Last reviewed 16 Sept 2026 · 7 min read
Types of wells
Open (dug) wells
Large-diameter (usually 1–6 m) shallow wells, masonry lined, yielding from the bottom and sometimes through weep holes in the lining. Suitable for small yields from shallow unconfined aquifers; large storage helps meet peak demand. Classed as shallow (resting on a pervious stratum) or deep (resting on an impervious layer and drawing from a pervious stratum below through a bore).
Tube wells
A tube well is a long pipe (casing + screen) sunk into the ground to tap one or more water-bearing strata.
| Type | Description |
|---|---|
| Strainer type | Screens (strainers) placed against water-bearing layers, blind pipe elsewhere; the most common type |
| Cavity type | Draws water from a cavity formed below a strong clay (impervious) layer; the pipe ends at the bottom of the clay; flow is spherical rather than radial — requires a firm, thick confining layer |
| Slotted type | Slotted pipe surrounded by a gravel pack (shrouding) |
- Shallow tube wells — depth usually up to about 60–70 m, small discharge, often with centrifugal pumps at the surface.
- Deep tube wells — deeper (often 100 m and more), larger discharge, with vertical turbine or submersible pumps.
Other groundwater structures
- Infiltration gallery — a horizontal perforated conduit laid in permeable material alongside or under a river bed; collects filtered water. For flow from one side: .
- Infiltration well — shallow wells in river beds connected to a jack well.
- Collector (radial) well — a large central caisson with horizontal radial laterals driven into the aquifer; very large yields near rivers.
- Springs — natural outflow of groundwater at the surface (gravity, artesian, contact springs).
Well drilling methods
| Method | Principle | Suitability |
|---|---|---|
| Cable tool (percussion) | Heavy bit repeatedly lifted and dropped; cuttings removed by bailer | Consolidated and unconsolidated formations; slow but simple |
| Hydraulic rotary (direct circulation) | Rotating bit; drilling fluid (bentonite mud) pumped down the drill pipe carries cuttings up the annulus | Fast in unconsolidated formations; mud supports the hole |
| Reverse circulation rotary | Fluid flows down the annulus, cuttings pumped up the drill pipe | Large-diameter wells in loose alluvium |
| Down-the-hole (DTH) hammer | Pneumatic hammer with compressed air | Hard rock — fastest in basalt, granite |
| Jetting | High-velocity water jet washes material out | Small wells in soft sand |
| Augering / boring | Hand or power auger | Shallow wells in soft soil |
| Driven wells | Well point driven by hammering | Very shallow sand aquifers |
Well screens and gravel packs
- Screen (strainer) — lets water in while retaining aquifer material. Types used in Indian practice include slotted pipes, wire-wound (continuous slot) screens and proprietary strainers; material: mild steel, stainless steel, brass, PVC/FRP (corrosion-resistant).
- Slot size — chosen from the aquifer grain-size curve so that fines near the well are removed during development while most of the formation is retained.
- Gravel pack (artificial pack) — graded gravel placed around the screen where the aquifer is fine and uniform; allows larger slots, increases effective well radius and reduces sand pumping.
- Entrance velocity through the screen openings is kept low (commonly not more than about 3 cm/s) to reduce head loss, incrustation and sand movement.
Well design steps
- Aquifer data from test bores and logs (lithology, grain size, water quality).
- Housing casing diameter to accommodate the pump (normally a few cm larger than the pump bowl).
- Screen length — depends on aquifer thickness (confined aquifers: most of the thickness; unconfined: lower portion, commonly one-third to half).
- Screen diameter and open area — keep entrance velocity within limits.
- Slot size and gravel pack design.
- Sanitary seal (grout) near the top.
Well development
Removes fine material from around the screen to increase permeability and yield and to stabilise the formation:
- Overpumping — pumping at a higher rate than design.
- Backwashing / surging — alternate pumping and reversing flow.
- Compressed air — intermittent air surging and air lifting.
- Mechanical surging — surge block moved up and down.
- High-velocity jetting through the screen.
- Chemicals — polyphosphates to disperse clays and drilling mud; acid treatment in limestone aquifers.
- Hydrofracturing — in hard rock, to open fractures.
Pumping tests
| Test | Procedure | Gives |
|---|---|---|
| Constant-rate test | Pump at constant ; record drawdown with time in pumped and observation wells | , (Theis, Cooper–Jacob), boundaries, leakage |
| Step-drawdown test | Pump at successively higher rates for equal periods | Well loss, formation loss, well efficiency, optimum pumping rate |
| Recovery test | Record residual drawdown after pumping stops | (independent of pumping fluctuations) |
FormulaWell losses (Jacob)
= formation (aquifer) loss (laminar); = well loss (turbulent flow through screen, pack and casing).
Plot against : straight line with slope and intercept .
Well efficiency
FormulaTheis recovery method
= residual drawdown; = time since pumping started; = time since pumping stopped. Slope per log cycle gives .