Approaching model of Manning’s coefficient due to an Effect of density and height of vegetation in open channel

Abstract

The presence of vegetation growing in the channel can cause increasing the Manning’s coefficient. The magnitude of Manning’s coefficient is depended on the characteristic and type of vegetation. The purpose of the research is to study and model the effect of density and height of vegetation on Manning’s coefficient in open channel. The study was conducted in open channel with 15.5 m length, 0.5 m width and 1.0 m height. At the centre part of the channel is planted with Elephant grass (Pennisetum Purpureum). The effect of different density and height of vegetation were run with fixed discharge to measure the velocity and water profiles in order to obtain Manning’s coefficients. The effect of those variables on the developed model was evaluated using statistical analysis of variance and paired t-test with significance level of 0.05. The results showed that Manning’s coefficient is increasing as increasing density and height of vegetation. If compared to un-vegetated channel, Manning’s coefficient increase in between 4.92 - 54.07%. Based on statistical analysis, it is found that Fcalculation = 367.776 > Fcritic = 19.452, tcalculation = 12.298 and 22.464 > tcritic = 2.571 and R2 = 0,967, showing that the density and height of vegetation significantly influence on the Manning’s coefficient with strong correlation variables in the model.