Escape from the Delta: preparation and evacuation for catastrophic flooding in California Emergency Management Agency Region IV
Yuhas, Timothy C.
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Executive Summary: We model the evacuation of inhabitants of Yolo, Sacramento, San Joaquin and Stanislaus Counties of Central California using a minimum cost network flow model of the regional highway system. Our model MINITRISK solves for "best case" evacuation routes and clearing times assuming perfect knowledge by all travelers of road conditions. Our model is large, but efficient, solving 35 separate scenarios in less than 45 minutes. By solving separate scenarios, we analyze model assumptions and the effect of interruptions to evacuation behavior for a range of "what-if" situations We develop two models to identify optimal evacuation routs as well as quantify highway demands during an evacuation in Yolo, Sacramento, San Joaquin and Stanislaus counties. MINATRISK is a single commodity minimum cost network flow model, and MINDIST is a shortest path optimization model which identifies the shortest path from every node in the network to every one of the possible evacuation points. We represent the systems of highways in Region IV as a network, with ZIP codes representing sources of evacuees, transshipment nodes as highway junctions, and arcs as highway segments. We establish a base case evolved from California Highway Patrol's Standard Operating Procedure which does not currently plan for contraflow, and apply this case to two baseline scenarios one in which Sacramento County is evacuated, and one in which ZIP codes which lie adjacent to the rivers of the region are evacuated. These scenarios differ only in the subset of ZIP codes which are directed to evacuate in the first epoch. Our model indicates that it is possible to evacuate approximately 1.2 million people from Sacramento County and River-Side evacuations in 24-hours and 15-hours respectively. We find that the shortest route for most evacuees is to travel to the East and in the Bay Area. We find that loss of access to the evacuation points east of the valley increases evacuation clearing times by 25% in the Sacramento County scenario and 40% in the River-Side scenario. We adjust parameters in the model to cause highway inundations and allow for the use of contraflow. Inundating highways did not substantially change evacuation results however, the inundation of I-5 combined with the loss of evacuation "PointsE" did cause more people to travel to evacuation point "PointsS" in the River-Side evacuation than in any other scenario. Furthermore, because we assume two passengers per vehicle, we find people evacuate six hours faster with the use of contraflow. However, because the evacuation of Sacramento County in its entirety in unlikely, and the River-Side evacuation more plausible, we find that our model and the analysis of its results does not support the establishment of contraflow if the evacuating population is not as concentrated as in the Sacramento County case. Our model results show, for each scenario the number of frustrated travelers in every time period over the planning horizon, and therefore paints a clear picture of the progress of the evacuation in each scenario. An important first step in understanding evacuations, the results of our model can provide insights to emergency planners for the positioning of supplies, determining emergency locations and personnel requirements.Executive Summary for an NPS Thesis https://hdl.handle.net/10945/5805
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