 This is Professor Kevin Ksu, he is a professor at Louisiana State University, and Kevin will talk about shelf sediment transport during hurricanes Katrina and Marita. Thank you, Edward. Can you hear me? Yeah. Okay. Good morning, everyone. My name is Kevin. I'm a sushi professor from SU. I also serve as the interim director of Coastal Studies Institute. So today, I'd like to talk about a paper published in 2016. At the beginning, I'd like to acknowledge my co-authors, including Ranjalee Meike, who is now in USGS SMP, Jim Chen from Northeastern, Corny Harris from WIMS, Rob Hetland from Texas NM, Colleen Hu, who is now at Tulane University, as well as Jiaze Wang, who is at UM CES, and she's also in the meeting. So why do we care about hurricane-induced sediment transport? Well, this has been a very hot topic over the past several decades. Many scientists would like to know the seabed erosion and deposition during the passage of hurricanes. Unfortunately, the observation of a hurricane-induced sediment transport is very, very limited. If you use the numerical model, in many situations, the model can blow up due to the extreme condition in the passage of hurricanes. So we have used a modeling system, which is based on regional ocean modeling system, and the sediment part was developed by CSTMS. Back in 2011, we published a paper on continental shelf research to look at the dispersal of the Mississippi and Achafalaya river sediment, so based on that work, we look at the seabed response during the passage of two hurricanes, Katrina and Rita. So we are fortunate to have some very exciting observations from Gurney et al. 2007. They actually went out after the passage of hurricanes to collect the sediment cores, and then they did some really new collide and X-ray analysis to quantify the post-hurricane sediment deposit. So when we run the numerical models, we had to do more than 22 sensitivity tests. The parameters we looked at were mainly on settling velocity, critical shear stress, as well as erosional rates. So now let's take a look at the model setup. So the top figure is the model grid, which was developed by Rob Hetland from Texas A&M, and you can actually see the passage of the track lines of two hurricanes. So here I'm using a red circle as a laser pointer. This is Hurricane Katrina, and this is Hurricane Rita. And then regarding the seabed sediment, we actually interpolated the mud fraction using U.S. seabed database, and we actually got some help from Chris Jenkins. So as you can see in the inner Louisiana shelf, you have lots of red area, which is very muddy, but we do have some coarser area, which is composed of lots of sand, including several major submarine shoals. And the southern boundary is in blue, and this is artificial. We actually just added lots of coarser sediment along the model boundary to minimize some artifacts. And let's take a look at the model validation. So we selected four stations, going from east to west. If you see those five-digit numbers, they are actually from the NOAA and DBC BOE stations. And BURL1 is right on the Mississippi Delta. So during the passage of Hurricane Katrina, you can actually see almost a 50 meter per second of wind speed, which is a huge number. And then after the passage, about one month later, there was Hurricane Rita, and Hurricane Rita also caused a lot of energetic wind in the western part of the model domain. And in general, our model matched the observation very well. But you can see that in panel B and C, we did not have much of observed data due to the damage of the Hurricane Katrina. And then we also compared the modeled wave height with observed wave height. During the passage of Katrina, you can actually see almost 18 meters tall of waves. And this is actually a huge number. And then in another station at CSI-6, we also saw a significant number of wave height, which was around six meters. And then during the passage of Hurricane Rita, we actually saw a really, really large number. You can also see a wider peak, which is in response to the slow movement of the Rita. So now let's take a look at some modeling results. We have a total of six panels. Left three panels are for Katrina, right three panels are for Rita. So if you look at the wind field, the maximum wind field are actually those warm colors over here for Katrina, over here for Rita, but I want to draw your attention to the asymmetrical wind field. In general, east of a hurricane track, you would normally see stronger winds and taller waves, as well as very large, near-bed wave orbital velocity. In Katrina, as an example, we even saw almost a three meter per second for maximum near-bed wave orbital velocity. In fair weather or moderate condition, normally the wave orbital velocity is like a 0.1 or 0.2 meter per second. So this is a very, very extreme condition. And now let's take a look at the conditions during the peak of the hurricane. Left two panels for Katrina, right two panels for Rita. So during the passage of the hurricane Katrina, this is right before the hurricane made the landfall, you can actually see very large wind field, very strong, very tall wave, east of the track line. But if you look at the bottom shear stress, you actually can see lots of high bottom shear stress in the inner and the middle part of the continental shelf. So to some degree, the bottom shear stress is mainly controlled by the topography of the symmetry. So now let's take a look at some numbers on the seabed. So we actually extracted information from a total of four stations. Going from east to west, we have four triangles. We have the MISS, which is a station near Mississippi. And we have AB5, 10B, 8C. And those are actually three stations mainly used for hypoxia studies by many, many scientists. So to the left, we have wind speed on top, which indicated a very, very strong wind during the passage of the hurricane Katrina, a very large shear stress generated here near Mississippi Delta, the black line indicated that the shear stress is almost a 50 Pascal. And if we compare this number with a fair weather condition, you know, fair weather condition, you probably have a number somewhere between 0.1 and 0.5 Pascal. And because of very extreme and energetic condition, we saw huge seabed erosion. So if we look at the black line, the Mississippi River Delta, about a one and a half meter sediment was eroded in the shallow water and transported into the deeper part of ocean. And then we also saw some centimeter to up to a meter level of a seabed change during the passage of Rita. So to wrap up, we have three major concurrence. So if we compare two hurricanes, Katrina followed a very short perpendicular track. It was moving very fast and the energy dissipated only within two days. In contrast, Rita followed a more short oblique track. So it went across the entire Gulf of Mexico and it actually moved a little bit slower over a longer distance in the Gulf area. Because of that, you will see a longer impact from Rita. And then if we think about the superficial variations, if you are used of the hurricane trip lines, most likely you will experience stronger winds, taller waves and deeper erosion and a thicker post-hurricane deposition as well. There are still lots of uncertainties in the model, but based on our sensitivity test, we believe that the hurricanes can actually disturb the sea flow at centimeter to meter level of change. And that's it. Thank you. Thank you, Kevin.