and stakeholder engagement, and public environmental education. ANP/WWF engaged Princeton Hydro to prepare the design and specifications for the Horta Fialho Weir removal and develop concept designs for the eight (8) additional barriers.
In October 2024, Mr. Goll spent a week in the field alongside ANP/WWF, surveying the Oeiras River and its tributaries, documenting blockages and ecosystem conditions, meeting with local dam owners and community members, and gathering field measurements to inform the designs and specifications.
The photos, kindly provided by Maria João Costa, Water Coordinator of ANP/WWF, show Mr. Goll and Ms. Costa in the field during the October 2024 survey of the Oeiras River and its tributaries.
The removal of the Horta Fialho Weir will reconnect 2.34 kilometers of the river and set the stage for removing the eight additional barriers, which would ultimately restore 143.4 kilometers of river connectivity. This ambitious initiative is expected to significantly enhance the river’s ecological health and improve habitats for native and endangered species, including freshwater mussels (Unio tumidiformis, Anodonta anatina, Unio delphinus), and their host fish (Squalius spp.), the migratory European eel (Anguilla anguilla), the Iberian lynx (Lynx pardinus), and the Eurasian otter (Lutra lutra).
Beyond ecological benefits, the project offers a unique opportunity to raise awareness about the advantages of dam removal and the critical importance of biodiversity conservation across Portugal. The European Open Rivers Programme is funding this landmark restoration effort.
Portugal’s ecosystem restoration projects illustrate the impact of international collaboration and knowledge exchange. By removing barriers, reconnecting habitats, and revitalizing ecosystems, these efforts are paving the way for a healthier future for rivers and the communities that depend on them. Through continued partnerships and mutual support, the journey toward sustainable environmental stewardship remains hopeful and promising.
Building on the success of these initiatives, Mr. Goll and the Princeton Hydro team look forward to continuing their work in Portugal and beyond, offering technical expertise in ecosystem restoration and barrier removal to support similar efforts around the world.
This work would not be possible without the dedication of ANP/WWF, the European Open Rivers Programme, the Dam Removal Europe team, The National Authority for Nature and Forests Conservation, Herman Wanningen, and all the local landowners who were committed to the restoration of the Oeiras River. Their commitment to river restoration and biodiversity conservation serves as an inspiration, demonstrating the transformative power of collaboration and shared vision. We encourage you to click the links provided to learn more about these vital organizations.
Princeton Hydro has successfully designed, permitted, and overseen the removal of over 84 dams to date. Mr. Goll holds a B.S. in Civil Engineering from Rutgers University and a Master of Engineering Management from UW–Madison. His knowledge encompasses water resources and geotechnical engineering, including sediment management, stream and river restoration, stormwater management, green infrastructure, freshwater wetland and coastal marsh design, dam design, and dam removal. He is recognized as a distinguished leader in advancing innovative and effective solutions for river restoration.
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