Investigation of analytical formulas for the travel and response time of irrigation canals (Case study: Bilevar irrigation network)

The improper operation performance of many irrigation channel is nearly a result of the lack in understanding transient flow phenomena due to the implementation of water delivery in the irrigation canal. Travel and response time are the most important characteristics of unsteady flow in open canal affecting the operation performance. Solving the Saint Venant equation and using hydrodynamic models is usual method to assess the response and travel time, but limited access and the complexity of the application of those caused to introduce simple methods for calculating them. Two analytical methods introduce to determine the travel and response time. The diffusion wave approximation and gravity wave can be used for the travel time and the diffusion wave and Ankum’s formula are used for the response time. In this study, the travel and response time has calculated using HEC-RAS and compared in approximate methods. The results show that the gravity wave is used to determine the travel time for short canal and the diffusion wave method is suitable for long canal reaches. In BLMC channel, the average response time error to distance of 3000 meters for Ankum’s formula is 5.1 percent, and the error of diffusion wave model is 5.5 percent from 3000 meters to the end of the canal. In this study, the effect of variation in input discharge on travel and response time are investigated. It has effect on travel and response less than 3 % and 5 %, respectively.