The Need for a Tidal Flood Stage to Define Existing and Future Sea Level Hazards

Abstract

The frequency of tidal flooding is considered through the use of a coastal flood stage, an elevation at which significant flooding is initiated. This paper explores the need for, and possible definitions of, such a coastal flood stage. Once adopted, the flood stage serves as a convenient reference elevation or threshold that future storm events can be compared to. A case study is carried out for Annapolis, MD, using a statistical flood stage at an elevation a few feet above mean higher high water. This is then used to evaluate the increase in flood depth and frequency associated with the occurrence of future storm events along with different future sea level rise scenarios. Introduction The term “Flood Stage” is commonly used by the National Weather Service (NWS), and by state, county, and local officials to define a river stage that is expected to initiate flood damages. The flood stage varies from location to location along a river, but has local meaning to residents and officials as way of conveying river flooding to level that begins to create a hazard. In general, the flood stage should indicate a river level that begins to flood ground elevations and cause damages to buildings and infrastructure. The NWS further defines “minor” flood stages as flood levels causing minor or nuisance flooding, as well as “major” flood stages causing serious widespread damage. The premise of this paper is that similar local flood stages should be established in all U.S. coastal communities as a way to better define coastal flood hazards. These “coastal flood stages” or “tidal flood stages” would be established relative to a fixed datum and would indicate a storm tide level (astronomical tide plus storm surge effects) that would begin to inundate critical infrastructure such as roads and buildings.