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Evaluation of Groundwater Quality for Irrigation in Bangladesh Using Geographic Information System

SHAMSUDDIN SHAHID
Department of Applied Physics & Electronics, Rajshahi University, Rajshahi-6205, Bangladesh

XIAOYONG CHEN
School of Engineering and Technology, Asian Institute of Technology (AIT), Thailand.

MANZUL KUMAR HAZARIKA
School of Engineering and Technology, Asian Institute of Technology (AIT), Thailand.

Abstract/ Executive Summary:

About 75% of water for irrigation in Bangladesh comes from groundwater. As the crop yield is directly related to the quality of water used for irrigation, an assessment of groundwater suitability for irrigation is essential for the growth of food production and poverty eradication. An attempt has been made in this paper to study the suitability of groundwater for irrigation in Bangladesh. A geographic information system (GIS) is used for the processing of groundwater quality data collected from 113 locations sporadically distributed over the country and the preparation of groundwater quality maps. The result shows that groundwater of the southwestern part of Bangladesh, which comprises 22.5% area of the country, is highly affected by salinity and sodium hazards. Groundwater in the 10.54% area of the country is also contaminated by Arsenic above the permissible level recommended for irrigation.

Keywords: Groundwater Quality, Irrigation, GIS, Bangladesh.

Location: Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Groundwater, Water quality

Objectives:

Bangladesh has a large proportion of groundwater potentially available for further development. However, despite plentiful water resources, poor groundwater quality for irrigation especially salinity is one of the major limitations to development. High salinity and sodium in some parts of Bangladesh has affected the crop production and soil problems

Methodology:

There are four basic criteria for evaluating water quality for irrigational purposes, viz. salinity hazard, sodium hazard, excessive concentration of toxic elements and excessive presence of other miscellaneous elements. In groundwater of Bangladesh salinity hazard, sodium hazard and excessive concentration of arsenic, nitrate-nitrogen and chloride has been reported to occur. Measurement of these quantities in groundwater and their classifications are described in the following subsections. Salinity hazard: Salinity in groundwater can be measured either indirectly by measuring the ability of water to conduct an electrical current or directly measuring the presence of various salts in water. According to the techniques used for the measurement of salinity, it is expressed in two different ways, either as electrical conductivity or total dissolved salts (TDS). Total dissolved salts are expressed in parts per million (ppm) or milligrams per liter (mg l^-1). Irrigation water is classified into three categories based on salinity, which considers the potential for damaging plants and the level of management needed for utilization as an irrigation source (Ayersand Westcot, 1985). The classification of irrigation water based on salinity by Ayers and Westcot (1985). Water with salinity less than 450 mg l^-1 is generally suitable for irrigation without problems. Successful use of water with salinity in a range between 500 and 2000 mg l-1depends upon soil conditions and plant tolerance to salinity. It might cause damage to plants with low tolerance to salinity. However, plant growth and quality can be improved with excess irrigation for leaching, and periodic use of low salinity water and good drainage. Under typical summer stress grow-ing conditions, the salinity of irrigation water should ideally not exceed 1500 mg l^-1 soluble salts. Irrigation water with salinity above this level damages plants even has a high tolerance to salinity. It is unsuitable as an irrigation source for any length of time (Ayers and Westcot, 1985). Data processing and suitability mapping For the study of arsenic contamination in groundwater, the British Geological Survey (BGS) and Department of Public Health Engineering (DPHE), Bangladesh, jointly collected groundwater samples from 119 sites in Bangladesh in the month of July 1998 (Kinniburgh, 2001). They examined the water sample for measuring the contents of 53 constituents of groundwater including Arsenic, Sodium, Calcium, Magnesium, Chloride and different salts, toxic and heavy elements. The data were collected mainly from tube-wells operating at shallow depth except in some places where data were collected from the deeper aquifer. In the present study, data that were collected from the shallow aquifers are used for the assessment of groundwater quality for irrigation as the shallow aquifer is mainly used for irrigation in Bangladesh. The groundwater quality data are incorporated in a Geographic Information System (GIS) for processing and analysis. The contents of different salts values are added to get the value of salinity in groundwater. The SAR is calculated from the Sodium, Calcium and Magnesium contents. The toxic and heavy elements, which exist above the permissible levels for irrigations are also identified. Only Arsenic, Nitrate-Nitrogen and Chloride content to some extent are found in some places above the permissible level. The point values of salinity, SAR and toxic elements are used to prepare the corresponding raster grid maps using the kriging method (Journel and Huijbregts, 1981; Isaaks and Srivastava, 1989). Variograms are computed to fit the data and obtain the best interpolation. First, the thematic maps of toxic and other miscellaneous elements in groundwater are prepared. These maps are integrated by using GIS to prepare the thematic maps of toxicity in groundwater). Finally, the thematic maps of salinity, SAR and toxicity in groundwater are integrated using the intersect method in GIS to prepare the map of groundwater suitable for irrigation. To study the suitability of groundwater for irrigation in paddy and wheat fields, thematic maps of salinity in groundwater and soil permeability are used. The soil map of Bangladesh given in the Bangladesh Country Almanac (BCA, 2004) is used to regroup the polygons according to their permeability values and the preparation of the thematic map of soil permeability of Bangladesh. The groundwater salinity map is first integrated with the soil permeability map. The polygons of the integrated map are then classified according to the salt tolerance ranges of paddy and wheat in different soils to prepare the maps of groundwater suitable for irrigating in paddy and wheat fields.

Source of Information: J. Hydrol. Hydromech., 54, 2006, 1, 3–14

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Bangladesh is blessed by plenty of groundwater resources. A huge amount of this resource is used for irrigation, domestic and other uses. There is still a large proportion of groundwater potentially available for further development. However, the poor quality of groundwater for irrigation in the coastal zone of Bangladesh is one of the major problems of this resource. Proper management steps to maintain the balance between groundwater charging and re-charging and constant monitoring of the salt-water interface is necessary to control the landward expansion of salinity. High salinity and sodium in southwestern coastal parts of Bangladesh have been affected crop production and soil problems. Proper management and favorable cultural practices are necessary for the region to avoid the impact of long-term salinity build-up.

Knowledge Management: Journal