A DISPERSIVE LONG-WAVE MODEL FOR PREDICTING COASTAL FLOODING DUE TO STORM SURGES AND SURFACE WAVES IN MANILA BAY

Manila Bay is a shallow coastal water encompassing the urban areas of Metro Manila and variouscities of sub-urban provinces in the Philippines. It is a relatively shallow semi-enclosed basinwith an average depth of 20 m whose coastal areas are crowded with residential, industrial,agricultural, and aquaculture production. Its shallow depths imply that the effect of wind stress onsea level becomes appreciable in driving storm surges even during enhanced Southwest Monsoonand the passage of moderate storms.Using a dispersive long-wave model coupled with the significant wave model of the CoastalEngineering Research Center (CERC), the occurrence of potentially devastating storm surgeflooding around Manila Bay was numerically simulated. A unique characteristic of the new modelis the inclusion of the dispersive terms in the associated momentum balance equations. Deepwater gravity waves are always dispersive and inclusion of the dispersive terms is expected toprovide more accurate modelling results.The predictive capability of the model was verified using observations during the passage ofseveral storms including Typhoon Milenyo (2006) and Typhoon Pedring (2011). The occurrenceof the anomalously high storm surge of about 2.5 metres during the passage of Typhoon Pedringfar north of the area was correctly simulated. Numerical integration of the dispersive long-wavemodel with the addition of higher order terms in the momentum balance appears to give accuratepredictions of the coastal flooding due to storm surges and waves.The hydrodynamic set-down which occurs in many coastal areas during strong typhoons can besimulated well by the model. A new empirical model for the hydrodynamic force exerted by thecombined action of storm surges, waves, and extreme currents is also presented. Initial calculationsof hydrodydynamic forces generated by an actual typhoon crossing Manila Bay are discussed.

Atmospheric Rivers Spur High-Tide Floods on U.S. West Coast

Researchers analyzed 36 years of data to understand how atmospheric rivers and other factors drive chronic coastal flooding.

A Coastal Flood Event Database for the Southeastern Georgia and Southeastern South Carolina Coast and the Operational Implementation of a Tide Forecast Tool

Coastal flooding occurs when saltwater inundates normally dry land and the resulting impacts can range from minor flooding of low-lying areas along the coast, to significant damage to property and structures. Previous research consistently suggests that if sea-level rise continues to increase along the East Coast of the United States, coastal flooding will occur more frequently. In order to document the history of coastal flooding along the southeastern Georgia and southeastern South Carolina coast, a coastal flood event database was created for National Ocean Service tide gauges located in Charleston Harbor, South Carolina and Fort Pulaski, Georgia. Trends from the data show that coastal flooding is occurring more frequently with time at both tide gauges, particularly over the last five to ten years. Because of the increased frequency and worsening impacts of tidal flooding, a tide forecast tool is implemented operationally in an effort to improve deterministic tide forecasts. This study extends the dataset used in the Charleston Harbor forecast tool, expands the tool to Fort Pulaski, and compares the synoptic category forecast equations to an all-inclusive equation that does not differentiate by synoptic category. Results show that there is virtually no difference in the forecast accuracy between the all-inclusive forecast equation and the specific forecast equations based on synoptic category. Furthermore, the all-inclusive forecast equation can be implemented operationally, will help improve deterministic tide forecasts, and will likely aid in the decision-making process for Coastal Flood Watches, Warnings, and Advisories issued by the National Weather Service office in Charleston, South Carolina.

Storm surge prediction and frequency analysis for Andhra coast of India

Storm surges associated with severe cyclonic storms are common occurrences along the east coast of India. The coastal districts of Andhra Pradesh have experienced major surges in the past. Storm surges and the rains associated with cyclones are major causes for coastal flooding in this region. An attempt has been made, in this paper, to simulate surges along the Andhra coast that would have occurred due to severe cyclones during 1891-1996. Inland inundation due to surges is also estimated by using an empirical formula. The computed results are validated with the available observations. The comparison using post-storm survey reports, appears reasonably good to assert that the model is capable of predicting the peak surge amplitude and its location. Frequency of occurrence relationships is obtained for various zones along the coastal region for the purpose of risk analysis.

Decision making in the coastal zone under an uncertain future

Coastal flooding is rated as the second highest risk of civil emergency in the UK, and can cause damage to coastal and estuarine infrastructure, communities, ecosystems, and even loss of life. Hydrodynamic, numerical modelling tools are used to identify regions susceptible to coastal flooding under current and future climate conditions. Modelling procedures and data inputs can lead to a range of uncertainties that need to be quantified for the simulations to be meaningful. Reported public scepticism of coastal hazard forecasting and flood warning accuracy may be due in some part to the way that flood dynamics and uncertainties in the computer model simulations of flood hazard are communicated to the end-users. The briefing explores key uncertainties in flooding predictions, and how these can be better communicated to the public and stakeholders. Improved communication can help to increase awareness and encourage behaviour change to build trust in warnings and forecasts.