Badania terenowe na zamarzniętym Zalewie Wiślanym | Wydział Inżynierii Lądowej i Środowiska Politechniki Gdańskiej

Podczas zimowych badań terenowych prowadzonych na Zalewie Wiślanym zespół w składzie: dr hab. inż. Tomasz Kolerski, prof. PG, doktorantka Sara Burgess oraz student koła naukowego Łukasz Rożański realizował pomiary dotyczące warunków hydrodynamicznych pod pokrywą lodową. 

Efektem tych prac jest nie tylko cenny materiał badawczy, który zostanie wykorzystany w dalszych analizach, lecz także niezwykle obrazowy opis terenowej rzeczywistości badawczej autorstwa Sary Burgess. Jej relacja pokazuje, jak wygląda praca naukowca w wymagających zimowych warunkach oraz jak zbierane dane terenowe łączą się z analizą satelitarną i modelowaniem numerycznym. 

Poniżej prezentujemy fragment relacji z badań: 

On the frozen Vistula Lagoon in the winter, the view is a constant vast expanse of white. The still morning air is broken by the alternating soft plod and crunch of feet as we tread over windblown dunes of snow and crusty ice. My watch buzzes to let me know we have reached our planned route but only after marching for over a kilometer. We take off our backpacks and work together to turn a large, bright red hand-auger to drill through the ice. As the hole becomes deeper the auger suddenly sticks and refuses to turn. It’s only a little further now. The blade has caught on the bottom of the ice. One final crank and the hole fills with water as the pressure of the water under the ice cover equalizes with the atmosphere. 

We measure the thickness of the ice with an ordinary tape measure and the depth of the water using PVC pipes that I made gradations with a marker at home. Next, my colleagues lower a sensor into the water. My fingers burn from the cold when I take them out of my gloves to record measurements. At the top of the hole the water is super cooled, maybe –0.25°C, but at the bottom the water temperature is +2°C. Anything above 0°C seems tropical in my mind when the air is –12°C and the wind is blowing. 

As I write, I notice that the temperature isn’t the only thing that changes. The upper meter of the water column is practically freshwater with a salinity around 0.6 parts per thousand (ppt), while near the bottom the water is brackish with a salinity of about 3.5 ppt. We often observe that the lighter, fresher water is much colder than the denser brackish water on the bottom. The layers are separated by an invisible boundary called the halocline. The ice cover blocks wind and waves from mixing the two layers. Still, as I lower an acoustic doppler velocimeter into the water, I can see that the water is moving at a few centimeters per second. It is slow under the ice, dragging on both the frozen cover and the sediments underneath. We finish the measurements, collect a sediment sample from the bottom, and prepare to move to the next hole. 

The work is slow, hard, and cold but we must hurry to get as many measurements as we can before warmer weather sets in. The ice will soon transition from its relatively stable “freeze-up” phase to a more dynamic “break-up” phase. Although the rivers are currently only a trickle, warm air, rain, and melting snow will soon send a surge of fresh water into the Vistula Lagoon, cracking and melting the ice. It won’t be safe to be on the lagoon when that happens. 

We can see from satellite imagery that year after year, the ice break-up on the lagoon leads to large rafts of drifting ice that flow and crash into whatever might be in their path. As part of my doctoral research, I’ll be using the data we collect now, satellite imagery, and numerical modeling methods to determine the forces that move the ice and the impact it has on the structure of the recently constructed sediment placement site, Wyspa Estyjska.

Badania te stanowią część projektu doktorskiego realizowanego przez Sarę Burgess. Zebrane dane terenowe, analiza obrazów satelitarnych oraz modelowanie numeryczne pozwolą określić siły odpowiedzialne za przemieszczanie się pokrywy lodowej oraz jej wpływ na nowo powstałą Wyspę Estyjską. 

Opiekę naukową nad badaniami sprawuje dr hab. inż. Tomasz Kolerski, prof. PG