Setting Goals in River Restoration: When and Where Can the River “Heal Itself”?

Ecological research demonstrates that the most diverse, ecologically valuable river habitats are those associated with dynamically migrating, flooding river channels. Thus, allowing the river channel to “heal itself” through setting aside a channel migration zone, or erodible corridor, is the most sustainable strategy for ecological restoration. The width and extent of channel can be set from historical channel migration and model predictions of future migration. However, the approach is not universally applicable because not all rivers have sufficient stream power and sediment load to reestablish channel complexity on a time scale of decades to years, and many are restricted by levees and infrastructure on floodplains that preclude allowing the river a wide corridor. A bivariate plot of stream power/sediment load (y axis) and degree of encroachment (urban, agricultural, etc.) (x axis) is proposed as a framework for evaluating the suitability of various restoration approaches. Erodible corridors are most appropriate where both the potential for channel dynamics and available space are high. In highly modified, urban channels, runoff patterns are altered, and bottomlands are usually encroached by development, making a wide corridor infeasible. There, restoration projects can still feature deliberately installed components such as riparian trees and trails with the social benefits of public education and providing recreation to underserved families. Intermediate approaches include partial restoration of flow and sediment load below dams and “anticipatory management”: sites of bank erosion are anticipated, and infrastructure is set back in advance of floods, to prevent “emergency” dumping of concrete rubble down eroding banks during high water.