By Dr. Marvin L. Rosenau. The gravel reach of the Fraser River, between Mission and Hope, comprises one of the most spectacular freshwater ecosystems in British Columbia. Approximately 30 species of fish can be found in this stream, the most in any freshwater environment in B.C. The gravel
reach is also home to the largest single salmon spawning run in the province (10 million or more
pinks in some years), and the largest fish species in North America, the white sturgeon, reaching
over 13 feet and weighing more than 1400 lbs.
The gravel reach provides passageway and rearing habitat for literally billions of salmonid (trout, char and salmon) smolts that pass their way from the north, central and southern parts of the Fraser River watershed upstream of Mission, during their spring outmigration to the ocean. The gravel reach is also home to a rich plant ecosystem, including increasingly rare black cottonwood forests, 5 listed fish species, and a myriad of non-fish species including plants and animals, both common (e.g., mallard ducks, black-tailed deer) and at risk (e.g., blue herons, bald eagles).
The Fraser River gravel reach, sometimes referred to as the “Heart of the Fraser”, has important
cultural aspects including 10,000 years of First Nations occupation and 150 years of European
settlement. The land uses by these two cultures were, and continue to be, largely based on
the high level of productivity of this landscape. While forest harvest occurred historically, and
continues to take place in the gravel reach now, to a much lesser degree and currently in the form
of cottonwood/poplar silviculture, agriculture remains the key economic driver for much of the
surrounding historical floodplain of the gravel reach. The rich silt-laden soils, deposited by the
Fraser River into the gravel reach, are the underpinning of farming in the eastern Fraser Valley.
And, of course, many 100’s of thousands of recreational days occur each year in the gravel reach
in the form of fishing, boating, camping and biking, which take place because of the beauty and
richness of this unique environment.
As part of the more recent human development of this landscape and alteration of the ecosystem,
much of the gravel reach has been diked for land use, specifically for farming, and more recently
for the development of housing. This has important ecosystem implications as the rich biological
aspects of the gravel reach were, and continue to be, dependent on the spring freshet flooding. The
main-channel overbank inundation of the floodplain allows for fish, sediments, nutrients, insects
and other biological and non-biological attributes, to be exchanged to and from the primary flows of the main channel, to the backwaters and floodplains of the gravel reach, during April, May,
June and July.
The freshet flooding renews and revitalizes this landscape every spring freshet, supporting the Fraser’s extraordinary biological and fisheries diversity. This is an important point, as human intervention on this landscape, over the last 150 years, has continually pushed closer and closer to the main channel, keeping more and more flood-waters off the floodplain, with the intent of developing, either for agriculture, forestry, or human habitation, every last piece of floodplain surface that is available.
The snowmelt flooding, while good for freshet-adapted ecosystems, is not good for houses, barns, roads and other human-constructed infrastructure.
To counteract the potential flooding of buildings, roads and fields, a diking system was built
throughout the floodplains of the eastern Fraser Valley of the gravel reach, to be high enough,
and strong enough, to withstand the flood of record (which occurred in the year 1894 and had
a maximum volume of 17,000 cubic meters per second at Hope), plus a buffer of 60 cm. Also,
large-scale bank hardening utilizing rip-rap (i.e., lining the banks with large angular boulders to
prevent erosion) has been engineered and put in place for much of the gravel reach. Rip-rapping large river banks is not good for river ecosystems. We now know that rip-rapping has
profoundly negative impacts on fish production and aquatic environments including interrupting
the recruitment of new gravels for spawning, as well as destroying foreshore vegetation.
One of the most controversial issues associated with the gravel reach of the Fraser River over the
last two decades has been the removal of sediment (sand and gravel) from the stream. Until the
mid 1990s, the extraction of gravel from the reach had largely been for the aggregate industry
to use for construction.
But as the fisheries agencies began to enact more protection of this extraordinary ecosystem, and refused more and more authorizations to mine, the gravel miners began to push back and looked for other ways to “rebrand” their business. The rationale became “we need to remove the gravel for flood protection”. Note that the primary extraction technique for the gravel reach of the Fraser River involves the use of gravel-bar scalping.
This means that the back-hoes and loaders simply remove the exposed sand and gravel sediments during the low-flow period in the winter months and truck them away. The large bars, incidentally, are extraordinary fish habitat during the higher-discharge seasons, as many juvenile Chinook salmon, mountain whitefish, sculpins, minnows and suckers use these environments for rearing.
It should be pointed out that because of the power of this stream’s flowing water, gravel moves
around and both erodes and deposits (piles up) at various locations within the reach. Why might this be of concern? Sediments of a variety of different classes—silt, sand, and gravel—pass through the gravel
reach and/or deposit therein, as a natural part of the freshet. Most of the silt (about 20 million tonnes per year) that enters the gravel reach simply passes through the gravel reach to the Georgia Strait and is deposited there.
Some of the annual sand budget (about 2 million cubic meters per year) settles into the gravel reach, but then similar amounts seem to erode as well, on average. Most of the sand-size class of sedimentary material passes through and settles in the Fraser River estuary downstream of New Westminster. Finally, there are about 200,000-300,000 cubic meters of gravel that appear to deposit in the gravel reach, from upstream of Hope. But this deposition is highly episodic in nature, is dependent on the prevailing flood conditions, and may, in part, simply be replacing any sand which erodes into downstream areas. In any event, the flood profile (computer-modeled flood elevation calculations that
are made by professional engineers, and are compared relative to the engineered dike-height elevations) does not appear to be rapidly (or even slowly) increasing very much in the gravel reach as a result of sediment deposition over the last 50 years. Any gravel that might be deposited seems to be absorbed onto the undiked wide and long floodplain, or within the active channel stretching from Laidlaw to Mission.
To provide some recent history, I give the following: in order to politically facilitate the removal of this
material for the aggregate industry, in the early part of the first decade, the government agencies in charge of flood protection collaborated with the mining industry to re-position the issue as a safety concern to the detriment of fish habitat. Ergo, “remove the gravel in the river and you will have better flood protection”. While it is difficult to get a good estimate on the effects to fish habitat, it is certain that the extensive and pervasive gravel removal that was occurring between 2004 and 2010 caused significant damage to the fisheries environment. Furthermore, this activity was going to destroy this part of the Fraser River if allowed to continue. In fact, one of the most bizarre impacts occurred in 2006 when several million pink salmon alevins that were just about to come out of their redd gravels, were killed when a large side channel was mostly dammed to facilitate gravel removal off of Big Bar at Rosedale. Perhaps, however, cooler heads started to prevail as we have now had three years with
none of this destructive activity in the gravel reach.
So, despite a three-year break in gravel removal, (2011-13 inclusive) why are some politicians continuing to call for a resumption of extraction despite the large-scale damage that it ultimately causes to this ecosystem, and, most importantly, despite a lack of engineering evidence that it results in any significant flood-control benefits? Well, “Just follow the money”, as they say in the movies, a catchphrase which refers to political corruption within government offices. At the end of the day, the hope is that cooler heads will finally prevail.
Everyone supports flood protection for human life and property in the gravel reach. However, no one should support the cavalier destruction of this extra-ordinary ecosystem, just to provide a few dollars in the aggregate industries’ pockets, and with no proven or demonstrated benefit to providing safety.
This exceptional part of the Fraser River, that we know as the gravel reach, or the Heart of the Fraser, needs to be protected, not only for our children and future generations, but because it is aninherently special and precious thing.
Dr. Marvin L. Rosenau is BCIT Fish Wildlife and Recreation Instructor
Today Media Group gratefully acknowledges the permission granted by the publishers of The Footprint Press to re-publish this article in its entirety from their 2013 Issue #10. You can view a downloadable PDF of the magazine
here or view it online at FootprintPress.ca.
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