Objectives |
- Augmentation of natural ground water
- Improving the quality of ground water
- Maintenance of water levels
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Principles and Processes |
- Infiltration
- Percolation
- Formation of recharge mound
- Detention time
- Changes in quality
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Infiltration rate is the rate at which water is picked up by the soil. Infiltration rate is high in the initial stage and gradually it decreases due to clogging. major reasons of clogging are Deposition of particles, Algal Growth and Colloidal Swelling |
Percolation rate is the rate at which the water is able to move downward through the soil. It depends on vertical hydraulic conductivity. Horizontal movement of water also is an important process.
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As water percolates beneath a spreading basin, a recharge mound in the water table is formed.
Under uniform recharge conditions mound continues to grow until some control provides a limit. There can be two types of limits:Potential limit or Lateral Limit.
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Detentiion time is the time for which water is meant to stay underground. Estimation of detention time helps in deciding the dimensions of the structure and improvement in ground water quality depends on detention time.
Detention time is estimated using the relation
where the symbols are in their usual meaning
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Major changes in quality of the recharge water include: (1) Removal of supended particles (2) Removal of pathogenic bacteria (3) Heavy metals, pesticides and radionuclides are greatly retained by adsorption and ion exchange on the surface of clay materials (4) Organic Matters aer broken (5) Soluble inorganic compounds are converted to insoluble compound.
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| Methods |
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Methods of Artificial recharge can be divided into 4 broad categories such as
(1) spreading methods
(2) injection wells
(3) induced recharge
(4) incidental recharge
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The method of spreading involves releasing water over ground surface in order to increase the quantity of water infiltrating into the ground and then percolating to water table. The major variants of spreading techniques are
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Basins Basins are excavated or existing tanks are modified to form the spreading basins
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Modified stream channels Water spreading in a natural stream channel Involves operations that will increase the time and area over which water is recharged. Losing streams are a prerequisite for such structures.Normally temporary structures are constructed every year using river bottom materials.Upstream reservoirs help in regulating erratic run off.
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Ditch and furrows Water is distributed to a series of ditches or furrows that are shallow, flat-bottomed and closely spaced to obtain maximum contact area for water
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Flooding involves formation of a thin sheet of water over the land, which moves at a minimum velocity. To avoid disturbing the soil, Water is diverted to spread evenly over a large area. Relatively flat topography is an importatnt requirement.Embankments should surround the flooding area.Storm run off may be used or stream water may be diverted for the purpose of flooding.
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Pit method It is used Where permeable formation underlie impervious top soil.
Usually provided with a layer of filtering material for protection against silt intrusion into the aquifer.Gravel pits and other excavations may be modified for the purpose when silt laden water is used. Recharge rate is higher in pits with steep side slopes
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Aquifer which is in hydrologic continuity with the river is pumped so that water from the stream is forced to enter the aquifer. Unlike other artificial recharge methods, induced recharge does not increase/ augment the groundwater storage, it only permits withdrawal at a higher rate.
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