Rainwater harvesting

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• Roof-top rainwater harvesting is a special case being increasingly used in urban areas for tank storage, urban irrigation and groundwater recharge. Rainwater from roof-tops is collected and conserved for either direct consumption or for recharge. The main purpose of recharging is to increase groundwater storage for times when it is needed. Advantages of collecting and storing rainwater in urban areas include the demand reduction on water supply systems as well as reducing the amount of storm-water runoff and consequent flooding
• Ground surface runoff collection systems represent a broad variety of techniques, which all aim to obstruct surface runoff from catchments and concentrate the water to be stored in the soil profile or the deeper aquifer. Whichever system is used, the aim is to significantly reduce surface runoff and evaporation in order to enhance groundwater recharge. In most cases, the purpose of ground surface runoff collection systems is to enhance agricultural production by recharging the groundwater and, as an added benefit, reduce soil erosion. These systems are perhaps the most widely applied of all artificial recharge techniques:
  
  
  • Barriers protruding from the ground surface: Barriers act as an obstruction to overland water flow on hill slopes. The barrier reduces flow velocity and water percolates behind it, increasing soil moisture and recharging the groundwater. The most commonly used barriers are bunds and ridges, which are small stone or earthen walls, usually constructed along the contour. Barriers are generally applied in arid regions where runoff is sporadic but intense, generating high surface runoff
  • Infiltration trenches, ditches and pits: After periods of high rainfall, overland flow on hill slopes can be trapped in these structures. These man-made depressions in the hill slope will catch the runoff water and infiltrate it through the bottom and walls, thus recharging the groundwater and/or increase soil moisture. Infiltration trenches, ditches and pits are very adaptable, and are available in many practical configurations.

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