Fraser River at Hell's Gate
General Plan of Fishways
Click on image to enlarge
The fishways at Hell’s Gate were designed to withstand all possible hydraulic forces, including impacts from water flowing at very high velocities (10-30 mph), and from moving bedloads, such as sand, gravel and boulders as large as 2-3 feet in diameter and impacts from large logs or bundles of logs purposely dumped into the river for low cost transport to lumber mills down river.

The success of the first fishways completed in 1946 and fishways built since that time, has been proven by the fact that salmon are now returning in large numbers to the watershed streams upriver of Hell’s Gate. The combined commercial catches and upriver spawning escapements of Fraser River sockeye and pink salmon as recorded in 1990 indicated that the salmon resource had recovered to more than 80% of historic numbers existing prior to 1914. The artificial spawning channels designed and built by IPSFC engineers prior to dissolution of the Commission in 1985 also contributed to the recovery of the salmon resource in the Fraser River system.

The capacity of the Hell’s Gate fishways have been proven by a passage count of 350,000 sockeye salmon through the two main fishways (on East and West Banks) in one day. Counts of migrating salmon through a vertical single slot fishway built at Hell’s Gate in 1989 indicate the passage rate of about 20,000 salmon in one hour. At the present time (year 2001), 7 vertical slot fishways and one weir type structure now provide fish passage at Hell’s Gate over a range of 82 vertical feet. This vertical range corresponds to river flows between 30,000 & 424,000 cubic feet per second covering all expected water levels during the sockeye and pink salmon migration period, which extends from mid-June to late October, every year.

Providing fishways to facilitate upstream passage for salmon, where they in the past had been adversely delayed or blocked, is now an established method in aid of fisheries enhancement. Fishways when properly designed have minimal interference with the natural environment and, as experienced in the Fraser River are extremely beneficial in preservation of the salmon resource.

The importance of assisting fish migration in the Fraser River Canyon became evident again when pink salmon were partially blocked at Hell’s Gate in the period late September-October of 1985. The blockage occurred at low water levels coinciding with the peak migration of pink salmon through the rapids at Hell’s Gate. In 1985, only one low water fishpass (weir type) existed on the East Bank at Hell’s Gate (built by IPSFC in 1966), and this structure was unable to facilitate the migration. There are no low-level fishpasses on the West Bank at Hell’s Gate and migrant fish swimming up-river on the West Bank are exposed to impassable turbulence. Generally these fish drop back, cross over to opposite bank where conditions are less severe.

Observations in previous years had indicated that up-river movement of fish in the Fraser Canyon slows down during hours of darkness and it was common to observe large accumulations of salmon in resting pools downstream of difficult passage areas during peak migration periods.

The pink salmon in 1985 were accumulating in very large numbers just below and within the East Bank low-level fishpass structure at Hell’s Gate, similar to what highway traffic would do if throttled from several lanes to one. In fast water areas such as Hell’s Gate, the salmon are forced to swim near the shores to avoid extreme velocities & high turbulence where they by shear numbers crowd and delay adding to the blockage problem.

More than a million pink salmon had been expected on the spawning grounds up-river of Hell’s Gate in 1985. As a result of the delay and blockage at Hell’s Gate and other locations in the Fraser River Canyon, less than 50% of the pink salmon were able to reach their spawning grounds in 1985. To avoid future low water fish passage problems it was apparent that additional low-level fishways would be required at Hell’s Gate. With dissolution of IPSFC in December 1985, the passage problem at low water periods at Hell’s Gate remained to be resolved.

As a temporary measure to lessen the potential blockage problem at Hell’s Gate during the next pink salmon migration through the Fraser River Canyon in 1987, a unique system of flood lights at Hell’s Gate was proposed and devised by Per Saxvik, then a Senior Project Engineer with DFO.

Justification for this unique and unconventional experiment using floodlights came about after the blocked pink salmon were observed in the Fraser River Canyon in the fall of 1985. These observations clearly indicated that the salmon migrating upstream were not just having difficulties moving through the rapids, they also slowed down and stopped to rest below difficult areas as soon as darkness set in. Knowing that migrating salmon are more active on clear nights with moonlight, Saxvik spent several nights at Hell's Gate in 1986 experimenting by shining a hand-held strobe light into the river just in front of individual sockeye salmon resting for the night, downstream of rapids. Moving the light beam (penetrating the water surface) slowly upstream, caused the salmon to follow the light up through the rapids and beyond. It was apparent that migrating salmon would actively swim upstream at nighttime if the water surface area was illuminated.

As a full-scale experiment and in time for the 1987 pink migration to arrive, several temporary floodlights were installed on the East Bank of Fraser River at Hell’s Gate. The floodlights were positioned so that the area where fish had congregated and delayed in 1985 could be illuminated during nighttime hours.
Hell's Gate, 1987, flood lights at low water to encourage migration of salmon during darkness
Click on image to enlarge
The water levels in 1987 turned out to be just as low as in 1985, and the arriving pink salmon were again delayed and blocked. The first tests, with "Floodlights Off", proved that accumulation of fish at downstream areas increased as soon as darkness set in. Observations upstream of the rapids at the same time indicated that very few fish were moving upstream and beyond Hell’s Gate. Subsequent tests with "Floodlights On", showed that the accumulation of fish at the downstream end of the rapids gradually reduced over a short period of time and pink salmon could be seen migrating up-river of Hell’s Gate. It was clear that the illumination was successful by the fact that by daybreak, very few pink salmon were seen downstream of the rapids. Pink salmon which likely had rested overnight at downstream resting areas, arrived shortly after daybreak to continue their migration and again bunched up when too many arrived at one time. Additional tests on subsequent nights with floodlights, alternately on and off gave the same positive results. In 1989, DFO, based on the 1987 experiment installed permanent floodlights at Hell’s Gate and other delay areas in the Fraser River Canyon. Floodlights however, will not replace fishways as the preferred method of passing large numbers of salmon up through difficult rapids areas.
Next Page