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Study on the Salinity Dynamics of River and Groundwater in the Southwest Region of Bangladesh-2006

Dr. Manorangan Mondal
SSO
IWMD, BRRI, Gazipur

Abstract/ Executive Summary:

Salinity of Kobadak river was also measured daily at Jetua and Gonali Ferryghat in Tala upazilla of Satkhira district, average of which is presented. The salinity dynamics of the river Kobadak was different than that observed in Kazibacha river. Salinity of Kabadak river was much higher than Kazibacha river during July and August 2005, remained almost at par during September 2005 to January 2006 and showed lower salinity levels than Kazibacha river during February to June 2006. Average salinity values of river Kobadak was high during April to August (2.3-16.4 dS/m), reached to its peak in May (about 19.0 dS/m). It was observed that river water salinity of the Kobadak river remained suitable for irrigation (<4.0 dS/m) from September to February, showed more potential for irrigation development in the dry season in Tala area than in Batiaghata area. In Tala area, many farmers are utilizing groundwater for rice cultivation in the dry season by installing shallow tubewell (STW) in the Jetua-Kanaidia polder, surrounded by Kobadak river and constructed by the Local Government Engineering Department (LGED). Although salinity dynamics in the observation well showed its suitability for irrigation, some farmers reported higher salinity in some STWs near the river side. In order to document the salinity dynamics of the aquifers of the polder, 28 STWs in six transects were selected to represent the polder area. Each transect, connected both sides of the Kobadak river has 3 to 7 STWs. Salinity of groundwater was measured during the dry season (January-May) once in a week per transect. It was observed that salinity of groundwater remained within 3 dS/m in almost all the STWs, except in two STWs it varied within 3-4 dS/m in April and May i.e., at the end of dry season. In the polder area, salinity of 19 STWs (68%) remained below 1 dS/m throughout the dry season (January-May 2006), 7 STWs (25%) had salinity values less than 3 dS/m and only 2 STWs (7%) had 3-4 dS/m, occurred during March to May 2006. Salinity values of the above 2 STWs were around 2.5 dS/m at the beginning of the dry season and increased (3-4 dS/m) as the dry season proceeded due to pumping of groundwater for rice irrigation. Groundwater salinity gradually increased from about 1.0-2.5 dS/m (during January-February) to about 2.0-4.0 dS/m (during March-May) in only five (STW #14, 15, 16, 20 and 21) STWs out of 28 selected STWs within the polder area. As perceived that these STWs are installed in the aquifers near to the river side and is threatened to salt water intrusion from the river Kobadak, salinity of which varied in between 8-16 dS/m (Fig. 15) during March to May 2006. Among 5 STWs, STW# 16 and 21 is most vulnerable as far as the salinity intrusion is concerned. Further study is needed to confirm the findings and long-term study is, therefore, needed to document the salinity intrusion issues in other locations of the polder.

Keywords: Surface water salinity, Groundwater salinity, SW

Location: Batiaghata and Tala upazila of Khulna and Satkhira districts

Start Date: 00-07-2005

End Date: 00-06-2006

Program Area: Risk Management in Agriculture

Commodity: Water quality

Objectives:

To determine salinity level of the river and groundwater in Bataighata and Tala area for irrigation development in the dry season.

Methodology:

The salinity dynamics of river and groundwater were monitored during July 2005 to June 2006 both in Batiaghata and Tala upazila of Khulna and Satkhira districts (Southwest region of Bangladesh). An observation well was installed in one corner of the experimental field at Kismat Fultola village of the Batiagahata upazila and Jetua village of Tala upazila to measure groundwater salinity.

Source of Information: Proceedings of BRRI Annual Internal Review for 2006

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Generally groundwater salinity in the experimental field at Batiaghata varied in between 3.0-5.0 dS/m. The lowest value of 2.77 dS/m was observed in December and the highest value of 4.83 dS/m in August. Groundwater salinity at Batiaghata remained less than 4 dS/m from November to May and considered suitable for irrigation. After that it remained unsuitable for irrigation. Whereas, groundwater salinity at Tala remained less than 1.0 dS/m during the study period and is considered suitable for irrigation development.

Knowledge Management: Report/Proceedings