Restoring Lateral Connectivity to Anthropogenic Riverscapes: Six Lessons From Stage Zero

ABSTRACT

Centuries of river modification, particularly straightening and incision, have severely reduced lateral connectivity between rivers and their floodplains. As a result, Stage 0 riverscapes, characterised by high lateral connectivity (e.g., anastomosing or wetland riverscapes), are now rare in anthropogenic landscapes. Restoration to a Stage 0 condition is gaining international momentum but remains relatively untested, particularly in human‐modified landscapes with novel constraints and challenges. Here, we provide a perspective on lessons learnt from restoration to Stage 0 in anthropogenically constrained settings. We draw on experience from the design, construction, and monitoring of two UK restoration projects, among the first valley‐floor reset rivers in Europe: the River Aller and the River Witham. Through infilling incised channels and regrading the floodplain, valley‐floor reset transformed the single‐thread, incised channels into multi‐thread, river‐ wetlandscapes and substantially increased river‐floodplain connectivity. In response, the water table elevation rose by about 1 m and baseflow wetted width increased by 9‐ to 20‐fold; for example, average baseflow wetted width at the Aller increased from 4 to 81 m (maximum baseflow width increased from 7 to 147 m). We summarise six lessons learnt: (1) Restoring dynamic riverscapes means embracing uncertainty and navigating societal expectations, (2) Stage 0 and valley‐floor reset are not appropriate everywhere: informed restoration is required, (3) Space exists for restoring river lateral connectivity, even in anthropogenically‐constrained catchments, (4) Interrupting long‐profile connectivity with grade‐control structures needs careful design, (5) Restoring lateral connectivity creates multi‐functional landscapes for water, wildlife and people, and (6) Structured, transdisciplinary research is needed to align restoration of natural processes with societal needs in a changing climate, and unlock the potential of river lateral connectivity to enhance biodiversity, river ecosystem services and climate resilience.