The Initiative for Green Habitats represents a long term commitment towards providing solutions for the creation of Sustainable Built Environments. This blog attempts to provide an insight to our views, commentaries on our work, ideas that we are working on, and provoke thought where there are more questions than answers.

Wednesday, November 30, 2011

Nair's Residence: An example of a Sustainable Water Management plan

Mr. Nair, a client who had retired from his active career and a man who enjoyed doing hands-on work approached us with a view to install a rain water harvesting system for his house in North East Bangalore. He could easily be counted as an eco-convert as he himself believed and was interested in many a green thing. He came to us at time when the construction of his house was nearing completion. We saw in this proposition of his an opportunity to address this in a more wholesome manner than just providing a system to satisfy his demand. Read on...

Project facts:
Location: Horamavu, Bangalore
Site area: 568sqm (approx)
Roof catchment area: 198sqm (approx)
Ground catchment area: 285sqm (approx)


Site plan: House on the east and landscaped area on the west 

The site was two plots of land with the eastern section being the house which was being constructed then adjoined by a vacant piece of land to it's west. This vacant land had a small patch of green,fruit and vegetable plants that Mr. Nair painstakingly maintained himself. At the north west corner of the site was a store which was to also include a driver's toilet later.
At IGH we believe that it is immensely more sensible to have a comprehensive strategy which involves reducing the water need first and then managing demand of water (through rain, etc) efficiently than blinker-eyed isolated interventions. Therefore we expanded the scope of just the rain-water harvesting proposition to a comprehensive water management scheme that took into account the following:
  • Rain water harvesting- to catch all the rain that fell on the building's roof and the site
  • Water conservation measures- to reduce overall water demand
  • Grey water treatment- to reuse water that would otherwise be wasted and reduce fresh water demand
  • Landscape and irrigation design- to ensure minimal use of water for external use
Comprehensive Sustainable Water management- Nair Residence

RAINWATER HARVESTING
The roof area of the house, approx 198sqm, was large enough to potentially harvest about 1,47,000 lts of water annually in Bangalore. This would meet an optimised water requirement of the Nair household of 5 members for about 9.8 months in a year- which can be a very substantial saving if rain water is managed well. Since the ground catchment area was nearly 1.5 times that of the roof, we suggested that Mr. Nair undertake surface water harvesting too, beyond just limiting it to roof rain water harvesting.

The overall plan was to use the rain water from the roof top for domestic consumption, as this would be relatively cleaner water thus requiring minimal filtration, while the surface rain water (water falling on the ground/ garden) would be harvested for ground water recharge to supplement the aquifer.

Roof Rainwater harvesting system
Roof top rain water harvesting:
The rain water down-takes from the roof of the house were already in place. The exposed roof area had 7 down-takes that were lead into the rear of the house, below ground level and already cemented over. This turned out to be a major limiting factor in the design of the RWH system as it did not allow for an above the ground, in-line system which could have been far sleeker than the underground system which was finally put in place, specially the first flush and filter units..

An important prerequisite for effective roof top rain water harvesting is the regular maintenance and cleaning of the roof. Though Mr. Nair had a 10 kl underground sump that would suffice the requirements of rain water storage, he opted to go for a separate underground tank as he did not feel comfortable about mixing rain water with that in his main sump. The terrace- the catchment for roof top rain water harvesting- he felt, despite his efforts to keep it clean, would have more contaminants than anticipated and so he wanted to play safe in separating the rain water from the main tank.This however, remained a contentious point as the source of his sump water was from a bore-well, definitely of a lower quality. A little more attention to keeping the terraces clean and less money would have been spent.

The rain water harvesting system designed here included:
  • Collection chamber to collect water coming from the down-takes via a combination of 3 and 4 inch PVC pipes. A sieve as leaf separator, placed on an incline, was included in this chamber to keep large particles out of the system. An overflow at the top level of this chamber led the water into the first flush chamber. 
  • First flush Chamber to flush out a specific volume of the contaminated first rains.The initial rains falling on the roof (especially after long dry spells) is usually contaminated by dust, bird droppings and other particulate matter. Depending on roofing material type, ambient pollution levels and total roof area a certain volume of water from these initial rains needs to be flushed out of the system to keep the system clean. A simple water level dependant float based diversion system was designed to be the first flush here. A dripper driven mechanism ensured that the water from this chamber was drained out over a period of 3 days after which the first flush would reset. The over flow from this would be cleaner water that would enter the filtration chamber. 
First flush diversion system
  • Filter to further clarify the water - Three grades of aggregate (top layer- 40mm, middle layer- 20mm and bottom layer- 10mm) in mesh cages, for ease of maintenance, are placed one over the other as filter media in this chamber. The outlet at the base of the filter leads the filtered water via a levelling chamber into the storage tank. 
  • Rain Water Storage tank to store the harvested rain water. A 5000lts capacity tank was designed with its overflow leading into a central water feature meant for ground water recharge. Though BWSSB regulations specify a minimum storage capacity of 20lts/sqm of roof area, which would have meant 3600lts, we thought it prudent to provide for a storage tank that would meet the water requirements of the family for about 7 days. Water from the rain water storage tank is pumped into the main sump from where it would be further pumped into the over- head tank for domestic consumption. Had the rain water harvesting system not been an afterthought, as it turned out to be, the plumbing could have been managed appropriately, integrating the RWH system with the main plumbing, to ensure a single operation of lifting of water from UG sump to the over head tank. 
System Maintenance: Each of the chambers have their own separate access hatches for ease of maintenance and upkeep. The dripper out from the first flush chamber needs to be checked for clogging. Setting the dripper to fully open position and then resetting it to desired flow ensures that it will remain clog-free, provided terrace is well maintained. The filter media (aggregates) is placed within steel meshes. This needs to be removed once in six months, brushed and washed with clean water before being replaced. The rain water storage tank is to be cleaned seasonally, ideally at the end of the monsoon period or along with general maintenance and cleaning of the main sump.

The surface rainwater harvesting scheme integrated into the landscape
Surface rain water harvesting:
Surface rain water recharge
The ground catchment area was about 260sqm. We designed a network of surface water harvesting systems which were a combination of recharge well, boulder trenches and a central pond. These were integrated as elements in the landscape design and for effective ground water recharge. 

Here again the regulation specified a minimum capacity of 10lts/sqm of open area (about 2600lts for this project), but we designed the system to be capable of handling a heavy rain of about 40mm in one day (Bangalore gets an average rainfall of about 16-20mm per day) and so for about 9100 lts. The recharge well can handle about 2000lts, the boulder trenches about 4500lts and the central pond about 2600lts.


WATER CONSERVATION MEASURES
The use of water efficient fixtures can reduce the overall daily water requirement by almost 30% depending on usage. It goes without saying that one can be wasteful even with most efficient of systems.
As we began chalking out measures for water conservation in this project, we made a list of fixtures- faucets and flushes that could help conserve water not knowing initially that Mr. Nair had already procured his sanitary and plumbing fixtures at the time of our engagement on this project. We however, convinced him about exchanging his fixtures- basin/ sink faucets and shower heads mainly, with more water efficient ones. Sadly, he had already gone ahead and installed the flush valves, which prevented us from securing about 15-20 lppd through the use of more efficient options.


Water efficient fixtures 
Extensive market surveys were carried out following which we made our recommendations about fixture selection. We assisted Mr. Nair with procuring recommended fixtures by tying up with suitable vendors. During this process of surveying the market we realized that the choice at the hands of a client was very limited, especially if one were to look for 'made in India' products as being water conserving. On the other hand the market seemed flooded by imported fixtures thanks to stringent water use laws in those countries. 

The few fixtures that met our needs seemed more abundantly available in the product manufacturer's brochure than in the market or the display shelves. Clearly, the consumer saw too little of these products and therefore wanted them even lesser. The general notion of most vendors was that these water efficient fixtures were solely meant for gaining points in green ratings and therefore applicable in large projects- hospitality or offices and hardly for individual homes, which was our area of application. Vendors did not seem too keen on pushing these water efficient fixtures and kept almost no stock of them because these, according to them, were not fast moving items. The sluggishness of the distributor to procure small quantities of these specialized items became increasingly evident as we had to keep moving from one to another.

An efficient landscape drip irrigation system was outlined as another means of conserving water. The treated grey water was to be reused for landscape irrigation, thus reducing the overall water requirement.

GREY WATER TREATMENT
Mr. Nair had already on his own accord chosen to separate the grey water line from his soil line. So water coming out from the basins & bath areas in the bathroom and the kitchen sink, known commonly as grey water having fewer pathogens was piped out on a separate line. Most waste water treatment systems available in the market do not cater to scales as small as that of an individual home. They also invariably are  mechanical systems that rely on an energy source. We wanted this grey water treatment system to be able to function without consuming power and also blend into the landscape. After much research and deliberation, we decided to go in for a reed bed based grey water treatment system. We worked on that integrated other plant containers apart from the main reed beds, and ensured that the whole system became a part of the overall landscape.
Grey water treatment system
The system we designed had the following sections
  1. Grease trap to separate out the grease and oil which would otherwise retard the system's functioning. Kitchen sinks are large contributors to oil and grease. It is important to remove, to the extent possible, these materials. This is achieved by a grease trap which is a chamber that has two baffles. These baffles cause water to flow between them in a manner where grease floats on the top and gets arrested between them. The overflow is grease free and the water is lead into the nest chamber which is a sedimentation tank. Obviously, exercising caution at the source could potentially reduce the loading on the treatment system down the line.
  2. Sedimentation tank to separate out large particles. This chamber has a single downstand baffle which assists in sedimentation of suspended solids, that persist in the system, by gravity. The sizing of this tank was based on a two days standing time. The overflow from this chamber is at an upper level and feeds the gravel bed. 
  3. Gravel bed to further filter the grey water. A graded gravel bed consisting of three descending grades of 40mm, 20mm and 10mm is used as a first stage filter for the water coming from the sedimentation tank. The partition walls of this filter bed were made as a perforated brick masonry walls with the overflow from here leading into the planted filter bed.
  4. Planted filter/ reed bed to oxidise and treat the grey water. A process of secondary filtration, the reed bed system relies on the ability of certain types of plants to decompose the organic pollutants present in the water. The water is held in this planted filter bed for a period of about 2 days before being let out and stored in the treated grey water tank. The plants/ reeds used in this project were sourced from a lake nearby the site itself. 
  5. Treated grey water storage tank to store water before being re-used. Water entering this tank is relatively clean and odour-free. It is now ready to be used for landscape irrigation. 
System Maintenance: Each of the enclosed chambers had their own separate access hatches for ease of maintenance and upkeep. The grease trap needs to be checked from time to time and the excess trapped grease removed from the system. General cleaning of the sedimentation and storage tank would ensure the removal of any minimal particle settlement. The gravel bed and planted filter beds need to be kept weed free and de-weeding undertaken as required. The reeds are to be maintained and can be done along with general garden upkeep.
This simple decentralized system of grey water treatment has been functioning efficiently since its completion in early 2010..

LANDSCAPE AND IRRIGATION DESIGN
As mentioned above, the site was actually two individual plots that Mr. Nair owned in a private layout. He built his house on one and on the other he had plans of maintaining a garden.

We expanded this mandate to integrate within the landscaped area the rain water harvesting systems, a reed bed based grey water treatment system and surface water management system apart from a kitchen garden, patches of native flowering plants and fruit trees that would attract various life forms. There was a requirement to have a kennel and a store with a driver's toilet too in this landscaped area.
A view of the landscaped area
The orthogonal grid for the landscape was formed by extending the logic from that of the built, a straightforward, rectangular building. A central water body, the pond (see surface rain water harvesting) with a pervious base was designed as a seasonal water body that would contain surface run off water in it during the monsoons and would dry up in the summer months- much like the tanks that once dotted this city. Around this pond was the permeable walk way which lead from the house to and around the landscaped area. The walkway was paved with open jointed paver stones with grass in intermediate spaces to ensure that it allowed water to percolate into the ground. By the side of the walk way on the south is the boulder trench, again meant for surface rain water harvesting. A secondary path of stepping stones led from this walkway to individual spaces like the store etc,.
The cascade from the driver's cabin roof to the central pond
The built- store cum driver's toilet- was designed to have its roof as a water cascade. The surrounding plot of lands were still vacant and so Mr. Nair had already built a compound wall along his plot's boundary. We used two of these walls on the north east corner as the back of this built feature. It's front was a rough hewn stone masonry walls with precast ferrocement troughs inserted for the water cascade. This water cascade was fed by re-circulated water from the central pond, powered by a small solar pump.

After some deliberation on the roof of this built section of the landscape, we decided to go with a ferrocement roofing system which would be supported on steel lattice girders and concrete beams anchored into the boundary wall. On the roof of the toilet was the drip irrigation tank that was fed by the treated grey water.

This project attempts to demonstrate how individual home owners could work towards resource independence- in this case water. By adopting measures first to reduce water consumption, efficiently harvest rain water and finally reuse and manage water sensibly, this project aims to optimally utilise a resource as precious yet heavily abused as water.

3 comments:

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