Parameter Estimation of Oxygen Transfer at Hydraulic Structures

Dissolved oxygen is an indicator of water quality, and a minimum of 4 ppm is required for the survival of aquatic life. The oxygen is transferred when water flows over the hydraulic structure by entraining air into the bulk of the flow. The entrained air breaks into small bubbles, increasing the surface area for oxygen transfer. The oxygenation of water removes organic matter, dissolved gases, volatile liquids, offensive taste, and odor, improving the quality of the water flowing in the rivers and streams. The oxygen transfer efficiency depends upon the liquid film coefficient and specific interface area. In this study, parameters, namely liquid film coefficient and specific interface area, are estimated from dissolved oxygen concentration data. The dissolved oxygen concentration data is generated using a liquid film coefficient of 500 m/s, a specific interface area of 0.00035 m²/m^3, and dissolved oxygen saturation concentration at 25⁰C. The Parameters are estimated through numerical inversion in which the numerical model representing oxygen transfer over hydraulic structure was optimized using genetic algorithm. The seed value used for optimization is taken as 0.6. The results show that it is not possible to estimate both the liquid film coefficient and specific interface area together from dissolved oxygen concentration data only, and at least one parameter should be known. This finding is supported by the presence of local minima in the liquid film coefficient-specific area parametric space.