Define artificial groundwater recharge. Write advantages of artificial groundwater recharge. Enlist methods of artificial groundwater recharge.

 Artificial groundwater recharge is a process by which the groundwater reservoir is augmented at a rate exceeding under natural conditions of replenishment. Any manmade scheme or facility that replenishes depleted aquifers may be considered as an artificial recharge system/structure. It may be planned as in the case of pit or well drilled for the purpose of storing water into an aquifer, or may be planned or unplanned or incidental to human activity, as in the case of surface water irrigation. Most artificial recharge projects are planned for the specific purpose of saving water or storing fresh water for its subsequent use for domestic or irrigation purposes.

Advantages of artificial groundwater recharge

1) The cost of recharge to sub-surface reservoir is lower than the surface reservoirs;

2) An ideal solution of water problem in areas having inadequate surface water sources like canals and lakes and village ponds;

3) Raises groundwater levels;

4) Groundwater is not directly exposed to evaporation and pollution;

5) Mitigates the effects of drought and achieves drought proofing;

6) Reduces runoff, which chokes the storm water drains and also reduces flooding of roads and parks etc.;

7) Improves groundwater quality;

8) Reduces soil erosion; and

9) Saves energy in lifting ground water - one meter of rise in water level saves about 0040 KWh of electricity.

Methods of artificial groundwater recharge

A wide spectrum of methods and techniques are used to recharge groundwater reservoir. Based on the hydro-geological conditions of an area, different methods are used for efficient results. The artificial recharge techniques can be broadly categorized as follows:

a. Direct surface techniques

· Basins or percolation tanks;

· Ditch and furrow system;

· Check dams Nala bunds/Gabion structures.

b. Direct sub-surface techniques

· Recharge pits;

· Recharge trenches;

· Recharge shafts;

· Injection wells or recharge wells;

· Dug well recharge.

c. Combination ofsurface and sub-surface techniques

· Basin or percolation ponds with pits, shafts or wells;

· Recharge pits with tubewells;

· Recharge shafts/trenches with tubewells.

Artificial Recharge methods suitable for urban areas

1. Recharge pits;

2. Recharge trenches;

3. Abandoned Tubewells recharge;

4. Recharge dugwells; and

5. Recharge shafts with or without tube wells.

Artificial Recharge methods suitable for rural areas

1. Gully plug;

2. Contour Bund;

3. Gabion structure;

4. Percolation tank;

5. Check dam/cement plug/nala bund;

6. Recharge' shaft;

7. Dugwell recharge;

8. Ground-Water dams/sub-surface dykes

1. Ditch and Contour Bunds

In areas with irregular, undulating topography, shallow, flat bottomed and closely spaced ditches/furrows or contour bunds are constructed for recharging the groundwater. The furrow depth is kept according to the topography and also with . the aim that maximum wetted surface is available along with maintenance of uniform speed. Ditches should have slope to maintain flow speed and minimum deposition of sediments. Ditches should be shallow, flat bottomed and closely spaced to obtain maximum contact area. Contourbund is most effective method of conserving soil moisture and is suitable in low rainfall areas like Rajasthan. Contour bunding is suitable on lands with moderate slopes without involving terracing. Spacing between . two contour bunds depends upon the slope of the area and permeability (the ability of water to flow through a soil is referred to as the soil's permeability) of the soil .

2. Percolation Tanks/Spreading Basin

Percolation tank is an artificially created water body so that surface runoff is made to percolate and recharge the groundwater. These are the most prevalent structures in India as a measure to recharge the groundwater reservoir both in alluvial as well as hard rock formation. Percolation tanks are water storage tanks with highly porous material as bottom surface material so that water percolates into the ground very rapidly. Percolation tanks are located on highly fractured and weathered rock formations or in boulder formations which are very ideal places for percolation tanks. To avoid erosion of embankment due to ripple action stone pitching be provided upstream up to highest flood level. The recharge area downstream should have sufficient number of wells and cultivable land to benefit from the augmented groundwater. Percolation tanks are designed for storage capacity of 30-60 million/litre.

3. Check Dams, Cement Plug and Nala Bunds

Check dams are constructed across small streams having gentle slope. The water stored in these structures is mostly confined to stream course and the height is normally less than 2 m. These are designed based on stream width and excess water is allowed ; to flow over the wall. To harness the maximum runoff in the stream, a series of such check dams can be constructed to have recharge on regional scale. Nala bunds are constructed across bigger nalas. A nala bund acts like a mini percolation tank. The width of nala bed should be at least 5 m and not exceed 15 m and depth of bed should not be less than 1 m. The bottom of nala bed should be sufficiently permeable. The site selected should have sufficient thickness of permeable bed or weathered formation to facilitate recharge of stored water within short span of time. The check dams are most popular and feasible in Bhabar, Kandi areas of Uttar Pradesh, Punjab and Maharashtra. To harness the maximum runoff in the stream, a series of such check darns can be constructed to have recharge on regional scale.

4. Recharge Pits and Ditches Pits:

Recharge pits are constructed for recharging the shallow aquifers which means sand is generally present from the surface onward. In hard rock areas, the surface soil and weathered formation is suitable for construction of pits and ditches. These are constructed 1 to 2 m wide and 2 to 3 m deep and are backfilled with boulders, gravels and coarse sand. A bore hole is constructed inside the recharge pit if impervious layer (clay layer) exists at shallow depth i.e. at surface and sand is present below the clay. Ditches or trenches are constructed when the permeable strata is available at shallow depths. Trench may be 0.5 to 1 m wide, 1 to 1.5 m deep and 10 to 20 m long depending uQon availability of water. These are backfilled with filter materials. Pits and trenches are suitable for small houses and green belts.

5. Recharge Shaft with Tubewells

If the aquifer (sand layer) is available at greater depth (20 m or more) and water levels are deeper than 15 m, a shallow shaft of 2 to 5 m diameter and 3 to 5 m deep may be constructed depending upon availability of runoff. Inside the shaft, a recharge well of 150 to 300 mm diameter is constructed for recharging the available water to the deeper aquifer. At the bottom of the shaft, a filter media is provided to avoid chocking of the recharge well. These types of recharge structures are most suitable for group housing societies, large residential and institutional buildings and office complexes and along roads etc.

For PDF copy of Solved Assignment

Any University Assignment Solution

WhatsApp - 8409930081 (Paid)