Determination of flexible vegetation resistance against the flow with rigid behavior

In this study, it is aimed to obtain roughness coefficients of flexible multi-stemmed vegetation standing upright against flow with rigid behavior. flow depths and discharges are measured; head losses causing from vegetation are calculated at 7 different points in 166 experiments for four different configurations. it is seen that chézy coefficient 𝐶, darcy-weisbach friction coefficient 𝑓 and manning coefficient 𝑛 cannot be expressed with a single function for all reynolds number. therefore, the data are analyzed for the two different cases of reynolds number lower and greater than 10000. dimensionless parameters for the roughness coefficients are determined as froude number 𝐹𝑟, reynolds number 𝑅𝑒, the relative roughness ℎ/ℎ𝑣, approach flow energy line slope 𝑆𝑓, and vegetation density 𝑘. the most suitable equations for estimating roughness coefficients are obtained by non-linear regression models. it is evaluated that for the reynolds number lower than 10000 the roughness coefficients are defined as 𝑓=𝑓{ℎ/ℎ𝑣}, 𝑛={𝐹𝑟,ℎℎ𝑣⁄,𝑘} and 𝐶={𝐹𝑟,𝑆𝑓}, and for the reynolds number greater than 10000 they are given as 𝑓={ℎℎ𝑣,𝑘⁄}, 𝑛={𝐹𝑟,ℎℎ𝑣⁄,𝑘} and 𝐶= {𝐹𝑟,𝑅𝑒,ℎℎ𝑣⁄𝑆𝑓,𝑘}. also, for relatively low reynolds numbers, the presence of plants caused an increase in resistance against the flow independently of other parameters as expected. it is observed that the regression equation coefficients could be influenced by factors such as surface area plant in the flow direction and plant density.