The quality of water obtained from the above 6 wells were analysed as per the BIS specifications
Observations
The depth of the bedrock from Chomu (90.01m) to PunanakSar (71.12 m) is decreasing gradu-ally over a length of 30 km. Just after the PunanakaSar and towards Sambhar Lake, the depth of bedrock has increased up to 54 m at Manda Bhimsingh.
Figure 9. One of the Geoelectric section showing aquifer in the channel
ALLUVIUM SAND
DRY MEDIUM TO COARSE SAND WITH OCCASSIONAL GRAVEL/KANKAR/PEBBLE DRY FINE TO MEDIUM SAND
KANKAR/PEBBLE & CLAY
KANKAR/PEBBLE/GRAVEL MEDIUM TO COARSE SAND WITH
OCCASSIONAL GRAVEL/KANKAR (AQUIFER) FINE TO MEDIUM SAND (AQUIFER)
FINE SAND WITH SILT
CLAY
WEATHERED ROCK
INTERMITTENT HARD AND SOFT ROCK
WATER LEVEL
Water level depth encountered in the bore wells range from 15.19 m (Manda Bhimsingh) to 22.96 (Fatehpura Ki Dhani). The total thickness of aquifer zones varies from 32 m to 59 m.
Further, the total thickness of the aquifers in the area is more or less same up to PunanaKaSar.
Beyond PunanakaSar toward Sambhar Lake, the aquifer thickness is decreasing.
The aquifer performance test data reveals high transmissivity 378.30 m2/day to 520.06 m2/day and hydraulic conductivity 7.26 m/day to 18.51 m/day. The discharge of water in the bore wells in the palaeo channel is ranging from 720 to 800 litre per minute (lpm) between Samod and PunanaKaSar as compared to 68 to 412 lpm in the wells out side the channel zone. Beyond PunanakaSar, however, the discharge is very low, which is an anomaly, presumably due to the presence of a natural barrier. The draw down in the buried channel is ranging from 1.68 m to 8.1 m and the recuperation in the bore wells in the buried channel is higher as compared to the wells outside the buried channel zone.
The quality of water in the channel is potable except in the Manda Bhin Singh where the water is saline, which may be due to its proximity to the Sambhar Salt Lake
The shallow depth of the water table, thickness of the water bearing horizons, fluviatile nature of the sediments, high water yield, low drawdown, high permeability and transmmisivity, indicate the presence of the palaeochannel with good water bearing potential and storage suitable for ground water development. The characteristic of the Anokhi palaeochannel may be summed up as
• Shallow Water Table (15 – 23 m bgl)
• More thickness of Water bearing horizon (15 – 59 m)
• Fluviatile nature of sediments
• High water yield (720 – 800 lpm)
• High permeability
• High transmissivity (378 – 520 m/day)
• Potable water quality.
Conclusion
Palaeochannels are such riverine geospheric features which harbored great human civilization in the past and have potentiality to help survive the present part of human civilization thriving in the arid to semiarid regions all over the globe if this geospheric features are properly identified delineated ,understood and managed Remote Sensing along with surface and subsurface geo-physical methods are highly appropriate tools to delineate the geometry of the channel and to assess the groundwater storage potentiality of the palaeochannel.
The Palaeochannels are being convincingly looked upon as possible reservoir of ground water with vast storage capacity. There is need to identify and to establish the storage potentialities of this landforms particularly in such regions where groundwater/water emergency situations
are anticipated and/or frequented. The artificial recharge of Palaeochannels to its full capacity may provide adequate long term storage of Groundwater which may be used to mitigate the impact of drought, Flash Flood due to storm water, lean/non supply of water through canal/transboundary aquifer/river and seismicity thus reducing the unsustainability of freshwater supply during emergency situations to the minimum.
We advocate that all of the sand and gravel layers of the alluvial fans and the sand layers of the palaeochannels be used as shallow well extraction zone. Large amounts of shallow freshwater should be extracted to evacuate the storage capacity so that an underground reservoir may be constructed through artificial recharge. This will not only alleviate the problems of drought, flooding and salinity, but also simultaneously make thorough use of our water resources. But there are some critical technical problems in using underground reservoirs for storage. These are:
(1) how to speed up the rate of infiltration, especially that of flood waters (or major amounts of transferredwater);
(2) how to enlarge the storage capacity; that is, how to gradually enlarge the freshwater storage of the palaeo channels while reducing the saltwater storage between channels
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