Dealing with rainwater and mice
On the morning of Eid al-Fitr, we had a heavy downpour. We couldn’t have a celebratory breakfast in the Humayun Gardens at the VC residence, although it was still outside. On most days we eat breakfast at 5:30am so we can start early before the heat of the day. For Eid al-Fitr, we ate our breakfast and went to bed around 9 am after prayers.
A group of local children helped Masudra drive a wagon full of equipment across the fields to our site.
Eid al-Fitr started our day late with the installation of magnetotelluric (MT) instruments in northeastern Bangladesh. These instruments use the sun’s electromagnetic radiation to observe Earth and see more conductive and resistive layers beneath the surface. We are conducting multi-day deployments to image the subducting grand thrust, the thickness of the sediments and the depth of the Moho at the bottom of the crust. To record data, we have to arrange electrodes and magnetometers around the central recorder.
When Ramadan ends and Eid al-Fitr begins, we see a lot of trucks and parties. Here we got stuck in traffic on a bridge behind one of them.
We first went to a site we had scouted the day before. It is located in a slightly raised area that exposes reddish, older Pleistocene sediments. We believe this is due to the uplift of sediments that folded as they entered the subduction zone. The rivers in the area have been widened by people to create vast flat land where rice can be grown. We drove through the forested highlands, where there were many jackfruit trees, and into the rice fields. We found that the fields we picked the day before now have an inch or two of water standing. We need another place. With more rain in the forecast, we are now worried about flooding at all of our sites.
When we picked up a plot in the rice field, we saw kites flying around.
Luckily, the farmers who were watching for us had some unsettled woodland nearby. Although there were rice fields nearby that were not flooded, we chose the forest as more rain was forecast. We walked over and found that if we shortened the electrode wires, the forest was large enough to accommodate our array. Since this deployment took a long time, we left it until the next morning. We continued eastward to the spot where Summer and Arman were scouting.
Oliver, Masud and Biplab act as washing stations in the mosque to remove dirt from their feet.
This is a site along a small river, along a path where the mighty Brahmaputra once flowed. The archaeological site of Wari-Betashwar is not far away. It is built on uplifted woodland, will not flood, and can lead to the Brahmaputra. It flourished as a trading center from 450 BC to 600 AD, when the Brahmaputra shifted its channel and another city took its place. It moved again before an even bigger tear moved the entire Brahmaputra system 100 kilometers west to its current location more than 200 years ago.
Arman walks through our forest site.
The ground is sandy due to the previous existence of the Brahmaputra. This means it drains well and won’t flood our equipment. This site is closer to the village and many children joined our team. One of them helped when we had to run the electrode wire under the frame of the planted squash. Then he and his friends also helped dig holes for the electrodes themselves. We made it, but still worried about finding sites that wouldn’t be overwhelmed.
We had our last breakfast at the VC residence in BOU before moving to a hotel further east.
The next day, we went out to pick up our first site and deployed it further along the transect. We found that one of the electrodes and the magnetometer cable had been cut. It could be a fox, but it could be a mouse, and they’re pretty big here. We also heard from a watchman at another site that the wires were cut. Now we have a new very serious problem. The electrode wires are coated with a substance that mice don’t like. We found that they took the first bite, decided they didn’t like it and left the other cables. By then, however, the damage had already been done. Once one of the electrodes or magnetometer cables is cut, the data will not be available. While a single wire in an electrode cable is easy to repair, a magnetometer cable with 8 thin wires is much more difficult.
Samer opened the trash bag with our equipment to see if it was still working.
After retrieving the first site, we went to the other broken site and picked that one up as well. We tried to find a new site without success. The area is densely populated with too many wires running in all directions. We drove back to the BOU where we were staying, but it was too late to go to another location. We just stopped for a bite to eat on the way.
Our team walked through the rice fields with our equipment.
The next morning, we were ready to move to another hotel. Our line is too far east of the BOU. We rented a pickup truck and packed everything. We stopped at the first LP site and found it was closer to the wires than we thought and one of the electrodes had been cut. At the next site, the first we installed, we found more disconnects. We are now starting to worry about collecting enough good quality MT data here. Also, we started working at 5:30am and didn’t come back until 8-8:30pm. Our pace is unsustainable.
Arman and Biplab buried the magnetometer cable in the ground to protect it from rats and foxes.
We need to pick up the plane early at the next stop because they need to harvest rice because of the rain. It’s finally intact. Maybe it’s because the wires go into the rice fields and hang from the straw instead of the ground. We were a little excited, but still worried about how to protect the wires from mice and foxes. We drove across the Megna River and checked into our hotel around noon.
Biplab recovers electrodes from rice fields.
We finally sat down for lunch for the first time since we arrived. We lowered our expectations. We need to slow down and put more effort into keeping the wires safe. Summer, Massoud, and I went to buy neem oil, which the mice didn’t like, but couldn’t find. Instead, we’ll try chili oil. If that doesn’t work, wrap the wire in PVC pipe or bury it. We will visit our last two remaining sites west of the river split. I went to the forest site and Summer went to the sand near the river. We found it still works. Just in case, we buried the magnetometer cable and covered the portion of the electrode cable with dirt. Samer’s team found that the fox had cut some cables. They put chili oil on the wires. While they managed to do it, they found that it wasn’t practical and the chances of people putting chili oil on their bodies and rubbing their eyes were too great. The next day we picked up both locations and crossed the Megna to Sylhet.
The kids who helped me run the electrode wires and dig holes in the sand.
We are working at an unsustainable rate, trying to install 2 sites every day from 5:30am to 8:30pm. We will reduce to 1 site per day, or through reconnaissance. We also need to pay more attention to site location and power lines, especially for LP sites. We will have to trench all our cables to avoid rats and foxes chewing on them. Although they didn’t like the taste, their first bite ruined the place. As we continue to move east, we will have fewer but more carefully selected locations. Following our revised plan, the next day, we picked up both locations and headed to Sylhet across the Megna.
