Authors: Bob Turner, Geoscientist and citizen scientist, Bowen Island, Howe Sound
Contributor: Scott Christie, Balanced Environmental Services Inc., North Vancouver
Reviewer: DG Blair, Executive Director, Stewardship Centre for BC
Banner Photo Credit: Nick Page
– Titus, J.G. 1998. Maryland Law Review. 57(4)
As the climate changes, winter storm surges consisting of big waves and high winds, and anomalously high “king tides,” will increasingly work in concert with sea level rise to threaten coastal communities and shoreline ecosystems (Figure 1). Public discussion can easily focus on fortifying soft shorelines with riprap and seawalls, or building bigger, better sea dikes. But such conventional engineering solutions can have unintended consequences: cause beaches to erode, eliminate habitat for birds, mammals and fish, and disconnect shorelines from upland habitats. However, there are more environmentally friendly alternatives, such as Green Shores, a program of the Stewardship Centre for British Columbia. In 2014, Green Shores won the Best Environmental Idea award at Simon Fraser University’s RISE event. Teams were asked to answer the challenge: “How can we design Metro Vancouver communities to adapt and thrive in the context of a one metre rise in sea level?”
Howe Sound can look to its neighbours for inspiration. The District of West Vancouver in collaboration with the West Vancouver Shoreline Preservation Society pioneered shoreline enhancement projects in 2006 that continue today and include construction of offshore reefs to dissipate storm wave energy and enhance beaches. The Green Shores Gold-rated project for the restoration at Jericho Beach in English Bay won the City of Vancouver’s 2014 Urban Design Awards in Landscape, Public Space and Infrastructure. The District of Squamish Integrated Flood Hazard Management Plan includes some long term sea diking options that follow the Green Shores approach.
Why is it important?
Shorelines in Howe Sound are critical habitat for diverse species and include the immediate upland, intertidal zone and shallow marine waters of rock shores, gravel and sand beaches, and marsh and fine sediment of estuaries. Like other shorelines around the Salish Sea, they have been greatly modified since the arrival of European settlers in the early 1800s. Shoreline forests were cut and cleared, estuaries diked and drained, stream flow changed by land clearing, and intertidal zones modified and sometimes polluted by settlements and industry. More recently private homes, docks, and shoreline alteration have proliferated and, looking forward, major shoreline residential and industrial developments are proposed.
– Sound Investment: Measuring the Return on Howe Sound’s Ecosystem Assets (Michelle Molnar, 2015, David Suzuki Foundation)
Against this backdrop of historic shoreline modification, sea level is rising as our changing climate causes oceans to warm and expand, and glaciers to melt, adding water to the oceans. Climate change-driven sea level rise results in a steady and irreversible movement of the natural shoreline landward, punctuated by storm surges that produce coastal flooding and erosion. The B.C. Government has advised local governments to plan for a rise in sea level of one metre by 2100 and two metres by 2200, though some climate scientists have recently suggested a “several metre rise in the next 50 to 150 years” is possible.
The potential impacts of sea level rise are large: increased risk to coastal infrastructure, including increased maintenance and repair costs, loss of property due to erosion, loss of cultural and historical sites, saltwater intrusion into coastal aquifers, and loss of habitat and reduced biodiversity. Costs of adaptation are high; an estimate for Vancouver and surrounding communities is $9.5 billion over the century. Possible responses to sea level rise in developed areas include shoreline armouring, allowing water in and adapting to its impacts through landscape design and building modifications, and abandoning the land and retreating inland.
What is the current status?
Not all shorelines are equally vulnerable to sea level rise in Howe Sound. Most of Howe Sound’s shorelines are rocky shores that are naturally-armoured. Shorelines with beaches backed by bluffs of sand and gravel, though widespread along the nearby Sunshine Coast and Point Grey, are less common in Howe Sound. Most occur along its west shores between Port Mellon and Gibsons, and scattered elsewhere on the mainland and islands such as Plumper Cove on Keats Island and Mannion Bay on Bowen Island. Bluff tops along these shores have been prime sites for residential developments, and these bluffs are more vulnerable to erosion as seas rise. Flat beaches, and estuary wetlands such as at the mouths of the Squamish River and McNab Creek, are especially vulnerable to erosion and inundation due to their low elevation depending on the relative rates of natural addition of sediment versus sea level rise (Figure 2). Where backstopped by hard barriers such as cliffs or sea dikes, beaches and wetlands cannot migrate landwards with rising seas, leading to loss of their area, a phenomenon known as “coastal squeeze.”
As part of a shoreline mapping project, the Islands Trust published a series of shoreline maps for Keats (2013) and Gambier Islands (2011) showing shoreline type, dominant direction of wave energy hitting each island, the locations of streams that supply sediment to the shores, estimated direction of local sediment movement, and vulnerable and valuable areas. The maps illustrate the sediment supply that is critical to maintaining beaches and estuaries in the face of rising sea levels. Mapping project results show that Keats Island has a slightly larger percentage of soft shorelines (Figure 3), which are vulnerable to erosion and most of which are also associated with high recreational value and high ecological value (e.g., pocket beaches and estuaries). Gambier has some “low lying areas” mapped as particularly vulnerable to sea level rise.
Traditional “hard” engineering solutions to armouring shorelines with seawalls or riprap can produce unintended consequences such as increased erosion or damage to shoreline environmental habitat. “Soft” shore armouring includes addition of imported sand and gravel (i.e., adding like material to the beach such as sand and gravel to reverse the changes that often occur with hard armouring), dune and wetland construction, shore vegetation preservation or restoration, and construction of near shore reefs. Beach shorelines prone to erosion and inundation by sea level rise are very amenable to Green Shores soft alternative armouring. Fortunately, this “soft” approach promoted by Green Shores has been found to be more cost effective than traditional “hard” engineering solutions, reducing costs by 30 to 70 percent, while also producing much better environmental outcomes for shorelines.
What can you do?
Individual and Organization Actions
- Learn how to care for your shoreline. The Islands Trust has a rich suite of resources on their website.
- Check out this site for further tips and to enroll your project with Green Shores.
- As a waterfront homeowner, trees are your best defense against erosion. They stabilize slopes with their roots. Trim or limb, rather than remove, to maintain your views. Think twice about sea walls; work with nature instead.
Government Actions and Policy:
- Use Green Shore approaches for protecting and enhancing public shorelines in communities.
- Join the Green Shores Local Government Working Group for Green Shores support and resources
- Adopt Green Shores approach as a policy