Groundwater management and planning for siwane sub - basin in Hazaribagh district, Bihar


Methodology
  1. Digital Basement Topographic Model ( DBTM )
    To understand the unconfined aquifer geometry , hydro-geophysical parameters derived with the help VES data has been used as inputs to the Terrain Modeling Program and Digital Basement Terrain Model has been generated ( Fig. 1 ). In the present study, 200 ohm-m surface has been assumed as basement surface based on correlation with available drilling litho-log. 

  2. Analysis of Hydro-geophysical Parameters at 11 m Depth
    Depth of majority of dugwell are in between 9 - 11 m b.g.l. Keeping in view of local practices, variation of aquifer hydro-geophysical parameter at depth of 11m has been analyzed in sub-basin perspective. This has helped in categorizing the entire area into different groundwater development feasibility classes. It has given fairly accurate information for planning sustainable development of groundwater through dugwell. 

  3. Estimation of Replenished Groundwater Reserves
    In hard rock area, groundwater reserves are generally estimated on the basis of National Ground Water Estimate Committee norms ( Battacharya, 1990). Parameters selected for the calculation are as follows : Normal rainfall = 1200mm , Natural recharge = 10% of total precipitation ( Athawale et.al. ), Irrigation requirement = 0.40m (CGWB norms), Drinking water requirement = 40 liters per head ( PHED norms). 

  4. Estimation of Aquifer Volume and Groundwater Reserves
    In reality, aquifer material lying below the lower extreme of water table ( taken as 10 m b.g.l ) up to the basement surface is also storing utilisable groundwater. But it is rarely estimated. Due to uncertainty about the basement topography, realistic estimation are generally not being carried out. The utilisable groundwater reserves can be estimated if volume of aquifer material is known. In present study volume of aquifer has been calculated with the help of DBTM. Total volume of groundwater stored in aquifer material has been estimated by multiplying average aquifer porosity to the aquifer volume.

    In study area, total average porosity of the aquifer has been assumed from the information available from other parts of the country under similar geological setting ( Karanth, 1994 ). The total volume of available groundwater within the aquifer has been further categorised on the basis of computation of effective porosity or specific yield. The retention porosity has been computed on the assumption that replenished groundwater is stored due to effective porosity of aquifer. 
Outputs of the Project and its Application

Digital Basement Topographic Model ( DBTM )
At least 17 sub-surface basins ( Fig 1a-c )have been identified which show anomalous depth of basement. These sub-surface basins and overall regional basement topography has helped in understanding the Aquifer Storage and Recovery ( ASR )/ Artificial Recharge and Retrieval ( ARR ) area. DBTM is also useful in identifying recharge area and storage of recharge in sub-surface basins in much more convenient way. The approach/ methodology seems to be rapid and cost effective. The DBTM ( Fig 1 a-c ) has provided regional variation of aquifer which is essential for groundwater development and management in watershed perspective. DBTM and its correlation has shown that the approach/ methodology adopted in this project can optimised the process of groundwater exploration in hard rock area. The methodology/ approach has further improved the accuracy and authenticity of the groundwater exploration. The missing parameter's of single planer feature i.e. remotely sensed lineament can be fulfilled through DBTM.


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