Estonian scientists uncover dangerous currents in Varna port canal

Strong currents and sudden water level fluctuations can develop in the narrow canal connecting Bulgaria’s largest port with Varna Lake, threatening navigation and disrupting port operations, ERR reports. Tallinn University of Technology scientists helped determine what causes the phenomenon in the canal linking the Black Sea with the lake.

Pilots have observed unusually strong currents in the 2.4-kilometre canal, which is 300 metres wide, for years. Academician and Tallinn University of Technology professor Maarja Kruusmaa and researcher Laura Piho worked with the Port of Varna to conduct detailed measurements.

“We used Hydromast measuring stations developed at Tallinn University of Technology’s Centre for Biorobotics. Three stations recorded the speed and direction of water movement and the water level at one-minute intervals,” Piho said.

Emeritus professor of oceanography Jüri Elken joined the researchers to help explain the unusual water movements. The broader aim of the measurements is to improve understanding of flow dynamics in canals, which could help other regions address similar problems, improve vessel navigation, forecast strong currents and provide rapid warnings of changing conditions.

Dangerous water oscillations

The measurements confirmed that, alongside the canal’s usual moderate water movement, strong oscillations with periods of several dozen minutes can develop. The most pronounced oscillations had periods of 37 and 19 minutes, Elken said.

The researchers believe the oscillations are linked to resonance in the canal and Varna Lake system. Under certain atmospheric conditions, this resonance can significantly amplify water movement.

Two exceptionally strong events were recorded during the study. In the first, the water oscillations began suddenly and lasted for several cycles. The event was caused by a meteorological tsunami, which can occur when a wind front moves over a shallow coastal sea at what is known as resonance speed.

The second major event occurred more than five hours after a storm, when winds from the land reached 20 metres per second. Over a 10-minute period, the largest changes in current speed reached 0.8 metres per second, while water levels changed by up to 0.8 metres.

The researchers said such strong fluctuations make passage through the canal highly dangerous for vessels, disrupt port operations and complicate the broader management of coastal areas.

Wider significance

The findings could improve knowledge of water movement patterns, supporting port management and navigation safety and contributing to environmental impact assessments.

The researchers said it is important to study events in which strong currents and resonant sea-level changes lasting less than an hour develop in bays and canals connecting them with upstream lakes and rivers.