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Groundwater Level Fluctuation and Its Response to Rainfall and River Stage at Comilla Sadar Thana

M.A. Mojid
Department of irrigation and Water Management, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

M.H. Rashid
Irrigation and Water Management Division, Bangladesh Agricultural Research Institute, Joydebpur, Gazipur 1701.

Abstract/ Executive Summary:

Groundwater levels monitored in four observation wells for seven year period (1982-1988) at Comilla sadar thana were analysed to quantify the annual fluctuation of groundwater level. Average annual maximum fluctuation during the seven year period was found to be 6.02 m. In two of the monitoring wells the water level dropped below the suction lift limit of all suction mode pumps during dry season. Dry season groundwater levels were found to fall progressively but remaining at a new equilibrium condition consistent with increased abstraction. The depletion was fully replenished during the wet season. Water levels in the monitoring wells on the two banks of the Gumti river showed that the river was hydraulically interconnected with the groundwater reservoir in the study area and was contributing to groundwater recharge. High capacity deep tubewells as well as tubewells with suction mode pumps were found to be inappropriate technology for groundwater basin at the study area. The area has future development potential for groundwater by low capacity deep tubewells.

Keywords: Groundwater level fluctuation, Rainfall, River stage, Comilla.

Location: Comilla sadar thana

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Groundwater

Objectives:

This study was undertaken at Comilla sadar thana

To determine the fluctuation pattern of static groundwater level over the year and year to year;
To determine the relationship between the river flow and the groundwater reservoir in the area, and
To study the recharge characteristics of the aquifer in the study area.

Methodology:

Four observation wells, installed at the representative sites of the study area were used to monitor groundwater, level once a week during the study period. The water level measurements were adjusted with respect to the mean sea level (MSL). Two other observation wells were installed- one on the north and another on the south bank (about 500 m away from river bank) of the Gumti river where a river gauging station of Bangladesh Water Development Board existed. The water of these two observation wells were used to determine the relationship of Gumti river with the groundwater reservoir in the area. All the observation wells were installed out of the circle of influence of the existing deep and shallow tubewells. The static water levels in the observation wells installed on the river banks and the river stages were recorded on a dailv basis. While drilling for installing observation wells, geologic samples at 3m depth intervals were collected and borelogs of some existing deep tubewells were made available to determine stratigraphic characteristics of the study area. In addition to these, rainfall, .evaporation and temperature data were collected from the concerned office(s). All these data were analysed mathematically and graphically. Annual potential recharge (maximum possible based on available rainfall), available recharge and future development potential were estimated based on available information (UNDP, 1982 and Karim, 1984).

Source of Information: Bangladesh J. Agril. Sci. 21 (2): 385-392, July, 1994

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

If the number of wells are considered, Comilia sadar thana aquifer may be regarded at its upper development limit. However, because of the installed capacity is highly underutilized, future development potential is still there. Due to the presence of a thick clay above the aquifer, a greater depth of annual storage depletion must be allowed to fully utilize the potential recharge. The fact that Comilla aquifer rejects recharge during the wet season indicating that water levels could be drawn down further without long term adverse effect. But lowering groundwater levels to maximize potential recharge will have significant effects on the dry season river flows as irrigation wells will preferentially use this water. It is, therefore, essential that surface and groundwater be planned conjunctively to examine the trade-offs and maximize water use benefits.

Knowledge Management: Journal