NEWS 2011

Posted October 12, 2011 (Updated October 21, 2011)

Event: November 2, 2011

GSE/CGS Cross Canada Lecture: Steven G. Vick, Colorado - Geotechnical Risk and Public Policy - The Other Side of the Wall

Location: Petroleum Club, Edmonton (11110 - 108 St)

Time: 6:00pm Registration, 6:20pm Dinner, 6:50 Presentation

Cost: $30 Members, $40 Non-members, $10 Students

Risk assessment for structures like dams and levees is not finished when the analysis is completed. The ultimate goal of risk assessment in a public policy setting is to improve public safety by informing the decisionmaker, who then acts on its findings. But how does this happen? Or for that matter, does it happen at all? This lecture looks beyond procedural mechanics to how geotechnical risk analysis is actually implemented in a public policy setting from two recent examples in the U.S.

Funded by Congress over a 50-year period, the New Orleans Hurricane Protection System was flawed from the start, a system in name only whose engineering compromises were driven by political compromise. Its glaring vulnerabilities cried out for systematic analysis of risks, yet none was ever performed until Hurricane Katrina made them tragically manifest in August, 2005. More than 600 of the 1460 fatalities were attributed to geotechnical failures of the levees, and the rest to overtopping. In a diaspora not seen in the U.S. since the 1930s Dust Bowl, 400,000 residents of New Orleans were scattered throughout the country. Only after the floodwaters subsided was a comprehensive risk analysis begun. Perhaps overly ambitious for the novel and highly complex problem of hurricane risk, its results were not produced until 2008 - too late for evacuees who had to decide without it whether to relocate or return.

The Herbert Hoover Dike encircles the 140-mile perimeter of Lake Okeechobee in south Florida. It lies at the convergence of 11 major hurricane tracks since 1928, when the deaths of 2800 persons from hurricane storm surge prompted the dike's construction of dredged sands. The lake's shallow depth and the cyclonic rotation of hurricane winds combine to produce a unique geotechnical phenomenon of cyclic gradient reversal within its vugular limestone foundation that can only be described as an internal erosion machine. By the mid-1990s increasing damage was evident with each hurricane that passed, and a risk analysis put the annual probability of dike failure at 1-in-6. Only repeated intervention had saved it and the affected population of 40,000 people. But these risk results had never been made known, resulting in the tragi-comic scenario of plans for hurricane evacuation of Miami directly into the potentially inundated area.

Six years after Katrina, work on the New Orleans Hurricane Protection System to be completed in 2011 will protect against the 100-yr storm surge, a major upgrade but still two orders of magnitude less than typical for dams. As for the Herbert Hoover Dike, its risks are now well-known by the public throughout south Florida, but slurry-wall repairs now underway may take decades to finish. The lesson in both cases is simple: a risk analysis is only as good as the public's knowledge of its results and the decisionmaker's willingness to act on them.

Author and independent consultant Steven G. Vick has based his practice in the mountains of Colorado for the past 25 of his 40 years in the profession. A veteran of Klohn Leonoff's former Denver office, Vick has always had close ties with the Canadian geotechnical community. Long specializing in mining geotechnics, his first book Planning, Design, and Analysis of Tailings Dams remains the classic text on the topic and has been in print continuously for almost 30 years. Beginning with graduate research at MIT, his other main interest has been risk and probabilistic methods.

The CCLT is organized by the Canadian Geotechnical Society, with funding through the Canadian Foundation for Geotechnique.

Sponsorship provided by:

• Klohn Crippen Berger
• BGC Engineering
• EBA Engineering
• Golder Associates