Field Log: Michoacán Coast, October 2023
The humidity hit us the moment we stepped off the boat at the Lazaro Cardenas terminal. It was barely 06:00, but the Pacific was already pushing heavy, grey swells into the harbor mouth. You can feel the energy here; it's not like the lazy tides of the Gulf. This port is a pressure cooker of hydrodynamic forces. We spent the first hour just watching the surface chop, knowing that the orbital velocities from those swells would likely wreck our top-bin data. In this part of Michoacán, the transition from the deep Pacific trenches to the dredged channels of the port creates a violent shear that makes standard current modeling almost useless.
The water was murky, a tell-tale sign of the late-season runoff from the highlands. I could see the suspended sediment plumes swirling near the quay walls. It's a nightmare for acoustic imaging. You're fighting a constant battle between signal attenuation and resolution. The wind was gusting from the southwest, pushing surface water against the man-made basins, which only added to the chaotic mixing. We had a narrow window to deploy before the next bulk carrier arrived to displace thousands of tons of water right over our sensor head.
What We Found
The data came back messier than I expected. The most jarring discovery was the sheer intensity of the localized eddies forming near the dredged channel bottlenecks. We clocked current speeds during the ebb tide that were nearly double the predicted astronomical values. It's a classic bottleneck effect. The port geometry forces the exiting water into these tight corridors, accelerating the flow. I've seen this in Japanese deep-water ports, but the scale here is different. We found 'ghost' velocities—spikes in the data that didn't make physical sense—which I later traced back to signal bouncing off the hulls of moored Ro-Ro ships. It's a noisy environment, both acoustically and physically.
We also noticed a strange vertical shear profile. While the bottom layers remained relatively stable, the mid-water column was a chaotic mess of opposing vectors. This is likely due to the interaction between the incoming Pacific swell and the outgoing tidal stream. At some depths, the water was literally fighting itself. We had to throw out the first three bins of data entirely. The surface wave orbital motion was just too aggressive to filter out mathematically. If you try to 'clean' that data in post-processing, you're basically just guessing. I prefer to be honest about the loss and focus on the reliable mid-depth signals.
Equipment Performance
We deployed a 300kHz ADCP, and honestly, it was the only right choice. A 600kHz unit would have choked on the turbidity spikes we saw after the morning rain. The 300kHz gave us the penetration we needed to hit the seabed in the approach channels without losing the signal to silt absorption. The mooring held steady, despite the significant bottom-shear typical of this seabed. I did run into some 'ringing' issues in the narrower sections of the port, where the acoustic pings hit the quay walls and bounced back. We fixed this by tightening the signal fence settings to prune the noise. It wasn't a perfect run—no field deployment ever is—but the 300kHz unit provided a sanity check that matched our secondary current meters.
Recommendations for Future Deployments
If you're heading back to Lazaro Cardenas, don't trust the textbook tidal charts. The ship-induced surges from the bulk carriers create a background noise that can mask actual current trends. You need a strategy that accounts for the high-energy environment of the Michoacán coast.
- Stick to 300kHz sensors to avoid signal attenuation from highland sediment runoff.
- Set aggressive signal fences to eliminate 'ghost' velocities caused by ship hulls and concrete walls.
- Ignore the top 5-10 meters of data during high-swell events to avoid orbital velocity contamination.
- Use heavy-duty mooring weights; the bottom-shear in the dredged channels can shift lighter rigs.
- Coordinate deployment windows with the port authority to avoid the wake of ultra-large carriers.
The key is ground-truthing. You can't just drop a sensor and walk away. You have to understand the port's breathing pattern—how it sucks in the Pacific and spits it back out through those artificial bottlenecks. Without that context, the ADCP data is just a collection of confusing numbers.
Field report by Elena Rodriguez. Elena is a specialist in underwater acoustics and oceanographic instrumentation with twenty years of experience in coastal sediment transport.
Field Deployment Report: Bottom-Mounted ADCP Profiling at Lazaro Cardenas Port