Incipient Motion Response Detection of Articulated Coastal Revetment Under Wave Loading

Abstract

Articulated coastal revetments (ACRs) are armoring options for abating earthen levee wave erosion. Stability criteria for ACR design typically allow initial, minor damage during design wave loading conditions (USACE, 2006). Minor wave damages may worsen progressively if not repaired before another design wave loading event. If minor ACR damages evolve under wave action to the point of unraveling, the underlying levee will become exposed to wave forces that could result in breaching (Pilarczyk, 1998). Vulnerability exists in this scenario for catastrophic flood risk management system failure. Current ACR stability limits for maintaining structural integrity under wave attack exist between the thresholds of structure incipient motion and that of initial damage criteria. Using an ACR stability limit that maintains structural integrity would greatly reduce the potential of repeat damage resulting in armor failure. A design challenge exists due to a knowledge gap in detecting and analyzing ACR performance between the thresholds of incipient motion and initial damage (Herbich, 1999). In this research, the threshold of incipient motion for ACRs is explored through small-scale experimentation. Data analysis, including correlations between hydrodynamic forcings and structure responses, extended our understanding of ACR system behavior in specific structural configurations and wave loading conditions. Keywords: incipient motion; articulated coastal revetment; wave loading INTRODUCTIONPilarczyk (1998) explains that wave action impacts have the potential to result in soil erosion on the seaward faces and crown of exposed earthen dike (i.e., levee) structures. Figure 1 illustrates the effect of near shore seaward slope wave breaking and run up on a vegetated earthen levee in the vicinity of Eastern New Orleans, Louisiana, USA, which caused stripping of the vegetation layer and embankment soil loss during Hurricane Gustav in 2008 (USACE, 2008). Conventional erosion-abating armor may impose loadings that induce subsidence of earthen levees and underlying foundation soils, presenting a challenge in maintaining required design crown elevations of flood risk management systems. A new approach using continuously-connected, articulated coastal revetment (ACR) systems may have potential to resist wave attack while being significantly lighter than traditional designs.Proper design for sloping revetments requires an understanding of the three modes of instability: uplift, sliding, and toe roll-up, which are summarized by McDonnell (1998), Pilarczyk (1998), andHerbich (1999). A field prototype-scale investigation was conducted in coastal Louisiana to assess the performance of ACRs in resisting a range of wave loading conditions (Russo, 2003). Previous work and this experiment demonstrated an increased need for understanding the processes leading to the incipient motion of ACR systems and translating this to the development of suitable design procedures. Design procedures should include:• optimizing armor dimensions to resiliently resis...