Matrimandir Lake mini test ponds research completed

The research was carried out under the supervision of a German technological institute, the LGA Nürnberg, and a Berlin-based Water-Construction Company headed by Harald Kraft.

The project had multiple targets. One was to study how best to build the lake and its embankment. Major techniques to build artificial lakes in India and abroad were studied to assess to what extent these could be used in Auroville taking the environmental and construction conditions into account. Of particular concern was if Auroville’s relatively inexperienced construction team would be able to create such a water-body, with the technological equipment which is commonly used in South India.

A second target was to test various sealants over a period of two years. The aim was not only to find out which sealant is technically best, but also to evaluate how difficult the sourcing of the sealing material is, the ease of installing each sealant, how to rectify any construction mistakes, and which sealant is most cost-effective in terms of purchasing cost and long-term maintenance.

The sealants tested were natural clay from the Auroville surrounding area, compacted clay provided by a specialized company in Germany, 2 mm thick high density polyethylene (HDPE) foil manufactured by the German firm of Naue combined with geo-textile, and bentonite mats consisting of two layers of geofabric with bentonite – the swelling component of natural clay – in between.

The ‘winner’ in terms of sealing quality is compacted clay from Germany, closely followed by polyethylene foil and natural clay. Bentonite mats proved to be a failure. Also in terms of ease of installation, compacted clay comes first, followed by natural local clay. Polyethylene foil and geo-textile required high vigilance and perfection and came last in the ease of laying.

But in terms of costs, compacted clay loses. The report uses the term ‘exorbitant’, as the costs include those of German clay, factory compacting, freight charges, import-duties and laying. The purchasing and maintenance costs of polyethylene foil are less, but only if no mistakes are made in the joining of the foils. For if a joint would open up and water would seep through, it would be extremely difficult to locate the mistake’ maintenance would be very expensive.

Natural clay, here, is the clear winner. The purchasing price is the lowest of all tested sealants. It has the additional advantage that a hole in the sealant will be ‘self-healing’, because the seeping water will close a hole with sediments of clay in the course of time. This makes natural clay a very attractive solution. But one of the problems of natural clay is the huge volume required – a layer of 40 cm thick has to be installed. To find such a quantity in a consistent and uniform quality is not easy. Other problems are there as well: it may be difficult to get permission to harvest the clay, and special permission is required to transport it to the construction site. If these problems can be solved, natural clay will be the best option. But if they are insurmountable, polyethylene foil combined with geo-textile would be the option of choice.

As a next step, a 10 metre deep test lake of 10% of the final lake area is planned to be built. This will show how the selected sealant behaves at this depth, if it expands or contracts and what happens when there is an earth movement. Sensors underneath the sealant will indicate if there is water seepage. As desalinated water is not yet available – the desalination plant is still in the planning phase – this test lake will have to be filled using ground and rainwater. The test will be over a period of one to two years.