TESTING THE VALIDITY OF MANNING'S n CALCULATED BY MODELING THE FLOW THROUGH RIGID NON-SUBMERGED VEGETATION

摘要

The flow of water through rigid non-submerged vegetation in wide floodplains was modeled. Rigid rods were used to model the vegetation. Different configurations of these rods represented different vegetation densities. Each configuration was tested at three flow discharges. Values of friction factor Manning's n for these different configurations were calculated. Results of this study were presented as functional relations that relate the friction factor to the flow and vegetation density parameters. The validity and the uncertainty of the friction factor values were tested. Tests were conducted to determine if the results of two trials for each experiment were consistent. It was found that 95% of the differences between depth readings from the two trials were less than 3.7%. This value was considered within the range of experimental errors. The Manning's n values across one, two, three, and four rows of rods were measured and used to determine whether the Manning's n could be calculated using the upstream condition. It was found that there were no significant differences between the n values computed for different numbers of rows. This confirms that the value of n can be calculated using the upstream conditions. Thirty six different configurations of rod densities and flow discharge values were tested. Twenty four values of n were calculated for each of these configurations. These values included two trials for each case, three values at the lateral dimension of the flume and four values of n measured for 1, 2, 3, and 4 rows. It was shown that all the data computed for a given configuration at a given discharge arise from the same population. The uncertainties of the data were found to be within an acceptable range given the large variation of reported Manning's n.