Evaluation of the application of some empirical concentration time equations for estimation of channel flow travel time

Time of concentration is one of the most important hydrological variables which plays crucial role in designing the flood control structures، spillways and so on. However، enough investigations have not been taken place about this important variable. The purpose of the study is to evaluate the application of empirical equations including Kirpich (1940) California (1944)، NRCS (1972)، Yen-Chow (1983)، Haktanir-Sezen (1990) and Zomorodi (2005) for estimating shallow concentrated flow travel time in the upper channels of Manshad and Deh-Bala watersheds located in Yazd province، Iran. Therefore، the estimations made by the equations were compared to measured values provided by Nacl 75 g/lit solution gulp injection. The estimations made by the equations were evaluated using statistical criterion including absolute percentage error (APE)، root mean square error (RMSE)، coefficient of determination (R2)، and correlation coefficient. The results showed that Haktanir-Sezen and Zomorodi revealed acceptable estimations of accumulated (sum of the travel times estimated for reaches) as well as partial (travel time measured per reaches) overland flow travel time. While none of equations presented a reasonable estimation of total travel time (travel time estimated using mean values of slope and roughness of the whole studied stream length)، although the estimations of Haktanir-Sezen، California and Zomorodi showed higher accuracy than others. Most of the equations underestimated overland flow travel time in comparison the measured values.