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By Md. Rezaul Hasan, Md. Shamsuddin, Md. Sohel Masud, Dr. AFM Afzal Hossain (Institute of Water Modelling) Revitalizing the Ganges Coastal Zone Conference 21-23 October 2014, Dhaka, Bangladesh http://waterandfood.org/ganges-conference/
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Groundwater Salinity Zoning in the Southwestern Coastal Region of Bangladesh
Presented
by Md. Rezaul Hasan
Senior Specialist, IWM
October 22, 2014
A Research Study Team Members: Md. Rezaul Hasan, IWM
Md. Shamsuddin, IWM
Md. Sohel Masud, IWM
Dr. AFM Afzal Hossain, IWM
Presentation Outline
l Justification of the Study l Methodology l Findings l Conclusion
Jus$fica$on of
the Study
Review of Issues Related to Coastal Area
l Coastal area covers about 32% of the country.
l Coastal area of Bangladesh has three distinct regions ~ southeast (Eastern Hilly), central and southwest.
l The southwestern region is characterized by the Ganges floodplains with low relief and numerous rivers and channels linked with the Bay of Bengal.
l Salinity exists in the surface water since long but it has increased significantly over the last four decades due to reduction of upland fresh water flow.
l Eventually salinity intrudes in the coastal aquifer towards upwards by each year.
Map Showing Coastal Region
River System in South Western Region
Groundwater in Coastal Region
l Due to influence of tide in coastal rivers, the livelihoods of the inhabitants of coast area have to depend on groundwater for meeting demand in respect of domestic, municipal, irrigation, industrial and other needs.
l Groundwater can be abstracted from aquifers at varying depths-shallow and deep. There should be an aquitard or aquiclude separating the shallow and deep aquifers (DPHE, 2000).
l Inland salinization also occurs due to the presence of paleo-brackish water entrapped in small areas during the geological period between 12000 and 10000 years.
Justification of the Study
l Very few studies on groundwater salinity for southwestern coastal region.
l Most of the research works to date have been carried out mainly on irrigation, drainage, flood control and diversion of Ganges flows during dry season.
l For optimal use of groundwater resource in coastal area, salinity zoning map is a useful tool for planned development to meet drinking water supply as well as boost up agricultural production.
Salinity Standard
l Salinity is the measure of concentration of dissolved salts in water such as chloride anions, usually expressed in parts per thousand (1 ppt = 1000 mg/L = 1000 ppm).
l In Bangladesh, the recommended range of chloride in drinking water is 150 to 600 ppm (ECR 1997).
l A higher value of salinity upto 1000 ppm for problematic areas including coastal belt is considered (DPHE 2006) for drinking.
l For rice production in Bangladesh generally salinity upto 3 dS/m (around 2000 ppm) is accepted (BARC 2013).
Study Area Boundary
The area covers Dumuria, Batiaghata and Paikgacha upazilas of Khulna district, and Tala upazilas of Satkhira district
The area is about 918.3 sq km.
River System: Kazibacha Kobadak Gangrail
The boundary of the study a r e a m a i n l y f o l l o w s e x i s t i n g r i v e r s a n d northern part fol lows administrative boundary.
ü Aman is the principal crop.
ü Agricultural use of groundwater is limited.
ü GW utilization is limited with domestic use through HTWs.
ü Mechanically driven tubewells are very few. ü GW remains within suction limit but the utilization is
restricted mainly by salinity and at some places by excessive Arsenic and Iron.
ü Shrimp farming is being practiced.
ü The study area lies within different polders of BWDB.
Overview: Study Area
Methodology
Methodology of the Study
l The present study was formulated on the basis of field activities conducted in April 2013.
l The field activities were carried out from two main considerations, namely i) hydro-chemical investigation and ii) qualitative survey.
Although hydro-chemical investigation reflects fairly the degree of salinity, the relevant sociological indicators are also useful in understanding the level of impact of salinity from social perspectives.
Hydro-chemical Investigation (Shallow Aquifer)
l Groundwater samples were collected from 130 SHTW.
l Shallow Aquifer: 35-120 m.
l Field test kit was used for measur ing groundwater quality parameters.
l GW quality parameters- pH, temperature, EC, TDS and salinity as Chloride were measured.
l Groundwater samples were collected from 115 DHTW.
l Deep Aquifer: 150-340 m.
l Field test kit was used for measur ing groundwater quality parameters.
l GW quality parameters- pH, temperature, EC, TDS and salinity as Chloride were measured.
Hydro-chemical Investigation (Deep Aquifer)
Hydro-chemical Investigation (in-situ)
Hydro-chemical Investigation (lab test)
l Field test kit – not shows high level of accuracy, requires modification based on relations derived from lab test results
l 28 water samples have been tested at the DPHE laboratory.
l Prior to the selection of the testing laboratory, samples of eight wells were tested in (BUET), (BCSIR) and DPHE laboratories.
l Since DPHE laboratory analyses matched satisfactorily to those of BUET results, DPHE laboratory was selected for lab analysis.
l Field values were modified according to relations derived from the lab test results.
Hydro-chemical Investigation (Field vs Lab)
Relationship curves: EC (µS/cm) -BUET vs Field (left); and EC vs Chloride (right).
Information on FGD and KII
l Qualitative data were collected by FGDs and KIIs using checklist.
l The FGDs were conducted at six unions with local level public representatives and people of different professional groups (farmers, businessmen, service holders, shopkeepers, teachers, housewives, etc).
l KIIs were held in the study area with Staffs of DPHE.
Verification of Qualitative Information
l To verify GW salinity especially at relatively less saline areas as noticed from qualitative survey, field tests were carried out at most of the locations.
l Samples were taken from at least three tube wells of each location.
l Thus, information of qualitative social survey verified by field test kit.
l Verified information has further been utilized for map delineation.
Findings
Public Consultation
l Change in groundwater salinity is not prominently perceived but there is apprehension of increase.
l During Rabi season, most of the agricultural land could not be cultivated due to presence of high salinity.
l However, the Boro cultivation is limited in the upper part of the study area where suitable groundwater is available.
FGD and KII
l Mostly of the tubewells belongs to government. l The study area covers both saline and less saline aquifers.
In Paikgacha, shallow aquifer is less saline at the adjacent areas of the Kobadak river while in the rest part is not suitable.
l Shrimp culture by intruding saline water is degrading the soil quality and poor paddy production.
Groundwater Salinity Zoning
l Both quantitative (i.e., hydro-chemical investigation) and qualitative (i.e., FGD, KII) data were used for proper evaluation with a specific range of salinity.
l The qualitative information that was verified by field test kit was superimposed on the salinity distribution map.
l Classification of GW salinity into different zones for various purposes including drinking purpose and rice cultivation.
l Ranges of salinity is of allowable limits.
l The zones with concentration are <600, 600-1000, 1000-2000 and >2000 mg/L respectively.
GW Salinity Zoning Map-Dumuria
Shallow Deep
<600 600-‐1000 1000-‐2000 >2000
12% 21% 57% 10%
<600 600-‐1000 1000-‐2000 >2000
75% 5% 3% 17%
GW Salinity Zoning Map-Batiaghata
Shallow Deep
<600 600-‐1000 1000-‐2000 >2000
1% 5% 89% 5%
<600 600-‐1000 1000-‐2000 >2000
68% 8% 18% 6%
GW Salinity Zoning Map-Paikgacha
Shallow Deep <600 600-‐1000 1000-‐2000 >2000
20% 4% 35% 41%
<600 600-‐1000 1000-‐2000 >2000
0% 4% 26% 70%
GW Salinity Zoning Map-Tala
Deep Shallow
<600 600-‐1000 1000-‐2000 >2000
71% 2% 27% 0%
<600 600-‐1000 1000-‐2000 >2000
36% 32% 7% 25%
Groundwater Salinity Zoning Map-Shallow Aquifer
<600 600-‐1000 1000-‐2000 >2000
20% 12% 54% 14%
Groundwater Salinity Zoning Map-Deep Aquifer
<600 600-‐1000 1000-‐2000 >2000
54% 9% 11% 26%
Conclusions
Conclusions
l The deep aquifer is less saline than that of shallow aquifer except Paikgacha
l For shallow aquifer that the zone of salinity 1000-2000 ppm covers 54% of the study area extending over northern, eastern and major portion of southern parts.
l The saline zone with salinity >2000 ppm also lies in the southern part (14%).
l Fresh zone (<600 ppm) covers only 20% of the study area in scattered manner.
Conclusions (contd..)
l In case of deep aquifer, fresh zone with salinity <600 ppm covers major portion of the study area (54%) with exception at the southern part.
l Saline zone (>2000 ppm) is prominent at the southern part covering 26%.
l A strip of three zones (600-1000, 1000-2000 and >2000 ppm) covers in scattered from north to south at middle of the study area.
Conclusions (contd..)
l Change in GW salinity is not prominently perceived by the local people but there is apprehension of its increase
l During Rabi season, most of the agricultural land could not be cultivated due to presence of high salinity.
l Shrimp farming has reduced rice production. l Similar study may be extended covering the entire
coastal belt for proper planning and development activities.
l Assessment of available fresh water resources in groundwater reserviour using state of art technology like mathematical model.
Thank You
Comparison of Aquifer System
UNDP (1982)
Aggarwal (2000)
BGS (2001) JICA (2002)
GWTF (2002)
Upper/ Composite Aquifer
1st Aquifer Upper Shallow Aquifer
Upper Aquifer
Upper Holocene Aquifer
Main Aquifer 2nd Aquifer Lower Shallow Aquifer
Mid Aquifer Middle Holocene Aquifer
Deep Aquifer
3rd Aquifer Deep Aquifer
Deep Aquifer
Late Pleistocene- Holocene Aquifer
References
l Aggarwal, P K, A R Basu, R J Poreda, K M Kulkarni, K Froehlich, S A Tarafder, M Ali, N Ahmed, A Hossain, M Rahman, S R Ahmed, 2000. A Report on Isotope Hydrology of Groundwater in Bangladesh: Implications for Characterization and mitigation of Arsenic in Groundwater. IAEA TC Project BGD/8/016.
l BGS and DPHE (2001), Arsenic contamination of groundwater in Bangladesh, Kinniburgh, D. G. and Smedley, P. L. (Editors), vol. 2, Final Report, BGS Technical Report WC/00/19, British Geological Survey, Keyworth, United Kingdom.
l GWTF, 2002. Report of the Ground Water Task Force. Local Government Division, Ministry of Local Government, Rural Development & Cooperatives, Government of the People’s Republic of Bangladesh.
l JICA, 2002. The study on groundwater development of deep aquifers for safe drinking water supply to arsenic affected areas in Western Bangladesh. Final Report. Kokusai Kogyo Co Ltd., Mitsui Mineral Development Engineering Co Ltd.
l UNDP, 1982. The Hydrogeological Conditions of Bangladesh. Technical Report DP/UN/BGD-74-009/1.
