| 摘 要： |
Among numerous flow resistance formulae for sand-bed channels, this study selected five for evaluation and in order to cover flow conditions in sand-bed river channels as widely as possible, a total of 1,636 sets of field measures were collected from the hydrological stations of two large river systems of China-the Yellow and Yangtze Rivers, in addition to the data compiled by Brownlie. The performance of the selected formulae in yielding the values of Manning resistance coefficient n was evaluated against the total of 6,805 datasets. In many cases, the formula of Ma et al. yielded unreasonable n values of <0, while that of Deng et al. and formulae 1 and 2 of Zhang et al. yielded n values with large errors. The formula of Wu and Wang yielded n values varying within the scope only in the case of n < 0.04. By dividing the absolute relative errors (AREs) from the selected formulae into six groups of 0-0.05, 0.05-1, 0.1-0.2, 0.2-0.5, 0.5-1, and >1, it can be found that, for all five selected formulae, ARE occurred in the group 0.2-0.5 occupied the largest percentage, while in each of the adjacent groups of 0.5-1 and 0.1-0.2 it also occupied a very large percentage. Hence, all five formulae still need to improve their predicting ability. |
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