Stockholm university

Msc project presentation: Jonna Källås


Date: Thursday 20 October 2022

Time: 13.15 – 14.00

Location: N399 and Zoom:

Turbidity Effects from Recreational Boating in Shallow Bays

Supervisors: Sofia Wikström, Baltic Sea Center & Clare Bradshaw, Department of Ecology, Environment and Plant Science, Stockholm University.

Examiner: Rachel A Foster

Operating a boat in shallow areas and causing turbidity is not a new finding, but at what water depth does boating activity start to cause turbidity and does the size of the engine/boat affect the depth at which the turbidity starts? And how much does the sediment type affect the resuspension of the sediment? This project investigated the effect of accelerating up to 3000 RPM with three differently sized engines (8 HP, 50 HP and 100 HP) at three depths (1, 1.5, and 2 metres) in two bays with different sediment types, one muddy and the other sandy. The results show a significant difference between the bays at 1 metre, where the muddy bay has more turbid water after the acceleration while the sandy bay does not get the same results. Generally, in the muddy bay the boats create a larger turbidity cloud. To compare different driving behaviours typical of recreational boating, we tested turning, passing by, full stop, and acceleration. These results showed that accelerating would significantly create more turbid water, and the turn was second highest while the full stop and passing by had similar values. Another experiment we did was by passing by at 1.5 m every 5 min for 30 min in both bays to see if there was an additive effect. However, with time limits, only one replicate was made. The data shows that there are some effects in the muddy bay but not in the sandy bay. The conclusions from this experiment are that piloting a boat in shallower water than 1.5 metre causes turbidity; passing by without accelerating, turning, or reversing is fine. But operating a boat in shallow areas without turning or any other behaviour is unreasonable.