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Trends of Groundwater Recharge in North West Region of Bangladesh Using Ground Water Table Fluctuation Method

Jahan K.
Jr. Hydrogeologist, Institute of Water Modeling (IWM), Dhaka, Bangladesh

Nowreen S.
Assistant Professor
IWFM, BUET, Dhaka, Bangladesh

Hossain S.
Junior Engineer
Institute of Water Modeling (IWM), Dhaka, Bangladesh.

Abstract/ Executive Summary:

Groundwater is a critical source of freshwater all over the world. In Bangladesh groundwater is also a critical and valuable source of fresh water due to its quality and also for demands. As the population continues to grow, more people will come to rely on groundwater sources, particularly in agricultural areas. Due to vast use of groundwater now a day’s recharge becomes an important component for Bangladesh. Groundwater in Bangladesh generally occurs at shallow (<10 mbgl) depth within widespread alluvial deposits. In some areas groundwater level are in declining mode. But recharge rates vary widely in space and time, and rates are difficult to directly measure. North-West region is considered to estimate the recharge and correlate how rapidly decline the recharge in every 12 yrs. About 450 stations of weekly measurements of groundwater levels in monitoring well stations of NW region, bore log information, 70 aquifer test results are considered to identify the aquifer characteristics and estimate recharge. Recharge calculation mainly focused on shallow and unconfined aquifers. Recharge rate is decline most of the Upazilas but obviously, it varies place to place like Bogra district, Dhunat Upazila average recharge during 1987-1999 and 2000-2012 is 5000.3955 and 370.078 m. On the other hand at kahalo Upazila, Bogra district recharge decline in small rate. The main objective of this paper is to provide a critical evaluation of the theory and assumptions that underlie methods for estimating rates of groundwater recharge.

Keywords: Ground water, IWM, Groundwater recharge, Irrigation

Location: In Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Groundwater

Objectives:

To provide a critical evaluation of the theory and assumptions that underlie methods for estimating rates of groundwater recharge.

Methodology:

In this study 17 districts are considered in NW region. To fulfill the research objectives the analyses have been done in 3 stages. One for classify the first aquifer type, a detail borelog and aquifer test have been done using secondary borelog data. Second, groundwater table trend analyses using long term observation well data in this region. Finally estimate the recharge for each of the observation well location and trend analyses over the period. About 800 borelogs were collected from different sources like BWDB, BADC, DPHE for this analyses. Probability of borelogs, specific yield of the each lithology, depth storage relation and spatial distribution have been done using the mentioned software. Besides these about 70 aquifer tests were considered for this aquifer type identification. Aquifer type identification mainly based on the clay thickness map, storage co-efficient and probability of the borelog analyses. Spatially the borelogs are uniformly distributed of this region. Aquifer test were analyzed using Jacob method (for all type of aquifer), theis method (for confined aquifer), Bolton (for both confined and unconfined aquifer), Walton (for both confined and unconfined aquifer). Installation depth of the well is an important parameter for selection the method. Storage coefficient data also verified with other method. Three types of aquifer are classified applying those methods. Confined aquifer (storage co-efficient value 0.0001-0.001), semi-confined aquifer (storage coefficient value >0.001) and unconfined aquifer (storage co-efficient value >0.01) specified following the mentioned storage co-efficient values. Not only is the hydraulic properties considered for identify the aquifer type but also considered the morphological characteristics also considered for that. For example, in Hatibandha upazila, Lalmonirhat district the analyses result indicated this as confined aquifer but from the geomorphologically this area under piedmont deposits and the monitoring well was installed near-surface water body and aquifer is directly related with surface water body. Considering the entire scenario finally it was revealed that the aquifer is unconfined in behave. This variability does not necessarily only relate to the upper clays but also the upper part of the aquifer within one generally sees a coarsening with depth. This assumption also used in the aquifer test analyses. Long-term weekly-measured Groundwater level monitoring data (1973-2013) and pumping test data sets have been collected from Bangladesh Water Development Board (BWDB). About 450 observation well stations are considered for 17 districts of the region. The depth of the monitoring well stations are varies from (3.94m to 79.25 m) m mostly installed in shallow aquifer. From the aquifer test the aquifer is also classified. The NW region mostly represents single aquifer system except lower part of the region. Another thing needs to mention that most of the monitoring well was shifted from dug well to piezometric well so the dug well data were not considered for estimate the aquifer recharge. Groundwater levels are referenced to a common datum (Public Works Datum, PWD) which was originally set to the mean sea level (msl) with a vertical error of ±0.45 m during the Great Trigonometric Survey in the Indian Subcontinent throughout the nineteenth century 12 . The impact of increasing groundwater development can often be clearly observed from hydrographs. Groundwater recharge can estimate from the long term hydrograph using the groundwater level at the start of the irrigation period is at least the net amount of groundwater abstracted from the aquifer system. Specific yield of upper finer particles (aquitard) can also determine from hydrograph using the equation (1). Q_net = SY * D_elh (1) Where, Q_net = Net abstraction of groundwater during irrigation period in mm, SY= Specific yield and D_elh= water table change over the groundwater extraction period in mm. Storage co-efficient values for unconfined aquifer those found from aquifer test analyses also verified with the specific yield of borelog analyses.

Source of Information: Conference Paper · January 2015

Article Link (Online Journal): https://www.researchgate.net/publication/348168704

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Groundwater stands in an alarming situation in NW region of Bangladesh due to a great demand of water in those areas for agricultural purposes. Recharge rate is also declined day by day. Where the recharge is below 50mm per year i.e. in Pirganj, Taraganj, Badarganj, Shapahar, Patnitola, Mohadebpur, Taras, Ullapara upazila groundwater development should be restricted and need to find the another source of water development. Otherwise, those areas become totally arid and that will be the greatest impact for this region. It is expected that this detailed study on recharge will greatly help the scientific community as well as planners to deal with monitoring of groundwater levels to ensure that the actual recharge rates do not exceed the potential recharge.

Knowledge Management: Journal