Shallowing of Seabed Bathymetry for Flood Preparedness: Designing Nearshore BMPs

Abstract

The devastating impacts of frequent coastal storms, such as Hurricane Katrina in New Orleans in 2005 or Superstorm Sandy in New York City in 2012, in major low-lying metropolitan areas have had repercussions far beyond previously experienced disasters. Two key findings that describe these repercussions related to these events were stated as follows: in the case of Katrina, there was a lack of holistic or system-based thinking, and in the case of Sandy, there was an insufficient integration of critical infrastructure. Among different remediation actions, inland placement of best management practices (BMPs) in order to protect coastal cities from storm surges has received a lot of attention. However, nearshore BMPs as a way of source (wave height) reduction have not yet been thoroughly investigated. Nearshore practices are especially attractive in coastal areas that experience significant wave heights as a total water level component. In this paper, the effects of bathymetric shallowing through an apron on reducing the wave height and water level during storms are investigated in coastal areas. Southern Brooklyn in New York City is selected as the case study. A hydrodynamic model is utilized to generate wave height and storm tide. A water-level hydrograph in ungauged areas of the case study is constructed, which has not been realized before in similar coastal flood studies. Water level variations are investigated to include generated storm surge and wave characteristics. The results show that shallowing can reduce the peak of wave height and water level by 47% and 10%, respectively, in open coastal areas. In a more contained bay area, the reduction of a water level was more than 13%. These figures show the potential of nearshore BMP applications that could significantly improve our flood preparedness plans. The proposed methodology can be applied to other coastal geographical settings.