 Hi everyone my name is Ma Heng Li from China from Shanghai and now I major in coastal engineering and port development and Dano is my professor. Now here is a place near Routedem, Mass Black 2 and we want to make make a research about the current. This is the third day and it's a little bit cold here and but anyway we are enjoying ourselves here and we can learn a lot from Dano from this experiment. This is much more than I expected. I never thought I can wear this suit. I'm excited really. This is the first time I swim in the ocean but I feel good. You can talk about the longshore current, you can make calculations of it but to actually feel it and to see it and to measure it is very important. To know what kind of dangerous currents can happen you first of all have to know what the bottom is like so you have to do measurements of the of the the symmetry as we call it depth in the surf zone. Now that is usually quite difficult to do because it's shallow you have big waves but these guys at the Delft University have developed this jet ski with the with an echo sounder underneath it and a GPS receiver on top of it so the GPS knows where the jet ski is exactly. The echo sounder knows how deep it is underneath the jet ski. With those two data you get X, Y and Z and you can construct the whole bathymetry. So they do that with jet ski underwater and I think you've seen already the little wheelbarrow with GPS receiver that walks the dry beach and then these two can be combined they actually overlap a bit because we do this with high water and we do the other thing with low water. So once you know exactly what the bathymetry is like then you can compute the currents. You can if you know what the incoming waves are like and you can measure those with boys or you can model them with operational models. You know the wave conditions you know the tide conditions and you can use a two dimensional model to actually predict where the dangerous rip currents will occur but you see it's a very complex reality and the even though you measure very accurately you always miss things. The models miss processes so we need to verify the performance of these models. We have to validate them against measurements. Now you can put an instrument into the water and measure the velocity at that point but then who says that that's an interesting point. The rip current may be just right next to it. So we have a much more flexible method that is using drifters. This was first developed in America and a colleague of ours Adreniers from Miami brought it to Holland and these to you guys developed it further. So the idea is you have these drifters where are they here are the drifters maybe we can go there. So these are drifters. You see they have very sophisticated water bottles empty water bottles that are the floating devices and we have the GPS receiver is on the top and in this watertight box is a logger a data logger that logs the GPS data from this receiver. What what we do is we put these things into the water. We note very well what time it is that we put in but of course the logger says that too and then on a sign we all release the the the drifters and they will go to different places depending on the current and later on when we extract the data from these loggers the loggers give us x and y and we can plot on the map and the map that we made with the help of the echo sounder we can plot the tracks of the drifters. We can see oh this drifter went outside and that was a rip current and maybe it goes back again and by doing that you can construct the velocity field and you can do the similar thing in your numerical model so you get one track from the data or ten tracks from the data you put the same tracks in your model and of course it it never is a good match but every time you learn and you improve it but just apart from improving that model it also gives us direct information about how fast these currents are so if you do a lot of these experiments you gain empirical knowledge that can help the life-safe lifeguards and help understand when the dangerous currents are. One of the important things you you learn during such a week of field work is is to keep track of everything to make notes of everything so we always have a couple of reporters students who have one task and note everything that happens and whether they're taking doing the surveys or supervising the drifter experiment this is a very important aspect and then as soon as we get back somebody types it into the laptop so we get a good data collection data set and then we work on it to validate it make plots of it see if it is worth it and then by that you get a validated data set that you can actually do something with. We are working on the data from yesterday we are trying to put them in a model so that we can visualize the setting of the of the bathymetry of the beach we have those line has been the path made by the jet ski in the sea and here is a water line and the brown lines are the paths made by the wheelbarrow that is the guy on the beach just to collect data about the topography itself yeah and from this we input it in the model in MATLAB to obtain this graph but this one will be maybe further refined to get maybe 3d 3d pictures about the beach topography the beach layout we are applying all what we have been learning from the beginning of the studies from module one up to now and for me personally and I guess for my friend also it's a real opportunity to put into practice what we've been what we've been learning in theory and I guess for me it will help a lot in our future career where we will be and we have a sound sound knowledge about practical things so we'll feel more comfortable in our in the future to apply for all the theories what we are doing in the course