Insufficiency of potable water is acute in southwest (SW) coastal areas of Bangladesh. The local population ignores the depth to saltwater/freshwater interface causing many unsuccessful waters wells drilling. In this context, a combined use of borehole logs, geophysical well logs, vertical electrical soundings (VES), electrical resistivity tomography (ERT) and electrical conductivity (EC) of sampled waters was performed to identify saltwater/freshwater interface depths in this coastal part. The study shows that the depth to freshwater/saltwater interface varies from place to place occurring commonly between 190 to 285 m, and locally as shallow as 146 m. The shallow freshwater/saltwater interface depth is greatly influenced by the upconing of fresh water from the deep aquifer (DA) near the major rivers and coast compared to the landward part and is mixed with more saline waters above. Vertically infiltrated saltwater is the main cause of brackish water in the upper shallow aquifer (USA), which is hydraulically connected with the lower shallow aquifer (LSA), and not directly recharged from the Bay of Bengal in the south. The study will contribute to find out the depth of the potential freshwater aquifer and assess the aquifer vulnerability in the coastal area of SW Bangladesh.

Chittagong, the second largest city of Bangladesh, is mostly developed in the hilly areas. Hills are mostly covered with loose and weathered tertiary sedimentary rocks susceptible to landslides. Generally, during heavy rainfall within a short time, water infiltrates into the loose rocks and soils, which increase the pore water pressure, and finally exceeds the shear strength of the materials to initiate landslides. Landslides history, slope characteristics, geology and geotechnical properties have been considered to divide Chittagong City and surrounding areas into four landslide hazard zones. Zone I in the east of Chittagong City persists as the most susceptible area for landslides, and the city becomes gradually less susceptible further westward up to zone IV. Prevention of landslides in most cases requires costly engineering solutions. Therefore, mitigation through timely evacuation of people from hazardous areas might be a good solution to combat landslides. Two automated rain gauges are installed at high risk landslide zones with built-in rainfall threshold values. Threshold values for early warning of landslides are set after statistical analysis of past landslides in relation to total amount of rainfall and local geology. The threshold values of rainfall are set to 100 mm in 3 h, 200 mm in 24 h and 350 mm in 72 h.

Chittagong, the second largest city of Bangladesh, is mostly developed in the hilly areas. Hills are mostly covered with loose and weathered tertiary sedimentary rocks susceptible to landslides. Generally, during heavy rainfall within a short time, water infiltrates into the loose rocks and soils, which increase the pore water pressure, and finally exceeds the shear strength of the materials to initiate landslides. Landslides history, slope characteristics, geology and geotechnical properties have been considered to divide Chittagong City and surrounding areas into four landslide hazard zones. Zone I in the east of Chittagong City persists as the most susceptible area for landslides, and the city becomes gradually less susceptible further westward up to zone IV. Prevention of landslides in most cases requires costly engineering solutions. Therefore, mitigation through timely evacuation of people from hazardous areas might be a good solution to combat landslides. Two automated rain gauges are installed at high risk landslide zones with built-in rainfall threshold values. Threshold values for early warning of landslides are set after statistical analysis of past landslides in relation to total amount of rainfall and local geology. The threshold values of rainfall are set to 100 mm in 3 h, 200 mm in 24 h and 350 mm in 72 h.

The Pourashava area of Manikganj, located in the central part of Bangladesh is treated as arsenic hotspot in the country as the outcome of various studies concludes that almost 80% of the domestic tube wells at this area exceed arsenic level of Bangladesh standard (50 µg/l) for drinking water. To enhance the potable water supply in the area, 15 geoelectric soundings survey using Schlumberger configuration with spreading AB/2 = 300 meters has been executed to decipher the subsurface lithology distribution and aquifers at different depths, to determine the lateral and vertical extent of aquifer at the area. Correlation of the analyzed VES results with primary and secondary borelogs, the subsurface sequence of the area is broadly divided into two geoelectric units. Firstly, the near surface geoelectric unit of resistivity less than 20.0 Ω-m represents the top soil composed of silty clay to clay. The thickness of this layer varies from 1 meter to 5 meters. The second geoelectric unit represents the sand layer and is characterized by a resistivity range of 21.0 to 190.0 Ω-m. This unit encompasses the very fine sand with variable thickness of 2 to 248m while resistivity is from 21.0 to 30.0 Ω-m, very fine to fine sand having thickness from 174-280m and geoelectric value ranges from 31.0 to 40.0 Ω-m, fine sand with resistivity from 44.0 to 50.0 Ω-m, fine to medium sand having resistivity from 51.0 to 70.0 Ω-m, medium sand and medium to coarse sand with resistivity value 75.0 to 110.0 Ω-m, and 140.0 to 190.0 Ω-m, respectively. The ultimate thickness of this unit could not be determined due to limited spread of survey but at least continues to a depth of 300 m. In the context of groundwater storage, the second geoelectric unit acts as the regional aquifer and is used for groundwater development in the Pourashava area for water supply.

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