The Coastal Resilience Safety Factor: A General Method for Coastal Design Under Deep Uncertainty, with a Vancouver Application

Desmond Rodenbour 

Global sea level rise is accelerating, and a substantial portion of the coming rise is now committed regardless of future emissions; coastal cities must therefore shift from preventing the hazard to designing for it. That shift poses a question every other safety-critical discipline already answers in its own domain: how large a design margin a structure should carry when the load is deeply uncertain and the cost of failure is catastrophic. This paper reframes coastal design through the engineering logic of the safety factor and develops a Coastal Resilience Safety Factor (CRSF): a general, portable heuristic decision rule that sums the independent drivers of relative sea level rise demonstrable on a given coast and multiplies the uncertain among them, which in a two-driver case like Vancouver is the whole sum, by a margin scaled to the consequence of failure. The paper sets out the method in full: how any coastal jurisdiction populates the rule with its own drivers, a stopping rule that bounds additive summation, the discipline for setting and reviewing the consequence factor, the standardization of the planning horizon, and a governance cadence that separates annual review from event-driven revision so the standard stays current without unsettling the design basis a multi-decade capital programme depends on. The method is then put to its first application, Vancouver, among the most exposed Canadian municipalities: a low-lying shoreline carrying high-value land and regional lifeline infrastructure, compounded by its position above the Cascadia subduction zone, where a great earthquake could lower the land by a metre or more, adding coseismic subsidence to the climbing sea. Vancouver’s technical study of the hazard is extensive, yet little attention has been paid to whether its adopted design standard is calibrated to the consequence of failure, or to what the gap will cost. For Vancouver the rule combines the climate-driven rise and the relative rise a Cascadia rupture could impose, both uncertain and upward, so that a coast whose dominant driver is instead well-constrained or sea-level-lowering remains the awaited test of the method’s full generality. The framework returns a defensible target near 3.4 m at central values and near 6 m for critical, long-lived assets, against the city’s present flood construction level of roughly 1.6 m, which sits at the conservative corner of the range. Extrapolating the province’s 2012 dike estimate to that standard places an all-protection response in the order of tens of billions of dollars, roughly CAD 25 to 50 billion for the moderate target, an upper bound on the most capital-intensive lever rather than the cost of the mixed strategy the paper recommends; even so, it remains a programme no municipal budget could absorb, and every year of delay raises both the price and the residual risk. Because such works require voter-approved borrowing under the Vancouver Charter, unfold over lead times measured in decades, and engage the authority of the Musqueam, Squamish, and Tsleil-Waututh Nations hold over their lands and waters, the paper concludes that the planning gap is one of calibration, financing, and governance rather than science, and that the prudent course and the affordable course are the same: to begin now.