Determining water surface profil in open channel, a hec-ras application for a case study of Nakkaş Creek

Accepted as a natural disaster, flooding keeps occurring in Turkey and all over the world causing destructive results for millions of people who have to confront the devastating consequences material and moral damages. Accurate prediction of water levels during flooding has primary importance in terms of damage minimization occurring in the affected region. Hence, many models are being used to determine the level of water surface in rivers. In this study, HEC-RAS coding has been used for modeling Standard Step Method and Manning formula which are used to define water surface profile. Nakkaş creek, in Küçükçekmece district of İstanbul, has been selected as a case study area. In 2009, major life and property losses occurred as a result of flooding in the area which has a great importance for İstanbul. In this study, an Excel worksheet was prepared applying the Manning Equation together with the Standard Step Method. In the same worksheet, the Simplified Universal Equation and the Keulegan Formula are also applied using field data to compute the mean flow velocity. The Standard Step Method is used, as done in HEC-RAS, to determine the water level. All these calculations are performed in Excel worksheets. Results of this study were then compared with outputs of the HEC-RAS. Comparison shows that the Manning Equation produced lower water levels than the Keulagan Formula and the Simplified Universal Equation. Capacity of the lined trapezoidal channel designed for the study area was found to be adequate with water levels resulting from all the methods used in this study.