Deployment Notes: Killybegs, County Donegal, October 2023
The wind was biting as we stepped off the quay in Killybegs, the kind of damp Atlantic chill that gets right into your bones. We arrived just as the morning fog was lifting, revealing a harbor crowded with heavy trawlers. The smell of diesel and salt was thick. My primary concern wasn't the weather, but the complex bathymetry of this specific port. Killybegs isn't a simple open basin; it's a working industrial hub where the interaction between the North Atlantic swell and the narrow harbor entrance creates erratic cross-currents that can push a loaded fishing vessel off course in seconds.
The water state was choppy. We saw significant surface turbulence near the main channel, likely driven by the tidal exchange between the harbor and the open sea. The salinity here is high, but the suspended sediment load varies wildly depending on the wind direction and the activity of the fishing fleet. This environment is a nightmare for acoustic sensors if you don't pick your frequency correctly. We had to account for the constant movement of large hulls in the vicinity, which creates massive acoustic shadows and potential signal blockage.
What We Found
The data surprised us. We saw peak current velocities that spiked far beyond the historical averages for this sector of the port. In the main navigation channel, we clocked surges that nearly doubled the expected tidal flow during the ebb. It's clear that the harbor's geometry acts like a funnel, accelerating water as it exits toward the Atlantic. This explains why local captains often complain about 'strange pulls' when navigating out of the berths. The velocity shear was aggressive; the water at the seabed was barely moving, but just three meters up, the current was screaming.
We also noticed some erratic 'noisy data' during the peak of the flood tide. I suspect this was caused by air bubbles entrained from the surface turbulence, which created a layer of acoustic interference. I had to manually scrub the first few bins of the velocity profile to get a clean signal. Honestly, the sheer volume of vessel traffic in Killybegs creates a chaotic acoustic environment. You aren't just measuring water; you're measuring a soup of engine noise and hull reflections. Still, the core data confirms that the current patterns here are far more volatile than the general charts suggest.
Equipment Performance
We deployed a bottom-mounted ADCP, and for the most part, it held its own. I opted for a higher frequency unit to get better vertical resolution in the shallower sections of the channel. It performed well, though we dealt with some bin contamination near the boundary layer. The mounting bracket stayed secure despite the heavy surge, which is a relief because losing a sensor in a working fishing port is a logistical disaster. I found the 600kHz range provided the best balance between range and precision here. Lower frequencies would have missed the subtle shear layers we were looking for, while anything too high would have been blinded by the turbidity of the stirred-up seabed.
Recommendations for Future Deployments
If you're heading back to Killybegs for a follow-up, don't trust the average tide tables for your deployment window. The local eddies are too unpredictable.
- Use a heavy-duty tripod mount with a concrete ballast. The bottom currents can shift the sensor if it's too light, ruining your orientation.
- Set your blanking distance slightly higher than usual to avoid the noise from the seabed interface.
- Schedule deployments during the neap tide to establish a baseline before attempting to capture spring tide extremes.
- Perform a sanity check with a handheld current meter at the surface to validate the top-bin data.
The key to success in a port like this is patience. You have to filter out the noise of the industry to find the signal of the ocean. We managed to capture a full lunar cycle, and the resulting profiles give us a clear map of the danger zones for incoming vessels. It's a messy environment, but the data is gold for port safety.
Field report by Dr. Kenji Sato. Dr. Sato is a specialist in underwater acoustics and river discharge, with over 20 years of experience deploying sonar instrumentation in extreme maritime environments.
Field Deployment Report: Bottom-Mounted ADCP Velocity Profiling in Killybegs Harbour