Dynamic behavior of fluid flow through a downscaled model of Bissokotuwa of the ancient reservoirs in Sri Lanka

Abstract

Artificial lakes were designed in Sri Lanka from ancient times to harvest rainwater and to detain floods. First, a network of smaller lakes was constructed, but with technological sophistication, later on medium to large lakes were reconstructed to cater the increasing human population. The Bissokotuwa technology was introduced to large lakes in order to channel water from the bottom of the lake, since techniques used for small and medium lakes are not sufficient to sustain the large static pressure of releasing flumes. The sluice gate of the Bissokotuwa is made of wood and outflow is regulated by a lever mechanism. This project investigated the kinetic energy (KE) losses inside Bissokotuwa and compared it with water channeling through a direct sluice with the aid of a scaled-down prototype model. The prototype model exhibited KE loss of ~43.5% due to Bissokotuwa and it was independent of the reservoir head. The motion of inflow confirmed subjecting to serve velocity gradient and turbulence inside the Bissokotuwa. This suggested forming shear stress within the water by reducing its pressure. Poiseuille's law supported justifying inflow and outflow are laminar for the prototype model; however, the same behavior cannot be expected for a real scenario according to terms in the Reynolds number formula.