Contrasting Landscape Influences on Sediment Supply and Stream Restoration Priorities in Northern Fennoscandia (Sweden and Finland) and Coastal British Columbia

Abstract

Sediment size and supply exert a dominant control on channel structure. We review the role of sediment supply in channel structure, and how regional differences in sediment supply and land use affect stream restoration priorities. We show how stream restoration goals are best understood within a common fluvial geomorphology framework defined by sediment supply, storage, and transport. Land-use impacts in geologically young landscapes with high sediment yields (e.g., coastal British Columbia) typically result in loss of in-stream wood and accelerated sediment inputs from bank erosion, logging roads, hillslopes and gullies. In contrast, northern Sweden and Finland are landscapes with naturally low sediment yields caused by low relief, resistant bedrock, and abundant mainstem lakes that act as sediment traps. Land-use impacts involved extensive channel narrowing, removal of obstructions, and bank armouring with boulders to facilitate timber floating, thereby reducing sediment supply from bank erosion while increasing export through higher channel velocities. These contrasting land-use impacts have pushed stream channels in opposite directions (aggradation versus degradation) within a phase-space defined by sediment transport and supply. Restoration in coastal British Columbia has focused on reducing sediment supply (through bank and hillslope stabilization) and restoring wood inputs. In contrast, restoration in northern Fennoscandia (Sweden and Finland) has focused on channel widening and removal of bank-armouring boulders to increase sediment supply and retention. These contrasting restoration priorities illustrate the consequences of divergent regional land-use impacts on sediment supply, and the utility of planning restoration activities within a mechanistic sediment supply-transport framework.