Sinking river delta could mean trouble along Fraser
This issue has been bothering me for a while now – as posts to this blog will attest.
The cause in the Fraser delta is that dikes, constructed to prevent flooding, force the river to carry its sediment load out into the Strait of Georgia so that none accumulates on deltaic lands. The delta is also sinking one to two milimetres each year under its own weight.
The survey data suggest that, by the end of this century, it will have sunk by more than a metre (130 centimetres), with the effects reaching as far upstream as Maple Ridge and Fort Langley. As elsewhere, a rise in sea level will accentuate the problem.
The warning about the Fraser river delta is coming from Canada’s Geological Survey but is replicated by satellite data, coupled with historic records, on many of the world’s deltas. Add rising sea levels due to global climate change, and our vulnerability to seismic activity and we have a recipe for disaster.
Roy Strang raises the same questions I have been asking
If these data are accurate and reliable, and one adds in the consequences of seismic liquefaction in the event of an earthquake, what is the future for the Vancouver airport and Richmond? Were such eventualities considered when expansion of Deltaport or the controversial South Fraser Perimeter Road were being planned? Are there contingency plans, or is the horizon too distant to be a concern for today’s politicians?
He does not answer these questions and the article then drifts off into other things. The only official comments I have seen recently came from Malcolm Brodie, the Mayor of Richmond. Which were simply a recitation of his complacency about the strength of our dykes.
I rather suspect that the boosters who have been so keen on expansion of the port and the airport have been deliberately quiet about these risks. But I do know that when emergency planners at the then GVRD assessed these risks during the period when the LRSP was being drawn up, advised that development should be directed away from flood risk areas. That is why Richmond was not part of the Growth Concentration Area. And of course the fact that the land was of very high agricultural quality was also a reason for not building on it. Indeed, protection of the Richmond farmland which had not already vanished under subdivisions was one of the main reasons for the creation of the ALR.
Of course ALR designation means nothing to the Port of Vancouver, who are happily buying up farmland to store containers on or to sell for industrial development. And the province is so taken with the huge land development profits consequent upon the SFPR that any considerations like food security, critical habitat or even carbon capture by bog lands have been steadily ignored. Or even denied. So flood risk is just another one of those tiresome objections to be swept under the carpet so the BC Liberal party supporters can go on making lots of money – which is all that matters as far as they are concerned.
Stephen Rees's blog 
I worry about this too. I am lead to believe that Richmond’s first dyke’s were simply dredged peat and clay and only later C. 1950’s, was stone and rubble used.
If the Delta is sinking then there should be some concern about the dyke’s.
I was amazed when I lived in Holland at the vast size of the great sea dyke’s and certainly makes Richmond’s look like poor second cousins.
zweisystem
October 1, 2009 at 10:48 am
Go to the source, Stephen. Some creative headline writing by the Science press, uncritically parroted by the local newz has stripped any reality from this story.
The Nature Geoscience Paper says only that delta growth is not keeping up with anticipated climate change (no surprise there). A few are actually sinking, but the causes are generally local and have little relevance to the Fraser Delta. The Fraser is not mentioned in the Paper.
Essentially, they figure the change in relative sea level is controlled by these factors:
“E” (eustatic sea level rise: this is the global rise or fall of sea levels, controlled mostly be global climate trends, although significant tectonic events may be a factor). This will affect the Fraser Delta the same as everyone else. No more, no less.
Cn and Ca (compaction of sediments, natural and accelerated). Cn is relevant in Richmond, and the airport (and small, local areas of Maple Ridge, Delta, and Pitt Meadows, etc.), but completely manageable. The alarm about this natural compaction actually went up in the 70’s, and the dyke authority is aware and makes it part of their regular planning. The factors leading to Ce are really not an issue in the Fraser Valley, where there is little pressure from oil or gas extraction (there just isn’t any there due to the geologic history), and the groundwater extraction from post-Pleistocene sediments is minuscule (though locally unsustainable: I’m talking about you, Langley).
M (non-eustatic changes) this is basically the tectonics of isostacy: the earth’s crust locally lifts and falls due to loads placed upon it. In the case of the Fraser Delta: we are still rebounding from deglaciation and there is continued uplift due to an overall collisional regime along the leading edge of the North American Plate. Not fast enough to outstrip anticipated eustatic sea level changes, but hardly “sinking”. They make the assumption (which they comment upon) that M is usually negative (sinking), which I would contend on all sorts of technical reasons too detailed to list here.
Other risk factors either do not apply to the Fraser (e.g. no upstream dams trapping the sediments) or actually result in improving the situation (channeling sediments to the Strait actually reduced isostatic loads upstream of the delta front). So the only relevance this story has to our situation is that it reminds us that at least thirty years ago, we discovered that natural sediments compact. Yawn.
Pat J
October 1, 2009 at 11:17 am
Pat
Of course the Peace Arch News provides no link to the source. But the Geological Survey also seem to think – according to the story – that there is an issue. And of course there is no source to that either.
You seem to speak with some authority – perhaps you might like to identify yourself
Stephen Rees
October 1, 2009 at 12:28 pm
Thanks Pat for what seems like an excellent response. I do have to comment on one thing: the leading edge of the north american plate is a subduction zone. That leading edge isn’t undergoing uplift, it’s being dragged down into the ocean by the Juan de Fuca plate. The Fraser Delta is a long way from the edge of the plate so at that point the overall direction may be upward.
David
October 1, 2009 at 1:14 pm
Oh, we’ve met, NWEP stuff. I have a certain geologic education. I didn’t mean this as a dig at you, more a dig at the way the media messes up science almost every time they report it. I have great respect for you and for the service you provide with this blog.
Dave, the location of the lower Fraser Valley is an interesting and complex tectonic regime, but there is no doubt that the resultant stress is towards collisional lifting in the current configuration. We have been in this setting pretty much since the Miocene, with the exposed roots of volcanoes (the coast maountain plutonic complex) as evidence.
Unfortunately, unless you have access to the academic press, you have to pay for the original Nature Geoscience paper:
http://www.nature.com/ngeo/index.html
Pat J
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