Does the constant friction coefficient fit open-channel friction calculation?

In the realm of one - dimensional hydrodynamics, the application of steady - state friction formulas, such as the Chézy formula, in unsteady flows has long been a source of uncertainty. This study breaks new ground by proposing a novel Chézy coefficient updating algorithm grounded in the Unscented Kalman Filter (UKF) framework. Through meticulous laboratory flume experiments and real - world river case studies, we directly compare the traditional constant - coefficient model with our UKF - based model. Strikingly, the UKF - based model achieves a remarkable leap in accuracy, reducing water level and velocity simulation errors by 80.99 % and 62.74 % in laboratory settings, and 88.9 % and 82.8 % in real - river scenarios respectively. Moreover, we uncover two critical errors in the constant Chézy coefficient approach: the peak simulation error, attributed to the fixed exponent parameter n in empirical formulas that cannot adapt to unsteady flow dynamics, and the process simulation error, arising from the interaction between the formula's division operation and hydraulic hysteresis. These findings firmly establish that traditional steady - state friction formulas are ill - suited for unsteady friction calculations. Our research not only paves the way for the adoption of new non - steady open - channel friction models but also underscores the urgency of further research into non - steady friction mechanisms, offering valuable insights for more accurate hydraulic simulations in the future.