# The Impact of Leveee Openings on Storm Surge: A Numerical Analysis in Coastal Louisiana
## 4 Conclusions  
Using Hurricane Isaac (2012) as an example, a pre-validated Delft3D-based hydrodynamic model was applied to study the effect of levee removals on storm surge in Barataria  
Figure 11: Flux (m\({}^{3}\)/s) analysis at the lower-crossing location for 02:45 UTC 8/29/2012 (top) and 16:45 UTC 8/29/2012 (bottom) during Isaac (2012). The thickness of flux arrow is proportional to the amount. (**a**) 02:45 UTC 29 August 2012. (**b**) 16:45 UTC 29 August 2012. Basin and Breton Sound of coastal Louisiana. Two removal locations (i.e., the upper crossing and the lower crossing) were selected in this study. Three scenarios were carried out, that is, the base case with existing conditions, the both-crossing case with two level removal locations and the no-levee case with the removal of all MR&T levees in the model domain, to demonstrate the effects of constructing these crossings/floodways through the mainstem MR levees. The model performance was further validated by four CRMS stations near the two levee-opening locations in Barataria Basin and Breton Sound. Isaac induced much higher storm surge (>4 m) in Breton Sound than in Barataria (~2 m). In the extreme and impractical no-levee case, the surge difference between two basins reduced to ~1 m, i.e., 3.5 m in Breton vs. 2.5 m in Barataria. In the more practical both-crossing case, however, the impact on storm surge in Breton was minor, only about 0.1 m of reduction closely confined to the two levee opening locations. The primary purpose of this study is to test if the levee removals can help reduce storm surge in adjacent basins. The reason the levee openings were not effective in reducing storm surge heights is the complex interaction between the cross flow from the surge and the MR flow. In essence, the MR water was diverted to Barataria and/or Breton, which resulted in an increase in water height, essentially defeating the primary objective of the levee openings. Based on flux analysis, Isaac pushed water from the MR to Barataria through the west bank of crossings. As for the east bank of the upper crossing, Isaac could cause water exchange in both directions due to the variation of hurricane wind direction. The impact of levee openings can be demonstrated by the difference flux pattern maps. In this study, four maps were analyzed for the two crossing locations during Isaac. The results of these maps can be grouped into two patterns:  
* Pattern 1: The reversed MR water from the south edge crosses riverbanks to Barataria and/or Breton (see Figure 8 top and Figure 11 top). This pattern results in an increase in water level in the basins. * Pattern 2: The basin water from Barataria and/or Breton enters the MR (see Figure 8 bottom and Figure 11 bottom). This pattern is beneficial to storm surge reduction in Barataria and/or Breton. It should be noted that only one hurricane was considered in this study. The impact of levee openings might depend on individual hurricane parameters (e.g., storm track, forward speed and wind intensity). On the other hand, among the four devastating hurricanes that affected coastal Louisiana recently, except Ida (2021), three of them, i.e., Katrina (2005), Gustav (2008) as well as Isaac (2012) in this study, induced much higher storm surge in Breton Sound than in Barataria Basin, which implies that Isaac could be a representative extreme storm event for coastal Louisiana. Overall, based on model results and flux analysis during Isaac, the effect of levee openings at the selected locations on storm surge reduction in adjacent basins of coastal Louisiana was minor and very limited. Conceptualization, K.H., E.M. and A.R. ; methodology, K.H. ; software, K.H. ; validation, K.H; formal analysis, K.H. ; investigation, K.H. and E.M.; resources, E.M.; data curation, K.H. ; writing--original draft preparation, K.H. ; writing--review and editing, E.M., R.R., N.S. and A.R. ; visualization, K.H. ; supervision, E.M. and N.S. ; project administration, R.R. ; funding acquisition, E.M. and N.S.