Mohammad Azizur RAHMAN
Irrigation Management Division, Institute of Water Modelling,Bangladesh,
Jackson ROEHRIG
Institute for Technology in the Tropics, Germany,
Bangladesh, Recharge assessment, Mathematical modelling, Groundwater, Low Barind
Resource Development and Management
DESCRIPTION OF THE STUDY AREA The study area is situated in the North-Western part of Bangladesh. The geographic boundary of the study area is 354971E, 691490N for the South-Western corner and 415953E, 755620N for the North-Eastern corner and covers approximately 210800 ha where the cultivated area is about 160952 ha. Bagmara, Puthia, Durgapur, Mohanpur upazilas of Rajshahi district, Raninagar, Manda, Atrai, and Naogaon Sadar upazilas of Naogaon district have been analyzed in the study. The topography of the area varies from 22 meters Public Work Datum (mPWD) in Mohadevpur (in the northern part) to 9 mPWD in Naogaon (in southern part) with a mean of 15.5 m. The study area is relatively flat, sloping towards northeast and southeast, and experiences a tropical humid monsoon climate with flood during monsoon. Annual temperature varies from 10°C to 35°C (MacDonald, 1983). The rainy season is quite wet with a range of 1200 mm to 2100 mm rainfall. Almost 80% of the rainfall occurs during June to October. The relative humidity in the study area varies from 46% to 83% (IWM, 2005). The study area is drained mainly by three major rivers: Atrai, Sib-Barnai, and LNagar, and a number of small rivers, which criss-cross the region. However, there are some low lying areas and small beels in the region. In the study area, the main winter vegetables are Rabi (November to March) crops, while Kharif-I (April to June) crops are HYV Aus, B. Aus, Jute, Kaon, Til and summer vegetables. During the Kharif-II (July to October) grows HYV Aman, local variety Aman and rainy season vegetables. Different fruit trees grow the year round. Irrigation depends mainly on groundwater being extracted predominantly by deep and shallow tubewells (IWM, 2005). Every year new DTW and STW are installed and some tubewells go out of operation. Flooding irrigation is practiced for both DTW and STW. The percentage of currently irrigation coverage is in the range of 72% to 97% of the net cultivable area. DATA ANALYSIS According to the modelling requirements, a significant amount of data has been collected. All the data are secondary and have been obtained from the Institute of Water Modelling (IWM), Bangladesh Agricultural Development Corporation (BADC), Barind Multipurpose Development Authority (BMDA) and Bangladesh Water Development Board (BWDB) etc. In addition to the data quality checking, data analysis also has been carried out for estimation of different model parameters. The subsurface lithological characterization of the study area and the configuration of the hydro-stratigraphic units for groundwater flow model have been prepared. A total of 1233 irrigation well logs from BWDB, BMDA and Local Government Engineering Department (LGED), distributed all over the study area have been reviewed. On the basis of subsurface lithological information, a regional (Manda, Raninagar, Naogaon, Bagmara and Mohanpur) hydrostratigraphic model, fence diagrams and cross-sections have been prepared using RockWorks 2004 software. The hydrostratigraphic model and fence diagram show the presence of two major aquifer systems in the study area, which is separated by a thin aquitard layer. Cross sections prepared for the study area also show that the aquitard 2 and aquitard 3 are not continuous in some places and the both aquifer constitute a big aquifer in those places (see fig. 1). The aquifer layer is composed of medium sand to fine sand, medium sand to coarse sand and occasionally coarse sand. The aquitard layer is composed of clay, silty clay and very fine sand. From the collected aquifer tests data and development tests data the hydraulic conductivity, specific yield and specific storage were calculated and used in the model. From the estimation, it has been found that specific yield varies fron 2% to 25 % and hydraulic conductivity varies from 11.72 m/d to 81m/d throughout the study area. These parameters are adjusted during the model calibration.
International Conference on Water & Flood Management (ICWFM-2007), 12 - 14 March 2007, BUET, Dhaka, Bangladesh
Report/Proceedings