Deployment Notes: Jamaame Coastal Reach, October 2023
We hit the shoreline at Jamaame just as the first light broke over the dunes. The air was thick with salt and the smell of drying fishing nets. My team and I spent the first hour fighting the tide to get the gear positioned. This isn't your standard open-ocean drop. Jamaame's coastline is a chaotic mix of sandy plains and sudden rock outcrops that make mooring a nightmare. One wrong move with the deployment cable and you're snagged on a reef that isn't on any of the official charts.
The water was surprisingly turbid for October. We saw significant suspended sediment plumes swirling near the bay's mouth, likely driven by the interaction between the receding tide and the local wind patterns. The wind was gusting from the northeast, pushing surface water hard against the coast. It created a visible rip in the current that made the small boat dance. We had to time our drop perfectly to avoid the gear drifting half a kilometer off-station during the descent.
What We Found
The data came back messy, but fascinating. The most striking point was the sheer velocity of the tidal currents within the narrow channels of the bay. We clocked peak flows that were nearly double what the regional models predicted. It turns out the underwater ridges around Jamaame act like nozzles. They squeeze the water, accelerating the flow and creating these intense, localized jets. I suspect this is why the seabed topography here is so fragmented; the currents are literally carving the floor into a series of sandy troughs and rocky ribs.
We also noticed a weird vertical shear in the water column. The surface layers were screaming toward the shore, driven by the wind, while the bottom layers were still pulling out with the tide. This created a massive rotational force in the water. I call it 'the Jamaame twist.' It’s a classic example of how local bathymetry overrides large-scale oceanic trends. If you're looking at satellite data for this region, you're missing the real story. The surface tells one lie, and the bottom tells another.
Equipment Performance
We ran a 600kHz ADCP for this leg. Honestly, it was the only choice. A higher frequency unit would have been blinded by the sediment load in the lower bins. We did deal with some noisy data during the peak flood tide—likely aeration from the breaking waves hitting the rocky outcrops—but the signal stayed clean enough for a reliable sanity check. The bottom-mounting bracket held firm, though the sand scour around the base was aggressive. I noticed some bin contamination in the lowest 0.5 meters, but that's par for the course when you're sitting in a high-energy sandy environment. It performed exactly as I expected for a high-turbidity site.
Recommendations for Future Deployments
If you're heading back to Jamaame, don't trust the depth sounder on the boat. The seabed shifts too much. I'd suggest the following for the next window:
- Use heavy-duty galvanized shackles. The salinity and oxygen levels here eat through cheap steel in weeks.
- Shift to a 300kHz unit if you need deeper profiling, but be prepared for lower resolution in the near-bottom layers.
- Deploy at least three stations across the bay's mouth to actually map the flow divergence. One unit just gives you a snapshot; three give you a map.
- Schedule the recovery for a neap tide to avoid the brutal currents that make hauling gear a physical battle.
The interaction between the wind-driven surface currents and the tidal ebb is what defines this coast. Without ground-truthing these flows with a bottom-mounted unit, you're just guessing. The complexity of the Jamaame bay isn't just a curiosity; it's the engine driving the entire local sediment transport system.
Field report by Elena Rodriguez. Elena is a specialist in underwater acoustics and oceanographic instrumentation with two decades of experience mapping coastal sediment transport.
Field Deployment Report: Bottom-Mounted ADCP Profiling in Jamaame Bay