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Groundwater Balance Study in the High BARInd, Bangladesh

A.H.M.Selim Reza
Department of Geology and Mining, University of Rajshahi, Rajshahi-6205, Bangladesh

Quamrul Hasan Mazumder
Department of Geology and Mining, University of Rajshahi, Rajshahi-6205, Bangladesh

Mushfique Ahmed
Department of Geology and Mining, University of Rajshahi, Rajshahi-6205, Bangladesh

Abstract/ Executive Summary:

The annual groundwater recharge and discharge of aquifer of the Sapahar and Porsha Upazillas is estimated by Thiessen polygon method varies from 106.41 to 244 Mm³ and 93.77 to 291 Mm³ respectively. The calculated groundwater recharge of aquifer of the study area shows that the rate of groundwater recharge of aquifer in Porsha Upazilla is higher than that of Sapahar Upazilla and is characterized by very suitable groundwater storage potential. The overall groundwater balance study in the study area indicates that there exists a balance between annual recharge and withdrawal up to 1993 but after period of 1993 discharge exceeds the recharge continuing till today. But here forth a cumulative annual deficit is found to exist because of progressive annual discharge in Sapahar Upazilla. 23.99 to 42.08 Mm³ of groundwater is discharged by discharging mechanisms. The rest of groundwater is discharged by natural seepage.

Keywords: Ground water; High Barind

Location: High Barind, Rajshahi

Start Date: 00-00-1993

End Date: 00-00-2000

Program Area: Crop-Soil-Water Management

Commodity: Groundwater

Objectives:

Recharge rates for aquifers must be estimated before ground water resources are evaluated.

Methodology:

The ground water system in Bangladesh is considered to be in dynamic equilibrium that is the annual recharge is approximately equal to the discharge. Recharge exceeds discharge during the rainy season and ground water level rises but during the dry season discharge exceeds recharge and ground water level declines. The accuracy of the estimation of recharge to ground water reservoir in case of water balance method depends on accurate accounting of all incoming and outgoing water in the area and actual evaporation. Is depends on extensive gauging and definite physiographic unit. Budgeting plot-wise soil moisture of the root zone of the plants throughout the year is practically impossible for variation of the types of soils, crops, and plants from place to place in the study area. Through water balance method the potential recharge is estimated which is mainly based on hydrodynamic data, dependent on the accuracy of data of rainfall, potential evapotranspiration and the run-off coefficient of different watersheds. Except for rainfall, accurate data of the other parameters are hardly available. So the water balance method is not suitable in evaluating the actual recharge of ground water. The well hydrograph method has been used to determine the ground water recharge of aquifer in the investigated area. In this method specific yield and cross sectional area of the aquifer is multiplied by the fluctuation in ground water levels. A quantitative assessment of groundwater recharge has been made for the study areas. Variety techniques can be used for estimating groundwater recharge. Generally recharge due to rainfall, surface water bodies and irrigation return are estimated individually using different formulas to have the total amount annual recharge. The well hydrograph method is based on the facts that all water that enters into the ground water which is being reflected in the rise of water table but some parts of it is continuously lost to the atmosphere when the water table lies very close to land surface and some part of it is lost by discharging to the nearby rivers and discharging to the lower areas. A fair indication of the maximum days of recharge to ground water is achieved from method. But in the present process annual recharge and discharge have been estimated only considering the fluctuation of groundwater table [2]. In the case of recharge the rising of groundwater table from dry to rainy season is considered and volume change between them is calculated. Then this volume is multiplied by the specific yield of that formation filled with groundwater to have the recharge/ volume of water. But the calculated volume may be within the formation of different specific yields. This can be formulated as follows Q = V x SyV = volume between dry and rainy season Sy = Specific yield within the fluctuation zone A quantitative assessment of groundwater discharges has been made for the study areas. A variety of techniques can be used for estimating groundwater discharge. For discharge estimation, volume covered by shifting water table from rainy to dry season is considered. Then this volume is multiplied by the specific yield of that formation filled with groundwater to have the discharge/ volume of water.

Source of Information: Rajshahi University J. of Sci. 39, 11-26 (2011) ISSN 1681-0708

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The calculated groundwater recharge of aquifer of the study area shows that the rate of groundwater recharge of aquifer in Porsha Upazilla is higher than that of Sapahar Upazilla and is characterized by very suitable groundwater storage potential. Thus the overall study in the study area indicates that there exists a balance between annual recharge and withdrawal up to 1993 but after period of 1993 discharge exceeds the recharge continuing till today. But hereforth a cumulative annual deficit is found to exist because of progressive annual discharge in Sapahar Upazilla. It is observed that during the period 1994 and 2000, the deficit of groundwater is maximum. The amount of water overdraft during the period of 1994 - 1995. It appears from the results that the amount of water withdrawn varies from 23.99- 42.08 Mm³ in the study areas of different Upazillas. 23.99- 42.08 Mm³ of groundwater is discharged by discharging mechanisms. The rest of groundwater is discharged by natural seepage.

Knowledge Management: Journal