January 31, 2017
Earthquakes, floods, sea-level rise and sudden shifts in river courses threaten many of the 150 million Bangladeshis living in the low-lying Brahmaputra River delta. This is the latest dispatch from a five-year project to understand the hazards and the possible hidden links among them.
After a night in Dhaka, our group temporarily split up. Chris and Dan headed to Khulna in the SW at 4 am to avoid the hartal (general strike) that was planned for 6am-2pm. Liz and I stayed in Dhaka for a day. I spent it mostly editing material for a new project. The next day Liz, Humayun, my partner from Dhaka University, and I followed the others to Khulna, crossing the Padma (combined Ganges and Brahmaputra) River by ferry at Mawa. After waiting an hour, Humayun used a connection from a former student to get us on the next ferry, a fast one. It is impressive how much the river has silted up since the last time I crossed here. Another few hours and we arrived at our compaction meter site SE of Khulna. We picked up one of the 4 sons from the family that takes care of the site. Mofizur, the second son, now a student at Chittagong University, is returning home for the first time in 6 months. Making the weekly
measurements has been passed along from the oldest to youngest sons. It made for a great welcoming by the Islam family when we arrived mid-afternoon.
The last time I was here, the river adjacent to the site was being dredge and widened. It had gone from 200 m wide to just a few and was now too small for boats except at high tide. The widening cut into the bank that held our instruments. While the engineer tried to leave us enough room, it clearly didn’t work. The pillar that holds the GPS antenna is tilting badly towards the stream. They have secured it with ropes to keep it from completely falling over. We got hold of a ladder and removed the unusable antenna. Mofizur climbed up, afraid that I weighed too much for the fragile system. Next, Humayun and I surveyed the monuments for the compaction meter wells.
We had to dig out the sediments covering the base. Liz measured the thicknesses, which were 4-7 inches. We could clearly see the finely layered sediments deposited from before the river was enlarged to the thick muds that accumulated afterwards. The sedimentation rate had clearly increased due to the river widening. The survey will give us the relative heights of the wells. When we get back we will compare it to earlier measurement to see if the wells have shifted, too. Without the GPS we cannot determine the absolute elevations. Our last task was to measure the lengths of the optical fibers in the wells. We brought along a new laptop to work with the electronic distance meter (EDM), but we found the recharger was still in Dhaka. We had forgotten it. With a dead battery and no way to recharge it, the measurements will have to wait until Humayun can send the recharger.
While we were there, we were served lunch, a huge banquet. Three finds of fish, chicken, rice, vegetables, two desserts. The three of us sat a table outside in the yard, while the family plied us with the delicious home-cooked Bangladeshi food. The more important the guests, the more food and were
suitably overwhelmed. And since it was after 3 pm, we were famished and did our best make a dent in it. Since the GPS is no longer usable, we left them the battery and solar panel that was powering it, doubling their electricity supply. Before we installed the equipment in 2011, they did not have electricity at all. After some heartfelt farewells, we headed to Khulna to meet up with Chris, Dan and Matt Winters, my TA from the class I taught in 2015. Fluent in Bangla, he has been working with Chris on field observations for his Master’s thesis at Columbia. He and some of his assistants will join us for a few days. The three of them had a dinner meeting, so my group headed to the M.B. Bawali, our home for the next 4 days. Smaller than the M.B. Kokilmoni, it is a perfect size for our group.
The next morning, we headed for Polder 32, the embanked island we have been studying. Humayun and I will visit the GPS station we set up there in 2012. It has a cellular modem so data can be downloaded remotely every day, but stopped working in November. It seemed that the receiver was not recording satellites, so we brought along replacement antennas, cables and lightning protectors. Another GPS station had a similar problem and there
the cable had to be replaced. When we arrived at the school, we found the receiver was tracking satellites. We didn’t have to track down a break in the system. But why wasn’t it recording data? The best we could ascertain was the modem had hung up; rebooting it fixed the problem. It was working, but I don’t understand what happened enough to be sure it won’t happen again. Hopefully, now that it is working, the engineers at UNAVCO can log in an work on it. When we doublechecked everything, we found that the grounding wire was missing. This is unsafe. If there is a lightning strike, the lightning protector blows the connection to the equipment inside and shunts the electricity down the grounding wire. We cannot put a school full of children at risk. The only wires we had were the coaxial antenna cables. We stripped the ends off a partial cable and wired it between the cut ends on the roof
and near the ground. We made a visit to the Hindu goddess of education and headed back to the ship having done all the repairs we could, and satisfied that the school was safe.