Study on spatial and temporal distribution of groundwater salinity in southwest region of Bangladesh using GIS technique

Abstract

Salinity is an important issue to the people of southwest region of Bangladesh. Due to presence of salinity in the water the people of the region are suffering from drinking water, irrigation, agriculture and other uses. Ecology of the southwest region especially in the Sundarbans is also concerned with salinity. As such the spatial and temporal distributions of groundwater salinity in the study area would help the planners and managers of the development works of the area in decision-making. The spatial distribution of salinity is one of the important aspects for developing the environmental management plan. Further the temporal distribution gives the progression trend of salinity in the region with time. Agricultural practices in the coastal area of the southwest region are largely governed by the salinity distribution with time and space. Shrimp and crop conflict is another crucial issue to be dictated by salinity in greater Khulna region. Shrimp cultivation is more profitable than other agricultural crops but in other hand continuous shrimp cultivation has a long-term negative impact on ecology also. Therefore, the spatial and temporal distributions with their severity levels should be determined for better social, agricultural, environmental and other water resources management plan of the area concerned. In order to have a better water resources and environmental management, this study aims to help the planners, engineers and decision makers through determining the spatial and temporal distributions of groundwater salinity with different ranges of salinity levels. Groundwater and soil salinity data from different monitoring sites of Soil Resources Development Institute (SRDI) and groundwater quality data of Bangladesh Water Development Board (BWDB) were collected for this study. The distribution and availability of collected groundwater salinity data are not uniform in space and regular for all the years. The spatial (GIS) analysis (from BWDB and SRDI data) shows that the groundwater salinity is highly concentrated at Khulna, Satkhira and Bagerhat districts more than that of other coastal districts. The study revealed that both the groundwater and soil salinity are high during March to May. The comparative analysis of spatial data (from SRDI) shows that a total of 104121 ha new land has been affected in the southwest region by various degrees of groundwater salinity during its three years from 1997 to 2000, which is about 5% increment of the total groundwater salinity area compared to 1997 area. The study also shows that areas having higher degree salinity classes (> 3, 5-10 an.d > 10 dS/m) have increased more compared to lower degree salinity classes « 3 dS/m) in the study area during the three years of the period. On the other hand the study also shows that a total of 1,82,310 ha new land is affected in the region by various degrees of soil salinity during its last three decades from 1973 to 2000, which is about 28% increment of the total salinity area compared to 1973 area. The analysis shows that the spatial extent of salinity has been under increasing trend and the movement of soil salinity has reached to Magura district about 240 km north from the coast. Theoretically, there is a relationship between groundwater salinity and soil salinity, i.e., higher groundwater salinity would produce higher soil salinity. However the analysis based on the available data under this study shows the reasonable correlation between groundwater salinity and soil salinity in general.