Resiliency Against Overtopping – Determining the Need for Armouring on the Levees of New Orleans

Following the devastation caused by Hurricane Katrina in August 2005, the US Army Corps of Engineers improved the Greater New Orleans Hurricane and Storm Damage Risk Reduction System (HSDRRS) to a 1:100 per year standard. Part of the remit in designing the improvements was to provide structural resiliency against overtopping, with armoring of landward levee slopes as an important element. This paper describes the innovative methodology to determine where armoring is needed. The methodology is based on a combination of the emerging Cumulative Excess Loading concept, practical engineering judgment and the outcomes of recent simulation research projects at Colorado State University (CSU) and in Europe. The paper describes in detail the judgments made to interpret physical modelling outcomes in order to arrive at a justifiable and practical method. The results show that the grass types and other circumstances in New Orleans make it possible to allow a much higher overtopping discharge than typically accepted for European grass under wave overtopping.