Deployment Notes: Cirebon Port, West Java, October 2023
The humidity hit us the moment we stepped off the boat at Cirebon Port. It was barely 5:00 AM, but the air felt like a warm, wet blanket. We were there to deploy a bottom-mounted ADCP to get a real handle on the current vectors near the main berths. The water was a murky, opaque brown—classic for this part of the northern coast of Java during the transition to the northwest monsoon. You can't see an inch past your knuckles in this silt.
Cirebon is a nightmare for acoustics if you aren't prepared. The mix of heavy riverine discharge and the shallow bathymetry of the Java Sea creates a chaotic environment. We dealt with erratic salinity gradients and a seabed that's more slurry than sand. The tide was pushing in hard, and the surface chop was agitated by the constant movement of medium-sized cargo ships and local fishing fleets weaving through the channels.
What We Found
The data surprised us immediately. We saw significant tidal asymmetry that the port's existing charts just don't capture. The flood currents were punching in much harder than the ebb was pulling out. In some bins, we recorded peak velocities that would make a ship captain nervous during a docking maneuver. It's not just about the speed, though. The shear was aggressive. We saw a massive velocity drop-off in the bottom three meters, which tells me the boundary layer friction here is intense due to the seabed composition.
Honestly, the most jarring part was the noise. Between the dredging activities and the sheer volume of vessel traffic, the acoustic environment is loud. We saw some spikes in the data that looked like outliers but were actually the sonic signatures of heavy machinery nearby. I spent three hours ground-truthing the velocity profiles against a handheld current meter to make sure we weren't looking at ghost currents. Once we filtered the noise, the signal became clean, but it proved that you can't just 'drop and forget' a sensor in a working port like Cirebon.
Equipment Performance
We opted for a 600kHz unit because of the shallow water depth. If we had gone with a 300kHz, we would have suffered from massive bin contamination—the 'blanking distance' would have eaten half our usable water column. The unit held its position well, but the turbidity was a challenge. In high-silt environments, the backscatter signal can get erratic. I noticed some ringing in the data during the peak flood tide. It didn't ruin the dataset, but it required a bit more scrubbing in the post-processing phase than I'd like. Still, the 600kHz performed better than any of the lower-frequency gear we've trialed in Indonesian ports.
Recommendations for Future Deployments
If you're heading back to Cirebon or any similar shallow-water port in Java, don't wing it. The environmental variables change too fast between seasons.
- Use 600kHz or higher to minimize the blanking distance in shallow berths.
- Double-check your mooring weights. The silt is soft, and gear can sink or tilt, which kills your directional accuracy.
- Schedule deployments outside of active dredging windows to avoid acoustic interference.
- Run a 24-hour sanity check with a secondary sensor to verify the ADCP's zero-drift.
- Increase the sampling rate during spring tides to capture the rapid acceleration of the flood current.
The port is expanding, and the throughput of agricultural goods is climbing. As the ships get larger, the margin for error during berthing shrinks. We need a permanent array of sensors here, not just one-off deployments. Without real-time current data, the pilots are basically guessing based on old tide tables (which are notoriously unreliable in these shifting channels).
Field report by Sarah Jenkins. Sarah is a specialist in underwater acoustics and continental shelf currents with 15 years of experience in oceanographic instrumentation.
Field Deployment Report: Bottom-Mounted ADCP Profiling in Cirebon Port