Engineering & Risk Assessment
Coastal Vulnerability.
Analyzing the structural threshold: Where hydrodynamic force meets the built environment.
Engineering & Risk Assessment
Analyzing the structural threshold: Where hydrodynamic force meets the built environment.
Structural Analysis
Understanding coastal vulnerability requires moving beyond simple elevation maps. It is an engineering discipline that evaluates how specific structures—residential homes, industrial complexes, and critical infrastructure—withstand the complex forces of a tsunami.
A tsunami is not just a rise in water level; it is a high-velocity flow laden with debris. At the Tsunami Evaluation Institute, we use specialized "Vulnerability Matrices" to quantify the risk to a community. This involves individual asset inspections and the application of "Fragility Curves"—statistical models that predict the probability of damage level (from minor to complete collapse) based on the maximum inundation depth and flow velocity at the site. This data is essential for insurance underwriting and long-term urban resilience planning.
Our vulnerability assessments are the primary data source for disaster risk reduction (DRR) strategies. By identifying which buildings are likely to fail, we can prioritize seismic retrofitting, recommend the relocation of critical services like hospitals and power stations, and design more resilient "soft" and "hard" coastal defenses. We also consider "Socio-Economic Fragility," understanding how factors like population density and age-dependency ratios amplify the physical risk.
Hydrodynamic Loads
Designing for a tsunami means designing for four distinct types of physical loads that act simultaneously on a structure during an event.
1. Hydrostatic Forces: The pressure exerted by the standing or slowly moving
water. This is proportional to the depth and can cause walls to buckle or foundations to shift
if the water enters the building.
2. Hydrodynamic Forces: The drag force created by the high-velocity flow. This
is a function of the water density, the drag coefficient of the structure, and the square of the
flow velocity. Even a few meters of water moving at 5 m/s can generate enough force to push a
house off its foundation.
3. Buoyancy (Uplift): As water surrounds a structure, it creates an upward
force. For light-framed wooden buildings, this often causes the entire structure to float away,
becoming a piece of destructive debris itself.
4. Debris Impact: Floating objects—cars, shipping containers, and even other
houses—act as massive battering rams. The impact of a shipping container can cause catastrophic
failure even in reinforced concrete structures that were otherwise surviving the water force.
| Inundation | Masonry | RC Frame |
|---|---|---|
| 0-1m | 15% Fail | 2% Fail |
| 1-3m | 45% Fail | 8% Fail |
| 3m+ | 95% Fail | 35% Fail |
Foundation Integrity
Many buildings fail not because the walls break, but because the ground beneath them is washed away by receding waves.
As a tsunami wave recedes, it carries a massive volume of water back to the ocean. This creates high-velocity "return flows" that can scour deep trenches around the base of a building. In granular soils like sand, the process is rapid and can undermine footings within seconds. Additionally, the rapid change in water level can lead to "Liquefaction-like" states in the soil, where high pore-water pressure reduces the soil's bearing capacity, causing the structure to tilt or sink. This is especially dangerous for seawalls and coastal roadways.
To prevent scour-based failure, engineers use "Deep Foundations" (piles or piers) that extend far below the potential scour depth. We also recommend the use of "Sacrificial Slabs" and rip-rap (large stones) around the perimeter of critical structures to absorb the energy of the flow and protect the underlying soil. Proper drainage design is also essential to manage the high volume of water trapped behind seawalls and within urban corridors, preventing the buildup of destructive pressure.
In areas where a high-ground "Safe Haven" is too far away to reach on foot, vertical evacuation—moving to the upper floors of a resilient building—is the only option. But not every tall building is suitable; it must be designed to withstand the hydro-seismic sequence.
The FEMA P-646 guidelines provide a rigorous framework for the design of tsunami-resilient structures. These buildings must be designed for "Multi-Hazard" resilience—withstanding both the initial earthquake and the subsequent tsunami forces. This requires reinforced concrete frames, "break-away" walls on the ground floor to reduce hydrodynamic drag, and deep, scour-resistant foundations. Furthermore, the evacuation floor must be at least 30% higher than the maximum predicted inundation depth to account for "splash-up" and modeling uncertainty. The structure must also be clear of potential debris impact zones.
At TEI, we certify existing commercial and municipal buildings for vertical evacuation. This process involves detailed non-linear structural analysis and a review of the building's utility resilience. We also help communities design dedicated "Evacuation Towers"—specialized, open-frame steel or concrete structures located in high-density areas. These towers provide a visible and reliable refuge, reducing the psychological stress of an evacuation and ensuring that even the most vulnerable populations reach safety in time. Our goal is to ensure that no coastal resident is more than 10 minutes away from a certified life-saving elevation.
Regional Risk
We maintain a global database of coastal vulnerability, allowing us to identify "Hotspots" where the combination of high hazard and poor building standards creates extreme risk.
Using cost-benefit analysis to determine which critical assets (schools, clinics) provide the highest life-saving return on investment for seismic and tsunami retrofitting.
Evaluating the vulnerability of maritime infrastructure to "Seiche" effects and high-velocity currents that can paralyze global supply chains during and after an event.
Integrating demographic data to understand how social factors—age, mobility, and income—amplify the physical vulnerability of a coastline.