Persevering with the Survey: Watermelon and Winds

Persevering with the Survey: Watermelon and Winds

As we head south alongside the Tetulia Channel in southern Bangladesh on the M/V Kokilmoni, the panorama is altering. The northern a part of this channel contained many chars (sandy river islands) that had been glorious for deploying our magnetotelluric (MT) devices. We’re utilizing them to picture the groundwater in coastal Bangladesh. In lots of locations the groundwater is saline, however beneath the saline water there’s freshwater from the final ice age. Because the electrical conductivity of contemporary and salty water may be very completely different, we are able to use electromagnetic strategies to map them.

Kerry directing the MT set up from the tripod in a watermelon discipline.

As we continued, the chars gave strategy to farm fields. We had been in search of fallow fields with cows grazing on the grass. Now we discovered only a few of them that had been dry sufficient for the gear. Nevertheless, we discovered that there have been patches of fallow land for the cows surrounded by crops. We had been capable of put the central recorder and battery within the fallow discipline surrounded by the three magnetometers, which must be buried. {The electrical} electrodes are positioned 50 meters away within the 4 cardinal instructions, however they’re small and will be buried with out disturbing the crops.

Russell, one of many ship’s crew, digs a gap for an electrode between crops.

We had been involved about Cyclone Asani, a uncommon March cyclone, but it surely made landfall nicely to the south of us. Nonetheless, we stayed in small protected channels every night time quite than the 5-kilometer-wide Tetulia Channel. One morning, the climate appeared regarding, so the Kokilmoni stayed in place till the climate cleared round 11 am.

Kerry checks the instrument readings earlier than closing up the recorder.

As we continued downstream, we stopped discovering fallow patches. Everybody was rising watermelons in all of the out there land. Fortunately for us, the farmers agreed to allow us to deploy of their watermelon fields. The fields are lower by irrigation channels and we may bury the three-foot-long magnetometers in these. There are additionally massive sufficient gaps between crops to place the recorder and the electrodes. Moreover, within the fields that had been ripe, we received contemporary watermelons as nicely. You’ll be able to’t get more energizing than consuming simply picked watermelon within the discipline it was grown in. The farmers are giving us watermelons a number of occasions a day.

Adrien fingers me a chunk of contemporary watermelon.

Thus, every thing was going easily. We had deployed 18 stations in 5 days. Then the climate modified and it grew to become very windy. The vast channel that we’re touring opens to the Bay of Bengal and the 20-knot winds had been elevating whitecaps.  After selecting up our stations within the morning, we headed right into a extra protected facet of the channel.

A fishing boat battling the wind and waves.

Our towed nation boat driving the waves. It was too windy to put in stations.

Whereas ready on the climate, I put in the marketing campaign GPS at a geodetic monument I visited in 2020 simply earlier than COVID. These monuments had been put in in 2002 by the Survey of Bangladesh. Remeasuring them in 2020 reveals how a lot they’ve subsided within the intervening 18 years. Since we’re close by, we headed over and put in it to get one other measurement.

Hasnat, Huy and Masud standing by the tripod with the GPS antenna over the monument. The gear field and photo voltaic panel are in entrance.

We stopped for tea at a neighborhood store earlier than heading again to the boat after selecting up the GPS. The proprietor had helped us in 2020.

The wind appears prefer it may proceed for a number of days, however we want MT stations right here to see the transition to saltier water as we strategy the Bay of Bengal. It was already lunchtime and we had not put in any new stations. In Bangladesh, you all the time must be versatile and resilient. We had was the Andharmanik River to get out of the wind within the vast fundamental channel. We determined to proceed alongside its course and observe it out to the ocean. It was a lot calmer on this narrower river in the midst of a big island. We managed to get two stations in earlier than nightfall.

The nation boat lands on fallow land outdoors the embankment.

Huy and Masud carry the MT gear field over a ridge of land connecting the embankment to the land past it.

As we’re getting nearer to the Bay of Bengal, the water is changing into extra saline. We will see salt deposits on the dry soil. The luxurious watermelon fields have given strategy to fallow rice paddies. Right here they will solely develop rice when the monsoon rains and overflowing rivers convey contemporary water. Through the winter and spring, the lands lie fallow. There is no such thing as a profitable watermelon crop right here.

Céline makes a gravity measurement shielded from the solar by her parasol.

Kerry takes a selfie with some native ladies. They’re standing on the dried stays of a fallow rice discipline.

The subsequent day, we continued alongside the Andharmanik River and put within the closing three stations of this transect. For the final station, we took the nation boat up a small channel crammed with fishing boats. This channel is just some kilometers behind Kuakata Seashore. We had made it to the tip of the road. We even sailed handed some mangrove forest close to the coast, however determined the open fields had been higher than combating our means by the forest once more.

Land eroding in entrance of an embankment. Usually the opposite facet of the island is rising new land reflecting the fixed shifting of the islands. Nonetheless, it made good steps for carrying the gear.

We have now completed 23 MT stations alongside this transect for a complete of 44 stations. On the finish of the cruise there will likely be a couple of extra achieved close to Khulna, however I’ll have left the boat earlier than then. We are going to now change to a special kind of electromagnetic measurement that will likely be towed behind the boat.

Fishing boats tied up alongside an embankment that has been secured with sandbags.

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