Overtopping of Seawalls

Anthony Mignone, National Weather Service
Seawalls and stone armored revetments provide a tremendous amount of protection against wave attack since they absorb and or deflecting most of the wave energy striking them. While they are an effective forward defense they do in many cases allow a tremendous amount of water to wash over their crests as large waves strike their face. This overtopping water can be hazardous to pedestrians or vehicles adjacent to the structure. Significant overwash can also result in flooding from ponding water and damage to infrastructure.

This presentation will describe techniques being developed and tested that combine high-resolution wave models with overtopping parameterizations to provide a way of quantifying the overtopping of seawalls and revetments. The parameterizations compute overtopping in units of volume per unit time that can be directly correlated to storm impact and is also useful for the design of drainage around the structure.

This discussion will be particularly geared to coastal engineers, highway departments, emergency managers, and residence living in the vicinity of shoreline exposed to the open ocean.

Hurricane Inundation Mapping

Cameron Adams, Maine Dept. of Agriculture, Conservation, and Forestry, Maine Geological Survey
Previously, the US Army Corps of Engineers (USACE) created hurricane inundation maps for Maine to aid emergency management planning. The National Hurricane Center’s Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model along with best-available topographic data (a 10-m cell size and vertical accuracy of 2.44 m RMSE) were used. Since then, the SLOSH model was updated by the NHC with higher resolution grids of potential storm surge heights, the entire Maine coastline was mapped using Light Detection and Ranging (LiDAR), and a bare earth digital elevation model (DEM) with 2-m cell size and a vertical accuracy of 0.15m RMSE was created. The Maine Geological Survey, in partnership with the Floodplain Management Office and funding from FEMA, used these datasets to create updated Potential Hurricane Inundation Maps, or PHIMs, for Category 1 and 2 hurricanes making landfall at mean and mean high tide. These maps were released through ArcGIS online. Since the creation of these maps, the USACE received funding to complete additional mapping of Category 3 and 4 scenarios. These datasets are vital to emergency management planning communities at the local, regional, and state levels to help prepare for the “what if” scenario of a hurricane landfall in Maine.

Creating Storm Surge Watch and Warning Maps

John Cannon, National Weather Service
Work with social scientists and the National Hurricane Center (NHC) continues on the "Social Science of Storm Surge" as water (storm surge) remains the most deadly aspect of tropical cyclones. To accomplish this, a panel of subject matter experts was combined with a private vendor (Eastern Research Group) under the guidance of NHC to interview meteorologists, broadcasters, emergency managers and other stakeholders. The goal was to produce a clear and understandable Storm Surge Watch and Warning maps to display such hazards. A prototype of this warning graphic was used during the 2014 tropical season in real-time, during land-falling situations. More importantly, a Storm Surge Inundation Map was created as a result of the social scientist interviews. The detailed inundation maps are dynamic, created “on the fly” in real-time and dependent on many storm factors.

Our findings reflect a "local flavor" from the outcome of a series of meetings with stakeholders along coastal Maine. The presentation will also include a brief discussion of cognitive, affective and social behavior and decision-making on whether to evacuate during these hazardous storm surge situations.

Forecasting Wave, Flooding and Erosion Potential
Qingping Zou, and Dongmei Xie, University of Maine
The southern coast of Gulf of Maine is prone to flooding due to Nor’easter storm. Accurate and timely forecasts of large waves, high storm level and coastal flooding are critical to the early warning and evacuation procedures to save life and protect community. Coastal inundation maps including sea level rise and storms are powerful visualization tools for vulnerable coastal communities to develop strategies to adapt to coastal hazards in a changing climate.

We will apply the state-of-the art two way coupled ADCIRC-UnSWAN model to study wave and storm level during extreme storm event and their contribution to coastal flooding. The objective of this study is two folds: (1) to provide real-time forecast of wave, coastal flooding and beach erosion potential; (2) generate coastal inundation maps including sea level rise and storm in low-lying areas in Maine. Previous wave forecast at Gulf of Maine is improved by using better wind fields at higher resolutions by the “Weather Research and Forecasting (WRF)” modeling. The multi-scale wave forecast and the tide and surge modelling results are fed into a surf-zone model to predict the overtopping/splash over and erosion at a beach or coastal structure. This "clouds-to-coast" system is then used to generate coastal inundation map including the contribution of sea level rise and storms.