The Christmas Eve storm: freak tides or freak luck?

  • Mon Jan 19th, 2004 9:00am
  • News

Submitted by Ian J. Walker, Assistant Professor, University of Victoria, Department of Geography –A few folks in the Tlell area may be counting their lucky stars in the wake of the Christmas Eve storm. It was clearly a rare and damaging one, but certainly not a freak of nature. In advance of high tides coming this week – estimated to be 7.3m or 24′ at 12:48 on Wednesday Jan. 21st – I would like to share some thoughts on why this storm was so extreme and on what this may hold for understanding and dealing with future storms.
As locals know, storms and high tides are common in Haida Gwaii. However, the right combination of tides and storms that cause excessive damage to the coast are less common. To a certain degree, chance (or luck depending on how you look at it) is at work here in terms of creating the right conditions. From what we know today, climate change may increase the chance of these conditions occurring more frequently. This may spell more trouble by way of storm hazards for the future of northeast Graham Island.
From PEI to QCI, I’ve heard lots of stories about tides and storms. One of the most interesting and perhaps misleading is that of the ‘freak tide’. This is somewhat of a myth and relates to a misunderstanding of the difference between tides and something called ‘storm surge’. Tides are caused by astronomical forces at work with gravity that push and pull on the ocean causing a rhythmic rise and fall in sea level. Locally, some geographic effects like funneling in coastal inlets may play a minor role. So, as sure as sunrise can be predicted, tides can be forecasted based on the position of the moon and sun relative to the Earth.
I often hear people say that tide charts are way off. Actually, the charts (and the fancy models behind them) do a pretty good job at predicting tidal heights and timing, but that’s it. As you would expect, they do not predict the weather. This is what causes differences between ‘tides’ and actual water levels. This extra water, or storm surge, is caused by winds (which pile-up water in the direction that they blow over the ocean) and atmospheric pressure changes (which allow the ocean to rise if the weight of the atmosphere drops). If timed right, these effects can cause water levels to rise as much as 1 m (3 feet) above the predicted tide! During clear days, high atmospheric pressure and calm conditions can actually cause levels lower than the predicted tide. For more info on tides and storm surges, see DFO’s webpage: http://www.lau.chs-shc.dfo-mpo.gc.ca.
The Christmas Eve storm was not a ‘freak’ event. In fact, few natural hazards are. They just have timing to their visits that is beyond the average human lifespan. For instance, the ‘100 year storm’ may only happen once in a lifetime if we’re lucky. This does not mean that a storm like this occurs every 100 years like clockwork though. Instead, consider storms like a game of chance. In this case, the storm has a chance of 1 in 100 (or 1%) of occurring in any given year. The 10 year storm has a chance of 1 in 10 (10%), etc. From what we know about climate change, we think that the chances for big storms may get better.
What was uncommon about the Christmas Eve storm was the timing of strong winds blowing from the right direction (SE) during a drop in pressure with a spring tide. In addition, river flows on the Tlell were high. These circumstances are not freakish by any means, just a slim chance.
Actually, there was some freak luck involved too. Why? The peak in the storm surge – an additional 70 cm of water – happened just after low tide at 9 am on Christmas Eve. Had this occurred a few hours later at high tide, the cleanup and repair efforts would have taken months and required natural disaster relief funding from Ottawa.
Based on evidence I’ve seen in old shorelines (hundreds to thousands of years old), these events have happened before and as we’ve seen, will continue to occur. They just don’t happen very often. However, climate change is altering the chances. Ocean levels may rise by 15 cm in the next 100 years increasing the height of water on the shoreline and in rivers. Storms may occur more frequently and with more force. Surges and wave damage may increase the ongoing 1-3 metres of erosion per year on the coast. In light of this, it is only a matter of time before a major engineering and/or relocation project must be considered. Let’s hope this is done before disaster relief is necessary.
To prepare ourselves over the short term, there are a few things to look out for. If high tides combine with rising winds from the SE and a rapid drop in the barometer (atmospheric pressure), be prepared – especially if rivers are in flood. It could be a matter of hours before the coastline becomes very hazardous and extensive damage could occur. Remember, though the chance of this is low, it could happen at any time. Over the long term, we need to consider planning options that could feasibly protect and maintain transportation and properties along the coast. In some areas, this may require ‘retreat’ which is a tough call. This will be no mean feat but with some insight, could be better informed and planned for.
I welcome any comments, feedback and experiences (including photos!) on the storm. I will be up on the islands in mid-February and will hold a public meeting that will be announced in the Observer and on the scroll. We need your input and involvement to help with our research on impacts to the coast and your communities. Please feel free to contact me via email at: ijwalker@uvic.ca.