Final Entry

Last Entry

Bangladesh is a target for natural disasters of all sorts including earthquakes, floods, tropical storms, drought, subsidence, and monsoons. However, without contest, those hazards which affect the drinking water supply of this country are the most dangerous. As with many earth-related phenomenon, many of these disasters are linked together as in a chain reaction.  I will review the disastrous effects of tropical storms and drought-related disasters (which include subsidence and other ground water issues).

A word about tropical storms: The tropical storms which Bangladesh is subject to are classified as cyclones (which is just another term for hurricane except that it is more commonly used in the Asian Pacific.) Cyclones/ hurricanes are low pressure systems. At the center on the cyclone spiral is the eye, which has the lowest pressure of the cyclone. Tropical cyclones are warmer low pressure systems which result from passing major thunderstorms. Tropical storms are definitely one of the main foci of the natural disaster mitigation and relief efforts in Bangladesh. The death toll during tropical such the cyclones which hit the coast on a fairly regular basis is usually instantaneous and devastating. As explained in previous entries, some of the most devastating cyclones to affect Bangladesh include the 1970 Bhola Cyclone which killed approximately 500,000 people, and the most recent storm was the Cyclone Sidr which hit Bangladesh in 2007 killed approximately 2,000 people. These storms also cause extreme property damage, wipe out coastal fisheries, cattle populations, deltaic crops, destroy the mangrove forest which protects the western edge of the coast and they contribute to the heavy erosion of the coastal sediment which then contributes to high salinity levels inland. Some years, the coast of Bangladesh is hammered with multiple large-scale cyclones (exp.  In 1983, both in October and November Bangladesh suffered from two separate cyclones).  Approximately 90% of the human loss of life is due to initial storm surge. Storm surge is the sudden wave of water which occurs during a storm such as a hurricane, not to be confused with a tsunami or rogue wave, it is more accurately described as an ocean based flash flood. Surges can travel as far inland as 25 miles and they wipe out nearly everything their path. Bangladesh experiences usually at least on cyclone per year and although the cost of human life has decreased significantly since 1970, the coast never really is allowed the opportunity to fully rebuild its infrastructure or way of life.

However, Bangladesh at least has designed mitigation plans specifically for Cyclones. Mitigation for cyclones includes the construction of cyclone shelters and a coastal warning system which makes it possible for people to leave their homes and either simply move to higher ground, further inland or reach a designated cyclone shelter, or simply the closest shelter to their current area. The coastal areas need to have a strictly regimented cyclone mitigation plan because the coastal population itself is high in number and also ill-organized with a weak infrastructure. The combination of those two components makes cyclones even more dangerous as when they do make land fall the area they strike is filled with people who live in weak structures in close quarters which can cause wide spread panic and miscommunication. The sheer population density, as would be expected hikes up the death toll for those people who remain simply on a statistical basis (the more people left on the coast, the more people killed in the initial storm surge).  Another cause of death is disease and injury as well as loss of livelihood which occur as a direct result of these storms. Furthermore, due to the damage cyclones cause to the sediment of the coast, potable water becomes yet another issue as the delta and the shore erodes salt water seeps into the coast line and moves north with each new surge making the soil barren and the water undrinkable. These cyclones rip up the mangrove forests, contribute to the disintegration of the coast islands (which also protect the central and eastern edges of the coast from storms much like a barrier reef would elsewhere).

The aforementioned brings us to a second major ongoing geological disaster which is water. The issue of water management, preservation and all issues regarding potable water are the most prevalent and dangerous which Bangladesh faces. There are many water-geological problems in Bangladesh; too many to cover in an entry such as this. They are all inter-related and as each new issue comes up there is a sort of domino effect as more and more systems are disturbed. The biggest problem which Bangladesh faces is water availability. In the Northern areas of the country, the ground water is heavily poisoned with arsenic which naturally occurs in the soil. Furth south and especially close to the coast, the ground water and surface water are becoming steadily more and more brackish as the ocean infiltrates the delta, its watershed and seeps into the soil. The aforementioned mangrove forest on the western coast can grow in somewhat brackish water but as the salinity of the soil increases their root systems die. Sea level is also rising (as it all over the world due to climate change). As sea level rises it contributes to the seepage of salt into the coast and it has begun to flood into the delta regions, giving it the same characteristics of a brackish estuary. Also as sea level rises, it erodes the coastal sediment away and the mangroves with weakened root systems do not have any solid ground to cling to so they wash away with the soil. When the mangroves wash away part of the coastal defense against storm surge is weakened which brings us all the way back to the dangers of storm surge in general and not excluding the further salinization of the soil inland.

Because drinkable water is hard to come by in Bangladesh the country has attempted has basically exhausted what little clean ground water by sucking the soil dry. The dryer the soil gets, the more it subsides and. As subsidence worsens, the pores where ground water would normally collect shrink, turning the layers beneath the farmland areas into clay. This makes it hard to grow crops. Clay is not porous enough to become an aquifer again so whenever the monsoons arrive (right around the time the cyclones roll around) instead of some of the rain water seeping back into the earth and replenishing the aquifers for potential extraction later, it all runs off into the ocean again over a weakened and eroded coast line, taking more sediment with it and exacerbating the problem even further.

Obviously, all of the above makes for a fairly constant disaster scenario. Unfortunately, there is very little being done to mitigate the issue. I honestly am not sure what Bangladesh could do to mitigate the water issues it faces short of building a desalinization plant somewhere near the coast. However, such a plant would be in danger of sustaining major damage every time monsoon/tropical storm season came about in the fall. A desalinization plant would also disrupt the local coastal processes, especially the shrimp farming industry as it would suck up anything big enough to fit past its initial grate filter. Bangladesh is fast becoming an inhospitable area especially in regards to water. I predict that as they run out of water options, the people of Bangladesh will be forced to relocate, potentially north or to either one of its neighboring countries, India or Myanmar. Personally I would not build my house anywhere in Bangladesh, but if I had no other choice: I would build my house on high ground to avoid the coastal problems and near the border of India so I could immigrate quickly if necessary. Finally, I would build my house with a large, sturdy rain-water collection system so as to avoid the arsenic in the ground water. I would also have to have a decontamination unit of some kind in order to avoid getting sick via bacteria. Or perhaps I would just have to ignore my personal morals and make a big deal with Pepsi so that I could have crates of bottled water delivered via parachute every week.

https://phulbarinews.wordpress.com/2008/06/24/dewatering-in-open-pit-mining-concern-or-benefit/

http://link.springer.com/chapter/10.1007/978-94-015-8719-8_9

http://www.sciencedirect.com/science/article/pii/S221209631300003X

http://en.wikipedia.org/wiki/Cyclone_Nargis

http://www.royalhaskoningdhv.com/en-gb/projects/cultivating-oysters-to-combat-coastal-erosion-in-bangladesh/107

Water

A running theme of these blogs has been potable water or rather, the lack thereof, in Bangladesh. The coastal conditions in Bangladesh are heavily influenced (as is every other geological condition in Bangladesh) by the monsoons the region experiences. The coastal conditions affect much of the coastal areas and even slightly further inland. The storm surges which occur during tropical cyclones which hit the coast of Bangladesh move weaken the coast and erode I making it more vulnerable to weather conditions.  Storm surges also push salt water from the ocean into the delta which then becomes brackish, undrinkable, unsuitable for crops, and detrimental to the soil conditions for years to come. When the storm surge brings salt water into the delta, it does not get washed away sufficiently. In fact, it may continue to ebb into the delta becoming a larger and wider-spread problem in years to come.  

The above is a general overview; however, one can easily predict the size of the snowball such conditions could cause. As it happens, much of the ground water, especially further north, are heavily contaminated by arsenic which obviously make them useless for drinking water as well as crop growth.  Interestingly, I read several academic publications regarding these issues to write this and all of them mentioned arsenic poisoning being a problem but I did not quite understand where the arsenic was coming from. It turns out that the tube wells which Bangladesh uses to retrieve ground water are to blame. Tube wells are wells which are formed by drilling large pipes or tubes into the ground and pumping the groundwater up through them with the use of an electric or gas powered motor. It is a pretty simplistic design and it should have worked quite well except that back in the 1970’s a clean water campaign drilled a huge number of these wells into layers which already contained toxic amounts of naturally occurring arsenic.  http://science.time.com/2010/06/19/study-says-arsenic-poisons-millions-in-bangladesh%E2%80%94but-theyre-not-the-only-ones/

This leaves only a few water options left: lakes, rivers, and other wells which are not contaminated by arsenic. The problem is; many of those bodies of water including the wells have extremely high salinity levels. Due to subsidence in the delta, the water table aquifers are shrinking which means that ground water is harder to come by and harder to replenish when the rains do come.

The water issue aside, as the coastal region is eroded it becomes more vulnerable to storm surge. As mentioned in my previous entry, storm surge is the most dangerous aspect of the tropical cyclones which fairly regularly make landfall in Bangladesh.  Sea level rise, as one would expect, has made these tidal and storm surges even more devastating. Even as sea level rises, it starts to bleed into the delta contributes saline to the delta. Currently Mangrove forests help protect the coast and hold sediment together with their root systems. There have been some interesting advances in attempting to use oysters as a sort of natural reef which would also accumulate sediment.  An oyster reef, if properly maintained, would potentially provide a solid source of coastal food- an oyster farm- and it would help reinforce the coastline and protect the mangroves.

http://www.royalhaskoningdhv.com/en-gb/projects/cultivating-oysters-to-combat-coastal-erosion-in-bangladesh/107

There have been some other, more concrete ideas as to how to mitigate the negative effects of tidal flooding such as; embankments, sluice gates, and changes in what the agricultural community grows seasonally. These all will hopefully help prevent salinity levels from rising inland. Soil salinity is difficult to combat because many of the mitigation tactics meant to prevent saline water from moving further inland into the deltaic zones involve planting sturdy vegetation which can also be consumed by the population and unfortunately, it is virtually impossible to grow anything in the soil near the coast because it is simply too salty to support the usual, climate-appropriate crops.

http://www.pakbs.org/pjbot/PDFs/38%285%29/PJB38%285%291359.pdf

http://teacher.buet.ac.bd/msalamkhan/teaching_msk_files/coastal_issues_bd.pdf

Cyclones

Cyclones: Finally a natural disaster which Bangladesh is not only familiar with but also somewhat PREPARED FOR. In case you missed the last episodes, Bangladesh should not be on your top ten places to live list. It turns out that Bangladesh does not have any of its own satellites and it relies on the NOAA and NASA satellites which send data remotely to the Bangladesh Space Research and Remote Sensing Organization, which is part of the Ministry of Defense. Apparently SPARRSO has a detailed “storm prevention” strategy (I think this is simply a poor choice of semantics on their part but it makes for rather amusing brain fodder to imagine a group of wizards at the ministry of defense combining their power to stave off the forces of nature). All joking aside, they have a volunteer force of approximately 32,000 people who are trained to warn and evacuate citizens especially in lower coastal areas and a network of 2,500 cyclone shelters. Petenga and Chittagong have built sturdy concrete levees to protect that part of the coast. After reading about how cyclones affect Bangladesh, I can see why they do not spend much time or money (comparatively) on earthquake or even subsidence mitigation. The Bhola Cyclone in 1970 killed 500,000 people (and that statistic is likely to be conservative). Over one million cattle were killed, 20,000 fishing vessels, 400,000 houses and 3,500 educational institutions were also destroyed. The wind during the Bhola Cyclone reached a maximum of 222km/hr and the maximum sure was over 10 meters. Bangladesh suffers primarily from tropical cyclones. They can last up to 24hrs and they produce  a huge amount of heart and moisture. They knock out power and contaminate what few potable water supplies Bangladesh has. In a country as heavily populated as Bangladesh, a power blackout could be devastating in itself as it would put hospital equipment out of commission and probably slow down the warning and guiding systems necessary to reach as many people as possible in a disaster.  http://en.wikipedia.org/wiki/List_of_Bangladesh_tropical_cyclones

In April of 1991 another massive cyclone hit the coast of Bangladesh. It is now known as the Bangladesh Cyclone. It killed approximately 15,000 people which is a lower death toll than the one recorded in the Bhola Cyclone but I believe this was due to the country’s mitigation techniques having improved since the 70’s. Still, many died because they refused to evacuate, believe the intensity of the storm to be less than forecasted. The Max wind speed was 260km/hr which was measured for a minute at a time. This is the timing scale Bangladesh uses to measure wind speed as opposed to being measured over a 3 minute period which is what most countries use.  What is surprising about cyclone death tolls in the area are the number of people who die from drowning. Most of the deaths in the Bangladesh cyclone of 1991 were drowning victims. This boggles my mind because I can see disease and water contamination as well as insufficient shelter being the cause of so many deaths but for some reason it is too surreal for me to comprehend. http://en.wikipedia.org/wiki/1991_Bangladesh_cyclone The initial dome of water which makes landfall is called the storm surge and it is caused by a combination of the hurricane’s winds and ocean surface which form not so much a tidal wave as a mountain of water to rise and then collapse on shore.  90% of the deaths in cyclone in Bangladesh are caused by the storm surge. The storm surges in Bangladesh are particularly deadly because the water nearest the coast is relatively shallow which means the surge does not have the depth or breadth of ocean space to disperse and loose energy. These surges can travel inland as far as 25miles and there is no method of prevention so the only mitigation option is to evacuate to a higher elevation.

Interestingly, although Bangladesh does utilize the hurricane rating system with the intensity scale of 1-5, it also rates its tropical storms on a scale of 10 to measure destruction.

Along with the initial storm surge there is of course torrential rainfall during a hurricane and this rain causes flooding and landslides which also claim property and lives.

In 2008 Tropical Cyclone Nargis hit Mayanmar, Bangladesh, India and Sri Lanka with winds reaching 215 km/hr (on the one minute time scale mentioned above). The total death toll was approximately 138,000 people. Only 3,500 of those were in Bangladesh. It was one of the most destructive cyclones in the history of the area, causing approximately 10 billion dollars in damage throughout all 4 countries. Yet, it seems as though Bangladesh is doing quite well for itself in regards to the road to Cyclone disaster prevention.

http://dhaka.usembassy.gov/acs_cyclones.html

http://en.wikipedia.org/wiki/Cyclone_Nargis

Subsid....en..c...e In Ba...n..gla...d...e...sh

As Bangladesh is built in the Ganges-Brahmaputra deltaic region it is naturally prone to the effects of subsidence. It experiences flooding and is in a seismically active area which means that given the right conditions the sediment of the delta to liquefy and fall, especially because the sediment would be extremely saturated during the monsoon season. The delta is in fact subsiding in some areas at about 2.2 cm per year and potentially at the same or faster rate in other areas. This is due to the isostatic adjustment of the underlying crust which is driven by the rise of the Himalayas. Isostasis is essentially how the lithosphere floats on top of the asthenosphere. Essentially, as the Himalayas are pushed further up in elevation by the Indian subcontinent subducting under the Asian continent, they erode (through various processes) and a bunch of that eroded material makes its way (usually via flooding) to the deltaic basin in Bangladesh. Over time that sediment accumulates at a faster rate than it washes out and as the weight of the sediment increases, the continent it is deposited upon will get pushed down a little. When the sediment gets washed away (which is does periodically) the continent sort of floats back up- this is called rebound.  Dewatering is another big contributor to the subsidence of the delta. As far as  I can tell from what I have read Bangladesh has recently gotten involved in some forms of coal mining which requires that the miners suck water from the water table in order to place mining equipment beneath the surface. This is basically how dewatering works. It is supposed make a sort of temporary  window for the equipment to be installed or for data to be collected but as would be expected, dewatering definitely has some permeant effects on the water table and on the layers of earth which are dried up in the process. As we all know, dried up sediment will fall without its regular amount of moisture to keep it up. Another contributor to subsidence is the practice of drawing up groundwater for drinking purposes. Bangladesh is facing a serious clean water problem. In the past drawing water up from wells has exposed people to arsenic poisoning but it is still cleaner than the water drawn from surface supplies, such as the rivers. Dhaka especially has been facing more and health issues caused by contaminated water sources. As sea level rises the soil in Bangladesh will become more saline as will the coastal bodies of water and eventually the delta and other areas further north. The more brackish the water become the less drinkable it will become and as the soil accrues more salt, it will become less fertile and the water table will become brackish as well, leaving Bangladesh fewer options for potable water. All of this would be caused by subsidence and the fact of the matter is that Bangladesh does not have either the infrastructure or the mitigation plan necessary to avoid the catastrophic results.

https://phulbarinews.wordpress.com/2008/06/24/dewatering-in-open-pit-mining-concern-or-benefit/

http://link.springer.com/chapter/10.1007/978-94-015-8719-8_9

http://www.sciencedirect.com/science/article/pii/S221209631300003X

Mass Wasting

So, thoughts on mass wasting in Bangladesh:

Bangladesh, as already stated, is located in a delta and situated at the base of a valley. This valley was actually formed by mass wasting caused by landslides in the Himalayan range. Bangladesh is accruing sediment as it washes down from the surrounding high elevations and it is thereby gaining land mass but it is simultaneously losing sediment as the river dumps it into the bay (as active deltas are wont to do).  It receives heavy rainfall seasonally which means that much of the region for a percentage of the year is saturated. The areas surround Bangladesh suffer from landslides due to mass wasting especially those countries such as Nepal, Pakistan, Bhutan and India- all of which are located near large mountain ranges and all of which also experience seasonal flooding. The few articles I was able to scrounge up regarding Bangladesh stated that not enough data has been collected to engage in a serious scientific debate of how large a role mass wasting plays in the country’s overall geological state. However, there are papers and articles published on the subject, they usually squeeze Bangladesh in an afterthought sort of fashion.  So I went back to the maps of Bangladesh to examine the elevation of areas which received the heaviest rainfall. The steepest of the river banks are the Chittagong and Padma. It is important to recall that many areas of Bangladesh are also severely arid (in fact tornadoes are another one of the many natural disasters Bangladesh is at risk of). I think that if the Chittagong Hills were hit with enough rain to get saturated but not enough to wash all the plant life holding the soil together away that those hills could continue to hold the moisture until the ground became to saturated and heavy to resist the pull of gravity- thus some form of mass-wasting. I do not think the landslides caused by mass wasting in Bangladesh would  cause the same amount or even categorization of damage as I does in the surrounding countries (Nepal suffers deadly mass wasting landslides during every monsoon season). I think if Bangladesh did sustain the same kind of damage from mass wasting, the data would be obvious. However, perhaps the monsoons wash away the soil to the alluvial plain before it can become saturated enough to trigger mass wasting in any other form than your garden variety torrential flooding.

The plan that Bangladesh has mapped out for mitigating calamitous mass wasting is similar to that which they drew up for the rest of their natural disasters. They will hopefully be able to communicate which areas should evacuate and what, if anything can be done. There are satellites in place to catch warning signs and evidence of mass wasting as it occurs over time in Bangladesh and hopefully that information will reach the people fast enough for them to move out of the way of a mass wasting event.

This is one of my favorite aspects of Bangladesh in regards to natural disaster/ catastrophe: Bangladesh is at high risk of all manner of natural disasters and their infrastructure as it stands will surely be unable to withstand a disaster. It seems to be on the brink of all kinds of natural disasters but it always either just misses the worst of the occurrence as with the 2004 tsunami or it is as if the earth just keeps putting off its doomsday as with the potential seismic activity and mass wasting.

http://en.wikipedia.org/wiki/Geography_of_Bangladesh

http://www.saarc-sec.org/userfiles/Large%20Publications/CCNDPPE/17-CCNDPPE-Chapter%20XIII%20-%20Mass%20Wasting%20and%20Land%20Slides.pdf

https://books.google.com/books?id=n2JhCnVni4kC&pg=PA81&lpg=PA81&dq=cases+of+mass+wasting+in+bangladesh&source=bl&ots=DBS9Gu-kFH&sig=DnrI7Zr72Xu230R5ZGSQarTzjDY&hl=en&sa=X&ei=XgooVb7CO463oQSavIDQBQ&ved=0CCUQ6AEwAQ#v=onepage&q=cases%20of%20mass%20wasting%20in%20bangladesh&f=false

http://link.springer.com/chapter/10.1007/978-1-4020-2792-5_8