HYDROLOGICAL MAPPING FOR SELECTION OF POTENTIAL SHALLOW TUBEWELL SITES FOR PIND DADAN KHAN TEHSIL

Transcription

1 HYDROLOGICAL MAPPING FOR SELECTION OF POTENTIAL SHALLOW TUBEWELL SITES FOR PIND DADAN KHAN TEHSIL DATABASE OF SHALLOW TUBEWELL USED FOR CHARACTERIZATION AND CLASSIFICATION OF HYDROLOGICAL MAPPING FOR PIND DADAN KHAN TEHSIL Dr. Shahid Ahmad WATER RESOURCES RESEARCH INSTITUTE NATIONAL AGRICULTURAL RESEARCH CENTRE PAKISTAN AGRICULTURAL RESEARCH COUNCIL ISLAMABAD March, 2001

2 HYDROLOGICAL MAPPING FOR SELECTION OF POTENTIAL SHALLOW TUBEWELL SITES 1. Background of the Project Barani Village Development Project is being implemented in the six selected Tehsils of the Punjab Barani areas. These are Attock, Talagang, Gujar Khan, Jand, Pindi Gheb and Pind Dadan Khan. The "Water Lifting Devices Component (WLDC)" of the project is designed to construct shallow tubewells with active participation of the farmers in Pind Dadan Khan Tehsil. For this purpose, hydrological mapping is one of the pre-requisite for sustainable development of water resources in Barani area. Shallow tubewells are used to harvest shallow seepage water due to the absence of well-established aquifer. The aquifer in the Barani areas is localized and dis-contiguous. Therefore, the development of groundwater is very costly and requires systematic work for the assessment of the potential. The reliability of the shallow seepage water is low and thus localized information is necessary. However, some information is essential to have better decision making for the selection of shallow tubewell sites. To accomplish this task the Office of the WLDC Component of the Barani Village Development Project enters into an agreement with the Water Resources Research Institute (WRRI), National Agricultural Research Centre (NARC), Islamabad to conduct a study for the preparation of the Hydrological Mapping to depict the potential for development of Shallow Tubewells in Pind Dadan Khan Tehsil. The overall objective of the Hydrological Mapping Study is to develop maps for characterization and classification of the potential for the installation of shallow tubewells. 2. Terms of References (TOR) The specific TOR is as under: Formulation of formats for field data collection and initial training of the WLDC staff; Collection of field data and information in collaboration with the WLDC; Digitization of the base map and relevant thematic maps using Arc-Info computer software; Development of hydrological potential maps using available hydrological information and field data collected by the WLDC staff; Training of WLDC staff in the use of maps; Workshop to present the output of the study to all the relevant partners of the project for further fine-tuning; Final preparation of maps and report. 3. Guidelines for the Use of Maps The hydrological potential maps for shallow tubewells were prepared using field data collected from farmers shallow tubewells located at the village level in the eleven selected teshils of Pind Dadan Khan. Detailed questionnaire was developed to collect information on hydrological parameters including number of wells, well depth and pump size. The shallow

3 tubewells are normally used for pumping of shallow seepage water and in most of the cases, it does not represent the groundwater (water table), therefore it is localized and discontinuous state of hydrological endowments. In practice, it is not possible to develop any hydrological map representing the shallow seepage porous media because test well approach can t be adopted due to limitation of the financial resources for detailed mapping and unavailability of well log data. Thus this is a case where some information is better than having no information. The specific guidelines are as under: Users must use these maps as indicative of hydrological potential and these maps can further be refined by collecting additional information or verification by the client. Users can use confidently the maps for installation of wells in very high and high potentials zones, whereas extra care is needed for the low-potential zone. For low potential zone, areas where either well was not developed or data could not be collected were also dumped in this zone. Therefore, there is a chance that within the low potential zone, some areas might be having higher potentials. In medium potential zone, more information should be collected, e.g existing perennial streams and geological formations, etc. As the maps are based on data collected at a particular time, therefore water levels in the well would be a function of seasonality. Water level in the well fluctuates with seasonal variations of recharge from rainfall, irrigated fields and streams. As data were collected before the current drought season ( ), therefore users must note the limitation for the decision-making. There might be significant changes in data if it were collected in the monsoon season. It is better to dug wells in the dry season so that farmer can have better understanding of the optimal depth of the well. Furthermore, it will be easy to construct the shallow tubewell because less or no dewatering would be required. Seepage water availability and recharge also depends on the lithology and geologic conditions of the porous media, therefore indigenous knowledge would be helpful to find the best location. Normally locations closer to the recharge sources have higher potential for wells. These maps do not cover the base flow of nullahs. In order to cater the base flow from the bed of the streams, PVC drainage pipes with appropriate envelope materials can be used. One similar system has already been installed at Nila Dulla closer to Chakwal by the WLDC. Depth and pump size of shallow tubewells are the major decision making parameters in the design of the shallow tubewells. As the depth of well increases, it will result into the increase of well yield. The bulk of volume excavated with the increase of pump size will also increase, but this will result in significant increase in the cost of the well. 4. Data Tables and Hydrological Potential Map Following tables and map are included in the report. Table 1: Database of hydrological parameters of shallow tubewells selected in the Pind Dadan KhanTehsil; 1

4 Table 2: Z-Scoring of hydrological parameters of shallow tubewells selected in the Pind Dadan Khan Tehsil; Table 3: Criteria for characterization and classification of hydrological potential of shallow groundwater for selection of shallow tubewell sites in the Pind Dadan Khan Tehsil; and Table 4: Ranking of tubewells in terms of hydrological potential of shallow groundwater for selection of shallow tubewell sites in the Pind Dadan Khan Tehsil. 2

5 Table 1. Database of hydrological parameters of shallow tubewells selected in Pind Dadan Khan Tehsil, Punjab, Pakistan. Union Council Number of Depth of Tubewell Pump Class Tubewells (ft) Pindi Saidpur Daulatpur Chack Shadi Jalalpur Sharif Haranpur Dharyala Jalap Gojar Saowal Goalpur Ahmadabad Tobha Misc.* Kandwal Lilla * Represents Union Council either having no shallow tubewells or information could not be collected. Table 2. Z-Scoring of hydrological parameters of shallow Tubewells selected for Pind Dadan Khan Tehsil, Punjab, Pakistan. Union Council Z-Scoring No of Tubewell Depth of Tubewell Pump Class Z-Sum Pindi Saidpur Daulatpur Chack Shadi Jalalpur Sharif Haranpur Dharyala Jalap Gojar Saowal Goalpur Ahmadabad Tobha Misc.* Kandwal Lilla * Represents Union Council either having no shallow Tubewells or information could not be collected. 3

6 Table 3. Criteria for characterization and classification of hydrological potential of shallow groundwater for selection of shallow tubewells sites in Pind Dadan Khan Tehsil, Punjab, Pakistan. Z-SUM (Range) Class Rank < Very high High Medium 3 > 0.5 Low 4 Table 4. Ranking of Union Councils in terms of hydrological potential of shallow groundwater for selection of ShallowTubewells sites in Pind Dadan Khan Tehsil, Punjab, Pakistan. No Union Council Rank 1 Kandwal 4 2 Ahmadabad 2 3 Lilla 4 4 Tobha 1 5 Goalpur 1 6 Gojar 2 7 Haranpur 2 8 Saowal 4 9 Dharyala Jalap 2 10 Daulatpur 3 11 Chack Shadi 3 12 Pindi Saidpur 4 13 Jalalpur Sharif 1 Rank of 4 was used with an assumption that at least low potential prevails in this area. Therefore extra care is needed for low potential area for decision making. 4