Groundwater is normally recharged naturally by rain, though this may be impeded by human activity such as paving ground or cutting down forests, which result in the water running off and flowing away down drains, creeks and rivers, shortly after falling as rain. Use of groundwater, especially for farming, may also lower the water tables. Thus, conscious planning and techniques to catch water and direct it into the ground are sometimes used.

Artificial groundwater recharge

Various techniques have been developed to increase groundwater recharge. The essential ingredient is to stop the flow of water and allow the water to seep into the ground. Physical barriers are the obvious method; choosing the surface of the ground also has an effect, with mulched ground absorbing more water, and excessive areas of paved surface causing greater runoff.

Some local councils (in Australia, for example) require new developments to include stormwater tanks (what's the correct name?) for runoff - these hold peak flows and reduce the

Some have been developed - or rather recovered, as some of these methods are very old - in India.

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Methods

Note that the type and size/depth of the structure used will depend on the nature of the rainfall. Tropical regions may have more intense rainfall, and need larger capacities to capture the water. In more temperate climates the rain may come more slowly, giving it more time to be absorbed. These are generalizations, and the specific location much be studied when choosing.

The website of the Directorate of Town Panchayats, India,^[1] (Describes a number of methods of groundwater recharge used to store rainwater). lists several techniques. For recharging shallow aquifers:

• Recharge pits, 1 to 2m wide and up to 3 m. deep, filled with rocks/gravel and sand.
• Trenches - similar in concept to swales, 0.5 to 1 m. wide, 1 to 1.5m. deep and 10 to 20 m. long depending up availability of water. These are back filled with filter. materials.
• Wells - existing wells may be utilised as a recharge structure. Water should pass through filter media before being put into the well.
  • Dug wells
  • Hand pumps: for recharging the shallow/deep aquifers
• Recharge wells, specially constructed for recharge - 100 to 300 mm. diameter, for recharging the deeper aquifers Water is passed through filter media to avoid choking of the well.
• Recharge shafts - for recharging a shallow aquifer located below a clay surface. Shafts of 0.5 to 3 m. diameter and 10 to 15 m. deep are made and filled with boulders, gravels & coarse sand.
• Lateral shafts with bore wells - For recharging shallow and deep aquifers. Shafts of 1.5 to 2 m. wide & 10 to 30 m. long depending upon availability of water with one or two bore wells are constructed. Filled with boulders, gravels & coarse sand. (This needs clarification.)
• Spreading techniques: When the top layer is permeable this technique may be used. Spread the water in streams by making check dams, nala bunds (does this mean a raised ridge of earth alongside the stream?) or percolation ponds.
  • Swales, level shallow trenches that follow the countour of the land, and allow water to soak in
• Percolation pits, similar to swales but just round or square, not of linear trench-like shape.
• Rain gardens, low lying areas planted with suitable species, that allows rainwater runoff from impervious urban areas such as roofs, concrete bitumen, or compacted soil or lawn areas the opportunity to be absorbed.

Note that soil permeability is a major factor in the design and operation of any groundwater recharge system - the more permeable the soil, the less runoff there will be, and the more easily a given amount of runoff will enter the soil. Permeability is closely related to soil health