Presenter/s: Neil Goeller
Symposium Session: 2020 - 03 An ecological approach to restoration
Topics covered: Canada, floodplain, monitoring, riparian, stream, and wetlands
A restoration program which the planning team will never live to see the result, San It is said that “The true meaning of life is to plant trees, under whose shade you do not expect to sit.”, (Nelson Henderson)
Forest harvesting in the San Juan River extends to the early 1900’s and little evidence remains of the pre-harvest channel conditions. Effects of historic activities emerged in the 1980s following assessments of fish habitat, channel morphology and riparian conditions. In the mid-1990s, the recently created San Juan Roundtable, composed of First Nations, Provincial and Federal Governments, Industry and other stakeholders brought a structured approach to watershed management and restoration leveraging government funding for projects.
Fish habitat, channel stability and landslide sediment delivery assessments prompted an upland restoration program targeting sediment source areas. Upslope remediation and improvements in forest management practices in the basin are generally accepted to have mitigated the majority of sediment sources with economical remediation potential. Sediment transport estimates have shown that the higher gradient upland streams are recovering as they are able to convey sediment to the floodplain. However; sediment delivered to the floodplain has had a detrimental impact to channel morphology and fish habitat. Loss of riparian structure and strength has resulted in morphological changes in the floodplain mainstem channel from which the river appears unable to recover.
In the 2010’s a process based restoration program was initiated by the roundtable. This program established the seeds from which the recovery of the river would eventually grow. The two primary projects undertaken by the roundtable partners were willow plantings on gravel bars and inter-planting conifer saplings in a broad corridor along the river. Willow plantings were intended to accelerate gravel bar vegetation succession and stabilization and attenuate sediment. The riparian planting was intended to begin establishing a resilient corridor of trees which will hopefully survive to maturity and begin to have an impact in the next 60 to 100 years. The long-term goal is to counteract the rivers aggressive reworking of the floodplain.
The British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development (FLNR) developed a research project to study this work. Current research has extended previous studies examining sediment dynamics, morphological changes and hydrological changes and their implications for fish habitat and restoration activities. Data collection included multiple LiDAR flights, drone based DEMs, historic air photos, sediment mapping, time lapse camera footage and a detailed sediment movement study using passive integrated transponder (PIT) tagged rocks.
Results have begun to show the channel changes in response to weakened riparian structure and historic restoration efforts. Gravel bar plantings are rarely lost due to erosion. Sediment tracking shows deposition occurs primarily at bar apexes. Sediment transport rates have been calculated using LiDAR differencing. Bank erosion is widely variable, with three bars (of 18 mapped) yielding the majority of sediment. High rates of bank erosion are associated with decaying riparian alder stands. The unstable channel morphology poses serious challenges for fisheries management in addition to the changing nature of flows attributed to climate change.Juan River, British Columbia, Canada.