Groundwater fluctuations in Bangladesh

Groundwater is an essential natural resource of our mother earth that constitutes about 95 per cent of the freshwater on our planet, making it fundamental to human life and economic development. The contribution from groundwater is vital; perhaps as many as two billion people depend directly upon aquifers for drinking water, and 40 per cent of the world’s food is produced by irrigated agriculture that relies largely on groundwater (Morris et al. 2003). Bangladesh, a small country is blessed with plenty of water resources being located in the basins of mighty Ganges, Meghna, Brahmaputra  and Karnaphuli rivers. With numerous rivers, Bangladesh is also affluent in groundwater resource. Since last couple of decades, groundwater is being extensively used for drinking, irrigation and several other purposes eventually declining the ground water level. Groundwater is a vital input for sustaining crop production.

Figure : Groundwater fluctuations 

Bangladesh is dependent upon groundwater to satisfy the enormous demand for domestic and agricultural water supplies. As reliable surface water resources have reduced significantly and the demand for water continues to rise there is an increase in groundwater reliance. In order to ensure future sustainability of groundwater supplies it is essential to make better utilization of such an important resource. A simplistic statistical approach (i.e., correlation) is done with the assumption that a strong relationship exists between these two variables particularly in case of a shallow unconfined aquifers. However, only 35% of the groundwater monitoring wells show high positive correlation with the corresponding rainfall observations. Poor statistics are found in cases where natural recharge condition might be absent due to the strong influence of irrigation withdrawal of GW or the closer proximity of the influent river(s) or the unfavorable impermeable topsoil condition. Some evidence shows that groundwater level is discharging to surface water level during the dry season while reversing behavior is observed during the wet season. Additionally, the study compares the GW level position during the dry (April–May) and wet (July–October) seasons for 1993–2017. Increasing dependency on groundwater over surface water shows a significant drop in groundwater position.

Causes of Groundwater fluctuations :

Groundwater levels change for many reasons. Some changes are due to natural phenomena, and others are caused by man’s activities. Missouri has many different aquifers. Some are relatively shallow unconfined aquifers that are affected by surface activities. Others are much deeper confined aquifers that are well isolated from surface or shallow subsurface influences. Some aquifers consist of competent bedrock units; others are composed of unconsolidated sediments. Some aquifers are heavily used for water supply while others receive very little use. All of these factors can influence how water levels in the aquifers change over time.

All of the observation wells record a water level every 30 minutes. The data graphs show depth to water below land surface plotted on the vertical axis, and time plotted on the horizontal axis. Water level is provided to USGS and they serve the data from the National Water Information System. The “real time” data category will automatically display the last seven days of 30minute data. Data can be viewed in the 30-minute increments, or as a

single daily average.

Water-level changes can be divided into several categories. Short-term changes can be seen only when water-level measurements are made many times a day. Long-term changes can be seen only after data are collected for many years. Minor changes of only a few hundredths of a foot, and changes that are hundreds of feet can be observed. Fluctuations are generally due to one of three major factors including a change in the volume of water stored in the aquifer, changes in atmospheric pressure, and changes caused by aquifer deformation.

It is known that ground water is largely used for drinking and other purposes together with its use for irrigation purpose. Keeping aside the use for drinking purpose, only irrigation usage and associated change has observed in this study. Based on the analysis, it was found that the declining rate of groundwater is highest in northcentral region

(0.072m/year) and minimum in southcentral region (0.01 m/year) whereas the average rate of groundwater decline was found to be 0.049 m/year .

The average groundwater level decline rate from 1985 to 2010 was found to be 0.05m/year across the study area whereas Zahid and Ahmed (2006) estimated the lowering trend of groundwater level during the last 32 years is 20 to 30 m with an average decline of more than 1.0 m/year.

Undoubtedly, extraction of groundwater for irrigation has adversely affected the lowering process of groundwater level regionally.

In Bangladesh, along with drinking purpose, groundwater is widely used for irrigation. Among the three varieties of rice, irrigation is largely required for Boro production. Variability of rainfall has also increased the use of irrigation for Aus and Aman rice production too. The contribution of groundwater in irrigation has increased from 41 percent in 1982/1983 to 75 percent in 2001/2002 and surface water has declined accordingly. This study reveals that the contribution of groundwater in irrigation has increased from 38 percent in 1980/1981 to 78 percent in 2011/12 and surface water has declined from 62 percent to 22 percent accordingly. Thus, there has been a distinct decline in ground water level across the country with some exception. The declining rate of groundwater is higher in northern regions in comparison with the southern region. Though, rice production has increased dramatically in recent years than the past, it is time to ensure its progression by ensuring the availability of all the external inputs like groundwater. In this context, proper measures should be taken to ensure sustainable use of groundwater. New rice varieties which require less irrigation should be invented so that it can minimize the use of groundwater for irrigation purpose. Moreover, groundwater has proved one of the major inputs of rice production and so proper attention should be given on sustainable use of groundwater that compliments the development of rice production.