Comparative Analysis of Some Existing Models for Estimating the Time of Concentration for Watersheds in Anambra State, Nigeria

This study considered the estimation of the time of concentration (TC) using 30 different watersheds in Anambra State, Nigeria. The study assessed the performance of some existing models for the estimation of time of concentration in the study area. Data for this research were collected from watersheds located at Awka-South Local Government in Anambra State. A measured time of concentration values was also obtained by using a tracer at the watershed divide and the time it took the tracer to get the outlet of the watershed was recorded. This was carried out on all the 30 watersheds at the same time. The length, slope and area of the 30 watersheds were also measured. Thereafter, the time of concentration was estimated using the 30 existing models. The extent of linear association between the observed and estimated time of concentration for the different models was determined. The outcome of the study revealed that the Ventura model (Tc12) developed in Italy recorded the highest correlation coefficient with a measure of 0.681, followed by DNOS model (Tc14) with a coefficient measure of 0.661 while the least performing model was Picking model (Tc13) with -0.423 correlation measure. There was also an obvious difference in the values of the time of concentration calculated using the different models. Therefore there is always a need to verify any model to be used for estimating the time of concentration in other to have a more robust design.