Evaluation of Physical Stability and Physiological Fatigue of Pedestrians in Tsunami Flooding Conditions in Puerto Rico

Abstract

This study evaluates the stability and mobility of pedestrians during tsunami-induced flooding in Puerto Rico. The research was divided into two main phases: the development of an analytical stability model (Phase 1) and an experimental fatigue study (Phase 2). In Phase 1, pedestrians were represented as rectangular prism and cylindrical monoliths to determine the impact of water depth and velocity on their sliding and overturning stability. Drag, buoyancy, friction, and body weight forces were considered. Anthropometric data from Puerto Rican adults and 6-year-old Colombian children were used to evaluate the analytical model. The results demonstrated that instability could occur at low water levels and moderate velocities, that sliding is the predominant cause of instability, and that the footwear-to-ground friction coefficient is the critical parameter. It was also observed that children and women are the most vulnerable populations. In Phase 2, a gait study was conducted using two concentric pools simulating an endless evacuation walk, monitoring heart rate and oxygen consumption with a portable spirometer at different flood levels (ankle, knee, and hip). Contrary to the initial hypothesis, the greatest physiological effort (measured by oxygen consumption) occurred at intermediate levels (ankle and knee). At the hip level, buoyancy reduced muscle load but drastically decreased walking speed. These findings demonstrate that horizontal evacuation routes should be designed with pavements that provide a high coefficient of friction, and that extended evacuation under flooded conditions may be infeasible, highlighting the need to integrate vertical evacuation options in high-risk coastal areas.