Rainwater harvesting is a system to – •Recharge the groundwater by rainwater through an artificial system at a rate more than that obtained under conditions of natural replenishment and/or- •Collect and store rain water.
The main goal is to minimize flow of rain water through drains / nallahs to the rivers. It is a known fact that the ground water level is depleting and has gone down in the last decades. Thus the rain water harvesting and conservation aims at optimum utilization of the natural resource water.
Basic requirement of artificial recharge 1.Availability of non committed runoff in space and time; 2.Identification of suitable hydrogeological environment and sites for augmenting subsurface reservoir through cost effective artificial recharge techniques.
Criteria need to be evaluated for planning the artificial recharge scheme:11
1.Identification of Area
•Areas where ground water levels are declining on regular basis.
• Areas where substantial amount of aquifer has already been desaturated. Areas where availability of ground water is inadequate in lean months. •Areas where salinity ingress is taking place.
•Urban Area where decline in water level is observed.
2.Hydrometerological studies
•Rainfall pattern in the area.
•Evaporation losses from the area. •Climatological features that effect the planning of artificial recharge.
3.Hydrological studies
•In‐situ precipitation on the watershed.
•Surface (canal) supplies from large reservoirs located within basin. •Surface supplies through trans‐basin water transfer. Treated municipal and industrial wastewaters.
•Hydrological investigations are to be carried out in the Watershed / Sub‐basin / basin for determining the source water availability.
4.Soil infiltration studies
•Control the rate of infiltration.
•Prerequisite study in cases of artificial recharge through water spreading methods.
•Infiltration rates can be estimated by soils infiltration tests using Cylinder or flood
•infiltro‐meters instruments.
5.Hydrogeological studies
•Firstly, to synthesize all the available data on hydrogeology from different agencies.
•Study of satellite imagery for identification of geomorphic units.
•Regional Hydrogeological maps indicating hydrogeological units, both at shallow and deeper levels.
•Water table contours to determine the form of the water table and the hydraulic connection of ground water with rivers, canals etc.
ARTIFICIAL RECHARGE TECHNIQUES AND DESIGNS
A wide spectrum of techniques are in vogue to recharge ground water reservoir. The artificial recharge techniques can be broadly categorised as follows: 11
a. Direct surface techniques
• Flooding
• Basins or percolation tanks
• Stream augmentation
• Ditch and furrow system
• Over irrigation
b. Direct sub surface techniques
• Injection wells or recharge wells
• Recharge pits and shafts
• Dug well recharge
• Bore hole flooding
• Natural openings, cavity fillings.
c. Combination surface – sub-surface techniques
• Basin or percolation tanks with pit shaft or wells.
d. Indirect Techniques
• Induced recharge from surface water source.
• Aquifer modification.
Flowchart showing the various Artificial Recharge Practices 11
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Urban Infrastructure and Network Study notes for M. plan Sem-III
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