Long term water level declines as a results of injudicious exploitation of groundwater resource, may lead to several vexing problems. Some of these problems are, reduced well yields, land subsidence, intrusion of salty water especially in coastal areas, leakage into the aquifer of highly mineralized water. In order to over-come these serious environmental implications the recharge potential of groundwater resource has to be equally or in some cases more important aspect than the abstraction potential.

Groundwater is derived primarily from rain and snow melt that infiltrates the land surface and slowly percolates to the water table. This process of adding water to underground storage is called "natural" groundwater recharge. Where the materials in the earths' surface are coarse and the slope of the land is gentle, there is generally more groundwater recharge than in areas where the strata consists of fine-grain material such as shale and clay, or where the slope is steep. The purpose of 'artificial recharge' is to increase the rate at which water infiltrates the land surface in order to supplement the quantify of groundwater in storage. Artificial recharge of groundwater has been practiced for scores of years throughout the world.

The type of artificial recharge system that can be developed at any specific site is controlled , to a large degree, by the geologic and hydrologic conditions that exist at that site . Site selection criteria, in addition to economic considerations should include at least the following

· Source of recharge water
· Chemical and physical characteristics of the recharge water
· Chemical characteristics of water in the aquifer
· Availability of an aquifer suitable for artificial recharge
· Thickness and permeability of the material overlying the aquifer, if any.
· Thickness and permeability of the aquifer.
· Proximity of the potential recharge site to an appropriate well field cone of depression.
· Water- level difference between the aquifer and the recharge site
· Topography.
· Availability of property (land)

Artificial Recharge techniques

Induced filtration

It is basically a method to artificially recharge the aquifers along river, lake or other such surface water bodies. The salient factors for this method are as follows :

· Depends to a large extent on the quantity of water that can be diverted from a stream or lake.
· Both horizontal and vertical wells are used.
· Permeability of streamside deposit and its linkage with aquifer to be recharged are the important controlling factor.
· During or after the floods resulting in deposition of low permeable material, dredging is recommended to restore the permeability   of river bed medium.
· Chemical characteristics of the recharge source is of prime concern.

Water Spreading

It involves spreading the water mantle over an extensive area with flat/gentle topography. The controlling factors are

· Water contact time
· Soil permeability
· Area of inundation

In this technique recharge is facilitated through flooding the available area, by excavating ditches, modification in natural channel by building low-head check dams, irrigation during growing season. An attractive prospect of irrigation involves treated sewage which further undergoes natural treatment and augments recharge of groundwater simultaneously.

Recharge Pits and Shafts

From a regional point of view, conditions permitting recharge through water spreading technique are rare. In more general cases where aquifers and land surface are separated by low permeable or impermeable material artificial recharge system must penetrate the less permeable strata in order to access the aquifer system to be recharged. Some of the salient issues with Recharge pits and Shafts are -

· They are one of the useful recharge facilities especially in relatively small areas/areas where space or land availability is difficult.
· Construction and maintenance is simple relative inexpensive.
· Low turbidity and low microbial contamination of the source water are some important pre-requisite and are to be seriously    looked into especially to avoid plugging of the pits and shafts..

Injection Wells

· In comparison to recharge pits and shafts , the injection wells tap deep aquifers
· Expensive to construct and maintain
· High tendency of plugging
· Introduction of well screen/casing is recommended to prevent caving of aquifer.

Artificial Recharge in Urban areas

Due to space constraints and excessive exploitation of groundwater the most acceptable and feasible mechanisms of artificial recharge in urban areas are a-Roof- top water collection, b-Storm run off collection and c-Street recharge pits/ trenches. These mechanisms, based on systematic hydrological studies to convey the collected water to aquifer zone, yield
impressive results.

Bianchi & Muchal, 1970                                                                    

Fig. 10 : Groundwater Recharge through river flow diversion