# The Impact of Leveee Openings on Storm Surge: A Numerical Analysis in Coastal Louisiana
## 3 Model Results and Flux Analysis
### Flux Analysis  
Figure 6 shows time series of water level at different sides of the west/east banks and flux through riverbanks at the upper-crossing location in the base case. Figure 7 shows  
Figure 5: Maximum surge (m, NAVD88) and surge difference (m) distributions by Isaac (2012). (**a**) Base case (existing conditions); (**b**) Both-crossing case; (**c**) No-leve case; (**d**) Both-crossing case— Base case; (**e**) No-leve case—Base case. White lines denote contour lines every 1 m. Blue lines denote contour lines with negative values every 0.1 m. Yellow lines denote contour lines with positive values every 0.1 m. Magenta line with dots denotes the track of Isaac (2012). the results in the both-crossing case. In the base case (see Figure 6), the flux across both riverbanks remained at zero because the surge height during Isaac never exceeded the levee height (4.7 m, NAVD88). The levee system blocked the exchange between river water and basin water. In the both-crossing case (see Figure 7), both riverbanks kept open during most of the period of Isaac. For the west bank, the water always flowed from the MR to Barataria. For the east bank, the water first flowed from the MR to Breton (positive flux), then quickly changed its direction and flowed from Breton to the MR (negative flux). Figure 8 compares flux patterns at two instances (see Figure 7 bottom-right) when the flux through the east bank attained its maximum value at the two opposite directions. Wind fields around these two instances can be found in Figure 3a,c, respectively. At 03:15 UTC 29 August, both riverbanks were never overtopped in the base case. The south and southeast winds (see Figure 5a) along the MR river caused the reversed river flow from south to north. In the both-crossing case, the flux across the river south was significantly increased, and a large amount of river water was diverted into both basins. It is to be noted  
Figure 6: Time series of water level (m, NAVD88, top) and instantaneous flux (m\({}^{3}\)/s, bottom) for the west (left) and east (right) banks at the upper-crossing location in the base case during Isaac (2012). The direction of positive flux is from west to east. Figure 7: Time series of water level (m, NAVD88, top) and instantaneous flux (m\({}^{3}\)/s, bottom) for west (left two) and east (right) banks at the upper-crossing location in the both-crossing case during Isaac (2012). The direction of positive flux is from west to east. that the easterly winds over Breton can retard the flux from the MR to Breton, but they were not strong enough to reverse the flux direction from Breton to the MR. The difference flux pattern map (Figure 8 top-right) indicates that the effect of levee removal caused the redistribution of river water from the south and the north to both basins. This effect is not good for surge reduction in Breton and Barataria. At 10:45 UTC 29 August, the river flow was changed from north to south with a very small amount (\(\sim\)300 m\({}^{3}\)/s) in the base case. The storm surge in the upper Breton Sound kept rising due to the continuous east and south winds. After the levee removal, a large amount of water from Breton flowed into the MR and Barataria. The difference flux pattern map (Figure 8 bottom-right) shows that 75% of the water from Breton entered the downstream of the river, 20% flowed via the MR into Barataria and the rest (5%) flowed upstream. This pattern was beneficial in terms of reducing storm surge in Breton. Figure 9 shows time series of water level at different sides of the west/east banks and flux through riverbanks at the lower-crossing location in the base case. Figure 10 shows the results in the both-crossing case. In the base case (see Figure 9), the west bank was never overtopped during Isaac, while for the east bank with no river or basin levee structures, the  
Figure 8: Flux (m\({}^{3}\)/s) analysis at the upper-crossing location for 03:15 UTC 29 August 2012 (top) and 10:45 UTC 29 August 2012 (bottom) during Isaac (2012). The thickness of flux arrow is proportional to the amount.