THE DEVELOPMENT OF A COASTAL FLOOD NOMOGRAM FOR SOUTHWEST COASTAL MAINE AND THE SEACOAST OF NEW HAMPSHIRE

Extreme tides and large, battering waves have the potential to cause hazardous conditions along the sandy southwest coasts of Maine and New Hampshire. Increasing storm tides inundate low lying areas, while building waves lead to beach erosion and structural damage. The combined effects of these dynamical forces are complex and not fully understood. According to a recent Northern New England coastal flood climatology (Cannon 2007), damage often occurred during Nor'easters despite tide levels significantly below the Portland Harbor flood stage of 12.0 ft. The empirical relationship between storm tides and large, battering waves demonstrated the need to create a forecast prediction scheme based on impact and not solely on water level. Hourly forecasts of water level and near-shore waves were plotted simultaneously to visually display oceanographic conditions on a single diagram. The East Atlantic Water Level Forecast (ADCIRC) and Wave Watch III models were used to produce the output. The result is a web-based coastal flood nomogram, which is produced twice daily at www.gomoos.org. When animated, users can monitor for critical splash-over and coastal flood benchmarks as thresholds are exceeded. The tool assists meteorologists and emergency managers in the forecast and hazard mitigation process.