Retardance Coefficient Analysis at Vegetated Channels for Triangular Ditches Analysis in Roads

Vegetated channels were used as sustainable drainages, but the main difficult of the design of ditches cover with vegetation is the adequate estimation of the retardance coefficient. There is a complex interaction of the vegetation in the flow patterns, for these reasons it is important study the effect of the vegetation in the retardance of the flow, these phenomena has been studied using the retardance coefficient. In this work the retardance coefficient was studied experimentally. Essays were done at an experimental setup with a channel of 3 m of length with a channel with triangular section with side slope of 1:2.5 (left) and 1:4.5 (right). The retardance coefficient were studied at a triangular channel cover by grass, and it were compared with a ground channel. Three different longitudinal slopes of the channel were tested (3%, 6% and 9%). The retardance coefficient and other hydraulic characteristics were analyzed. ANOVA analysis were used to compare the velocity and the flow depth in the ground ditch and grassed ditch, and significance differences were found. For similar flow conditions, the mean velocity of the flow in the ground ditch was 41% greater than the velocity at the grassed ditch, but the flow depth at the grassed ditch was 120% greater than flow depth at the grassed ditch under similar condition of the flow. Vegetation also acts as a filter, propitiating sedimentation. This reduction of the sediment load could be explained because the vegetation reduces the velocity of the flow and reduce the erosion. Relationships between the flow velocity and sediment load were found at the ground ditch with a Pearson correlation coefficient between 0.93 and 0.97 and for the grassed ditch between 0.98 and 0.99. The sediment load at ground ditch was 21.7% greater than sediment load at grassed channel. It shows that vegetated channels could be used as a protection of the channel against erosion. Ground channel has an estimated rugosity coefficient between 0.01 and 0.0039 and the grassed channel has a retardance coefficient between 0.006 and 0.019. Relationship between the retardance coefficient and the Froude and Reynolds numbers were made, and good correlations were found, with a correlation coefficient between 0.98 and 0.9998 with the Froude number and the retardance coefficient and a correlation between 0.96 and 0.97 with the Reynolds number. Vegetated channels were a good alternative to be used as a ditch at roads.