Established at present as a multifactorial origin

KATTAKADUWA (INTERCEPTOR)

This is an elongated murky meadow with turbid water in between the outer toe of a tank bund and paddy field. When halophytes such as mee, kumbuk, lunuwarana, thimbiri, val beli, and vetakeyya are grown in over the rim of the meadow salts on the water is reduced (Tennakoon, 2015). Scientist have observed the higher electrical conductivity in this area. This observed higher salinity concentration is due to seepage of water from a dead storage area of the tanks where there is a buildup of salinity in most of the tanks. However, this Kattakaduwa area also acts as a downstream wind barrier and helps to protect soil from erosion as the majority of species consists of well-developed root systems. Hence this ecofriendly structure, Kattakaduwa improves the water quality of the command area by removing excess salts, nutrients and sediments.

This command area is the catchment for the next downstream tank in the tank cascade system.

Iswetiya or Potawetiya is an upstream soil ridge made on either side of the tank bund to avoid sediment particles entering from upper land slopes towards the tank. In addition, Godawala

and Kuluwewa were constructed to trap sediments reaching from the ephemeral stream to the tank.

Godawala which is found in association with a small tank, is a manmade waterhole.

Whereas Kuluwewa a small tank/pond above large reservoirs trap sediments and provide water for cattle and wild animals which may be a strategy to avoid man-animal conflicts. Construction of these Iswetiya or Potawetiya,

Godawala or Kuluwewa ensures the good water quality and combat siltation of the tank.

In addition, during the dry spells with the frequency of 3 to 5 seasons, villages were used to identify the more silted places of the tank bed and arrange shramadana campaign to remove muds (Kattikapeema).

Moreover, the place of the spillway of the tank is generally designed to open to a low rounded rock outcrop area so that erosion is minimized from the spilt water. Hence, the tank water was sustainably used for drinking, bathing, washing and irrigation. Raising the dam or spill was not required as at present to accommodate a sufficient quantity of water for irrigation.

In the command area of the tank where paddy was grown, the old natural stream was used as a common drainage line. It was called as Kiul ela and it could remove salt and iron from polluted water and improved the drainage condition of the paddy fields (Dharmasena, 2004).

Because, along with the drainage line (Kiulela), there are tree species such as

karanda, mee, mat grass, etc. Those trees are capable of trapping excess nutrients and salts and this shows that the drainage water is purified to a considerable extent even at the command area.

This drainage water subsequently reaches to the next downstream tank through the

Wew Ismaththa (closer catchment) and Wew thaulla in the cascade system. Dharmawardana (2015, 2017) stated that the origin of kidney disease was linked to water of

high ionicity damaging the membranes in the tubules and other components of the kidney via the Hofmeister mechanism. Ionicity of water substantially is low in tank water when the water passes through these Kattakaduwa

– Kiwul Ela system. At present, these systems are neglected in some of the tanks that may result in increased salinity.

Fig 05 : Schematic representation of the profile of a small tank and its components ( Produce by the Authors)

The benefit of tank cascade system is that the downstream tank captures the excess water from the tank above. Thus water is not wasted but recycled.

However, this age-old concept has not been continued during the 1950s to 1970s where short-sighted efforts have been increasingly made by the water resource managers.

If all these tanks were in operation (around 15,000), we hope there is no need of excavating groundwater for drinking or even farming. Use of groundwater for drinking has been one of the causes of CKDU because of its higher ionicity. We hope still there is a possibility to adapt to these tank cascade system and integrate the ancient technology with the novel watershed management techniques so that we could supply quality drinking water to dry and intermediate zone of the country. Sri Lanka needs a water policy

formulation addressing the water quality issues and identifying the tank cascade system as the lifeblood of the dry zone rather than water of trans-basin water diversion system such as the Mahaweli system.

Components of the tanks need to be well delineated and recognized as vital areas in improving the water quality.