Deployment Notes: Pipavav Port, Gujarat, October 2023
The humidity hit us the moment we stepped off the boat at the Pipavav quay. It was 05:30, and the air felt like a warm, wet blanket, thick with the smell of salt and industrial diesel. We were racing the clock to deploy the ADCP before the morning traffic of container ships choked the channel. The water here is tricky. Unlike the open ocean, the approach to Pipavav is a battleground of extreme tidal ranges and heavy suspended sediment loads—typical for the Gulf of Khambhat.
The water was a murky, opaque brown. You can't see an inch past your knuckles. This high turbidity is the real challenge here; too many particles in the water column can cause signal attenuation or, worse, create 'noisy data' that makes it impossible to distinguish actual current velocity from suspended silt. The wind was light, but the tidal surge was already picking up, pulling hard toward the coast.
What We Found
The data surprised us immediately. We saw velocity spikes in the lower water column that completely contradicted the surface readings. In some bins, the current was practically stalling, while just a few meters above, the water was screaming toward the berths at nearly 1.2 m/s. This kind of shear is common in ports with heavy dredging and complex bathymetry, but the intensity here is wild. It's a reminder that relying on a single-point surface measurement is a gamble in a place like Gujarat.
We also noticed a strange correlation between the tide peaks and the sediment plumes. As the flood tide pushed in, the acoustic backscatter increased significantly. Honestly, I suspect the bottom-mounted unit was picking up 'bin contamination' from the seabed during the lowest tides. We had to aggressively filter the bottom few bins to get a clean signal. If we hadn't done a sanity check against the local tide tables, we might have misread the near-bottom flow as a massive surge when it was actually just seabed interference.
Equipment Performance
I used a 600kHz ADCP for this run, and it was the right call. I’ve used 1200kHz units in similar coastal environments, but they struggle with the attenuation caused by the silt in the Gulf of Khambhat. The 600kHz unit punched through the turbidity with much better reliability. We did have one scare where the mounting bracket shifted slightly during a particularly violent ebb tide (likely due to the sheer volume of water moving through the channel), but the internal tilt sensor caught it. We corrected the data in post-processing, but it proves that in high-energy ports, your mooring has to be overkill. If it's not bolted or weighted down with a massive footprint, the current will just walk your equipment right across the seafloor.
Recommendations for Future Deployments
If you're heading back to Pipavav or any port in the Gujarat region, don't wing it. The environment is too aggressive for basic setups.
- Use lower frequency transducers: Stick to 600kHz or lower to avoid signal loss in high-turbidity water.
- Over-engineer the mooring: Use heavy-duty galvanized steel frames. The sediment transport here can scour the seabed around your tripod, leading to tilt or instability.
- Tighten the binning: Set shorter blanking distances to capture the near-bottom flow, but be ready to prune the data for seabed echoes.
- Sync with dredging schedules: The bathymetry changes. A spot that was 15 meters deep last month might be 18 meters today thanks to the port's maintenance dredging.
The port's infrastructure is impressive—the gantry cranes and deep-water berths are top-tier—but the underwater physics are chaotic. Measuring currents here isn't just about dropping a sensor; it's about fighting the silt and the surge. Once you account for the noise, the data is gold for vessel traffic management and understanding how sediment settles in the channel. Without these profiles, the port is essentially flying blind regarding the hydrodynamic forces acting on docked vessels.
Field report by Elena Rodriguez. Elena is a specialist in underwater acoustics and oceanographic instrumentation with twenty years of experience in coastal sediment transport and acoustic imaging.
Field Deployment Report: Bottom-Mounted ADCP Profiling at Pipavav Port, Gujarat