There is currently renewed interest in locating historical streams that have long been paved over and lost in Vancouver and the Lower Mainland. Mapping these historical landscape features offers a connection to the land that has been lost through urbanization and highlights opportunities for restoration.
40 years searching for lost streams
Much of the work to discover and map the historic streams of Vancouver was carried out by Sharon Proctor and published by the Vancouver Aquarium in 1978. In her study Proctor put these streams back on the map primarily through talking to long time residents of Vancouver who had fished and lived next to these stream earlier in their lives. In all, Proctor delineated approximately 120 kilometers of salmon streams that no longer exist in the City of Vancouver alone.1
Her work was extended upon in subsequent years. In 1997 the Department of Fisheries and Oceans Canada (DFO) published their assessment of “Wild, Threatened, Endangered, and Lost Streams of the Lower Fraser Valley”. In that report lost streams originally outlined by Proctor were expanded to include streams in Richmond and further east into the Fraser valley. Through analyzing surveyor field notes and historical maps from the late 19th century, the results indicated that approximately 117 streams have been lost from the Lower Fraser Valley since the first records started to be kept. These numbers are recognized to be a conservative estimate due to the challenges of using historical sources, and the widespread conversion of many streams to ditching systems.2
What the maps don’t show
I became interested in quantifying the lost streams in the Lower Fraser in my pursuit to understand what fraction of the historical salmon habitat of the area remains accessible today.
My initial attempt to map additional lost streams followed the DFO approach of digitizing the contents of archived maps. After visiting the BC Archives at the Royal BC Museum and trolling through countless records in municipal archives it became clear the historical maps would not be enough to improve upon the DFO estimates made in 1997. Historical mapping was largely focused on locating valuable timber or farmlands. While some of the larger rivers exist on these maps, smaller tributaries that may have been important for salmon were largely overlooked. In order to sharpen the historical picture I needed to look in a different way.
Digital elevation models
One approach that hasn’t been used to identify the potential locations and extents of lost streams in the Lower Fraser is the use of a digital elevation model (DEM) derived stream networks. Creating stream networks from DEMs is a common practice for estimating stream networks where data on the locations of streams doesn’t exist. In BC however, there has been systematic mapping of existing streams at a 1:20,000 scale, which is freely available through the BC Freshwater Atlas. Through comparing a stream network created from a DEM with currently mapped streams in the Freshwater Atlas we can identify differences between the two networks. The locations of these network differences offer us a glimpse of where the landscape is indicating a stream may have existed historically, but is no longer in existence.
Plenty of limitations exist for this approach to estimating lost streams. One primary concern relates to the changes to the topography from historical conditions due to the built environment. The minor elevation changes may have particular impacts in extremely flat areas like Richmond resulting in changes in the precise location of where a stream might meet the coast or the Fraser Mainstem or how it meandered across the floodplain. In any case, the precise locations of streams change dynamically through natural processes, particularly in these flatter regions.
Other limitations, such as imperfections in the currently mapped streams, can lead to overestimation of the amount of streams that have been lost and should definitely be considered. The major strength of the approach is in its systematic application across the landscape, providing an assessment of the entire region for lost stream systems. When it comes to quantifying the extent of lost streams this method may provide more insight than the use of strictly historical materials that show bias towards omitting streams from their record and exist in varying quality, scale, and detail.
Lost streams, shifting baselines and restoration targets
By combining an estimate for the locations and extents of lost streams with information on barriers to fish passage in Lower Fraser Streams we can estimate the proportion of historical salmon habitat that remains accessible. The inclusion of lost streams in this estimate is important in informing our understanding of remaining habitat as it guards against shifting baselines and can help inform targets for restoration. The rest of my research will focus on quantifying the benefits of removing fish barriers and assessing the quality of what freshwater habitats that remain. By explicitly considering the costs and benefits of restoring access past each known barrier we can map a way forward towards restoring these historically productive ecosystems in a way that is economically efficient and ecologically valuable.
By combining the historical perspective with modern systematic planning ideas, my research helps to illustrate what once was, and will support the efforts of Raincoast and others to protect and restore freshwater habitats throughout the Lower Fraser into the future.
I look forward to updating you as this work progresses.
- Proctor, S. 1978. Vancouver’s old streams. Journal of the Vancouver Aquarium 3(1): 1-32. ↩
- Precision Identification Biological Consultants. 1997. Wild, threatened, endangered, and lost streams of the Lower Fraser Valley summary report 1997. Prepared for Fraser River Action Plan, Fisheries and Oceans Canada. Vancouver BC. ↩