Deployment Notes: Dinowda Coastline, November 2023
The humidity hit us like a wall the moment we stepped off the tender. We arrived at the Dinowda shoreline just before 0400 hours to catch the peak flood tide, hoping to see how the bay's unique geometry funnels the incoming surge. The water was an eerie, translucent green, sparkling under the early light, but the surface tension told a different story. There was a nervous chop to the waves, driven by strong onshore winds that usually signal a shift in sediment transport across the bay.
Dinowda is a nightmare for standard hydrography if you don't know the terrain. The seabed is a chaotic mix of rocky outcrops and sudden sandy slopes. This makes securing a tripod-mounted instrument a gamble. We spent two hours just scouting for a stable footing that wouldn't result in the unit tipping over once the tide turned. The water temperature was surprisingly warm, and the salinity gradients were shifting rapidly as freshwater runoff from the hinterlands pushed against the saltwater wedge of the bay.
What We Found
The data was a wake-up call. We clocked peak velocities that blew our initial estimates out of the water—hitting nearly 1.2 m/s in the mid-column during the ebb. Most of the flow is concentrated in a narrow jet along the center of the bay. It's a classic funnel effect. The local topography squeezes the water, accelerating it as it exits toward the open sea. I noticed some weird shearing in the lower bins, likely caused by the friction against those rocky outcrops I mentioned earlier.
The most surprising part? The wind-driven surface currents were fighting the tidal flow for about three hours every afternoon. This created a messy, turbulent layer in the top five meters. We saw significant vertical mixing that you wouldn't expect in a bay of this size. It's a high-energy environment. If you're trying to map nutrient distribution here, you can't just rely on a few snapshots; you need continuous profiling or you'll miss the chaos entirely.
Equipment Performance
We deployed a 300kHz ADCP for this run. I’ll be honest: the signal-to-noise ratio was a struggle during the peak flood. The water in Dinowda carries a heavy load of suspended organic matter and silt, which creates a lot of acoustic backscatter. We dealt with some annoying bin contamination in the first two meters. I had to aggressively filter the noisy data during post-processing to get a clean signal. That said, the unit held its position perfectly. The heavy-duty tripod kept it vertical despite the current's attempt to walk it across the seabed. I'd trust this setup for a long-term soak, provided you're prepared to scrub the data.
Recommendations for Future Deployments
If you're heading back to Dinowda, don't wing it. The interaction between the wind and the tide is too volatile for guesswork.
- Swap to a 600kHz unit if you only care about the upper 20 meters; you'll get better resolution and less noise in the shallow bins.
- Use a heavier ballast weight than the manual suggests. The funneling effect in the bay creates localized surges that can shift lighter frames.
- Sync your deployment with the lunar cycle. Spring tides here are aggressive and will move your gear if the footing isn't rock-solid.
- Perform a sanity check with a handheld current meter at the surface before dropping the ADCP to verify the initial flow direction.
Getting a ground-truthing measurement on the seabed is the only way to be sure about the bottom-track velocity. Without it, you're just guessing based on the GPS, and in a place as dynamic as Dinowda, guessing is a quick way to lose an expensive piece of kit.
Field report by Capt. Marcus Thorne. A maritime acoustics specialist with 20 years of experience in port hydrography and deep-sea instrumentation.
Field Deployment Report: Bottom-Mounted ADCP Profiling in Dinowda Bay