Frontiers in Environmental Science (Feb 2022)
Applicability of Flow Resistance Formulae for Sand-Bed Channels: An Assessment Using a Very Large Data Set
Abstract
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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