Terrestrial water load and groundwater fluctuation in the Bengal Basin

Groundwater-level fluctuations represent hydraulic responses to changes in groundwater storage due to aquifer recharge and drainage as well as to changes in stress that include water mass loading and unloading above the aquifer surface. The latter ‘poroelastic’ response of confined aquifers is a well-established phenomenon which has been demonstrated in diverse hydrogeological environments but is frequently ignored in assessments of groundwater resources. Here we present high-frequency groundwater measurements over a twelve-month period from the tropical, fluvio-deltaic Bengal Aquifer System (BAS), the largest aquifer in south Asia. The groundwater level fluctuations are dominated by the aquifer poroelastic response to changes in terrestrial water loading by processes acting over periods ranging from hours to months; the effects of groundwater flow are subordinate. Our measurements represent the first direct, quantitative identification of loading effects on groundwater levels in the BAS. Our analysis highlights the potential limitations of hydrogeological analyses which ignore loading effects in this environment. We also demonstrate the potential for employing poroelastic responses in the BAS and across other tropical fluvio-deltaic regions as a direct, in-situ measure of changes in terrestrial water storage to complement analyses from the Gravity and Climate Experiment (GRACE) mission but at much higher resolution

Review: Hydraulic head measurements - New technologies, classic pitfalls

The hydraulic head is one of the most important metrics in hydrogeology as it underlies the interpretation of groundwater flow, the quantification of aquifer properties and the calibration of flow models. Heads are determined based on water-level measurements in wells and piezometers. Despite the importance of hydraulic head data, standard textbooks used in groundwater curricula provide relatively little discussion of the appropriate measurement procedures. This paper presents a review of the literature dealing with the determination of hydraulic heads, and aims to provide quantitative guidance on the likely sources of error and when these can be expected to become important. The most common measurement procedures are discussed and the main sources of error are identified, i.e. those related to (1) the measurement instruments, (2) the conversion from pressure to heads, (3) time lag effects, and (4) observation well defects. It is argued that heads should be determined following welldefined guidelines, and that it should become standard practice in hydrogeology to provide quantitative estimates of the measurement error.Water ManagementCivil Engineering and Geoscience