WEBVTT 00:13.409 --> 00:15.631 Precipitation totals across much of the 00:15.631 --> 00:17.687 central portion of the United States 00:17.687 --> 00:19.520 this summer have not only caused 00:19.520 --> 00:21.631 drought conditions in multiple states 00:21.631 --> 00:23.576 but have also led to a smaller and 00:23.576 --> 00:26.079 weaker Mississippi River . As a result , 00:26.090 --> 00:28.312 salt water from the Gulf of Mexico that 00:28.312 --> 00:30.423 is normally held back by the force of 00:30.423 --> 00:32.520 the Mississippi river is now slowly 00:32.529 --> 00:34.740 making its way up the river causing 00:34.750 --> 00:36.861 significant threats to communities in 00:36.861 --> 00:38.806 South Louisiana and their drinking 00:38.806 --> 00:41.490 water . The US Army Corps of Engineers 00:41.500 --> 00:43.333 and emergency officials in South 00:43.333 --> 00:45.389 Louisiana are responding to the 00:45.400 --> 00:47.369 emergency and are rated by the 00:47.380 --> 00:49.990 experience and expertise of engineers 00:50.000 --> 00:52.069 and scientists at the US . Army 00:52.080 --> 00:53.969 Engineer Research and Development 00:53.969 --> 00:57.490 Center or dic that expertise date back 00:57.500 --> 00:59.529 decades and includes the ability to 00:59.540 --> 01:01.560 model saltwater movements and a 01:01.569 --> 01:03.900 critical understanding of the physics 01:03.909 --> 01:06.349 behind saltwater intrusion and the 01:06.360 --> 01:08.849 dynamics of mitigation efforts such as 01:08.860 --> 01:11.879 developing a sill or underwater dam to 01:11.889 --> 01:14.010 slow the salt water . So there's 01:14.019 --> 01:16.075 saltwater intruding from the Gulf of 01:16.075 --> 01:19.230 Mexico up the river . And as that salt 01:19.250 --> 01:21.306 wa as that salt water approaches the 01:21.306 --> 01:23.194 water surface , it approaches the 01:23.194 --> 01:26.059 drinking water intakes . Um and salt is 01:26.069 --> 01:27.739 not something that you can uh 01:27.750 --> 01:30.410 conventionally deal with , uh with 01:30.419 --> 01:32.530 drinking water filtration , you can't 01:32.530 --> 01:34.697 filter it out of the water and also it 01:34.697 --> 01:37.000 corrodes the pipes so it prevents them 01:37.010 --> 01:39.010 from being able to use the drinking 01:39.010 --> 01:41.066 water . They're gonna have to either 01:41.066 --> 01:43.010 bring in bottled water or bring in 01:43.010 --> 01:45.199 water from upstream or other resources 01:45.209 --> 01:46.987 which all would are being uh uh 01:47.105 --> 01:50.165 mobilized currently , when uh fluids of 01:50.175 --> 01:52.119 different densities encounter each 01:52.119 --> 01:54.525 other , uh which in , in this case , 01:54.535 --> 01:56.313 saltwater is is more dense than 01:56.313 --> 01:58.591 freshwater . They tend , they tend not , 01:58.591 --> 02:00.535 tends not to be mixing between the 02:00.535 --> 02:02.646 fluids , they tend to , to stratify . 02:02.646 --> 02:04.868 So what happens is the freshwater flows 02:04.868 --> 02:06.924 over the saltwater and the saltwater 02:06.924 --> 02:08.979 flows under the fresh water . Um The 02:08.979 --> 02:11.091 bottom of the Mississippi river , the 02:11.091 --> 02:13.313 bed of the river is actually much lower 02:13.313 --> 02:15.646 than the Gulf of Mexico . Well upstream . 02:15.646 --> 02:17.702 So the salt water , I if there's not 02:17.702 --> 02:19.535 enough fresh water to , to apply 02:19.535 --> 02:21.702 pressure to keep the salt water in the 02:21.702 --> 02:23.479 Gulf of Mexico , then it slowly 02:23.479 --> 02:25.424 migrates upstream . Uh Currently , 02:25.424 --> 02:28.110 there is a very low river uh conditions 02:28.119 --> 02:29.841 right now that the flow of the 02:29.841 --> 02:31.952 Mississippi river is very low and has 02:31.952 --> 02:34.175 been for a long time . So saltwater has 02:34.175 --> 02:36.008 been steadily migrating upstream 02:36.008 --> 02:38.341 against the current along the river bed . 02:38.341 --> 02:40.063 And as long as those low river 02:40.063 --> 02:42.063 conditions persist , then that that 02:42.063 --> 02:44.669 upstream migration will persist . We 02:44.679 --> 02:46.735 have much understanding of the basic 02:46.735 --> 02:49.550 physics of , of saltwater wedges and a 02:49.559 --> 02:51.559 lot of that pioneering research was 02:51.559 --> 02:54.350 done right here uh at Ti uh Garbs Kigin 02:54.360 --> 02:56.527 was one of the first people to develop 02:56.527 --> 02:58.638 that work . And he did a lot of the , 02:58.638 --> 03:00.860 the theoretical work of salt wedges and 03:00.860 --> 03:03.082 what's called an arrested sailing wedge 03:03.082 --> 03:05.138 uh when , when the the forces are in 03:05.138 --> 03:07.304 equilibrium . Uh And then a lot also , 03:07.304 --> 03:09.416 there was a lot of the ear , early uh 03:09.416 --> 03:11.638 physical and numerical modeling of salt 03:11.638 --> 03:14.089 wedges was developed here as well as 03:14.100 --> 03:16.080 the original design of the uh the 03:16.089 --> 03:19.000 saltwater uh wedge sill to prevent the 03:19.009 --> 03:21.231 sill that helps to prevent the upstream 03:21.231 --> 03:23.176 migration , which has already been 03:23.176 --> 03:25.231 built . That design was done here at 03:25.231 --> 03:27.453 TIC in conjunction with the New Orleans 03:27.453 --> 03:30.240 District uh by several researchers uh 03:30.250 --> 03:32.940 Billy Johnson and Bill mcinally among 03:32.949 --> 03:35.199 them in the , in the eighties . So uh 03:35.210 --> 03:37.377 there's a lot of work that's been done 03:37.377 --> 03:39.210 and we , we so we understand the 03:39.210 --> 03:41.321 fundamentals of it very well . Um And 03:41.321 --> 03:43.479 we also bring to bear a lot of the um 03:44.020 --> 03:45.964 knowledge of stratified flows from 03:45.964 --> 03:48.076 atmospheric physics and various other 03:48.076 --> 03:50.298 things . But the model that we're using 03:50.298 --> 03:52.298 right now is more of a tool uh that 03:52.298 --> 03:54.298 we've developed , which is somewhat 03:54.298 --> 03:56.520 simplified tool where we basically have 03:56.520 --> 03:56.440 a what's called the laterally average 03:56.449 --> 03:58.560 model of the river with average . But 03:58.560 --> 04:00.449 we have two layers in the model , 04:00.449 --> 04:02.282 there's a freshwater layer and a 04:02.282 --> 04:04.393 saltwater layer and they interact the 04:04.393 --> 04:06.282 physics of the interaction at the 04:06.282 --> 04:05.990 interface is dictated by our 04:06.000 --> 04:07.833 understanding of the , the basic 04:07.833 --> 04:10.000 physics that I described earlier . The 04:10.000 --> 04:12.111 reason we're using that is because it 04:12.111 --> 04:14.278 is this is an emergency operation . So 04:14.278 --> 04:16.389 we wanna do a really quick turnaround 04:16.389 --> 04:18.500 and we wanna be able to just do a lot 04:18.500 --> 04:20.667 of assessments . Uh not only of the of 04:20.667 --> 04:22.667 what may happen in the future , but 04:22.667 --> 04:24.778 also what some of our interventions , 04:24.778 --> 04:24.700 some of the interventions that we're 04:24.709 --> 04:28.160 imposing uh may um and what their 04:28.170 --> 04:30.337 effects may be . And so this is a tool 04:30.337 --> 04:32.392 we can run very rapidly and do quick 04:32.392 --> 04:34.281 assessments with . And since it's 04:34.281 --> 04:36.392 emergency operations , we're using it 04:36.392 --> 04:38.281 daily in conjunction with the New 04:38.281 --> 04:40.114 Orleans District to sort of make 04:40.114 --> 04:42.448 decisions on the fly in the 19 eighties . 04:42.448 --> 04:42.079 When there was , there was an 04:42.089 --> 04:44.311 authorized deepening of the Mississippi 04:44.311 --> 04:46.367 River , uh where where the Corps was 04:46.367 --> 04:48.367 gonna authorize the deepening . And 04:48.367 --> 04:50.533 there had to be associated with that . 04:50.533 --> 04:52.756 There was a mitigation measure that was 04:52.756 --> 04:54.533 put in place to uh mitigate the 04:54.533 --> 04:56.756 additional the , the assumed additional 04:56.756 --> 04:58.756 salinity intrusion that will result 04:58.756 --> 04:58.673 from that . And that mitigation measure 04:59.032 --> 05:01.713 is to basically build uh what is 05:01.722 --> 05:04.763 essentially a um a dam , an underwater 05:04.773 --> 05:06.829 dam in the river and build it out of 05:06.829 --> 05:09.083 sand . We just basically pour sand in a 05:09.092 --> 05:11.148 mound in the river . And so when the 05:11.148 --> 05:13.156 salt is upstream , you imagine it's 05:13.165 --> 05:15.443 sort of like water filling a reservoir . 05:15.443 --> 05:17.554 We have a , a dam down there . And so 05:17.554 --> 05:19.721 the salt has to fill the space in that 05:19.721 --> 05:21.665 reservoir and over before it could 05:21.665 --> 05:23.776 overtop that dam . So it's a delaying 05:23.776 --> 05:25.943 tactic uh that enables us to delay the 05:25.943 --> 05:28.165 ingress of the , of the salt wedge . Um 05:28.165 --> 05:30.605 And then it's , it's a very clever uh 05:30.615 --> 05:32.782 development that they did because it , 05:32.782 --> 05:35.515 it , it's a self cleansing uh dam when 05:35.526 --> 05:37.693 the , when the river rises just scours 05:37.693 --> 05:40.510 away . Um One of the things we've done 05:40.519 --> 05:42.519 in conjunction with the New Orleans 05:42.519 --> 05:44.420 District is to um help design an 05:44.429 --> 05:46.262 augmentation to that dam for the 05:46.262 --> 05:48.096 particular emergency we have now 05:48.096 --> 05:50.207 because the dam , that dam that still 05:50.207 --> 05:52.151 has already been overtopped by the 05:52.151 --> 05:54.318 current ingress of the salt wedge . So 05:54.318 --> 05:56.318 what we've done , we , we wanted to 05:56.318 --> 05:58.540 elevate that dam as much as possible to 05:58.540 --> 06:00.762 mitigate further intrusion , but we had 06:00.762 --> 06:03.130 two constraints . One is we have to 06:03.140 --> 06:05.251 allow navigation in the river . So we 06:05.251 --> 06:07.473 can't elevate the dam above the , the , 06:07.473 --> 06:09.529 the , the draft of the vessels . And 06:09.529 --> 06:11.751 the other is if we elevated the dam too 06:11.751 --> 06:13.918 far , um It would scour away , it , it 06:13.920 --> 06:15.809 would just be too shallow and the 06:15.809 --> 06:17.864 velocity would scour . So what we've 06:17.864 --> 06:19.976 done is , and you'll hear this talked 06:19.976 --> 06:19.529 about in the news , we've created a 06:19.540 --> 06:21.859 notch , a notch dam which is what's 06:21.869 --> 06:23.980 being built right now . There's a low 06:23.980 --> 06:26.369 section that the vessels can go through 06:26.390 --> 06:28.501 and then the rest of the , the dam is 06:28.501 --> 06:31.154 been elevated up to uh about uh 30 ft 06:31.165 --> 06:33.332 below the water surface . Uh The notch 06:33.332 --> 06:35.498 is at about 55 and the rest of the dam 06:35.498 --> 06:37.443 will be about 30 ft and that's our 06:37.443 --> 06:39.721 optimization of those parameters . And , 06:39.721 --> 06:41.887 and we worked with the New Orleans New 06:41.887 --> 06:44.054 Orleans District to , to design that , 06:44.054 --> 06:46.276 that augmentation . We owe a lot of our 06:46.276 --> 06:48.443 knowledge of , of the salt wedge and , 06:48.443 --> 06:50.665 and salt dynamics to a lot of work that 06:50.665 --> 06:52.609 has been done here at TIC over the 06:52.609 --> 06:54.943 years and over by many different people . 06:54.943 --> 06:57.420 And uh so that it's been very helpful 06:57.429 --> 06:59.679 in this , in deve uh addressing this 06:59.690 --> 07:03.170 emergency . But also uh we want to take 07:03.179 --> 07:05.235 into account that we , you know , we 07:05.235 --> 07:07.457 are working very hard with the district 07:07.457 --> 07:07.309 to try to mitigate this as much as 07:07.320 --> 07:09.376 possible . Because we recognize that 07:09.376 --> 07:11.487 this is a , a serious situation for a 07:11.487 --> 07:14.250 lot of people in uh in the New Orleans 07:14.260 --> 07:15.910 area and downstream in New Orleans .