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. Scientists from Lamont-Doherty, Dhaka University and other institutions have begun a five-year project to understand the hazards and the possible hidden links among them. Lamont geophysicist Michael Steckler keeps us up to date on the work.
Geohazards in Bangladesh
Completing my fieldwork and returning to Dhaka
Our surveying of scores of old geodetic monuments installed by the Survey of Bangladesh in 2002 is going well. By determining their exact elevation with precision GPS, we can determine how much the land has sunk, or subsided, over the last 18 years. This is of critical importance in the low-lying coastal zone of Bangladesh. The balance of sea level rise, land subsidence and sedimentation will determine what land loss the region could experience in the future.
We have worked our way south to the beach town of Kuakata on the Indian Ocean. Since installing the GPS just behind our hotel took longer than expected, we split into two teams to install our equipment at the other two sites near here. My group was to do the site to the northeast. The challenge was how to get there. While there are roads that directly go there, they are probably not passable for our van. Instead, we headed north.
We will have to take ferries to get to the corner of the island where the site is. After a lot of asking around, the best route turned out to be to drive east to the new large Deep Sea Port that is being constructed with a wide new road leading to it. We then went along the crumbling embankment road to a local country boat ferry. There were wooden boardwalks at each end to get to the boat for the short trip across.
On the other side, we were able to get a rickshaw van for about a third of the way to the school with the monument. The four of us had to walk the remaining half a mile. We were shown the monument adjacent to the school, which was surrounded by shallow water from an unused rice field. At least that meant that it had an excellent sky view. We took off our shoes and sandals, rolled up our pants and waded to the monument through foot-deep water.
The monument was in good shape and the set up went quickly. The only challenge was making sure the tripod was stable in the soft mud. After meeting the local school headmaster and having tea, we walked back to reverse our route. The other team was able to drive to their site, which was also in the middle of water with only the top of the monument sticking out. Unfortunately, it had sewage from latrines draining into it, so they decided to skip it.
Since they could not install that one, they got to pick up the GPS that was set up the day before. Since it was set up late the previous day, they had time to eat lunch and visit a beach. When we finished and made our way back, we had some free time in the evening, unlike the last few long days. We returned too late to catch the sunset, but were still able to enjoy a walk on the beach. When I was here in the summer, the water at the beach was fresh instead of salty.
This is due to the enormous water flow from the Ganges and Brahmaputra Rivers during the monsoon. The flow pushes the salty ocean water away from the coast. Now in the winter, the water was somewhat salty, but still not at a level of the normal ocean. We also had an easy morning, at last. We needed to wait until 11 AM to pick up the station outside our hotel, so we had plenty of time to pack and check out. Then the entire team went to our site from yesterday.
I opted to stay on the school grounds and let others wade through the water to pick up the equipment. When that was done, we were free to head back north to Barisal. Since it was the weekend, traffic was light and we got there in the early evening. With Hasnat and his students trained, it was time for me and most of the others to return to Dhaka. Céline will stay a few more days to work with them. We rearranged all the equipment in the cars, so we could install a site on the way back to Dhaka. Mondal, Sober, Salam, Masud and I went with the two GPSs returning to Dhaka and one to install. Hasnat, Nahin, Saif and Céline went to install two other sites. This time, the site was in a jute factory not too far off the main road to Dhaka. With both professional surveyors in our car, the installation went quickly, the factory manager arranged for security and showed me the facilities.
Based on expected traffic, we took a longer route and took the shorter ferry at Aricha near the confluence of the Ganges and Brahmaputra Rivers. While the route was longer, there was little traffic until we reached Dhaka and not much wait at the ferry. With five people and equipment to drop off, we had multiple stops in Dhaka. We spent almost as much time (almost four hours) in Dhaka as getting to Dhaka from the last site (4.5 hours. For me now, there are a few days of meetings in Dhaka, then the long trip home.
Meanwhile, Hasnat and his students will continue to survey the geodetic monuments for the next two months. Today, while I am in Dhaka, they installed one more site and picked up the equipment from the previous day’s three sites. I will pick up the equipment I brought in March. The trip has been very successful, with the usual rearranging the schedule on the fly.