Restoring natural geomorphic process to river environments influenced by practical design constraints

Abstract:

The process restoration philosophy promotes the reinstatement of natural process (particularly the continuum of sediment transport processes) at the catchment scale. Associated with this approach is the concept that river biological communities, having evolved under natural/ un-impacted conditions, will respond positively to the reinstatement of natural physical function. The application of this ‘let-the-river-do-the-work’ approach is regarded as providing a sustainable alternative to traditional more ‘hard engineering’ approaches. However, often the reality is that full restoration of the controlling physical processes at the catchment scale is not feasible due to a variety of constraints (e.g. altered geomorphic regime, agriculture, infrastructure/ services, urban development, costs, etc.) and less ambitious objectives have to be set. Thus, under these typical constrained circumstances, can process restoration still be applied and, given the fundamental assumption of biophysical linkage, can ecology still be expected to respond positively? To elucidate these issues, we present four case studies from Scotland which represent the spectrum of process restoration application relating to almost no design constraints to very significant limitations (culvert daylighting within a housing development). We highlight that, despite significant constraints, physical river processes can (and should) always be considered in restoration design. The case studies demonstrate that natural physical processes (evidenced through indicators of sediment transport) quickly reinstate following construction; this was despite significant local constraints but reliant on physical/ geomorphic process being explicitly incorporated into to the design approach. Furthermore, evidence of associated improvements to the ecological/ habitat/ biotic condition of the restored sections of river were observed.