Assessment of Redd Desiccation and Salmon Alevin Mortalities Resulting from the Partial De-watering of a Side Channel Due to a Causeway Construction to Facilitate Gravel Removal at  Big Bar Island on the Fraser River, Winter 2006

Executive Summary

On or around the first week of March 2006, a large causeway was constructed across a major side channel of the Fraser River—from Island 32 at Ferry Island Provincial Park, Rosedale, British Columbia—for the purposes of aggregate removal from Big Bar Island.  Big Bar Island is located approximately 1 km downstream of the Agassiz-Rosedale Bridge adjacent to the true-left bank.  The causeway was built with rip-rap, filter cloth and gravel in order to enable vehicles to access the island.  The design of the causeway did not include provision for flow passage (e.g., culverts or bridges) in order to maintain flows into the Big Bar Island side channel for the protection of fish, habitat and/or incubating fish embryos or alevins, although a minimal amount of water passed through the structure due to the porous nature of its rip-rap base.  The drop in water-surface elevation at the causeway was c.a. 1 m.  The change in water height midway down the side channel at the assessment area over the study period, was measured at 84 cm, most of which could be attributed to the causeway construction.  Several hectares of stream bottom were dewatered along the length of the side channel as a result of this action; the dewatered area could easily be visually determined downstream of the causeway as a result of the difference in the coloration of the newly exposed river gravel.

The newly dewatered area in the Big Bar Island side channel downstream of the causeway included many salmon redds.  Most of these redds appeared to be the result of pink salmon spawning activity which was extensive in the Fraser River from Hope to the Sumas River confluence during autumn 2005.  The recently dewatered redds could easily be differentiated from the un-spawned stream bottom because of the difference in structure of the two type of stream bottom—spawned areas were clearly undulating in topography versus the relatively flat profile of un-spawned locations.  The redds which had been recently dewatered could also be discriminated from higher-elevation redds which had been previously and naturally dewatered over normal-winter hydrograph declines.  This was done in two ways: 1. there was a clearly observable recent high-water mark along the perimeter of the newly exposed redds, and 2. the redds that had been exposed to the air for a much longer time through natural seasonal de-watering showed extended weathering and a clear difference in texture and coloration of the surface gravel compared to the recent event. 

Due to the concerns that the construction of this causeway resulted in a large-scale unauthorized harmful alteration, disruption or destruction of fish habitat as a result of the causeway construction, members of the British Columbia Institute of Technology Fish, Wildlife and Recreation class, and directors of the Fraser Valley Salmon Society, commenced monitoring and assessing the impacts of the channel de-watering on incubating salmon alevins.  Perimeter and area measurements were made of the most densely spawned and recently dewatered area on the true left bank on a large dry gravel bar located approximately halfway downstream in the Big Bar side-channel in the estimated dewatered area.

The recently dewatered area of densely aggregated redds was also assessed for live or dead embryos or alevins.  Recent mortalities (based on body freshness and lack of decomposition or fungus infections) of pink salmon alevins were extensively observed throughout the surveyed area of recently dewatered redds.   These dead salmon alevins were observed up to a maximum distance of 40 metres from the water’s edge on March 9, 2006.  With the subsequent removal of 80-90% of the causeway around March 17, 2006, the water surface elevation immediately rose in the Big Bar Island side channel.  The re-watered area of the side channel now extended to an area similar to the extent of the perimeter of the assessed dewatered area high-water mark.  No such con-current increase in flows or water-surface elevations were recorded at Hope for the Fraser River on this date.  Because the discharge of the Fraser River at Hope was similar between March 9 when the de-watered area was surveyed, and March 17, 2006 when the channel was re-watered, the re-watering of the area was taken to be virtually identical to the area that was originally thought to be dewatered through the action of the causeway construction.

The survey of the most densely spawned area of recently exposed redds measured 6,534 m2 at 688 cubic meters per second measured at the Hope Water Survey Canada gauging station for Fraser River.  The discharge at the Hope Water Survey Canada gauging station for Fraser River on March 1, 2006 measured 740 cubic meters per second.  Using bio-standards, including published survival rates for pink salmon, we have conservatively estimated that this de-watering event resulted in the loss of 1 million to 1.5 million incubating alevins in the surveyed area.  Based on inventory of downstream migration of pink salmon fry on the Fraser River at Mission by April 1, 2006, few of these fish had emerged from the gravel by March 1, 2006 in this watershed.  While the death of up to 1.5 million young fish is based on a survey of the area that was most impacted, the total number of fish mortalities were significantly higher in that the other exposed redd sites affected by causeway-related dewatering (both downstream and across the channel) could not be surveyed due to logistical constraints.  While these adjacent areas were not spawned as extensively as the main survey site, it is reasonable to estimate that they would add another 50% to the mortality totals, bringing the estimated causeway-related losses of young pink salmon to between 1.5 and 2.25 million .   

On the evening of March 9, 2006, two culverts were placed into the causeway apparently with the objective of increasing the discharge into the side channel for the protection of fish and alevins.  However, over the length of the 100 meter causeway, these two culverts still did not allow for adequate flow and there is no indication that this provided any improvement in the re-watering of redds as the change in surface elevation of the side channel and re-inundation of the spawned area was negligible.  Our survey also clearly showed that the salmon mortalities had already occurred by then.  We did observe, however, that the installation of these culverts contributed to measurable amounts of silt being entrained into the side channel by the activity of the construction.  Also, there was no indication of an environmental monitor on site, or sediment monitoring during the culvert installation, in contravention of agreements amongst agencies for Fraser River gravel removal.

It should be noted that the day after the March 9, 2006 survey and the installation of the culverts, the water surface elevation stream channel actually dropped a further 0.04 m on March 10, 2006, and a further several meters (cross-channel) of redds were dewatered along the length of the gravel bar that we had surveyed.  A large negative spike in discharge was noted on the Hope Water Survey Canada gauge in the form of a flow drop of about 100 cubic meters per second; this was apparently due to a scheduled plant shutdown at BC Hydro’s Seton Generating Station some hours earlier.  This ancillary 0.04 m drop, and the subsequent extensive de-watering of salmon redds at the survey site is not thought to be part of the de-watering resulting from the causeway construction.  The channel resumed its March 9, 2006 water-surface elevation on March 11, 2006 which is co-incident with the resumption of similar flows a day later at the Hope Water Survey Canada gauging station.  

Over the period of assessment it was also determined that salmon redds had been dewatered along the toe of the mainland rip-rap bank inside of the large gravel bar on the southern perimeter of the channel.  They were identified as chum salmon redds due to the type of fish skeletons found at this location (size and morphology of the fish jaws and head) and the location, shape and size of the redds.  These redds were not originally recognized as having been de-watered but once the causeway was removed and the Big Bar Island side channel re-watered, the redds were subsequently inundated with water.  The resumption of hydraulic pressure through the bar appeared to cause a groundwater recharge and a re-watering of the redds.  No assessment was undertaken to determine mortalities of alevins at this location but it is assumed that extensive fish deaths also occurred where the chum salmon had spawned.

The primary responsible environmental agency for the protection of fish and fish habitat is Fisheries and Oceans Canada.  However, regarding this particular project, the Department of Fisheries and Oceans appears to have been negligent in enforcing the Canada Fisheries Act.  Fisheries and Oceans Canada also did not ensure adequate assessment or mitigation of impacts as required under both Canadian law and the agreements for gravel removal between Fisheries and Oceans Canada and Land and Water BC Inc,.  Further, there was a lack of diligent care and attention following the causeway construction with the result that both Section 32 (destruction of fish by any means other than fishing), and Section 35 (harmful alteration, disruption or destruction of fish habitat) of the Canada Fisheries Act were violated. 

These aspects of Canadian law appear to have been knowingly ignored in the process of facilitating the construction of the access causeway for aggregate extraction from Big Bar Island.  In addition, the statements of some DFO representatives in the media regarding this incident have been a cause for concern amongst river stewards.  For example, in a recent Chilliwack Progress newspaper article,  — “Jim Wild, DFO's area director for the Lower Fraser River, says it's "totally inappropriate" to blame a causeway built by the contractor with federal fisheries approval so that trucks could access the gravel bar located in the river…” and "Unfortunately, it's a natural occurrence. It happens quite often," he says. "It's not just a local problem with this (causeway)..." as well as “…Dale Paterson, the DFO's area chief of habitat, says the good news is that many of the salmon alevins (hatchlings) had emerged from their nesting sites called redds before the low water levels exposed them….” (Chilliwack Progress March 17, 2006).  Based on our survey results, both these statements are incorrect and misrepresent the events that actually unfolded around this particular incident.   

In conversation with Fisheries and Oceans Canada Conservation & Protection staff, we have been advised that Fisheries and Oceans Canada habitat staff may have knowingly refrained from enforcing the Canada Fisheries Act regarding the authorization of gravel removal at Big Bar Island through the subsequent construction of the causeway.  Given the severity of the impacts that ensued and the significant legal implications, a criminal investigation may be warranted. 

At the very least however, it’s essential that we learn from what unfolded here and it’s our hope that such an incident will never take place again along the Fraser River. Just as importantly, the extensive adverse environmental impacts that occurred in this case could have largely been prevented had an adequate bridge structure or a conveyance system been incorporated similar to what was used in Minto Channel in 2000. Finally, this issue highlights the need to ensure that, in future, all such work is done in a sustainable and environmentally appropriate manner that meets legislative, regulatory and policy requirements.  The consequences of doing otherwise will be catastrophic for the Fraser River and its aquatic ecosystem.

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