Silt blocking submersible pump in borewell - Water yield and quality is good, but motor not working - How can this be solved?

Hi
I had a borewell drilled on 12th Sept 2012 but there seems to be problems with regard to frequent blocking of pump due to silt accumalation. I got the pump cleaned once, reduced the depth of the pump location and reinstalled. But the problem still continues.

Details are as found below:

Dia of Bore 6.5 " (165 mm dia)
Static water level 50' to 60 ' from ground level ( G/L)
First spring touched at 75' to 90' with yield of 1"
Second spring touched at 150' to 165' with yield of 1.5 " to 2"
Third spring touched at 245 ' with yield of 2" and

Final yield of borewell 2" ( 3015 LPH)
Total depth borewell 245 ' from G/L
Length of casing pipe inserted 40' PVC pipe
Pump - 1 hp /12 stage at 220' from G/L

Pump worked for couple of hours. When switched off and switched on to test the pump, the pump did not start again - reason small granules of rock (1mm) in the form of silt. Then we removed the pump after 2 days, cleaned the pump and reduced the depth of the pump from 225' to 200' . Pump worked for couple of hours. But when switched off and switched on again, pump did not work , again due to silt blockage

Please suggest the means by which I can overcome the problem as I see good yield of water and the water is pretty clear except for small granules of stones (less than a millimeter) getting accumulated over a period of time.

Thanks

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