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Studies on Groundwater Potentials for Some Micro-basins of BINA: Ii. Water Table Fluctuation and Its Response to Rainfall for Sustainable Use

A A Sarker
PSO
Agricultural Engineering Division, Bangladesh Institute of Nuclear Agriculture, P. O. Box. 4, Mymensingh

A A Hassan
CSO
Agricultural Engineering Division, Bangladesh Institute of Nuclear Agriculture, P. O. Box. 4, Mymensingh

N N Karim
SSO
Agricultural Engineering Division, Bangladesh Institute of Nuclear Agriculture, P. O. Box. 4, Mymensingh

M H Ali
SSO
Agricultural Engineering Division, Bangladesh Institute of Nuclear Agriculture, P. O. Box. 4, Mymensingh

Abstract/ Executive Summary:

An attempt was made to study the water table (WT) fluctuation and its response to rainfall at the micro-basins of the Bangladesh Institute of Nuclear Agriculture (BINA) head quarter in Mymensingh and its sub-station in Ishurdi. For this purpose, WT data was monitored in observation wells (OW) for five to ten years in the study locations and the results were compiled. Monthly rainfall data was also recorded to see its contribution to recharge. It was observed that normally from November to February / March there was scanty or no rainfall. As a result, WT started declining gradually from October / November to March / April and went below the lifting capacity (>7- 8 m) of suction mode pumps like shallow tubewells (STWs) in both the locations during the peak irrigation demand period from January / February to March / April. However, WT responded to the monsoon rainfall. But in Mymensingh, in every alternate year the aquifer was found to replenish more or lagging behind than the previous year's minimum WT level. The regression analysis of wet season WT depth with the corresponding rainfall indicated that monsoon rainfall had significant response to the groundwater recharge and the respective year's relationship has been produced. Rainfall probability analysis was also made with return period for predicting its possible impact on WT fluctuation and aquifer recovery.

Keywords: Tubewell, Groundwater, Aquifer

Location: Mymensingh and Ishurdi.

Start Date:

End Date:

Program Area: Farm Mechanization

Commodity:

Objectives:

a) To determine the range of WT fluctuation over the year and year to year b) To evaluate WT response to the annual rainfall and c) To observe the WT declining trend for selecting irrigation pumping equipment and crops for the studied locations.

Methodology:

The study was conducted at BINA head quarter in Mymensingh and at its sub- station in Ishurdi. Five to ten years' WT data was collected from these locations, and rainfall and evaporation data were collected from the nearby weather station. The study could not be done for its other sub-stations in Rangpur, Comilla, Magura and Satkhira, because sufficient data could not be collected over there. In Ishurdi, shallow observation wells of galvanized iron having 2 " diameter, 50 ft long with 10 ft strainer was installed. In Mymensingh, one shallow and one deep observation well were installed with the same specification but for deep observation well strainer was set up to the middle of the strainer of production well. The measured WT depths were adjusted with the fixed benchmark of the locations. An automatic WT indicator having an ameter connected with electric wire with a weight at the lower end of the wire was used to monitor the static WT depth.The probabilities thus found were plotted on log-probability paper. From the best fitted-straight line, the magnitude of rainfall events corresponding to 10, 20, 30, 50, 70, 80 and 90 % probability of occurrence were recorded. Thereafter the return period (T) of each event under respective probability level was computed using the following equation as: T = 1/P

Source of Information: Journal of the Institution of Engineers, Bangladesh Agricultural Engineering Division, Vol. 31/AE, No.1, Dee, 2004

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

WT monitoring was done for 5 to 10 years from 1994 to 2003 for the two locations: BINA head quarter in Mymensingh and its sub-station in Ishurdi. The results provided a detailed picture of the WT fluctuation range across the two regions, the decline of WT during the irrigation season due to groundwater pumping and their recovery in the subsequent monsoon. More precisely it revealed that from October / November to March / April, WT progressively declined and dropped below the lifting capacity of suction mode pumps in Mymensingh and Ishurdi. Thus, in these two locations suction mode pumps were found unsuitable for use during this time and deep setting of STWs will be near its practical limit. Notwithstanding, the declined WT during the dry season were alternatively replenished by monsoon rainfall. Moreover, regression analysis of wet season rainfall with the corresponding WT depth showed highly significant relationship indicating the contribution of monsoon rainfall to the recharge of the aquifer. Rainfall probability analysis in Mymensingh revealed that the WT is supposed to behave similarly if the present groundwater withdrawal trend remains same. But if there is more abstraction of groundwater in both Mymensingh and Ishurdi through further boring of DTWs or rice irrigation expansion, then the aquifer seems to be quite unable to sustain water and. WT will decline more causing groundwater mining i.e. more withdrawal than its reservoir capacity. This may invite many inherent natural hazards like the already evolved arsenic problem along with deforestation and land subsidence, etc. To overcome these devastating situations and reduce the undue pressure on the valuable groundwater resources, low water demanding crops should be cultivated. Therefore, in the problem areas strategies should be made to grow more non-rice upland crops for reducing groundwater withdrawal to maintain safe aquifer yield.

Knowledge Management: Journal