Deployment Notes: Pangkal Balam, Bangka Belitung, November 2023
The humidity hit us the moment we stepped off the boat at Pangkal Balam. We arrived just as the flood tide began pushing into the harbor, bringing a thick, brackish slurry of suspended sediment that made the water look like café au lait. It was a messy start. My team and I spent the first hour fighting with the deployment frame, trying to keep the instrument stable while the current ripped at our gear.
This isn't your typical deep-water shelf. Pangkal Balam sits in a complex intersection of coastal currents and riverine discharge. The water is turbid, warm, and highly variable. We noticed a strong salinity gradient almost immediately; the freshwater runoff from the hinterland creates a stratified layer that can mess with sound speed profiles if you aren't paying attention. The wind was gusting from the northeast, typical for the monsoon transition, which added a choppy surface layer to an already chaotic subsurface environment.
The real challenge here is the bathymetry. The channels are dredged regularly to keep the port operational for palm oil and spice exports, but the edges of those channels are jagged. This creates localized eddies and shear zones. If you place an ADCP just a few meters off the center line, your data is useless because you're measuring a boundary layer eddy rather than the main flow. We spent three hours ground-truthing the coordinates just to ensure we weren't sitting in a dead zone or a fluke current spike.
What We Found
The data jumped out at us immediately: the tidal asymmetry is aggressive. We saw peak flood velocities that dwarfed the ebb currents, a classic sign of the complex morphology in this part of Indonesia. In one specific bin, we clocked a surge that nearly doubled the expected velocity for a standard spring tide. It's a navigator's nightmare. If a captain is trying to dock a medium-sized cargo vessel during that window, the lateral drift is significant. Most of the local pilots rely on intuition, but the numbers show a dangerous level of unpredictability in the cross-currents near the berths.
I was surprised by the sheer amount of 'noise' in the lower bins. We saw significant backscatter from organic debris and sediment plumes moving along the bottom. Honestly, the vertical velocity components were erratic. It wasn't instrument failure; it was the environment. The water is just too thick with particulates. We had to apply a strict filter to the data to separate the actual current flow from the sediment transport. Once we cleaned the signal, the pattern became clear: the port acts like a funnel, accelerating the tide as it pushes into the narrower basins.
Equipment Performance
We deployed a 600kHz ADCP for this run, and it was the right call. A 300kHz unit would have had too few bins in this shallow water, leaving us blind to the surface-bottom shear. The instrument held its position well, though the biofouling started almost instantly. By the time we recovered the unit, the transducer faces had a thin film of slime. It didn't kill the data, but it did increase the signal attenuation toward the end of the deployment. I found the internal compass slightly off—about 2 degrees—which required a manual correction during post-processing. It's a common annoyance, but if you don't catch it, your entire vector map is shifted.
Recommendations for Future Deployments
If you're heading back to Pangkal Balam, don't wing it. The environment is too volatile for a 'drop and forget' approach. You need a rigorous sampling strategy to account for the monsoon influence on current direction.
- Use a heavy-duty tripod with a wide footprint to prevent tilting in the dredged channels.
- Increase the ping rate to capture the rapid velocity shifts during tidal transitions.
- Deploy a separate CTD (Conductivity, Temperature, Depth) sensor to get real-time sound speed corrections; the salinity swings here are too wild for a constant value.
- Schedule recovery before the peak of the rainy season to avoid losing gear to extreme runoff events.
The port's growth means more traffic, and more traffic means we need better data. Right now, the discrepancy between the charted currents and the actual velocity profiles is too wide for comfort. We need a permanent mooring array if the port authority actually wants to optimize vessel docking safety.
Field report by Sarah Jenkins. Sarah is a specialist in underwater acoustics and oceanographic instrumentation with twenty years of experience profiling continental shelf currents.
Field Deployment Report: Bottom-Mounted ADCP Profiling at Pangkal Balam Port