In the water conservation system, rainwater harvesting schemes are employed. In the rainy season, the soil is already saturated with water, then it can not accommodate additional water received from the rooftop rainwater harvesting system. The water is required to pass at a depth to meet underground water. In porous soil/ rock media, it may possible up to a certain extent. But, there is no guarantee to get a soft rock everywhere to absorb more water. In the rainy season, definitely efficiency of ground water recharge is very less. How efficiency can be improved?
I think You are absolutely right... and on top of that very few waters ob tained from roofs are clean enugh to be infiltrated into soil without a pretreatment. So it is always wise to have a biologically active infiltration step.
Groundwater capture by roofs may have limited capacity to augment nearby groundwater supplies during wet periods especially also due to compaction and impervious surfaces found around many buildings. Many harvesting use large containers or perhaps ponds to help store water for irrigation or sometimes other uses. Drinking rainwater without some treatment is risky. Assuming you had a supply of treated rainwater suitable for groundwater, actually pumping water into the ground at some depth with suitable hydraulic conductivity to accept the pressurized water should be more efficient than relying on gravity alone. Less impacted areas such as forests are known to be able to use more water, but also accept more water due to higher infiltration rates. If one were to pipe and pumped the stored, harvested water to irrigate a forest, it may well be able to accept more water and raise local groundwater level and perhaps augment local streamflow, filtered through soil. Altering hydrology by forcing extra water into karst terrain might contribute to sinkholes. Water tables and aquifers have recharge zones, and we don’t always know where these are, maybe fault zones, stream channels or skeletal soils nearby or far away. If the rain water runs off, degrades channels into gullies, the local groundwater levels may decrease. Maintaining stable stream channels, quality forests or cover vegetation help to infiltrate water, so water tables can be supported, rainwater can be naturally filtered. Gravity in many ways is efficient, if we conserve the soil and it’s ability to accept and store water.
It is not clear from your question that you want information for plains or hard rock area. If You want to recharge GW through roof water harvesting in plain area ( not in hard rocks) then it will totally depend on the Water table position in monsoon season, If water table is in monsoon season with in 1-3m then recharging GW through roof water will not work. If water table during monsoon season is more than 5 m. it will certainly work. In case of Hard rock regions, than you have bore well for GW recharge and depth of bore well should be more than 30-40 m, then in these bore well there will be certainly number of fracture zone they will help for fast GW recharge, We have successfully implement this techniques in hard rock region of Agra ( Jagner Block) U.P., India for GW recharge through Bundies ( earthen embankment for water harvesting ) by having borewell depth 55-60 m.
Dear Ishwar Sonar, thanks for this question. Rainwater harvesting on rooftops with systems in single building level are widely applied and their functioning has been thoroughly researched. Rainwater harvesting on a regional scale is not implemented as of yet. Hardly any research has been performed to the potential of rainwater harvesting on a regional scale, with catchment on roofs and other surfaces. Agree with William F. Hansen , who stated groundwater capture by roofs may have limited capacity to augment nearby groundwater supplies during wet periods especially also due to compaction and impervious surfaces found around many buildings. Why isn't roof top rainwater harvesting also associated with the city's (non-potable) water supply? Especially during wet periods. The use of rainwater can play a key role in the dynamic water resource management in the built environment. This means achieving self-sufficiency of cities by considering the re-use of supplied (potable) water and the use of alternative water sources to limit groundwater extractions. This is an attractive ambition and is further justified by the 1st pillar of the Water Sensitive City framework: building flexibility and adaptability in our water sources – “Cities as Water Supply Catchments” (Brown R. et al, 2008 & Asian Development Bank, 2016).
Catchment of the roof is a factor. In the drought prone area like Barind Tract of Bangladesh where scarcity of water is common, poor natural recharge due to thick top clay layer, continuous depletion of groundwater level, recharging using rooftop rain water plays a significant role.
Yes, You are right. Md. Iquebal Hossain. The problem needs an innovative solution.
I think rooftop rainwater harvesting needs to be implemented as part of the solution. It is also important to improve the water conductivity (infiltration capactiy) and water retention capacity of the soil.
Thank you for your contributions? From a sustainable point of view, conservation of water along with our progress in the form of infrastructure is the need of the hour.