Post-Earthquake Water Supply Restoration
For fifty years, post-earthquake fire spread models used the basic empirical, macro approach developed by Hamada in 1951. Recently, however, a few physics-based models have emerged in which different modes of fire spread (e.g., radiation, branding) are modeled separately, more realistically, and in more detail. In this project, we have developed a new physics-based model that simulates the spread of post-earthquake urban fires. Adapting and integrating compartment fire models, this new model explicitly represents: (1) the evolution of fire within a room or roof; (2) room-to-room spread within a building through doorways, by burning through walls and ceilings, and by leapfrogging between windows; and (3) building-to-building spread by window flame impingement; radiation from window flames, room gas, and roof flames; and branding. Using a case study for Los Angeles, this research illustrates how the new model can be used to estimate how much, how fast, and where fires spread, and also to provide insight into how fires spread and factors that influence fire spread.
In another effort as part of this project, we have developed a new approach to statistical modeling of post-earthquake fire ignitions and to data collection for such modeling, and applied it to late 20th century California. Generalized linear and generalized linear mixed models (GLMs and GLMMs) are used for this application for the first time. The approach recognizes that ignition counts are discrete, examines many possible covariates, and uses a small unit of study to ensure homogeneity in variable values for each area unit. Two datasets were developed to explore the effect of missing ignition data, each with a different assumption about the missing data. For one dataset, the recommended model includes instrumental intensity; percentage of land area that is commercial, industrial, or transportation; total building area; percentage of building area that is unreinforced masonry; and people per sq. km. The other includes the same, except area of high-intensity residential development replaces total building area, and median year built over all housing units is also included. The models should be useful in estimating the number and locations of post-earthquake ignitions in future earthquakes.
In this project, we developed a discrete event simulation model of the post-earthquake restoration process for the Los Angeles Department of Water and Power (LADWP) water supply system, the largest municipal utility in the U.S. This is the first application of discrete event simulation to post-disaster water supply restoration, and one of the first for any infrastructure system. Discrete event simulation offers many benefits for restoration modeling compared to alternative methods. The water supply system and restoration process are represented in great detail with few simplifications. The utility company’s decision variables (e.g., number of repair crews, repair prioritization rules) are included explicitly, allowing exploration of their effects on the speed of the restoration. Uncertainty is represented explicitly.
The model, developed with extensive input from LADWP managers and engineers, mimics the real-life process in detail, simulating the movement of different types of crews as they inspect, reroute around, isolate, and repair system damage. For any given earthquake, the model provides restoration curves with uncertainty bounds, maps showing the spatial distribution of outages over time, and crew and repair material usage information. It can be useful for loss estimation and resilience assessment, evaluating the effectiveness of hypothetical restoration strategies, and improving understanding of the restoration process and its key determinants.
The model was run using historic damage and system data from the 1994 Northridge earthquake. Results for the calibration simulations suggest the model is capable of accurately estimating the time and spatial sequence of the restoration. The model was then applied to estimate durations of post-earthquake water supply outages in Los Angeles for five possible earthquakes. The analysis suggests that earthquakes on different faults can cause significant variability in damage as well as the duration of the loss of service. Finally, the model is being used to evaluate the effectiveness of key post-earthquake water supply restoration strategies that the LADWP plans to use following a major earthquake: (1) maximizing the groundwater pumped into the system, (2) connecting raw water emergency storage reservoirs, (3) rationing water use, and (4) all three. For each of five realistic earthquake scenarios the restoration with and without implementation of the key restoration strategies are compared. The results suggest that opening the reservoirs and rationing are effective post-earthquake restoration strategies that would help to minimize the water outages.
Study Related Publications
Brink, S., Davidson, R., and Tabucchi, T. Strategies to reduce durations of post-earthquake water service interruptions in Los Angeles, in review.
Tabucchi, T., Davidson, R., and Brink, S. Simulation of post-earthquake water supply system restoration. Civil Engineering and Environmental Systems, in press.
Tabucchi, T., and Davidson, R. 2008a. Post-Earthquake Restoration of the Los Angeles Water Supply System. MCEER technical report, MCEER-08-0008, Buffalo, NY.
Study Related Presentations
Brink, S., Davidson, R., and Tabucchi, T. Estimated durations of post-earthquake water service interruptions in Los Angeles, TCLEE2009 conference (ASCE Technical Council on Lifeline Earthquake Enginering), June 28-July 1, 2009, Oakland, CA, Invited paper. Peer-reviewed.
Tabucchi, T., Davidson, R., and Brink, S. Restoring the Los Angeles water supply system following an earthquake. Proc., 14th World Conference on Earthquake Engineering, October 12-17, 2008, Beijing.