Background Description
This is a case study of setting up a rainwater harvesting solution at the Easter Heights, Santa Cruz, Mumbai.
Easter Heights is the luxury apartment society located in the Santacruz East, Mumbai. Developed by Ambrosial developers, the society is an epitome of construction design and quality parameters.
The developers worked towards providing a comfortable home environment since the time of its initiation, in the year 2004. The apartments in Easter Heights are the best example of unbound convenience, a blend of modernity & elegance with provisions for all modern amenities.
Challenges
With several families living in the society, there was a subsequent demand of water especially for the activities like flushing and gardening. It was estimated that the daily water requirement for these activities would be 5000 litres. To cope up with the demand, a borewell measuring 4.1/2” in diameter and 75 feet deep was drilled in the year 2004 which had a yielding capacity of 15,000 litres/day. But while drilling it was discovered that the underground water table or the aquifer in the society area is a brackish water found at a depth of 50 feet.
Brackish water is a water which has more salinity than freshwater but of course, not as much salinity as the seawater. But it cannot be used for gardening as its salinity is not appropriate for most of the plants. Also, the brackish water is not considered suitable for the use in flushing as its prolonged use may result in deposition of salt at the bottom of the pot and the drain pipes, resulting in clogging and blemishing of the sanitary system.
Alternative method like collecting fresh rainwater was proposed by Chaitanya and implemented under rainwater harvesting scheme in the year 2008.
Insights of the premises and water requirement
For the success of rainwater harvesting system, some dimensions and calculations were made by the site engineers of Chaitanya:
| S. No. | Description | Units |
|---|---|---|
| 1 | Total plot area | 627 sq. mtrs. |
| 2 | Terrace Area | 206 sq. mtrs. |
| 3 | Volume of water harvested considering 25mm rainfall per hour | 12.54 Cu. mtrs. |
| 4 | Volume of water annually harvested | 1128.6 Cu. Mtrs. |
The number for volume of water annually harvested was reached by using the following rainwater runoff calculations.
| S. No. | Description | Units |
|---|---|---|
| 1 | Plot Area x average Rainfall per hour x Runoff co-efficient 627 Sq. Mt x 0.025mm x 0.8 | 12.54 Cu. Mt |
| 2 | Annually water harvested: Plot Area x Annual Rainfall x Runoff co-efficient 627 Sq. Mt x 2.25 Mt x 0.8 | 1128.6 Cu. Mt |
This was a high potential rainwater harvesting situation. We suggested them to encash it.
To prevent the harvested water from getting mingled with brackish water aquifer, the solution of desilting the borewell was suggested by Chaitanya Rain Harvest Products & Systems Pvt. Ltd.
Proposed RWH solution- Recharging Pit with Desilting Chamber
The most effective way of getting salt free harvested water was through installation of a recharging pit around the borewell with a desilting chamber bedded at its mouth. This helped in replenishing the brackish water aquifer using surface rainwater along with removing the salinity of the borewell water.
In the system, the surface runoff water was diverted from collection trenches to rainwater harvesting unit.
The surface rainwater passed through desilting chamber measuring 0.9 Mt x 0.9 Mt x 1.5 Mt depth and was getting transferred to recharging pit of 3.5 Mt x 3.5 Mt x 4 Mt depth with borewell, using the gravitational force. The filtration of water for removing the salt and other debris was done through Apollo ‘Vee’ wire screens, which were installed at the mouth of the borewell. The wire screens measured 6”dia x 12”dia x 1 Mt length.
By 2010 monsoon, the society was able to retrieve non-saline water from the borewell.
Economic viability – Total Implementation cost & Payback period
The whole solution system incurred the following cost and expenses
| S. No. | Type of Expense | Cost (prices in INR) |
|---|---|---|
| 1 | Implementation cost of the complete recharging pit with a desilting chamber system | 3,50,000 |
| 2 | Annual Maintenance Cost which includes: • Cleaning before onset of monsoon season • Cleaning of desilting chamber and collection trenches after the monsoon retreats | 6000 |
| 3 | Annual Cost of 182 Water Tankers that would be needed for gardening and flushing purposes | 91,000 |
| Total | 447000 |
The implementation cost of the system is believed to pay off within the time frame of 4 to 5 years. It was indeed a valuable investment by the residents.
Results
The residents of Easter Heights were freed from problems of brackish water and water shortage for daily chores. Clean and non-saline water was available in abundance. We provide them regular post-sales services for the maintenance and smooth functioning of the rainwater system installed.
More about Chaitanya RWH Products & Services
Apart from offering wire screens, Chaitanya systems deals in rainwater harvest services for understanding the rainwater harvesting potential of the concerned area. These services include preparation of rainwater harvesting reports, designing rainwater harvesting layout, designing detailed engineering drawings, conducting hydrogeological and borewell surveys and providing feasibility reports.
Gravels of size ranges from 5mm to 10mm which are used for filling the borewell pit are available too with the company. Furthermore, they have Fibre-reinforced plastic (FRP) Roof rainwater drainage gutters, Apollo Rooftop Rainwater Harvesting Filters, Precasted RCC Hume Pipes collar rings of 3 feet, 4 feet and 5 feet outer diameter sizes.