Water Table Trend—A Sustainability Status of Groundwater Development in North-West Bangladesh

Abstract

Historical trends of the annual maximum and minimum depths of groundwater tables (GWTs) that are indicative of sustainability status of groundwater resources still remain inadequately studied in the North-West (NW) hydrological region of Bangladesh. This study aimed at evaluating long-term trends of GWTs of 350 monitoring wells and their impacts on groundwater development status in that region. The trends of the annual maximum and minimum depths of GWTs were determined and evaluated by using MAKESENS trend model. The functionality of suction-mode pumps was identified based on the annual maximum depth of GWTs. A significant (p ≤ 0.05) falling trend of the annual maximum depths of GWTs in 65.71% of the monitoring wells revealed continuous increase in groundwater abstraction. A significant falling trend of the annual minimum depths of GWTs in 69.71% of the monitoring wells revealed groundwater mining. GWTs remained below the suction limit (≈6 m) for 3 to 6 months in each year in 59.72% of the monitoring wells and for the whole year in 15.14% of the monitoring wells, making suction-mode pumps inoperable and creating domestic water scarcity. Therefore, groundwater extraction in many locations has become unsustainable, and hence, measures such as artificial recharge to the aquifers and water-saving technologies are needed to prevent groundwater mining.2 of 15 usages, especially for irrigation. Irrigated crop fields also contribute to groundwater recharge; especially, for shallow aquifers much of the irrigation water returns to aquifer [7]. Prior to widespread abstraction of groundwater from the mid-1980s and onwards, water tables in the mostly unconfined aquifers of Bangladesh were generally shallow with a weak seasonal fluctuating trend. After the monsoon period, groundwater tables were near, or in some places, very close to the ground surface. At the end of the dry season, GWTs receded, mainly due to evapotranspiration and inter-basin flow out of the aquifers. Much of the potential recharge from rainfall and flooding in the monsoon period was rejected due to the limited storage capacity of the aquifers. However, with increasing abstraction of groundwater, GWTs fall at a greater rate during the dry season, when pumping for various usages and base flow to the rivers deplete the aquifers. The deepest GWTs are now found from April to mid-May and the shallowest GWTs are found in November [8].Most parts of the NW region of the country are flood-free zones and the main source of groundwater recharge is rainfall, which is also the lowest in this region. Moreover, the expanding presence of plough pans due to the increasing practice of conservation agriculture, and especially, the thick sticky clay surface (6.10−21.34 m) of the Barind Tract act as aquitards and hinder groundwater recharge by increasing surface runoff. As a result, groundwater use in the Barind area has exceeded recharge and GWTs have been successively falling over the years, with increasing withdrawal of groundwater for irrigation [8,9]. Rajshahi, Pabna, Bogu...

An Integrated Method for Identifying Present Status and Risk of Drought in Bangladesh

“…Therefore, considering the finding of this study that "there is meteorological drought in NWB" and the finding from existing literature [12,56,59,60] that the "underground water table is declining in an unsustainable manner due to large abstraction for irrigation", it is highly likely that there will be an imbalance between the availability of underground water and requirement for irrigation. The probable scarcity of underground water in the future may transform the existing meteorological drought into severe agricultural drought, which is at present is observable in only a small part of the study area (NWB).…”

“…Nevertheless, the future drought risk factor can be explained by the fact that in the past, several notable severe drought incidents were observed during this season in NWB due to low rainfall and high temperature. However, the drought scenario began to change after the introduction of irrigation activity in the mid-1980s, when the groundwater began to be used as a major source of water supply for rice cultivation [36,56].…”

“…It is obvious that at present, the groundwater based-irrigation systems, in NWB and throughout Bangladesh, not only significantly reduced the severity of drought, especially in the pre-monsoon season, but also helped meet the increasing food demands of the rapidly growing population in Bangladesh [12,56,57]. However, there is a growing concern that the groundwater table in NWB as well as the other parts in Bangladesh is gradually declining in an unsustainable manner due to large abstraction by the irrigation projects [58][59][60].…”

“…However, there is a growing concern that the groundwater table in NWB as well as the other parts in Bangladesh is gradually declining in an unsustainable manner due to large abstraction by the irrigation projects [58][59][60]. Prior to the widespread abstraction of groundwater for irrigation, water tables in the mostly unconfined aquifers of Bangladesh were generally shallow with a weak seasonal fluctuating trend [56].…”

“…Study [12] indicated that the groundwater table had a declining trend over the last 30 years (1981-2011), which implies that groundwater use is not sustainable in NWB and found that the magnitude of the decline in the groundwater table has been between −2.3 and −11.5 m during the pre-monsoon period. Studies indicated that this gradual declination is mainly due to the over exploitation of groundwater rather than recharging the aquifer, since about 95% of irrigation water for Boro rice cultivation comes from groundwater, which is extracted mainly by shallow tubewells (STW) and deep tubewells (DTW) [56,61]. Moreover, [12] pointed out that in NWB, the most severely depleted areas are Rajshahi followed by Pabna, Bogra, Dinajpur, and Rangpur.…”