Fight towing equipment, fix GPS and home

Fight towing equipment, fix GPS and home

Having completed the deployment of a magnetotelluric station (MT) on land to image the distribution of freshwater and saline groundwater along two rivers in Bangladesh, we now turn to a complementary towed TEM (transient electromagnetic) system to improve the imaging. Where surface water and groundwater are fresh has a huge impact on agriculture. We are also imaging deeper freshwater beneath the saline groundwater that can be used as drinking water.

Before we start the TEM, we first have to pick up the MT station that was deployed the previous day. Due to high winds, my group traveled by road to the last stop. The country boat took us to the bridge on the south side of the nearby main road. There, our guide Romeo hired two auto rickshaws to bring our group to the facility. While the main road was fine, the smaller roads on the access to our instrument were very bumpy. Eventually, we got there, packed everything, and headed back to Kokilmoni. Another team used a country boat to pick two other instruments.

Take the auto rickshaw to our last MT station. Mark, Nafis, Bepropp, Romeo and Russell are carrying the equipment.

When we returned, Kerry had begun assembling the raft to carry the instruments. There is a rectangular frame made of Kevlar, which is taut with ropes. Coils are wound around the wires of the transmitter and receiver, and a smaller receiver will be towed on the inflatable kayak. The entire frame is mounted on inflatable boats, tubes and kayaks. Assembling it took the rest of the morning.

Begin onshore assembly of Kevlar and rope racks for carrying TEM gear.

We towed it to Kokilmoni using a country boat and set up the tow line. Then start the debugging process. We sailed down the Andalmanic River and began to feel how fast we could drag. Round buoys flip easily and must be better secured. We also added weight with a 5 gallon tank full of water as ballast. We’ve spent the whole day doing this and still haven’t started investigating, so we’re behind schedule.

Kerry and crew are adjusting the buoys holding the raft and adding water bottle ballast.

Overnight, the crew went ashore to buy long bamboo poles. As we dragged the Rube Goldberg devices back to the start of our investigation, we stopped and the crew added them to the frame, strengthening the frame considerably. We started heading north, but now the kayak with the smaller receiver keeps flipping. We added one and then two legs with plastic pots. Finally, it has a lifebuoy under its bow, making it impossible to dive underwater.

Biplop, Masud and Kerry monitor the echo sounder, side scan and TEM on the top deck of Kokilmoni.

Still, we weren’t able to tow the system quickly and safely. We found that 5kph was close to the speed limit we could tow it, and most of it was slower than that. Even taking advantage of my emergency day, I’m not sure I’ll be able to get back to Barisal on time. It wasn’t until late afternoon that we left the Andamanique and entered the greater Tetulia Strait. It took us a day and a half to build the towed TEM system and get it working. It’s collecting good data, but we’re making very slow progress on the ground.

The raft is now reinforced with long bamboo poles to collect data in the waves.

Then things started to change. The larger fairways were rougher, but we hit high tide and suddenly we were going 9 km/h. With the sea that followed, we started to make up the time. At the end of the day, the captain decided to keep going after dark, taking advantage of the tides as much as possible. We went to a nice place to spend the night.

Kokilmoni likes to get stranded on the shore at low tide. The tides here can reach 3-4 meters. We were stuck until the tide came in.

We were almost there when the Kokilmoni ran aground. Part of the river was shallow and we hit a submerged sandbar. We spent a tense ½ hour securing the TEM raft while trying to maneuver the Kokilmoni to free it. Finally, we did that and headed south, bypassing the shallows of the river. We almost succeeded.

Some local boys stared at our stranded boat and the strange raft we were towing.

A little further from where we had crossed deeper water earlier, Kokilmoni had to swerve to avoid the fishing boats. As a result, we walked fast in the dark and ran aground again. This time we were firmly trapped, although the water was a little deeper on our side. We cannot be free. Instead, we had to wait for the next high tide in the morning to be free, or so we thought. The two orgasms of the day were unequal. We got stuck at high tide. The early tide didn’t reach the level that set us free, so we had to wait for the evening high tide. Going with the flow for a few extra hours now takes us a full day.

Kerry, Céline, Adrien, Russell, the captain, Marin and others played in the mud and water while we were stranded.

We disconnected the TEM raft to free the boat, which can easily happen once the water level is high enough. The next morning, we reconnected everything and restarted our Beihang. Because, we wasted so much time, Adrian and I left the speedboat shortly after breakfast, along with Celine and Massoud, who will do the gravity station on land and rendezvous with Kokilmoni in Khulna at the end of the cruise . To save time, we will drive directly to Patuakhali, which is closer than Barisal, and meet Sanju and 2 others there. They arrived in Barisal from Dhaka on an overnight ferry that morning. It turned out to be more of an adventure than we thought.

Kokilmoni towed a view of the TEM array as we left in the speedboat.

The speedboat had to slow down a lot for the nets, so we were slower than expected. Then we came across a sandbar where the water was too shallow. It took a while to get back into deeper waters, including Romeo getting off and pushing the boat. Then we circled to the other side of the river. As we did, the wind picked up and the water became choppy and sprayed at us. When we got to the other side, we hid in a small side passage.

When we finally reached the foot of a mountain, Malik, Sanju and Shohan were there waiting for us.

At that time, we were only 5km ahead of Kokilmoni after almost 3 hours of speedboat travel. She caught the high tide and rode north at good speed. She came to pick us up and gave us a ride. Over time, we changed our plans. The car continued east from the university where our GPS was located, while we sailed north, crossing the river on Kokilmoni, and meeting the car with Sanju via a set of passages and a small river on a speedboat.

Lecture on my work in Bangladesh at Barisal University. Hasnat sits in the middle with Adrien and Sanju on the left.

Then we drove back to the GPS station. The problem turned out to be a faulty cable. We didn’t have a spare, so with the help of Sarah Doelgar of UNAVCO in Colorado, we put the receiver in a working location, and Sarah was monitoring it in the middle of the night in the US. Then we headed north to Barisal University, where I gave a speech but was delayed by our misfortune.

Masud, Hasnat, Céline, Adrien and Sanju conduct gravimetric measurements at Barisal University, while several of Hasnat’s students watch.

To wrap up the field trip, Sanju, Adrien and I took an overnight ferry from Barisal to Dhaka, something I’ve always wanted to try. It did not disappoint and we arrived in Dhaka early in the morning. After two successful GPS repairs and our extensive EM surveys (MT and TEM), the first of its kind in Bangladesh, it’s time to go home. After a quick COVID test and meeting in Dhaka, we headed to the airport to fly home.

The view from the upper deck hallway and the higher quality cabin we stayed in. The lower deck has open floor space for groups to speed up the blanket.