RAIN WATER HARVESTING
The never ending exchange of water from the atmosphere to the oceans and back again is known as the Hydrological Cycle. This cycle is the source of all forms of precipitation (hail, rain, sleet & snow), and thus of all water. Rain Water is the first form of water we know in the Hydrological Cycle & hence is a primary source of water for us. This is where rainwater harvesting becomes important.
Rain Water Harvesting is a three tier process of –
1. Harvesting –
Harvesting is an act or the process of collecting / channelizing the rain water from the catchment area to the Rain Water Harvesting unit. Diverting the Rain Water from your existing Storm Water Drain (SWD) system is the reasonable option, as the total rain water (Terrace + Compound) flows out from the SWD, & it is convenient to synchronize with the RWH unit; instead of diverting only the terrace water as it incurs the plumbing cost & may require the periodic monitoring & maintenance.
2. Charging –
The recharging of ground water is a process by which borewell water aquifer is augmented at a rate exceeding that obtained under natural conditions. This recharging technique enhances the sustainable yield of the borewell aquifer. Theoretically this will imply that the vertical hydraulic conductivity is high, while the horizontal hydraulic conductivity is moderate.
Recharge Technique normally addresses to the following issues –
a. Enhance the sustainable yield of the borewell.
b. To improve the quality of existing Ground water through dilution.
To charge 1 litre of rain water there must be 1 litre of borewell water source available, if there is no water aquifer in the borewell no charging is possible.
Withdrawing –
The Rain Water Harvesting system design must be sized for making provision of the water in the non rainy season period of the year, i.e. the RWH system must be designed taking into consideration the yearly volume water required by the society for all the secondary purposes.
Basic Calculation for Rain Water Harvesting system design –
Development of RWH unit’s design & Scope of Job for the total project is based on the following calculations which are as follows –
(i) Effective Catchment Area of the Plot = 3,229 Sq.ft (approximately) i.e. 300 sq.mt
(ii) Average Seasonal Rainfall of your plot = 32” inches
- 1” Rainfall in 1 Sq.ft area = 3 ltrs water
Therefore, total 32”- (ii) in 1 Sq.ft area = 96Ltrs (32” x 3ltrs) per Sq.ft
- Total Rain water available for charging = 96 ltrs per Sq.ft x 3,229 Sq.ft - (i)
= 03,09,984 Ltrs
Therefore, Total Rain Water available for charging from the above mentioned site shall be 03,09,984 litres of water in the monsoon. In the rainy season, there will be replacement of the water withdrawn from the unit.
Therefore, for charging of this huge water quantity, there must be equivalent no.s of underground water sources in the water bearing strata zone, for synchronizing all the under ground water resources-via-harvesting units; Vertical borewells for making possible the withdrawal & charging process from the RWH unit for round the year requirement of the water.
We must make NATURE TO WORK, Nature's job human beings cannot do & should not do as it would involve cost & maintenance cost, the Rain Water Harvesting system design must be with synchronization with the natural cycle of water for NO MAINTENANCE.
