Stream restoration

Stream restoration or river restoration, also sometimes referred to as river reclamation, describes work conducted to improve the environmental health of a river or stream, in support of biodiversity, recreation, flood management and/or landscape development. Stream restoration approaches can be divided into two broad categories: form-based restoration, which relies on physical interventions in the stream to improve its conditions; and process-based restoration, which advocates the restoration of hydrological and geomorphological processes (such as sediment transport or connectivity between the channel and the floodplain) to ensure the stream's resilience and ecological health. Form-based restoration techniques include deflectors; cross-vanes; weirs, step-pools and other grade control structures; engineered log jams; bank stabilization methods and other channel reconfiguration efforts. These induce immediate change in the stream, but sometimes fail to achieve the desired effects if degradation originates at a wider scale. Process-based restoration includes restoring lateral or longitudinal connectivity of water and sediment fluxes and limiting interventions within in a corridor defined based on the stream's hydrology and geomorphology. The beneficial effects of process-based restoration projects may sometimes take time to be felt since changes in the stream will occur at a pace that depends on the stream dynamics. Stream restoration or river restoration, also sometimes referred to as river reclamation, describes work conducted to improve the environmental health of a river or stream, in support of biodiversity, recreation, flood management and/or landscape development. Stream restoration approaches can be divided into two broad categories: form-based restoration, which relies on physical interventions in the stream to improve its conditions; and process-based restoration, which advocates the restoration of hydrological and geomorphological processes (such as sediment transport or connectivity between the channel and the floodplain) to ensure the stream's resilience and ecological health. Form-based restoration techniques include deflectors; cross-vanes; weirs, step-pools and other grade control structures; engineered log jams; bank stabilization methods and other channel reconfiguration efforts. These induce immediate change in the stream, but sometimes fail to achieve the desired effects if degradation originates at a wider scale. Process-based restoration includes restoring lateral or longitudinal connectivity of water and sediment fluxes and limiting interventions within in a corridor defined based on the stream's hydrology and geomorphology. The beneficial effects of process-based restoration projects may sometimes take time to be felt since changes in the stream will occur at a pace that depends on the stream dynamics. Despite the significant number of stream restoration projects worldwide, the effectiveness of stream restoration remains poorly quantified, partly due to insufficient monitoring. However, in response to growing environmental awareness, stream restoration requirements are increasingly adopted in legislation in various parts of the world. Stream restoration or river restoration, sometimes called river reclamation in the United Kingdom, describes a set of activities that aim to improve the environmental health of a river or stream. These activities aim to restore the river system to its original state or to a reference state, in support of biodiversity, recreation, flood management and/or landscape development. Stream restoration is generally associated to environmental restoration and ecological restoration. In that sense, stream restoration differs from: Improved stream health may be indicated by expanded habitat for diverse species (e.g. fish, aquatic insects, other wildlife) and reduced stream bank erosion, although bank erosion is increasingly generally recognized as contributing to the ecological health of streams. Enhancements may also include improved water quality (i.e. reduction of pollutant levels and increase of dissolved oxygen levels) and achieving a self-sustaining, resilient stream system that does not require periodic human intervention, such as dredging or construction of flood or erosion control structures. Stream restoration projects can also yield increased property values in adjacent areas. In the past decades, stream restoration has emerged as a significant discipline in the field of water resources management, due to the degradation of many aquatic and riparian ecosystems related to human activities. In the USA alone, it was estimated in the early 2000s that more than one billion US dollars were spent each year to restore rivers and that close to 40,000 restoration projects had been conducted in the continental part of the country. Stream restoration activities may range from the simple improvement or removal of a structure that inhibits natural stream functions (e.g. repairing or replacing a culvert, or removing barriers to fish passage such as weirs), to the stabilization of stream banks, or other interventions such as riparian zone restoration or the installation of stormwater management facilities like constructed wetlands. The use of recycled water to augment stream flows that have been depleted as a result of human activities can also be considered a form of stream restoration. When present, navigation locks have a potential to be operated as vertical slot fishways to restore fish passage to some extent for a wide range of biota, including poor swimmers. Stream restoration projects normally begin with an assessment of the stream system, including climatic data, geology, watershed hydrology, stream hydraulics, sediment transport patterns, channel geometry, historical channel mobility and flood records. Numerous systems exist to classify streams according to their geomorphology. This preliminary assessment helps to understand the stream dynamics and determining the cause of the observed degradation to be addressed; it can also be used to determine the target state for the intended restoration work, especially since the 'natural' or undisturbed state is sometimes no longer achievable due to various constraints. Two broad approaches to stream restoration have been defined in the past decades: form-based restoration and process-based restoration. Whereas the former focuses on the restoration of structural features and/or patterns considered to be characteristic of the target stream system, the latter is based on the restoration of hydrological and geomorphological processes (such as sediment transport or connectivity between the channel and the floodplain) to ensure the stream's resilience and ecological health. Form-based stream restoration promotes the modification of the stream channel to improve the stream conditions. Targeted outcomes can include improved water quality, enhanced fish habitat and abundance, as well as increased bank and channel stability. This approach is widely used worldwide, and is supported by various government agencies, including the United States Environmental Protection Agency (US EPA).