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Application of GIS to Identify Spatial and Temporal Extent of Critical Condition for Rural Drinking Water Supply During Dry Season

S.M. Tanvir HASSAN
Institute of Water Modeling (IWM),

A.K.M. Saiful ISLAM
Bangladesh University of Engineering and Technology, Bangladesh,

Abstract/ Executive Summary:

Huge drawdown of the groundwater table is one of the environmental hazards due to large scale groundwater withdrawal during dry period. Hand tube wells (HTWs) and shallow tube wells (STWs) operated under gravitational force, are the main supplier of drinking water in rural areas may be dry out due to excessive drawdown. This study was conducted to identify the unit areas (upazillas) within Dinajpur district of Bangladesh where groundwater goes under critical level (6m) using observations wells data during 1995-2003. Three interpolation methods available in GIS tools namely, inverse distance weighted (IDW), Thin-plate Spline and Kriging have been tested to construct groundwater level surface from the observation well data and Kriging with ordinary linear semi-variance model was given the most accurate result. The maximum duration of critical period for drinking water supply in the study area was found as 120 days in 1999. The maximum critical areas were 49.7% of the study area which causes severe drought in 1995.

Keywords: Hand tube well, Shallow tube well, Spatial Analyst, Upazila

Location: Dinajpur district of Bangladesh

Start Date:

End Date:

Program Area: Knowledge Management

Non-commodity: GIS

Objectives:

The present study was conducted to identify the areas where groundwater goes under a certain level of safe yield from which water cannot be withdrawn with hand tube wells under gravitational force. The study would be useful to identify the areas where shallow and hand tube wells under gravitational force become inoperative during dry season. It will also help to develop sets of guideline for possible solutions to mitigate the rural drinking water supply problem during the dry seasons.

Methodology:

DATA AND METHODOLOGY: Dinajpur district of Bangladesh consists of thirteen upazilas. But due to data unavailability seven upazilas has been selected for the study area. The study area includes seven upazilas of Dinajpur district namely Biral, Birganj, Bochaganj, Chirirbandar, Dinajpur Sadar, Kaharole and Khansama. The area is bounded by Tangon river in the west, Thakurgaon district in the north, Nilphamari district in the east and Indian border in the south. The analysis has been done from groundwater observation well data, reports, and maps of existing deep tube well project of greater Dinajpur district. These data have been collected from Bangladesh Water Development Board (BWDB) and Institute of Water Modelling (IWM), Dhaka. The collected groundwater (GW) observation well data have been processed with Microsoft Excel spreadsheet and analysed using ArcViewGIS. Software (ESRI, 1999): A maximum of 6 meter depth to groundwater table from ground surface was considered as safe yield limit to ensure the drinking water supply in the study area through HTWs and STWs respectively with full operational efficiency. Using this GIS software at first the method of interpolation was selected on the basis of finding out interpolation and extrapolation errors. A number of available interpolation techniques available in GIS have been considered which are briefly introduced below: a. The inverse distance weighted (IDW) interpolation method is a local method that assumes that the unknown value of a point is influenced more by nearby control points than those further away; b. Thin plate Splines creates a surface that passes through control points and has the least possible change in slope at all points. In other words, thin-plate splines fit the control points with a minimum-curvature surface; c. Kriging is a geo-statistical method for spatial interpolation. The technique of kriging assumes that the spatial variation of an attribute such as changes in grade within an ore body is neither totally random nor deterministic. Assuming the absence of a drift, ordinary kriging focuses on the spatially correlated component. The measure of the degree of spatial dependence among the sampled known points is the semivariance that can be fitted with a mathematical function or a model such as spherical, circular, exponential, linear, and Gaussian. Once the interpolation method is selected, critical areas have been delineated in each year from 1995 to 2003 taking the highest groundwater draw down data in a particular date of each year. To delineate critical areas for drinking water supply an interpolated surface of groundwater level (GWL) has been made from the collected GW observation well data. The GWL surface has been deducted from the surface of digital elevation model (DEM) to calculate the depth of GW table (GWD) from the earth surface. Then the GWD has been reclassified in two types of areas i) GW depth is less than 6 meters, and ii) GW depth is above 6 meters i.e. the critical areas. Finally, customized tools have been developed using Avenue scripts (built in object-oriented programming language in ArcView GIS) in ESRI’s ArcView GIS 3.2 software with Spatial Analyst 2.0 extension to make the delineation of water scarce area for different time on the basis of available data.

Source of Information: International Conference on Water & Flood Management (ICWFM-2007) 12 - 14 March 2007, BUET, Dhaka, Bangladesh

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Based on the study findings, major conclusions and recommendations have been summarized below. a. The groundwater table and quality monitoring should be done regularly following the guidelines for assessment of annual safe yield and groundwater budgeting. Large scale groundwater withdrawal by DTWs should be limited during dry period up to safe yield limits (6m below ground elevation). b. In severe drought areas where groundwater table goes below the suction limits, the HTWs should be replaced by Tara pumps (extended piston HTWs). The suction limit of a tara pump is about 12 meters below ground elevation. c. An alternative to Tara pump, DTWs can be installed for rural drinking water supply in the severe drought areas. If DTWs are installed, water supply would be piped. So cost will be higher. d. Existing dry period irrigation practice in the study area is mostly from groundwater source, a major portion of which is being abstracted through STWs. At present, high yield variety (HYV) crops covers nearly 47% of all cultivable land. HYV require more water for irrigation in the dry period than the local crops. It has been suggested to cultivate local crops which required less amount of irrigation to make the water resources sustainable for the future.

Knowledge Management: Report/Proceedings