Field Deployment Report: Velocity Profiling at Nhava Sheva, Jawaharlal Nehru Port

Deployment Notes: Nhava Sheva, Maharashtra - October 2023

The humidity hit us like a wet blanket the moment we stepped off the tender at Nhava Sheva. It was 0430 hours, and the Arabian Sea was churning with a restless, silt-heavy energy. I watched the massive container ships looming in the distance, their silhouettes cutting through a thick haze of salt spray and diesel exhaust. We weren't here for the scenery; we were here to get a real-time look at the current shear in one of India's busiest maritime gateways.

Monitoring water movement at Jawaharlal Nehru Port (JNPT) is a nightmare for any acoustician. You aren't dealing with clear open ocean. You have a volatile mix of high-volume shipping traffic, constant dredging activity, and the lingering influence of the retreating Southwest Monsoon. The water is opaque, loaded with suspended solids that scatter acoustic signals. If your equipment isn't tuned for high attenuation, you're just recording noise.

What We Found

The data surprised us immediately. We saw velocity spikes in the mid-water column that didn't align with the predicted tidal charts. We were seeing localized eddies near the deep-water berths that could easily push a drifting vessel off course during a slow docking maneuver. It wasn't a steady flow. It was chaotic. The current was shearing violently, shifting direction by nearly 30 degrees over a vertical distance of just ten meters.

I suspect the port's geometry and the specific dredging profiles of the channel are creating these anomalies. When you have deep-water berths adjacent to shallower approach channels, the tide doesn't just move in and out. It swirls. We caught a peak flow of 0.9 m/s during the flood tide, but the velocity profile was jagged. Some bins showed almost zero movement while others just a few meters above were screaming. This kind of shear is exactly why pilots at JNPT have to be so precise with their tugs.

Equipment Performance

We deployed a bottom-mounted ADCP, and frankly, the 600kHz unit was the only thing that gave us a clean signal. I'd avoid the higher frequency units here; the turbidity is too high and they lose the bottom track too quickly. We did run into some bin contamination near the seabed—likely due to the high concentration of silt and organic debris kicking up from the bottom—but the mid-column data remained rock solid. The instrument held its position despite the heavy wake from passing ULCCs (Ultra Large Container Vessels), though the vibration noise in the raw data was significant. We had to filter out a lot of the 'ghost' velocities caused by ship-induced turbulence to get a true tidal signature.

Recommendations for Future Deployments

If you're sending a team back to Nhava Sheva, don't rely on the standard deployment window. The monsoon runoff changes the salinity gradients and the acoustic properties of the water column drastically. I suggest the following:

• Use 600kHz or lower transducers to penetrate the turbid water.
• Increase the bin size to 0.5m to average out the noise from suspended sediment.
• Deploy heavy-duty mooring weights. The current surges here can shift a light tripod, ruining your orientation.
• Perform a manual sanity check with a handheld current meter at the surface to ground-truth the ADCP's top bins.

The port's efficiency is legendary, but the underwater environment is an entirely different story. Between the silt and the shipping traffic, it's a hostile place for electronics. However, getting this data is the only way to actually understand the risks during berthing operations. Without a proper velocity profile, you're just guessing based on a chart that's likely out of date.

We spent three days on site, battling heat and salt, but the resulting data set gives us a clear picture of the hydrodynamic stress on the berths. It's not a pretty picture, but it's an accurate one. The sheer volume of cargo moving through JNPT means there is no room for error in navigation. Knowing exactly how the water is moving—and where it isn't—is the only way to keep those ships moving safely.

Field report by Capt. Marcus Thorne. A veteran oceanographer and maritime consultant with 20 years of experience in acoustic instrumentation and port hydrography.