The Presence of Jeringau (Acorus Calamus) as Flexible Vegetation Type in the Channel Against Flow Resistance

Flow resistance in the channel is influenced not only by material forming the bed and slope of channel, but also influenced by abstraction due to the presence of vegetation in the channel, so called vegetated channel. The presence of vegetation may greatly affect the conveyance of a channel. The study is aimed to investigate the effect of flexible vegetation density of jeringau (Acorus calamus) to flow resistance. The research is conducted in the laboratory by using a channel-flume with dimensions of 15.5 m length, 0.5 m width, and 1.0 m height in which in the central part of 1.4 m length of flume is planted with Jeringau in submerged condition. The vegetation density is set in 6 variations, namely: 0, 6, 12, 18, 30 and 42 plants/m2. Flow velocity at surface, 0.2 h, 0.6 h, 0.8 h and bed level are measured using micro-current meter to see velocity distribution profile in three parts of upstream, central (vegetating part) and the downstream of channel. At those point are also measured the water depth using point gauge to see the head losses for analyzing Manning's roughness coefficient (n). Based on the measurements and analysis, it is obtained that the presence of Jeringau might change velocity distribution compared to unvegetated channel. The more increase the density of Jeringau, the more increase the head losses which result on increasing Manning's roughness coefficient. The largest n value is 0.053, obtained from maximum density, and 0,022 for unvegetated channel. The result shows that n value increase 2.41 times due to the presence of Jeringau vegetation. It can be conclude that the presence of vegetation can increase the value of roughness coefficient affecting flow resistance, so as to disturb the water flow in a channel.