One Size Does Not Fit All Evaluating Dam Breach Parameters for Small Urban Distribution Reservoirs

Flood inundation maps due to dam breach failure scenarios are often provided as guidance to emergency management for emergency preparedness downstream of dams. Dam breach parameters estimation using regression equations are typically applied in development of these inundation maps; however, the empirical relationships in the regression equations are based on failures of larger facilities and are commonly applied to dams of reservoirs with substantial storage volumes and dam heights. The East Bay Municipal Utility District, a water utility that serves approximately 1.4 million people in northern California, owns and operates twenty-six reservoirs of which nineteen are local dam impounded distribution reservoirs (‘open-cut’ reservoirs) used for storing treated water. Among the distribution reservoirs are a group of smaller open-cut facilities with a typical dam height of 20 feet and individual water storage capacities ranging from 7 acre-feet to 30 acre-feet. These smaller facilities reside in heavily urbanized areas and necessitate emergency action planning for a potential dam breach failure. An evaluation to determine appropriate dam breach parameters was performed focusing on six commonly referenced breach parameter estimation methods along with six peak flow estimation methods (based on dam height, reservoir volume) and applied to the selected facilities. The results of the sensitivity analyses and the implications of the findings are then presented.