Sailing off the coast of Bangladesh

I am now on a boat in southwest Bangladesh, M/V Kokilmoni. Getting to this point, however, was the most logistically complex work on any project I’ve worked on here. We face issues with insurance, equipment shipping, getting the right batteries, visas, and the list goes on. Finally, everything worked out and we started our 25 day cruise a few days later. This trip, we’re doing a new kind of measurement, shows me a different problem.

M/V Kokilmoni, our home for the next 25 days as we sail around Bangladesh taking measurements

In most of the coastal areas of Bangladesh, groundwater is salty. This limits rice cultivation to only rain-fed Omani rice from summer to autumn. For drinking water, they must store monsoon rain in ponds. However, deep in the earth, in the sediments of the last ice age, fresh water can be found. It’s used in some places, but a well deep enough is too expensive for most farmers. Another problem is that little is known about the extent of this deep freshwater aquifer. Working with a new group of colleagues, I have imaged both saltwater and freshwater along the coast of Bangladesh.

Kerry filmed the meerkats living in the garden of the Dhaka hotel.Double click on the video link

Since salt water conducts electricity much better than fresh water, we will use two electromagnetic methods to image the distribution of fresh and brackish groundwater along two rivers in Bangladesh. For this, we shipped 1400 lbs. equipment here. Kerry Key, also from Lamont, is our Electromagnetics Specialist, and Mark Person from New Mexico Tech, who is the project leader, is our groundwater specialist. We came here with their students, Anwar Bhuiyan and several students from Dhaka University.

Kerry helped us load the equipment onto the truck so we could drive to Khulna

We arrived in Dhaka a few days early for the meeting and made sure we got the equipment released from customs in a timely manner. With Anwar’s help, we got it the night before leaving Dhaka. On the day we left, we had to wait until we got the right deep cycle battery to go. Then we drove to Khulna to meet the boat. With Anwar’s help, we got VIP treatment on the ferry crossing the Padma River, as the Ganges and Brahmaputra are known to confluence, and it didn’t take long to get on the boat. We were even invited for tea by some government officials on board. A new bridge across Padma is nearing completion and will open this summer, significantly reducing the drive time to Khulna.

Our caravan was loaded onto the ferry and crossed the Padma River

We arrived in Khulna around 6pm and our 3 vans and a truck drove directly to the ghat (pier). The ship’s crew met us and carried a lot of equipment boxes and luggage to the waiting wooden country boat. We settled in, had our first dinner at Kokilmoni, and started finalizing our site. Chris Small processed Sentinel-2 satellite data to show the percentage of vegetation, water or shade, and substrate (soil) per 10-meter pixel. This allows us to choose the exact location of the wasteland for our deployment.

We cross the almost complete 6.1 km long Padma Bridge

We focused on the first day of training, so the whole group of 12 stayed together. Only a few of us have experience with this measurement. The magnetotelluric (MT) instrument uses radiation from the sun to image the structures beneath the instrument. High frequencies give shallow results, while low frequencies give deeper results. Since we are focusing on the upper few hundred meters, we will only deploy the instrument overnight.

Kerry explains how to set up the device while holding the magnetometer cable.

At each site we have a central recorder and battery. They are connected by cables to the north-south, east-west and vertical magnetometers. These are cylinders about 3 feet long that need to be buried. The hardest was the verticals, and we brought in the pit diggers to dig them into the ground. Finally, small electrodes of the electric field are placed about 50 meters from the center in the four cardinal directions using a compass and an electronic rangefinder. They also need to be buried to minimise noise.

Huy made sure the magnetometer was level and north-south aligned before burying

Arriving at the first site, we found a large fallow field to install the MT station. Kerry explained all the components and the process of installing them and we slowly got to work. At each site, we hired local farmers to guard the equipment overnight. It is important that no one enters the deployed 100 mx 100 m area, as the device is sensitive enough to detect passing people. By the second site we were noticeably faster and had everything deployed. In fact, we became efficient enough that we managed to install a third site on day one. At the second and third stations, we discovered a problem that Chris Small’s satellite imagery couldn’t capture: cows and goats. Not only do they cause signal distortion, but goats in particular can eat the cable. Choosing fields to reduce grazing livestock becomes just as important as other aspects of choosing a location.

We brought the post hole excavator for mounting the vertical magnetometer.

The next day, we looped back and restored the sites, learning how to do it properly so they were ready to be deployed again at the next site. We spent the morning restoring all three locations and paying our overnight guards. Then in the afternoon, we deployed another three sites. One of the locations is in the hometown of one of our crew members. We met his mother and uncle while working on that construction site. Our original plan was to split into two groups for recovery and deployment. However, the deployment and recovery were very quick with the help of the crew, especially the Kokilmoni, so we decided to try and continue as a team. Crews on board are doing all the heavy lifting of equipment for each site and digging holes for the magnetometers.

Leaving the country boat carefully, it took us into the mud along the Pusur River.

Meanwhile, Kerry had a preliminary look at the dates for the first sites, and they looked good. We are all excited about the potential success of this new approach, which has never been used in Bangladesh before.