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To adapt to climate change, a collaborator’s rather than a conqueror’s approach to natural processes is needed. We propose a simple yet bold solution, shaping a resilient living coastal system that borrows natural processes, absorbs storm surge, and addresses sea level rise.
The Problem Lower Mainland sea levels are predicted to rise one metre over the next 100 years1. Dykes are the standard solution, but the challenge is that the combination of sea level rise and storm surge would require raising them from 3.5m to approximately 8.0m. Is there a way to address storm surge through offshore interventions, and in doing so, substantially reduce the need to raise dykes?
The Opportunity The Fraser River deposits twenty million tonnes of sediment into the Strait of Georgia annually. The Roberts and Sturgeon Banks are a product of this, and serve as natural breakwaters, wildlife habitat, and flood control. Jetties and other human inventions maintain shipping channels by directing sediments out into deep waters, but have prevented the banks from growing along with rising sea levels, thus contributing to their erosion. Losing the banks means losing flood protection.
The Solution Rather than inventing new technologies, we propose combining known, landscape-based techniques. Firstly, natural sediment transport and accretion processes are restored. Secondly, networks of new barrier elements are constructed to collect sediment and encourage more accretion. Finally, with storm surge vastly reduced, dykes only need raising to 5.0m to meet sea level rise. Resources are shifted from dyking to foreshore works.
1 BC Ministry of Environment Climate Change Adaption Guidelines for Sea Dikes and Coastal Flood Hazard Land Use, 2011
The five million tonnes of material currently dredged from shipping channels and dumped out at sea will be placed in the foreshore to grow the banks and barrier islands. River water will be directed back over the banks through strategic breaks in existing jetties, allowing sediment to accrete behind the islands. Over time, these human-caused changes will help to restore natural geomorphic and ecological processes.
Simple materials and techniques already in use in the Fraser Delta will be employed. The foundational material for the banks and barrier islands includes dredgeate, timber river pilings, and Lower Mainland clean construction fill. These placements, combined with jetty breaks, will cause sediment and organics to settle out, accelerating accretion. This in turn will further buttress the islands, and allow the new and existing marshland to rise in tandem with sea level. With storm surge mediated by the new built form, the need for dyke improvements will be substantially reduced.
Timber pilings will be the first visible feature, installed to encourage the formation of the “Pile-Up” barrier islands. Driftwood, which often damages plants through tidal movement, will be gathered and added. The islands will in time protect the marshes from new driftwood movement. Throughout, salt-tolerant terrestrial and aquatic plant species will provide both stability and wildlife habitat. The resulting increase in biomass will improve carbon sequestration. Like a traditional Salish fish trap, a simple structure built across the water will help us remain in our coastal home.
This scheme requires neither relocation nor new building technologies for coastal settlements to thrive in situ. The works proposed will be located almost entirely seaward of Richmond and Delta. The barrier islands present significant recreational opportunities that enable humans not just to adapt but to thrive. These include trails, parkland and wildlife viewing on the islands, boardwalks between them, boating and even low-tide wading around them.
The barrier islands will have a beneficial effect on flora. Near the shore, the Fraser Delta traps both riparian and marine sediment and organics. Zonal ecosystems develop tolerance to flooding and salinity. Further out, organic-rich mudflats transition to deeper water, and distinct marsh communities form zones from the mudflats to the shoreline. These are typically resilient and adapted to storms, tides, and shifting river sediment patterns. They are also expected to respond proportionately to changing sea level if the delta front is not deprived of sediment and organics. Low energy sites inland of the Pile-Up islands will enhance and sustain this sediment accretion and marsh creation.
The Fraser River Delta is globally important for migrating waterfowl, shorebirds, and fish. Maintaining its health and scale is essential in a proper response to sea level rise. Fortunately, opportunities exist to restore or create habitat, including a series of new ecologically diverse and productive areas seaward of the existing delta front, as Pile-Up proposes. Providing a zone where native marsh and mudflats can expand will ensure that habitat is enhanced.
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