Water table
- Ground water is simply the subsurface water that fully saturates pores or cracks in soils and rocks. This water is consumed by evaporation, plants and human pumping, and is recharged by precipitation.
- Below the ground, at a certain level is the “saturated zone”. This is generally close to the level of water in a nearby surface water body. Above it is the “unsaturated zone”. In this unsaturated zone, there usually is at least a little water, mostly in smaller openings of the soil and rock; the larger openings usually contain air instead of water.
- Shallow ground water is more likely to occur in larger quantities under valleys than under hills, because ground water obeys the law of gravity and flows downward just as surface water does. In arid regions the presence of “water-loving” plants is an indication of ground water at shallow depth. Any area where water shows up at the surface, in springs, seeps, swamps, or lakes, must have some ground water, though not necessarily in large quantity or of usable quality.
- An “‘aquifer” is any body of rock that contains a usable supply of water. A good aquifer must be both porous enough to hold water and permeable enough to allow the continuous recharge of water to a well. Gravel, sand, sandstone, and limestone are among the best aquifers, but they form only a fraction of the rocks in the Earth’s crust. Most rocks are fine grained or otherwise ‘“tight” and store or carry little water.
Picking a hole/ point
- Some use diviners, others hydrologists (electrical resistivity survey, who look for special vegetation, rock lines etc..). For small sites, it does not matter much.
Yield
- Yields hard water.
- Yield is measured in V-Notch Reading in Inches or Approximate Discharge Rate in l.p.h. 2-3 inches is considered high yield.
- Yield estimate: Using already existing borewells, one can estimate the possible yield (amount) from conducting long duration pumping tests and monitoring recovery results.
Borewell
Drilling
- After picking a point, one drills down. Depth depends on water table level and desired water security. One may hit multiple aquifers at multiple depths. (120ft, 180ft … 480ft in a ceratin site in sahakAranagara.)
- To prevent collapse and silting, one lays in casing pipes, which have slit in them to allow in water while keeping dirt out. These prevent motors from getting clogged.
- Cost - 165000 in late 2019. Texmo motor 50k (2 repairs guaranteed in first year).
Recharge with rainwater
“Shivakumar has also dug percolation pits in the garden around his house that help in the direct recharge of the ground water table. (Incredibly, within one year of recharge, the groundwater table around Shivakumar’s house ‘Sourabha’ rose from 200 ft to around 40 ft!)”