Assessment of groundwater resources in Bogra district using groundwater model

Abstract

Groundwater is the largest source of usable fresh water in the world. Domestic & irrigation water needs are being met in many parts of the world using groundwater, especially where surface water supplies are not available. The use of groundwater compared to surface water is much higher in north-western districts in Bangladesh. Due to over abstraction in the recent years of north-western districts, groundwater is lowering at an alarming rate. The objective of the study is to analyze the trend & extent of groundwater table due to expanding status of water demand. To assess groundwater resources of Bogra district due to future water demands, change in crop pattern & increase of water demand is considered. MIKE SHE hydrologic model has been used to simulate fluctuating water table to assess groundwater resources. MIKE SHE is a deterministic, physics-based, distributed & integrated hydrologic model, deals with entire hydrologic cycle. Precipitation, evapotranspiration & groundwater abstraction are fundamental hydro-meteorological & hydro-geological inputs. The rainfall data was obtained from daily records of eight BWDB stations; evapotranspiration data was obtained from only one BWDB station in the study area. Groundwater abstraction is assumed as the integration of irrigation & domestic water needs. The model inputs regarding land use classification, topography & lithologic layers underneath the upper soil were incorporated directly from IWM. Few input data has been projected using suitable projection models. Model has been simulated within the period from 2006 to 2030. The simulated phreatic surface & their trends have been compared with the observed levels & their trends. Finally, the model has been adjusted using calibration parameters. Lower phreatic surface & higher depletion rate is found in south-western upazilas of Bogra district. The depletion rates vary from 0.00 to 2.92 cm/year for mean depth of phreatic surface. Maximum depth of phreatic surface varies from 1.20 cm/year to 14.45 cm/year. After a drought rainfall year, lower phreatic surface is observed. However this is regained in subsequent years with an average rainfall. Contribution to groundwater recharge in Bogra district is mainly due to rainfall.