Geohazards in Bangladesh
Humayun Akhter, my main collaborator in Bangladesh, joined me at the airport and we flew together to Kolkata. We spent the night at a nondescript hotel near the airport. The next morning, we met up with film makers Doug Prose and Diane LaMacchia in the airport and all flew together to Aizawl, the capital of Mizoram state in NE India. Doug and Diane have funding from NSF to expand the 5-min YouTube video they made about our project two years ago (https://www.youtube.com/watch?v=WTETuqJPygs) to a ½ hour TV special. Their previous films have been shown on PBS.
The Sumatra subduction zone, source of the 2004 earthquake and tsunami, continues to the north where it encounters the Ganges-Brahmaputra Delta. The 15-20 kilometer thick delta sediments are folded and faulted as they enter the subduction zone. Because of the huge amounts of sediments, this is the only subduction zone whose front is subaerial – entirely exposed on land. In Bangladesh we can see the beginning of this process. Here in Mizoram, farther east, the former delta sediments are folded up into a very hilly terrain. The steep slopes are subject to frequent landslides. One that started last October has moved again and blocks the main road from the airport to the city of Aizawl. As a result, we had to take a longer, slower, bumpier and dustier road to get to the city.
We met up with Nano Seeber and Paul Betka from Lamont at breakfast. They have been doing geologic mapping the region and returned to Aizawl late the night before. We spent the day circling the city and visiting outcrops, many ones I had seen my last time here. We had several interesting discussions on differences of interpretation of the strata. I had visited most of these outcrops before, but it was the first time for Humayun. At the end of the day we were joined by
Vineet Gahalaut from the mainland, as the rest of India is considered here. The people here look Asian and the Mizo language is a tonal language in the Tibeto-Burmese family. Plus, almost all Mizo are Christian. Mizoram is part of India, but also distinct, like many of the other states in NE India. Part of the sense of separation is that the 7 NE states are only connected to the rest of India by the narrow 23 km (14 mi.) Siliguri Corridor between Bangladesh and Nepal – the chicken neck. We spent the evening talking with Vineet about future joint projects in this region.
The next day we were joined by Victor Ralte, our partner from Mizoram University, who became a proud father of a fourth daughter last week. We all headed north, visiting geological sites and filming
beautiful vistas, dropping Vineet off at the airport and continuing on to Kolasib, a small town about 70 km north as the crow flies, but probably twice that on the windy roads of Mizoram. We stayed in Hotel Cloud 9. I had been told since I was a child that I was always off on Cloud 9 and now I was actually here. However, the electricity wasn’t for the first few hours, so showers were cold, but the dinner was hot.
The next day we headed still farther north to see some complex faulting associated with the growth of the anticlines – the hills of folded strata. As we examined each outcrop, it was also clear that we were passing through several kilometers of rocks in which the environment that were deposited in shallowed from the inner continental shelf (10s of
meters water depth) to the tidal zone to estuaries like the present Sundarbans to fully fluvial (river). This represents the ancient Brahmaputra Delta passing across this area as it grew southwards. That several kilometers of sediments were deposited while the environment only shallowed by 10s of meters indicates that there was a lot of subsidence to make space for the sediments. I will have to model this when I return.
Stopping for a beautiful sunset over the hills, we finished heading back to Aizawl for a last dinner together. In my room as it turned out since the restaurant closed for some repairs. The six of us ate a mixture of American, Indian, Chinese and Mizo food with plates dishes and ourselves filling all available surfaces. Today, a quick stop at Mizoram University and then back to Kolkata for my last leg before home.
For our last morning, we did a dawn silent boat ride up a tidal channel. Since the students did one the day before, a few sat out. The ones that remained stayed silent to increase our chance of sighting animals. We saw many birds: kingfishers, kites, egrets and others. There were numerous mud skippers – fish that come out of the water to avoid predators – and a wild boar. The highlight was sets of fresh tiger tracks. The first set came down one bank and up the other. Tanjil, our guide, estimated that they were 5-6 hours old. After returning to the ship, we headed north through the Sundarbans towards Dhaka, a day and a half journey.
Along the way, we had a quick stop at a small village along the Baleshwari River. Chris Small had noticed that the width of the villages in this area had doubled between 1989 and 2010. We wanted to find out why. A small party went ashore to talk to the villagers. Unlike Polder 32, the water here is fresh and it shows. Lots of trees and a more prosperous and happier population. Boys jumping
into the creek from the top of the sluice gate. The trees included betel nut, papaya and other fruit trees and well as trees for wood. The local policy is that for every tree they cut down, they plan 4 new ones. This accounts for the increased size of the villages, a net switch from rice field to trees. After only a ½ hour, we had to return to the boat, drop off Carol and Saddam where a car would take them back to Khulna, and continue on our way.
We decided not to stop for visiting Barisal or swimming and thus were able to get to Dhaka the next afternoon rather than at night. Instead of spending the night on the Kokilmoni on the polluted, smelly, Shitalakshya River, we went into Dhaka and back to the Ambala Inn. More importantly for the students, we arrived with time to
shop. After checking in, we formed groups of 2 US and 1 Bangladeshi and sent them off by foot and rickshaw to New Market for shopping. The lack of shopping opportunities was the main complaint about the trip. They made up for it with clothes for themselves and presents for friends and family. That accomplished, we gathered for a final dinner in Bangladesh at Voot, one of our favorite restaurants. The slow service with cooking for 22 allowed plenty of time for socializing and picture taking. The students showed off their new Bangladeshi togs and a good time was had by all.
The next morning was our chance to see Dhaka. We met our counterparts the university and headed to Old Dhaka. We stopped at the 800-year old Dhaleshwari Temple where a child was getting
her first solid food in a Hindu ceremony. Then on to the Lalbag Fort built by the Mughals in 1676, or so we thought. Sunday is its day to be closed. We decided to go to the Ahsan Manzil, known as the Pink Palace. As we drove through the narrow streets, traffic got slower and slower. Finally, we stopped and decided to walk the last quarter mile. Now we all got a true taste of Old Dhaka, dodging rickshaws, hand trucks, pedestrians, and workers balancing parcels on their head. We managed to get all of us there and toured the grounds overlooking the Buriganga River then the massive palace built by the Nawab of Dhaka in 1872.
After the chaotic walk back to the vehicles, we spent an hour going the few kilometers back to Dhaka University. When we finally got back, we
had to abandon our plans for visiting the National Museum. We went to lunch at a very Bangladesh restaurant, picked up our luggage at our hotel and headed to Aarong. It is an upscale shop that sells all Bangladeshi clothes, crafts and products. The students got their last fill of shopping. Satisfied with their gifts, we headed to the airport. They went home, while I started my next leg in Kolkata and Aizawl, India.
We left Hiron Point with the high tide and sailed through small channels of the Sundarbans Mangrove Forest. As a tidal marsh, the Sundarbans is crisscrossed by channels with sizes that range from 10 km across to less than a foot. The tides rise and fall periodically inundating all of the land. Mangroves are trees that are adapted to living in brackish water. Different tree species are found in different parts of the Sundarbans, adapted to different levels of saltiness.
We arrived at Kotka in the afternoon. Most of the group went on a forest walk with Tanzeel, our guide. A smaller group of us split off to visit thee remains of 300-year old salt kilns. We passed Chital deer and a wild boar on the way. A stag was silhouetted at the coast before it ran off. The
people that built the kilns used to allow seawater to flow into evaporation pans at Spring high tide. Before the next Spring tide they would bake the concentrated brine in clay pots to produce salt. The kilns are surrounded by innumerable potsherds, and quite a few intact clay pots. It is thought that the operation was suddenly destroyed, abandoned and buried, perhaps by a 1699 cyclone that killed 50,000 people. Recent erosion, include the destruction by Cyclone Sidr in 2007 have unearthed them.
Since the age of the kilns is known, it is a good site for Liz to use OSL dating to determine the sedimentation rate. We drilled several auger hole to determine the stratigraphy, the deepest one was 5.8 meters. Liz drilled assisted by two crew from
the Kokilmoni while I took notes and photos. The kiln site is now in the intertidal zone – exposed at low tide and covered at high tide. This means that they have subsided since they were last used. The rate is estimated as 4.1 mm/yr by a German group that worked here. We completed 3 holes, but ran out of daylight before we could take the OSL samples. We returned to the ship, walking past buildings destroyed by Sidr with our larger group who ended their forest walk at the kiln site.
We returned at dawn the next morning – with a guard to protect against tigers – while the remainder of the group went on a silent ride up a tidal creek. We collected 3 OSL samples from different depths, the last one completed as the rising tide reached over our knees. Whenever the
sampler was removed from the hole, one of us had to keep our hand in the hole, usually Matt, so we could find it again. Happy with our successful sampling, we returned to the ship for breakfast.
Back with the others, we set out for a forest walk to Kotka Beach. Climbing an observation tower, we got an overview of the region. There are old shoreline deposits here that are above the high water level. These sediments provide evidence of the seaward progradation of delta. As a result there is a meadow and many non-mangrove species as the area doesn’t regularly flood. This attracts a lot of deer and, as a result, tigers. However, we only deer. We also walked through the muddy mangrove forest and finally emerged at Kotka Beach where we went swimming in the Bay
of Bengal. We continued along the beach for a few kilometers passing hordes of scurrying crabs. Finally, we rejoined the Kokilmoni for a late lunch.
In this area, plans always have to be adjusted according to the tides and weather. As a result, we switched our visit to Bird and Egg Islands to later in the afternoon instead of the following morning. These two islands emerged from the sea about 20-25 years ago and have grown and merged. In answer to the age old question, the Egg came first. While a few people skipped the walk after the morning’s trek, most of us went along. It is a great place to see the biological succession that develops on a new island. The coast is bare sand with the high water mark littered with plant debris. Beyond the wind-blown coastal dunes, grasses
have taken hold. Then tall grasses and a scattering of shrubs and then trees in a muddy salt marsh. Finally in the distance is a full-fledged mangrove forest. We saw tracks and spoor of deer and monkeys, but as of yet there are no tigers on the island.
An unsuspected bonus was a tidal channel near the beach. Here at small scale, we could see all the features of river systems that we discussed in class: cut banks and point bars, meanders and avulsions, small deltas and chars. All at a scale that brought the geology to life for the students far better than any lecture or photos. It was a long and very successful day in the Sundarbans.
We sailed downstream to join the M/V Bawali with the Vanderbilt-Dhaka-Khulna group working on Bangladesh late at night and awoke to greet old friend and meet new ones. After breakfast, we all headed to Polder 32. Polder 32 is one of the islands that had embankments constructed around them to prevent flooding and improve agriculture. They use the Dutch term polder for the embankments. Polder 32 was one in which the polders failed during Cyclone Aila in 2009. As it turned out, while the polders improved agriculture as planned, it also led to subsidence of the island. It is now over 4 feet lower than land outside the island. This led to widespread flooding of the island after the cyclone that lasted for almost 2 years. We have been studying the causes and impact for the last few years. The subsidence inside the polders put everyone at risk as an unintended consequence of keeping out the natural flooding and sedimentation to improve agriculture. How to manage this system now is a difficult problem.
We also learned about the water problems at Polder 32. The groundwater is saline and not usable for either drinking or irrigation. They can only grow one crop a year, so the fields are all fallow except for some vegetable gardens by the homes. In other parts of Bangladesh 2 and even 3 crops a year are possible. We saw the abandoned tube wells installed by a wealthy donor after Cyclone Aila. They are all saline. Kazi Matin showed us his MAR site – managed aquifer recharge. They are attempting to create a pool of fresh groundwater over the heavier salt water providing a source of sweet water. Nearby, the Vanderbilt team is
installing equipment to measure water levels and flow at different depths, trying to better understand the groundwater system.
While the students fanned out to discuss agriculture with the farmers and test what few tube wells they could find, a small group of us took a speed boat to a large industrial shrimp farm on Polder 33. We found the site to be surrounded by a barbed wire fence. We found out later that it is to protect the site from tigers as it is on a peninsula surrounded on 3 sides by the Sundarbans. There was a rumor that the shrimp farm had closed and could be used to calibrate remote sensing data, but it was fully running. They grow 2 crops of jumbo shrimp a year over 9 months and spend the
remaining 3 months cleaning the ponds and preparing for the next season’s crop. They were one of the first large-scale shrimp operations in Bangladesh.
We sped back to the ship to find that the others had all returned and were having a swim break. I barely managed to change into my swimsuit and jump in before we all had to return to the ship to sail to Hiron Point. The strong tides in southern Bangladesh set our schedule as we try to catch tides going our way and avoid sailing against the tide. We sailed down channel between Polder 32 and the Sundarbans to the Shibsa River. At the end we passed Kalibogi. It is a peninsula at the end of Polder 32 that has had about a kilometer of erosion. It is now very narrow and the
embankment has been moved north of the peninsula, abandoning it. The shrimp farms that were once here are gone. There are only homes poorly protected from the elements and fishing is their only livelihood.
We sailed down the Shibsa to the Pusur River and overnighted in a narrow channel across from Hiron Point. In the morning we crossed. This stop is manly for me to service our GPS installation. We are using the precise measurements to determine the subsidence rate of this part of the delta. There is a tide gauge here that monitors the relative level between the sea and the land. While intended for navigation, over time it records the combined effect of land subsidence and sea level rise. With the GPS, we will be able to separate the two rates.
We all took the small wooden launch into the channel to the Forest Station. The Kokilmoni stayed outside lest it get trapped behind the mouth bar when the tide goes out. Hasnat and I, with Sabrina filming went to service the GPS while Liz demonstrated how to auger to get stratigraphy and sample for OSL dating. Small groups also took turns going up the observation tower. I discovered that I did not have my internet adapter – Apple have eliminated them from the newest Mac. I was stuck. Hasnat rushed back to the ship with the launch to get his computer. I could only wander around. I was shown the small spring with natural gas bubbling up. It could even be lit on fire. Finally Hasnat returned and we were able to download all the data since my last visit and upgrade the firmware of the receiver. We finished right at high time and rushed back to the ship to sail to our next stop. Thanks to Hasnat, we were able to accomplish our goals here.
The shortest route to where we are headed has silted up and is no longer passable. Farmers have moved in and started shrimp farming there. As a result, we and others have to take a longer route through the Sundarbans Mangrove Forest. Our first tantalizing sight of the forest we will return to later. Will lots of ship traffic on this route, the inevitable happened. Last December a ship collision resulted in an oil spill. With initial inaction by the government not wanting to face it, the local people went in and cleaned up the oil themselves by hand. Without any protective gear from the toxic oil, they saved the situation. Now only a slight oily film is visible at low tide. We started at 2 am to travel through the passage with the rising tide.
By 10 am we had passed through the Sundarbans to the Pusur River and stopped to pick up Carol Wilson and Saddam Hosain. They will join us for a few days from another boat that a Vanderbilt-Dhaka University team is using for research work at Polder 32. We continued up to Khulna ghat (dock). We had lunch and transferred to land by launch. In three vans we drove for and hour to asite where we installed instruments to measure the compaction and subsidence of the sediments. In 2011 we drilled 6 wells with depths from 20 to 300 meters installed optical fiber strainmeters. The fibers are stretched like a rubber band and every week one of the sons from the Islam family uses a device to measure its length, watching to see the change as the sediments compact.
While I service the equipment, my students spread out in several groups. Four of my students, each with a Bangladeshi partner spread out over the area with Chris Small to interview farmers about their farming practices, what crops they grow and changes through time. The information the agriculture team collects will help calibrate remote sensing observations. The other 6 students work with Kazi Matin Ahmed of Dhaka University form 5 teams to measure arsenic levels in the wells that provide drinking water. Finally, Liz Chamberlain and Carol use an augur to drill into the sediments. They will look at the stratigraphy and collect a sample for dating. The river that flows through the area used to me 300 meters (1000 ft) wide, now it is only a few meters. The silting in banks have been occupied by squatters using the new land for shrimp farming. The Islam family moved here in 2002.
When we arrive, it is hard to recognize the site. The government is excavating the river, widening it so boats can use it again. There are large piles of mud everywhere. Finally we find the right place and are relieved to find that they went around our instruments. In the afternoon, I met the engineer doing the work and he reassured us that our instruments will be untouched. Only time will tell if the measurements will be affected.
I was the least successful of the groups. We collected the data from the 6 compaction meters and surveyed between the GPS and wells to look at changes in the surface elevation. However, the cap of the well collecting water level data was rusted shut. When we really tugged on it, the pipe started to bend. We will have to return with WD-40.
Even worse the GPS was dead. Some problem with the solar panel system, but with the tool kit back in the states, I couldn’t diagnose it. I will take the receiver back to Dhaka to download the data, but Humayun will have to come to repair the power system. At least the students had a more successful time talking to farmers and measuring arsenic. It was their first time talking to rural Bangladeshis and spending time in the countryside. They thoroughly enjoyed it.
I am once again teaching a Sustainable Development course on hazard in Bangladesh. The highlight of the course is that the 10 students, the teaching assistant and I are all traveling to Bangladesh over Spring Break. However, our plans have been disrupted by the continuing political unrest in Bangladesh. The opposition BNP party is calling for new fair elections by calling for a continuous blockade of travel and periodic hartals – general transportation strikes. They have been trying to enforce it by tossing Molotov cocktails at vehicles that defy it. Over 120 people have been killed so far. The ruling Awami League refuses to give into violence and neither the UN, EU or US
have been able to make a dent in the situation. The two parties and their women leaders hate each other. Neither side will back down on the unrest that started with the Jan 5 anniversary of the election. While more and more people are defying the blockade, after 2 months people have to make a living, the risk is too high to take a bus load of undergraduate students around the country.
Our solution, Plan B, is to stay off the roads and travel the country by boat. Dhaka, the capital is quiet, so we are visiting there at the beginning and end of the trip. The boat we were planning to use to visit the Sundarbans Mangrove Forest came up to Dhaka to meet us after we had a difficult trip. The 14 of us (Chris Small of Lamont and Liz Chamberlain of Tulane University are also joining us) made it to JFK skirting traffic
only to find a 4-hour delay on our flight. The airline nicely rebooted us for the next connection to Dhaka and escorted us through the airport to catch it. However 4 bags missed the connection. By the time we got to our hotel it was midnight and we still hadn’t had dinner. It was two AM by the time we go to bed. My TA, Matt, had to go back to the airport in the morning with Sukhen, but only 3 of the bags arrived. The missing one was Matt’s, but having lived in Dhaka, he had clothes in storage there.
The rest of us went to Dhaka University to meet our Bangladeshi counterparts, 8 students and 2 professors that are traveling with us. After a quick tour of a few spots around Dhaka, we headed to meet the Kokilmoni. I have sailed on her twice before. With Plan B, we will have to skip some areas, like the Brahmaputra River, that we cannot get to by boat in our limited time. However, we will get more time at other spots of interest and see what will be new parts of the country for me from a different vantage point. We started on a the Shitalakhya River east of Dhaka and sailed south in larger rivers finally passing the confluence of the Padma (combined Ganges and Brahmaputra) with the Meghna River before tying up at Chandpur for the night.
A boat is a much more pleasant way to travel than a bus with more places to hang out and rest from jet lag. The food is good and plentiful. The cabins are tiny and hot, while the showers are cold. The main thing the students missed is any opportunity to buy Bangladeshi clothes. Along the way we made two quick stops, one above and one below the confluence, for Liz to take samples for OSL analysis, a dating technique that uses electrons trapping in quartz to determine the last time the sediments were exposed to sunlight. The samples, collected by hammering a tube into the outcrop, must not be exposed to sunlight. Otherwise, these first days are quiet as it will take us until tomorrow afternoon to reach our first extended field stop. Boats are a comfortable, but slow way to travel.