Fig. 5.1 In the place where foreign engineers recommended to construct the sluice gate of the present day Maduru Oya
dam, a sluice gate which had been built hundreds years ago, was discovered. These are the ruins of that sluice gate.
and its height is 44 feet. You can understand how
strong an artificially built soil bund should be, if
it is to hold the pressure caused by its magnitude
of water after the tank is filled.
The robustness is essential if the stability of the
tank bund needs to be protected. To maintain
this situation a systematic methodology has
been applied when the tank bund was built. To
understand this technology the archaeologists
examined the tank bund of Sigiri Mahawewa tank
by excavating it. What was seen here was that the
tank bund had been constructed of several soil
layers. It had been made of several thoroughly
beaten layers such as, a layer of clay, soil, gravel
and clay (Kirimeti) layer, kept one on one. Even
today you may have seen soil layers being beaten
in constructing roads to prevent them from
sinking. Though today we have machines to do
those things, in ancient time animals may have
been used to do so. The historical sources say
that elephants were used to beat soil layers in
constructing the foundation of the Ruwanweli
Seya.
Ralapanawa – When a tank is filled with water,
waves occur on its surface. It happens so because
of the wind and motion of the water. The structure
that is built to prevent the harm of eroding the
tank bund due to the power caused by water
waves is known as Ralapanawa. The Ralapanawa
is made by keeping stones on the interior slope
of the tank bund. Realizing the power caused by
water waves and using a method to prevent it was
a result of the scientific thought of our ancestors.Sluice- Releasing water from tanks in which
magnitude of water contains, is a task that should
be done carefully. In parallel to the distribution
of water filled area in a tank, the height of its
bund, which is holding water, also increases.
Then, the height of the water level also increases.
An extreme pressure is created due to the height
of water. When releasing water out of such a
place, one has to be highly careful because there
is a possibility of turning it to be disastrous every
time.It seems that the engineers who lived in our
country in the ancient time had thought of this
well. The structure that they built to take water
out of the large scale tanks is known as ‘Sorowwa’
(sluice). The sluice was built at a specific level on
the tank bund using huge pieces of stones. In the
Wessagiriya inscription made by king Mahinda
IV, the two words ‘Mohol Naga’ could be seen.
It says that ‘having set the stick which controls
the water in the sluice’. The sluice was built using