I'm finishing up the last two sites of this part of my trip. GNSS (generic term for GPS) is installed in the building to measure the subsidence under the building, and RSET-MH (Rod Surface Elevation Table Marker Horizon) is used to measure the consolidation and subsidence above the rod that is driven into the ground. On this trip, we are also using an auger to sample the upper few meters of sediment. During this part of the trip, you will travel by boat through the interconnected waterways of the Sundarban mangrove forest.
On our way north from our final destination, Hiron Point, we spent the night at a place called Kaga Dubaki, which is still in the Sundarbans mangrove forest. We continued sailing north for much of the next day. Once we left the Sundarbans, cell phone service was restored and we quickly downloaded email and made a call. In the afternoon we arrived at our next destination, Joosing.
While the RSET and Auger teams headed to the station, Zofur and I went to the school/cyclone shelter where the GNSS receiver was located. Since it was a Friday, the principal and the administrator greeted us and let us in. The equipment box is located in an unused former restroom by the principal's office. This site has not submitted any data for her in a year. I checked the battery and it was fine, but the problem was with her SIM card and modem. The SIM card was locked and the modem was still configured with the old VPN. However, since it was the middle of the night, I was unable to contact my contacts in the United States for help.
Fortunately, the RSET team was only able to run one RSET, so they will have to run another one in the morning. They are in pairs, one inside and one outside the embankment, protecting the area but also endangering it. Because flooding and sedimentation are restricted within polders (islands surrounded by dikes), these areas sink and lose elevation without sufficient sediment. That spelled disaster for Polder 32's last stronghold. There, in 2009 Cyclone Islay breached the polder (levee) and flooded the island for almost two years until the embankment was safely rebuilt. We measured the land there to be 1–1.5 m below the natural level outside the polder. Approximately 10,000 households were evacuated due to this disaster. Therefore, understanding subsidence, sedimentation, and elevation changes is very important here.
Zofur and I joined the RESET and Auger teams who were finishing up. Then I attended a volleyball match in the school courtyard while waiting for the country boat back to Bawari. The players were very good and no more than a fraction of my age. I tried my best to keep up.
In the morning, Zofur and I returned to GNSS and called Ken Austin, who was scheduled to join us in Bangladesh within a week. He guided me to upgrade his VPN, but I still had issues with the SIM. While I was waiting, Zofur went out to get a new one. When she arrived with her new SIM card, she was able to connect to the mobile phone network. Ken still couldn't connect. There is a little more work that can be done remotely from the US. Just to be safe, Zohur practiced connecting to her GNSS and downloading data. This way, the RSET team can download data from the esoteric GNSS as needed during the twice-yearly RSET service runs. A speedboat took us to the RSET venue, but by the time we arrived the other boats had finished.
Once finished, we headed north to Polder 32. As this was the focus of a previous project, there are eight of his RSETs here, four in the Sundarbans of Sterhari and four within the poldar of Sreeja, both on the south side of the island. there is. Furthermore, I learned that there is also SSET (Shallow Surface Elevation Table). There were two, but one was destroyed. RSETs exist in pairs near embankments and coasts, and inside polders and forests. My boyfriend's GNSS is located in Gunari, in the northwest corner of the island. It takes two days to run all these RSETs. We have been studying the subsidence of Polder 32 since 2012. Although brought to the attention by the Polder 32 disaster, many diked islands face the same problems of subsidence and flooding as their interiors are below river level. .
We started with the Sundarbans site. We all woke up early, but due to fog we couldn't go into the forest until 10am. The forests where the Royal Bengal Tiger lives have poor visibility and are not safe. The first site was near the forest ranger station where we did a deep auger hole while the RSET team did his RSET and SSET. The second site took a long walk behind it and we all helped him take a quick RSET measurement. To get to his next RSET site, we took a country boat up a stream. Once that was done, we headed back to Bawali for lunch.
The tide was high enough that we were able to follow the tidal channel several kilometers back to the last RSET site. Along the way, we saw many birds, including herons, kingfishers, and storks. We also performed an auger here. The soft mud of the Sundarbans was easy to pass through, and the depth was over 4 meters. We played loud music to keep the tigers away. The previous Sundarbans site has become even more fun. There were tracks of deer and boars, but no tiger tracks. After returning to Bawali, we sailed the short distance to Srinagar.
The next morning, RSET and the Augur team arrived on the coast in a country boat, and Zofur and I, along with Bawari's Rifat and Iyasin, took a speedboat to Gunari and circled half the island to Gunari, where my GNSS was located. When we arrived, the ghat was gone. I wasn't too disappointed as the walk from the ghat to the coast was always very scary. Instead, we simply raked sandbags to protect the shore. Rifat came along, thankfully he was carrying a heavy 80 Ah battery. The manager let us in. Switching out the batteries didn't take long. I immediately called back to the US and after the work he confirmed that GNSS was still online.
Returning to Srinagar, we met up with the rest of the team and headed to the 'inside' site. The tide was low so we had to walk through thick mud to reach the island. We joined them and set a new record by reaching 5.85 meters (19.2 feet). At one of his RSET stations, a very kind family who owns the land added mud to improve the access to the property, thereby changing the elevation on one side. As Southad puts it, „over-hospitality ruined data collection.“ At the end of the meal, the family enjoyed some fresh tamarind and boroi (a small fruit that looks like a cross between an apple and a pear. These boroi were more sour than sweet. Apparently this is the original fruit before it was made sweet by human modification. That's it.)
All data collection and equipment maintenance along the coast of Bangladesh has now been completed. The Bawali is scheduled to return to Khulna. Tomorrow morning we will leave the boat and Rafiq will pick us up in a van and take us back to Dhaka with all the data we have collected and 100-150 sediment samples from the auger ring. The next day, Austin returns to New York. Another postdoc, Lin Sheng, and geodetic engineer Ken Austin are scheduled to arrive the next day. In the meantime, several more meetings are scheduled in Dhaka. The three of us, along with Sanju Sinha and our long-term driver Babu, head east and north to earthquake-hit areas in Bangladesh. We will spend another week here repairing, servicing, and installing GNSS. In the meantime, I can bask in the successful completion of the first part of my fieldwork during the four-hour journey back to Khulna.