May be of interest. Locals test the depth to the gravel and bedrock with a 5mtr length of 19mm reinforcing bar. They round one end and then manualy drive it into the ground as you would if you were makeing a hole for explosives. If they dont hit gravel at about 3mtr then they dont dig. The whole process takes about 15 minutes per test. Local knowledge and utilisation of internal resourced and materials. Just a bit of useless informstion in this age of techknowledgy. GLTY Dredgemaster : im gone.