Over-extraction of Groundwater reacts to water level declination toward Yangon sinking


1. Object 

Firstly, the realistic building settlement and ground-level reduction case happened because of over-extraction in Mayangone TS in December 2021. This case study paper approved that 'Sinking Yangon' was detected by T. van der Horst who studied M.Sc. Degree in TU Delft, last five years ago.

Myanmar Earthquake specialists warn that a high magnitude earthquake in Yangon could happen and affect tube wells' liquefaction and sinking. So, groundwater and wells monitoring and watch are better to save humans and the environment earlier. Myanmar Universities and overseas Universities should conduct further field studies of building settlements and ground settlements, mostly downtown Yangon, Western and Eastern parts of Yangon. It is time to take a survey of groundwater use. 

2. Introduction

Yangon is at the convergence of the Yangon and Bago Rivers, 40 km (25 mi) away from the Gulf of Martaban, with coordinates of 16° 48' North and 96° 09' East. The elevation is an average of 23 meters above sea level, and the lowest is 3-4 meters

Yangon has fluvial geomorphology and sedimentation patterns based on the river system. The Yangon River flows from the Pegu and Myitmaka rivers. Hlaing and Pan Hlaing rivers flow into the Yangon river. The Pazundaung river and Bago River join the Yangon River at the City's eastern part. Finally, the Yangon River (the estuary) flows into the Gulf of Martaban.

The rapid urbanization of Yangon City increased large numbers of tube wells, but administrative regulation is not action to control the water wells industry. Subsidence could be a critical factor as a second issue in the Yangon City area, referring to sea-level rising with extreme weather events and dense population. The first problem is the flood because of tidal affected rivers closed. Yangon covers an area of 800Km2 and is currently business and home to 5.4 million people in 2021. Yangon City Development Committee (YCDC) manages 33 of Yangon city.

3. Climate

Yangon has a tropical monsoon climate under the Koppen climate classification system. The City features a long-wet season from May through October, where a reasonable amount of rainfall is received, and a dry season from November through April, where little rain is being.

Temperature: Summer in Yangon becomes hotter than regular and high due to climate change. Average, the temperatures are always high. The warmest month is April with 37.0° Celsius (98.6° Fahrenheit), the annual maximum temperature is 33.0° Celsius (91.4° Fahrenheit). The annual minimum temperature is 22.0° Celsius (71.6° Fahrenheit). August is raining with cooling month.

Fig -1 Climate, Yangon

Rainfall: Yangon has an average of 2681 mm (105.6 in) of rain per year. The rainy season falls in the months: May, June, July, August, September, and October; on average, there are 125 days per year. The wettest weather is in July and August, when an average of 602 mm (23.7 in) of rainfall (precipitation) generally occurs. The driest weather is in January and February, when an average of 2 mm (0.1 in) of rainfall (precipitation) occurs. Yangon has dry periods in January, February, March, and December.

Humidity: August is the most humid, January is the moistest, and the average annual percentage of humidity is 74.0%.

4. Geology and Tectonic

Alluvial deposits (Pleistocene to Recent), the non-marine fluviatile sediments of Irrawaddy formation (Pliocene), and massive sandstone of Pegu series (early–late Miocene) are host rocks of the Yangon area.

Fig -2 the geological map of Yangon

Alluvial deposits are composed of gravel, clay, silts, sands, and laterite, which lie upon the eroded surface of Irrawaddy formation at 3 - 5 m above sea level. The anticlinal ridge occupies the central part of the Yangon area as a backbone, about 25-30 m above mean sea level. Sands, sand rock, soft sandstones, shale, clays, and laterite of Irrawaddy formation occur along the central part of Yangon except for the downtown area, southern region. The compact sandstone and shale of the Pegu series can be found at the northwest corner of Hlawga lake with NNW–SSE strike dipping to the east.

The Quaternary sediments, as valley-filled deposits and the alluvium, are occurring in the surrounding areas of the ridge. The valley-filled residues include the Pleistocene older alluvium of unconsolidated gravels, sands, and silts, and the alluvial is younger age clayey deposit. And the Quaternary sediments are widely distributed at the outskirt of the Yangon.

Yangon stands along the Sagaing Fault, located about 40 km east of the Shwedagon Pagoda, is a regional right-lateral strike-slip fault trending in the north-south direction. 

 5. Hydrogeology

Yangon is rich in groundwater resources conserved by unconsolidated Tertiary-Quaternary deposits, mainly Alluvial and Valley-filled. The second source is Ayeyarwady formations.

Pliocene Series occurs in highly groundwater available areas, and recent deposits cover approximately 75 percent of the Yangon city. The groundwater source of Yangon can be divided into two sub-regions, namely the low and high potential areas. The low likely regions are composed of rock units of Hlawga Shale, Thadugan Sandstones and Basepet Alternation of upper Pegu Group (Miocene epoch), and Danyingon Clays Irrawaddy rocks.

The Aquifer system of the Greater Yangon is composed of Alluvial, Valley Filled, Irrawaddian, and Peguean aquifers. An alluvial aquifer is unconfined with a thickness of 20 meters (250ft) yield (45 – 2200) m3/day. Valley Filled Aquifer, whose thickness is from 35 to 90meters (120 to 300 feet), is a principal aquifer with a high yield (1000 – 4000) m3/day. The thickness of the Irrawaddian aquifer ranges from 250meters (800 feet to more), with a yield of 70m3/day to 2270m3/day. Peguan Group is poor Aquifer discharge and low yield with non-potable water quality. Generally, the rock type in Greater Yangon is mainly soft rock.

6. Groundwater & Wells

The Yangon City Development Committee (YCDC) supply water from four reservoirs and 645 tube wells. It covers 50 % of the Yangon population.

Mostly 60% of Yangon people rely on groundwater. Private wells are unregulated by the government after 1988. It could be more than 250 thousand associated tube wells in 2020 are pumping day by day. The daily discharge rate could be 180-200 million gallons or more in 2020.

Drafted Groundwater law in 2019 and ready to approve in 2020. Politic changed again.

Water wells industries are still free enterprises. Water well drilling and pumping are non-stop. So,groundwater level decline Citywide and saltwater intrusion in areas close to the tidewater influence zone are adverse effects. The graph shows the groundwater level decline at 14 Townships in Yangon's western part and southern. See graph.

Fig.3 - Groundwater level decling graphs of the townships, Wester part of Yangon City

On the other side, Climate change and natural disasters are dangerous characteristics. Peoples have less knowledge that could be threatening groundwater and wells. A natural disaster can cause not only the losses of life and damage to the properties and civil environments, but water wells also could flush the groundwater out or miss the aquifer out.

The case study of a real affected house because of groundwater discharging for years is below:

7. Case study of building settlement and ground-level reduce in Mayangone TS, Yangon

In early December 2021, I got information about a building settlement and ground-level reduction because of groundwater extraction for years in Thamine Ward, Mayangone Township, Yangon.

Fig. 4 – case study area map

It is a case history of a tube well in a house owned by my friend. The event related to groundwater extraction after 25 years happened that made building (house's door) settlement and ground-level decline. The 2-inch tube well constructed in 1995 drilled up to 100 ft, and groundwater level was 10ft with 4500 gallons per hour discharged.

The well is 10ft away from the house. Discharge is every day, but well and home have not affected until 2000. At that time, the number of tube wells was not too much in their ward. He measured water level was around 16ft while repairing pumping device in 2005. After 2000, wells increase yearly.

As a reference, I got some photos after discussing with my friend about this happening history. The groundwater level is dropping from 10ft to 40ft at 2021. The house's door frame lowered ½ inch and now could not open and close; it needs repair.

The owner recorded the water level by chance. The water level has been declining continuously since 2000. See the graph 

Fig.5 – Groundwater level decline of well at a case studied house.

Discharge increases year after year. The cause of the settlement was the over-extraction of groundwater from wells. After 2000, some homes had deep wells because drilling deeper to get more yield than the shallow aquifer they expected for the owner. Finally, there are two aquifers, the shallow aquifer is 100ft ±, and the deeper aquifer goes 300+. So, the discharge became nearly double from two aquifers, and so water level declined more. 

The number of wells is increasing yearly. Each house has a well different size of well. There are two types of tube wells; shallow wells – 100 ft ± and 300ft ±. The event at that house had the sign of the settlement—the crack line on the bathroom wall and door is downward. The crack line is approved shown in the picture that is a category of building settlement measured 0.5 inches (12.70mm) by the house owner is shown in the photo that ground checked is approved. (Show in photo).

Fig.6 – Some measures at case study house
On the other side, recharge becomes more diminutive and discharges more because people pump water more. And climate change has been acknowledged since around 2017.
So, the groundwater level gradually lowered. Here, the author made a desk study based on a topographic map of Burma (Reference to the ONE INCH map 94 D/1 ) and Yangon Topographic Map reference to https://en-ca.topographic-map.com/maps/l6a7/Yangon/.
Study the estimated ground elevation for 2000-2021 and reach the ground elevation image from the second one from those maps. Reducing of ground level was drawn shown in the graph below. Reduce Levels of ground are 28.95ft in 2000, and 26.24ft in 2021 are work out.
Fig. 7 – Building settlement and Ground settlement graphs

Mayangon Township is one of the 33 Townships managed by the Yangon City Development Committee (YCDC). The township comprises ten wards and shares borders with Insein Township and Mingaladon Township in the north, North Okkalapa Township and Yankin Township in the east, the Hlaing river, and Hlaingthaya Township in the west, and Kamaryut Township and Hlaing Township in the south. Settlement happened in Thamine Ward, close to Hlaing River, has low land topography above sea level is approximately 8meter (26.24 ft) at the highest place, and near Hlaing River is 3-4meter.

The township area is 25.34 km2 (9.782 sq mile) with 4 miles in East-West and 5 miles in NorthSouth. The tributaries, namely Mine Chaung, Yoe Chaung, Ngamoeyeik Chaung, and Zwe Chaung of the Hlaing river, flow between township boundaries. The population is more than a hundred thousand at 24450 houses. Estimated tube wells could be more than 20000.

8. Conclusion 

Groundwater and Wells are essential to people living in Yangon, especially new townships, public society, and industries. The number of tube wells after 1988 is more than ten times, but the storage capacity of groundwater is becoming less because of unstable recharge due to climate change.

There is no regulation by law for water well drilling and groundwater supply. It is feeble in the groundwater industry.

This paper with ground factual data and information is the first research paper. The previous research paper by an M.Sc. student from TU Delft showed noticeable signs. This study is preliminary so, YCDC with Hydrogeologists and Geotechnical Engineers should do a more comprehensive ground study citywide because 'Sinking Yangon' is happening but needs to approve with quantitative reference. Note that the Yangon could be affected by Sagaing Fault. It considers a disaster. If an earthquake of magnitude more than 6.5 scale occurs in Yangon, there would be more severe damage to the buildings, water wells, and more loss of human lives. 

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