In this blog post, Virgilio Hermoso explains how to plan the recovery of longitudinal and lateral connectivity to restore free-flowing rivers in their latest study.
Rivers are more than lines on a map—they are living networks. They connect mountains to coasts, nourish floodplains, and support incredible biodiversity. But over the past century, we have fragmented these systems with dams, weirs, levees and floodwalls, breaking the natural flows that sustain both wildlife and people.
There’s now growing momentum to reverse this damage. In Europe, the new Nature Restoration Regulation sets a bold target: restore at least 25,000 km of free-flowing rivers by 2030 (EC, 2020). But what does “free-flowing” actually mean? And how do we make sure that restoration efforts lead to real ecological recovery—not just nice numbers?
A new study in Spain’s Duero River basin offers a roadmap. It shows how we can move beyond piecemeal restoration and instead plan strategically, targeting the barriers whose removal will deliver the biggest ecological benefits.
Beyond just removing dams
The EU defines a free-flowing river as one that’s not interrupted by artificial barriers and remains connected to its floodplain (Van De Bund et al., 2024). That means thinking not only about longitudinal barriers (like dams and weirs), but also lateral ones—such as levees or embankments that stop rivers from spreading into their natural floodplains.
Both dimensions matter. Longitudinal connectivity allows fish to migrate and sediment to move. Lateral connectivity allows rivers to flood their floodplains, supporting wetland species, recharging aquifers, and storing carbon.
Too often, however, restoration efforts focus mainly on removing old, unused dams—projects that are easier and cheaper. But this narrow focus can miss the bigger picture. For example, removing small barriers in headwater streams might help us hit kilometre targets, but won’t restore the ecological function of entire river networks.
Smarter planning, better results
To explore better options, this study used spatial planning tools (commonly applied in reserve design) to prioritise barrier removal across the Spanish portion of the Duero basin. Both longitudinal and lateral barriers were considered, mapping where their removal could reconnect habitats for freshwater fish and restore floodplain ecosystems.
This study also considered the opportunity cost of restoration. This cost depicts what might be lost or disrupted, like farmland or infrastructure, when we remove barriers. Four planning scenarios were tested, ranging from traditional uncoordinated approaches to more integrated strategies.
The results were clear: coordinated planning that considers both types of barriers and their costs leads to more effective and efficient restoration. It ensures, for instance, that floodplains restored by removing lateral barriers are also receiving natural flows upstream—a key ingredient for real ecological recovery. Uncoordinated approaches, in contrast, often failed to align these efforts, limiting their impact.
Looking ahead: from symbolic to functional restoration
As river restoration accelerates, it’s critical to look beyond total kilometres reconnected rivers and streams, as stated under the current policy context. Restoration must support not just structural connectivity, but functional recovery of rivers, including natural flows, species movements, sediment transport, and floodplain processes. Moreover, the European Union (EU) suggests focusing on removing old or unused barriers, as these projects typically involve fewer trade-offs or costs (EC, 2022).
However, removing only obsolete barriers may not be enough to meet ambitious river restoration goals. For example, while taking out many unused barriers in small headwater streams could reconnect up to 25,000 km of rivers, it would do little to restore the natural flow and ecological processes across entire river systems. In other words, this approach might be cost-efficient, but not very effective at improving the health of rivers overall.
Integrated planning offers a way to align ecological needs with policy goals. By identifying where coordinated barrier removal can restore whole ecosystems—not just fragmented pieces that usually results from opportunistic decisions, so we can bring rivers closer to being truly free-flowing.
Read the full article “Restoring free-flowing rivers: Planning for longitudinal and lateral connectivity recovery” in Journal of Applied Ecology.
