Physical modeling of flow in the ancient inlet sluice barrel of Nuwara wewa reservoir, Sri Lanka

he growth of the Sri Lankan hydraulic civilization developed new techniques in water management systems, such as reservoirs and irrigation canals. This is considered one of the most advanced irrigation systems throughout the history. Reservoirs were built to keep the water table up by storing water by clay embankments across valleys. This water has been conveyed as irrigation water, creating a life cycle that has existed for many centuries. The sluice and sluice gate is one of the most important components in a reservoir, and these components are the control devices of a reservoir. Control devices save the reservoir bund without damaging it by the velocity and pressure created by water outflow. The ingenuity of the Sinhala irrigation engineers is best exemplified by the invention of the Bisokotuwa (which means queen’s enclosure), later termed by Parker in 1909 Bisokotuwa, the enclosure where the water level lowers. As stated by Parker in “Ancient Ceylon (1909)”, there is a special arrangement before Bisokotuwa, called an inlet barrel, extended toward the middle of the irrigation tank. Some of these barrels extended more than 30.5 m, and spectacularly “Nuwara wewa” ancient sluice barrel extended up to 44.8 m, which were constructed in 1st century bc. Therefore, there must be an unrevealed hydraulic mystery about this kind of sluice barrel in some reservoirs in the ancient Anuradhapura and Polonnaruwa era, since our ancient engineers may not misspend their time and labor in vain for such kind of construction. To investigate the performance of the inlet sluice barrel, physical model testing has been carried out based on the roughness values of ancient sluice structures made of granite. The hydraulics of this ancient mechanism is revealed in this research.