Mumnunul Keramat

Deciphering transmissivity and hydraulic conductivity of the aquifer by vertical electrical sounding (VES) experiments in Northwest Bangladesh

AbstractThe vertical electrical soundings (VESs) are carried out in 24 selective locations of Chapai-Nawabganj area of northwest Bangladesh to determine the transmissivity and hydraulic conductivity of the aquifer. Initially, the transmissivity and hydraulic conductivity are determined from the pumping data of nearby available production wells. Afterwards, the T and K are correlated with geoelectrical resistance and the total resistivity of the aquifer. The present study deciphers the functional analogous relations of the geoelectrical resistance with the transmissivity and the total resistivity with the hydraulic conductivity of the aquifer in northwest Bangladesh. It has been shown that the given equations provide reasonable values of transmissivity and hydraulic conductivity where pumping test information is unavailable. It can be expected that the aquifer properties viz. transmissivity and hydraulic conductivity of geologically similar area can be determined with the help of the obtained equations by conducting VES experiments.

Study on the seasonal changes of land cover and their impact on surface albedo in the northwestern part of Bangladesh using remote sensing

In the present work, the dynamic behaviour of surface albedo of a coupled soil–vegetation–atmosphere (SVA) system has been studied in relation to landform characteristics, seasonally varying surface cover, and hydro‐meteorological condition using multi‐temporal Landsat TM data. Two adjacent, sharply contrasted and physiographically different land areas, (1) the semi‐arid Barind Tract area and (2) the flood plain areas of the rivers Ganges and Mahananda situated in the northwestern part of Bangladesh, have been selected for this study. Spatio‐temporal analysis of Landsat TM‐derived spectral signatures manifests quite contrasted response characteristics for different physiographic land units in the two study sites and shows a seasonal trend that is consistent with field observations. Coupling of satellite‐derived land cover information with landform and hydro‐climatic data reveals that the observed variability in surface cover and its condition, as well as seasonal transformation of surface categories (e.g. soil, vegetation, and water) over time and space, are a function of landform characteristics and the prevailing hydro‐climatic condition of the area. Particularly, depth of flooding in relation to land elevation during the wet season in the flood plain areas and soil moisture deficit during the dry season in the Barind Tract area seemed to be the two major determinative variables governing land use of the area. Climatic variables, particularly precipitation, appear to be the main driving force that brings out the dynamic changes in the geo‐environmental condition in both study sites. The changes in vegetation cover in response to the rainfall amount show a much higher sensitivity of the Barind tract areas in comparison to the flood plain areas. Land cover information as derived from multidate Landsat TM data demonstrates a relatively high change (about 68 per cent) in the aerial extent of vegetation cover in the Barind Tract and a small change (only about 8 per cent) in the flood plain areas between summer and the rainy season. The flood plain areas are found to be moderately vegetated throughout different seasons, which is in contrast to the semi‐arid Barind Tract area that remains either mostly bare (about 90 per cent) or highly vegetated (vegetation cover greater than 75 per cent), depending on the season, though both sites receive an almost similar amount of seasonal and annual precipitation. Variation in soil moisture and vegetation condition, as well as transformation of bare land into a vegetated or seasonally flooded area in response to seasonally varying precipitation, introduce sequential variability in the surface absorption level, thereby provoking seasonal rhythmic variation in the surface albedo over the area. It is found that the transformation of bare land into a crop area in the Barind Tract reduces the surface albedo values by about 60–75 per cent. Relatively higher spectral responses in summer over most of the semi‐arid area depict a deficit in moisture content in the soil layer, as compared to that in the relatively moist flood plain area, except the sandy area, whereas transformation of land into water due to seasonal flooding, especially in the flood plain areas in the wet season, associates a decrease in albedo from 13 per cent in summer to about 6 per cent in winter. Increased albedo, particularly over the river area in summer, indicates the presence of suspended sediments originating from erosion due to surface runoff and nearby riverbank shifting. As a whole, surface albedo seems to be a land type‐dependent seasonal indicator of the area.

GIS integration of hydrogeological and geoelectrical data for groundwater potential modeling in the western part of greater Kushtia district of Bangladesh

Geographical Information System (GIS) has been used in this paper to delineate groundwater resources potential in the western part of greater Kushtia district of Bangladesh, where urgent attention for augmentation of irrigation water supply is required. Thematic maps of transmissivity, hydraulic conductivity, specific yield, net recharge, aquifer thickness, surface water bodies, aquifer resistivity, overburden aquitard thickness and its resistivity have been prepared and assigned weight according to their relative importance using Analytical Hierarchical Process for the preparation of groundwater potential model. Since the values within each thematic map vary significantly, they are classified into various ranges or types and assigned ratings. Finally, the thematic maps are integrated using GIS to prepare the groundwater potential map for the study area in terms of Ground Water Potential Index (GWPI). The evolved map indicates that 22.51% of the study area have GWPI more than 0.70 and therefore, have excellent prospective for exploitation. About 69.12% of the area with GWPI ranging from 0.50 to 0.70 is also quite promising for groundwater abstraction, while the rest 8.37% area having GWPI below 0.50 indicates moderate potential. The obtained map of groundwater potential is found in good agreement with the yields of available pumping test data.

Groundwater resource evaluation in the western part of Kushtia district of Bangladesh using vertical electrical sounding technique

Geoelectrical sounding, borehole litholog, and groundwater data have been used for the exploration of groundwater resources in the western part of greater Kushtia district, Bangladesh. This study aimed to delineate the boundary and the depth of aquifers, and assess their vulnerability to near-surface contaminants. Fourteen geoelectrical sounding data are interpreted and the corresponding geoelectrical logs are correlated with the available nearby horehole lithologs. Four distinct geoelectrical layers are identified within the depth of 105 m, namely thin topsoil (8.0–97.6 Ωm, 0.5–3.6 m), conductive clay-silt-sand layer (8.6–27.5 Ωm, 1.3–49.4 m), medium resistive fine grained aquifer (25.8–45.0 Ωm, 10.1–30.4 m), and high-resistive coarse grained water-bearing aquifer (35.0–64.9 Ωm, 30.0–76.9 m). The shallow aquifer (third layer) is found to occur at a depth ranging between 1.7 and 51 m, whereas the deeper aquifer (fourth layer) is found to occur within the depth between 14 and 52 m, both saturated with water. The groundwater resistivity and formation resistivity factor in the study area is found to vary from 15 to 30 Ωm and 1.93 to 2.68, respectively. The narrow low-protective layer has made the shallow aquifer highly vulnerable to surface contaminant in the study area.

Pattern analysis of trace gases over Bangladesh using satellite remote sensing

Trace gases are important components for climate change process, and Earth’s climate is sensitive to change in their atmospheric concentrations; therefore, proper assessment of trace gases is essential for ongoing global climate simulation. The spatio-temporal variations of four trace gases, namely carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3), and carbon dioxide (CO2), over Bangladesh during the last decade are analysed using the remote-sensing data sets of the Atmospheric Infrared Sounder (AIRS) and Ozone Monitoring Instrument (OMI). Monthly, seasonal, and annual mean variations of trace gases were assessed. Higher CO, O3, and CO2 concentrations show west-to-east gradient, indicating the impact of both local meteorology and emissions on variations in trace gases. On the other hand, total NO2 concentration increases over Dhaka because of large population density, high traffic emission, larger industrial activities, and highly polluted air. The inter-annual variations of trace gases are mainly due to large-scale climatic phenomena such as El Niño and La Niña conditions. All the trace gases show strong seasonality, with higher levels during pre-monsoon season and lower levels during monsoon season, which are caused by the seasonal variations in biomass burning (BB), long-range transportation, and rainfall in South and Southeast Asia (S–SE Asia). However, O3 concentration reveals minimum loading during winter season, associated with the reduction of O3 formation in cold days due to insufficient heat. These findings are important to estimate regional climate variability due to trace gases.