People at the tidal flats 2: Projected climate change and coastal hazards

This is the second part of a three part series of posts about my masters work in Iqaluit, Nunavut. This project was partially funded by the C-Change ICURA,as well as the ArcticNet Network of Centres of Excellence, and the Department of Geography at Memorial University.  In the first part we introduced the project and discussed the setting of Iqaluit. In this second part we’ll identify the nature of projected changes for the area, and we’ll look at the results of the hazards analysis. This leads into the third part, which discusses the implications of the results on coastal hazards in Iqaluit, and draws some conclusions from the research.

It’s important to build a picture of the coastline we’re talking about here, which the first post began to do. Placed along the high tide line of the sandy sorted beaches of Iqaluit are a number of structures with varying uses. Moving out onto the tidal flats you see scattered fishing nets to catch Arctic char at high tide, as well as an increase in large boulders spread around you. You’re walking through a mixture of sand and mud with pebbles, unless it’s between November and June, in which case you’re carefully climbing over eight foot mounds of sea ice floes piled by the edge of the landfast ice. As you walk out over the tidal flats, which are nearly 1.2 km wide in some areas, you start to notice that the boulders are becoming more common and you have to change your apth frequently to keep from having to climb over them. If it’s winter, you’ve made it past the ice pile near the beach, and are now on a relatively flat sheet of ice that is roughly 1 m thick and which is floating on 2-4 m of frigid Atlantic water. After walking for about 10 minutes, you reach the edge of the flats. The boulders are huge, and the the seaweed is all around you. If it’s winter, you probably shouldn’t be out this far by yourself, so you look around and see the point where the flats stop and the ice surface turns to a completely smooth sheet. In the distance you see a group of snowmobiles racing over the ice into the inlet, their head lights twinkling in evening air.

Description of the Iqaluit tidal flats

Projected Climate Changes

There are many ways that a changing climate can introduce or augment natural hazards. Here we’re dealing with a suite of changes that have been found in previous work around the world to drive coastal changes, and therefore coastal hazards. These are: relative sea-level change, warming air temperatures, and sea-ice change. These are chosen based on their studied impact on coastal infrastructure. Let me explain:

Relative Sea-level rise

Obviously, when sea level rises, infrastructure on the coast becomes more likely to flood. But is sea level rising uniformly all over the world? No, it is not – there are a number of things that make it more complicated than that.The relative sea level in Iqaluit is complicated by vertical land motion.Continued glacioisostaic rebound (the raising of the land from the weight of the glaciers during the last glacial maximum) means that not only is sea-level rising but the land is rising as well, meaning that the relative sea level in the area is rising at a lower rate than in other parts of the world. A Geological Survey of Canada (GSC) study developing projections for relative sea-level change in a selection of Arctic communities predicted a range for Iqaluit between 0-70 cm above present mean sea level by 2100.

Sea ice change

Sea-ice is an important shaper of the coast, and warmer air temperatures in the Arctic are changing the formation and ablation of sea-ice, which in turn can augment hazards for coastal communities.  In some parts of the Arctic, the diminishing of sea ice cover along the shore is allowing an increase in wave energy to reach the coast, resulting in increased rates of erosion (read more). One aspect of sea-ice change is the later freezeup and earlier breakup measured from satellite imagery. We developed a trend for Iqaluit, which shows that since 1979 (when satellites began measuring sea-ice freezeup and breakup) there has been a trend in freezeup of 0.5 days/year and a trend in breakup of -0.5days/year. This means that the ice free season has been getting longer by about 1 days/year since 1979. Current models predict a continued increase in air temperature, and assuming this is the primary driver of these variables, we can expect to see the ice free season in Iqaluit to get progressively longer in the coming decades.

Coastal Hazards

Erosion

Erosion is a serious hazard in many Arctic communities, but in Iqaluit the usual drivers of increased erosion are altered by the setting of the community.Erosion is usually caused by a mixture of high water levels from storms, strong currents, hydraulic forces on permafrost coasts. In Iqaluit the large tidal flats fronting the coast alter these usual drivers. Waves are less able to erode the coast because (1) the waves in Iqaluit are small because of limited fetch, and (2) because the large boulders that are scattered over the flats seem to dissipate incoming waves, making them less able to move sediment once they reach the high water level. The coast is primarily made up of low slope sand beaches and bedrock cliffs. These are fairly insensitive to erosional forces. A look at aerial photography of Iqaluit’s coast, and the results of a three year study we did from 2009-2011, showed no significant erosion at the coast.

Flooding

We modelled flooding potential in Iqaluit. For this we set up a simple experiment. We set up a static model of the coast, and then put high water levels on top of it to see where the flood waters might go. For this to work we first had to map the topography and bathymetry of the inlet, and then we had to determine – with the best available data – the high water levels that could be expected in Iqaluit over the next 90 years. There are three contributors to our predicted flood water levels: historical high water, sea-level rise, and wave runup.  In this project we developed a topographic model of the area from a mixture of satellite derived elevation points on land, GPS surveys in the intertidal areas, and sonar elevation points from boat-based surveys. For historical high water we went to the tide gauge record in Iqaluit to extract the highest recorded water level. Sea-level rise was assumed to be the worst case scenario of 70 cm by 2100 according to James, et al. (2010). Wave runup potential was modelled using a simple numerical model based on hydrodynamic studies from the Netherlands in the 1970s.

illus_hwl

The results of this experiment indicate that the inclusion of sea-level rise projections on top of recorded high water levels would inundate a number of coastal structures, and significantly constrain the freeboard (space between high water and the foundation of the building) of other buildings. A vast majority of the buildings flooded are the sheds and seacans that local fishermen use to store their gear.

Extent of flooding model using various high water level scenarios. The three areas are within the inlet around Iqaluit.

Extent of flooding model using various high water level scenarios. The three areas are within the inlet around Iqaluit.

Sea-ice

Our results suggest that hazards from sea-ice to coastal infrastructure are diminished by the tidal flats. Two forms of sea-ice hazard are common in the northern latitudes: pile-up and ride-up. Pile-up describes large groups of sea ice floes that are pushed up onto the shore in a chaotic way to produce a large accumulation at the coast. Ride-up is very similar, only it is characterized by these floes being kept horizontal and then sliding onto the landfast ice closer to shore, and pushing farther into the backshore. While both of these were observed in 2011 and 2012, they were almost always far away from the high water level. This is due to the low slope tidal flats off the beach, which cause the deeper ice floes to ground well offshore from the coastal infrastructure. This was not the case in one part of the coast: the engineered coast by the main breakwater. Here the coast has been artificially steepened by rip rap, and the ice floes were able to float right up alongside the infrastructure, causing the city to clear large ice pile-up (3 m high) from the coast.

ice_ride_up ice_pile_up

Summary

In this post we’ve outlined the expected effects of projected climate change on the factors that drive coastal change in Iqaluit: sea-level rise, storm flooding, and sea-ice change. From this we set up two simple experiments:the first is to use a static model to find which structures flood water levels would affect, and the second is to bring in a rough understanding of sea-ice dynamics to make a judgment on the importance of erosion and sea-ice pile-up/ride-up in damaging infrastructure on the Iqaluit coast.

In the next part of this three part series on coastal hazards in Iqaluit we’ll discuss some of the implications of the findings for the sustainability of this small stretch of coastline.

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One response to “People at the tidal flats 2: Projected climate change and coastal hazards

  1. Pingback: People at the tidal flats, Part 1: the landscape and development of Iqaluit’s coastline | Coastal Change Student Blog·

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