An expert system for predicting aeration performance of weirs by using ANFIS Ahmet Baylar a, * , Davut Hanbay b , Emrah Ozpolat a a Firat University, Civil Engineering Department, Elazig, Turkey b Firat University, Electronic and Computer Science Department, Elazig, Turkey Abstract A free overfall jet from a weir plunging into downstream water causes entrainment of the air bubbles if the free overfall jet velocity exceeds a certain critical value and hence aeration occurs. This study investigates the free overfall jets from triangular sharp-crested weirs and effect on their air entrainment rate and the aeration efficiency. An expert system based on adaptive network based fuzzy inference system (ANFIS) was obtained for predicting air entrainment rate and aeration efficiency of weirs. The performance of ANFIS model was compared with multi nonlinear and linear regression models. There were good agreements between the measured values and the values obtained using the ANFIS model. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: ANFIS; Aeration efficiency; Air entrainment rate; Weir 1. Introduction In a natural setting, oxygen is added to water by atmo- spheric diffusion at the surface, by wind circulation and by photosynthesis. Photosynthesis accounts for most of the oxygen in water. The oxygen content of water increases with increasing atmospheric pressure and decreasing tem- perature and salinity. The amount of oxygen in water is measured as milligrams per liter dissolved oxygen. Oxygen is a natural cleanser. It is the key ingredient for quality water. The level of dissolved oxygen is one of the best indicators of overall water quality. Oxygen is a neces- sary element to all forms of life. Adequate oxygen levels are necessary to provide for aerobic life forms which carry on natural stream purification processes. As dissolved oxygen levels in water drop below 5.0 mg/L, aquatic life is put under stress. The lower the concentration, the greater the stress. Oxygen levels that remain below 1–2 mg/L for a few hours can result in large fish kills. Total dissolved oxy- gen concentrations in water should not exceed 110%. Con- centrations above this level can be harmful to aquatic life. Hydraulic structures increase the amount of dissolved oxygen in a river system, even though the water is in con- tact with the structure for only a short time. The same quantity of oxygen transfer that normally would occur over several kilometers in a river can occur at a single hydraulic structure. The primary reason for this acceler- ated oxygen transfer is that air is entrained into the flow in the form of a large number of bubbles. These air bubbles greatly increase the surface area available for mass transfer. The physical process of oxygen transfer or oxygen absorp- tion from the atmosphere acts to replenish the used oxygen. This process has been termed re-aeration or aeration. Aeration performance of hydraulic structures has been studied experimentally by a number of investigators. These studies are reviewed by Wilhelms, Gulliver, and Parkhill (1992), Chanson (1995), Ervine (1998), and Gulliver, Wilhelms, and Parkhill (1998). Recently, Baylar and Baga- tur (2000, 2001a, 2001b, 2006), Baylar, Bagatur, and Tuna (2001a, 2001b), Baylar (2002, 2003), Baylar and Emiroglu (2002, in press), and Emiroglu and Baylar (2003a, 2003b, 2005) investigated weirs having different cross-sectional 0957-4174/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.eswa.2007.08.019 * Corresponding author. Tel.: +90 424 2370000; fax: +90 424 2415526. E-mail address: abaylar@firat.edu.tr (A. Baylar). www.elsevier.com/locate/eswa Available online at www.sciencedirect.com Expert Systems with Applications 35 (2008) 1214–1222 Expert Systems with Applications