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The rainwater endowment of an area is the total amount of water that is received in the form of rainfall over an area. The water harvesting potential is the amount that can be effectively harvested. The important factors that influence the rainwater harvesting potential of a site are the eco-climatic conditions and the catchment characteristics.
Among the eco-climatic conditions rainfall quantity and pattern are the most important factors. Rainfall quantity is the most unpredictable variable in the calculation. Hence reliable rainfall data for a period of at least ten years is considered to calculate the potential rainfall supply for a given catchment. The rainfall data from the nearest stations with comparable conditions are preferably considered. Rainfall pattern or the number of annual rainy days influences the need and design for rainwater harvesting. The need for the collection of rainwater in a region is more if the dry period is long or the annual rainy days are fewer. Big storage tanks would be needed to store rainwater if the dry period is too long. In such regions using rainwater to recharge groundwater aquifers is a better alternative than storing it.
The area and type of catchment over which the rain water falls and the surface features determine the runoff. Runoff coefficient for a catchment area is the ratio of the volume of water that runs off a surface to the volume of rainfall that falls on the surface. The runoff coefficient is used in all calculations relating to the performance of rainwater catchment systems taking into consideration the losses due to spillage, leakage, infiltration, catchment surface wetting and evaporation, which together contribute to the reduction in the amount of runoff. Kerala builders are trying to use the optimum method to reduce rainwater wastage and utilize maximum rainwater.
Among the eco-climatic conditions rainfall quantity and pattern are the most important factors. Rainfall quantity is the most unpredictable variable in the calculation. Hence reliable rainfall data for a period of at least ten years is considered to calculate the potential rainfall supply for a given catchment. The rainfall data from the nearest stations with comparable conditions are preferably considered. Rainfall pattern or the number of annual rainy days influences the need and design for rainwater harvesting. The need for the collection of rainwater in a region is more if the dry period is long or the annual rainy days are fewer. Big storage tanks would be needed to store rainwater if the dry period is too long. In such regions using rainwater to recharge groundwater aquifers is a better alternative than storing it.
The area and type of catchment over which the rain water falls and the surface features determine the runoff. Runoff coefficient for a catchment area is the ratio of the volume of water that runs off a surface to the volume of rainfall that falls on the surface. The runoff coefficient is used in all calculations relating to the performance of rainwater catchment systems taking into consideration the losses due to spillage, leakage, infiltration, catchment surface wetting and evaporation, which together contribute to the reduction in the amount of runoff. Kerala builders are trying to use the optimum method to reduce rainwater wastage and utilize maximum rainwater.
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