Scope and limitations of Ground Water Prospects Maps
Scope:

• Ground water prospects maps may be used by the field Officers of the departments concerned in the respective states to select the sites at appropriate places.
• It helps mainly in identification of prospective zones for narrowing down targets for follow-up detailed hydro-geological and geophysical surveys at appropriate places for drilling.
• These maps are the good inputs for aquifer mapping.One of the input for resource estimation for future ground water development for the given area.
• This map can be used for locating recharge structure on the ground.
• The maps are prepared based on the availability of recharge conditions i.e. rainfall, depth to water table, availability of water in the water bodies during the period of the mapping.Hence depth and yield will vary.
• VIBGYOR colour scheme is maintained for indicating yield and hatching pattern for depth. It does not mean that entire polygon gives the same yield but it varies within the unit due to heterogeneity.Hence sometimes yield may go one step up or down.It is because of rain fall variations.
• Maps help in identifying the ground water exploitation areas (through ground water irrigated patches) for addressing the suitable recharge structures for improving the ground water levels.
• Groundwater Quality (GWQ) point observations represents the ‘Pre and Post Monsoon’ water quality of that habitation.
• Groundwater quality observations are collected from Integrated Management Information System (IMIS) portal of Ministry, which has been provided by respective state line departments like PHED/RWSS in the states.

Limitations:

A.Pin pointing bore / tube well points (41/2” & 61/2” dia) may not be accurate.
  Reasons:
    --   Scale of mapping (1:50,000 scale)
    --   Accuracy of map: The accuracy of the map is around 100 meters (which includes satellite data accuracy and other mapping errors).
    --   Heterogeneity of the terrain: These maps are generated with limited field checks hence in many cases the hydrogeomorphic units are extrapolated with the help of satellite image features.
  Recommendations:
    --   Ground survey to estimate the detailed hydrogeological conditions
    --   Ground geophysical survey (electrical resistivity)
    --   Up scaling keeping the map as base to assess the micro level changes

B.Depth variations
  Reasons:
    --   Dynamic hydrological conditions
    --   Varying subsurface condition.
  Recommendations
    --   Deeper depths to tap the multi layer aquifer system
    --   Drilling of the well near to the fracture system

C.Yield variations
  Reasons
    --   Depletion of water table due to scanty rainfall
    --   Porosity and permeability variations within the unit
  Recommendations
    --   Implementation of recharge structure at the time of development of well
    --   Detailed ground geophysical survey

D.Variations in estimated success rate
  Reasons
    --   Non availability of well information.
    --   Inaccessibility of the terrain
  Recommendations
    --   Drilling within the network of the fractures.

E.Low yields/poor yields along the fracture areas
  Reasons
    --   Heterogeneity within the fracture aquifers.
  Recommendations
    --   Drilling within the intersection of the fractures and confirmed fractures with proper survey.
    --   Null values in Groundwater Quality parameters represents ‘not available or not analyzed’ conditions.
    --   Water Quality observations in the habitation represents Generalized Water Quality scenario. However, actual quality may vary in space and time.

Ground Water Quality Information System (Disclaimer)

• Habitation wise Ground Water sample were collected, analysed for the ground water quality parameters by respective state (PHED/ RWSS) line departments. The Ground water Quality observation data were hosted in Ministry of Drinking water & Sanitation’s (MoDWS) website (http://indiawater.gov.in/IMISReports/). The same point database has been geotagged based on habitation and hosted in Bhuvan Bhujal portal. The responsibility of quality of the input data analysed by state PHED/RWSS lies with the line departments only.
• Ground Water Quality parameters are dynamic, in terms of depth of observation, season and time period of observation. The groundwater quality information hosted in the portal are valid to that point source during the time period of observation and season of observation mentioned for the same.
• Potable / non potable ground water source classification is being made based on Geo-spatial integration of available Groundwater quality parameters. Ground Water Quality parameter with ‘0’ value indicate that the same parameter was not analysed (NA).
• The ground water quality information needs to be seen in conjunction with hydrogomorphic unit for understand the spatial extent.
• Groundwater Quality classification (potable/non-potable) is based on the 2015 BIS standard.