Bisokotuwa

Sri Lanka with a written history over 1500 years has been practicing soil and hydraulic engineering from about the same period of time. Rice and grain being the islanders staple diet, its community has been rice farmers and needed to store rainwater to cultivate the dry zone. The storage of this excess rainwater needed earthen embankments built across the valleys.These expertise brought about a society that practiced soil engineering which created a unique hydraulic civilization. The growth of this hydraulic civilization expanded with enhanced knowledge and developed new techniques with state patronage. In a broader sense a practice of water management that became a culture.

Initially it was a technique to sustain the water table by storing water on the ground with earthen embankments built across valleys. The water so stored was made to percolate into the ground replenishing the ground water table. This water was re extracted and put back on the soil as irrigation water and the cycle was to continue. This simple water cycle was improved with enhanced knowledge on soil engineering by storing large volumes of water behind strong earthen embankments that created large lakes or tanks. These large tanks managed to irrigate large tracks of land producing rice at commercial level that boosted the state coffers.

Building such large and deep lakes brought about new challenges in controlling and handling water in a safe and non-destructive manner. The greatest problem faced was to release the stored water into earthen canals with controlled velocities while dissipating the enormous potential energy stored in the water. It was a requirement that the very earthworks that held these water needed to be protected. A breached embankment would wipe-out the entire community that lived besides it. The first technique used was a devised called the “Keta Sorowwa” presently known as a VT sluice or a Vertical Tower Sluice. [Sorowwa – Sinhala term for Sluice] The modern-day “Moring Glory” spillway is an advancement of the Keta Sorowwa. A type of structure adopted when natural ground conditions are not favourable to site the excess water spillovers in reservoirs. The Bomburu-Ella reservoir in Nuwara Eliya, Sri Lanka on the way to Horton Plains is facilitated with a Morning Glory spill. So named as the structure depicts the shape of the Morning Glory flower.

The Keta Sorowwa is a devise formed with a number of funnel type chute units of burnt clay placed one on top of the other to reach the water surface. This stack is connected to a burnt clay conduit placed at the bottom of the embankment leading to the canal which distributed the water to the paddies. The theory being that… the water pressure at the top of the surface is less and the stored energy is manageable. The surface water of the reservoir was transferred through the tower of chutes into the canal by the clay conduit. Once the water level of the reservoir reached the level of the uppermost chute unit the discharge ceased, and the top most chute was removed manually, re-activating the discharge of water to the