High-order Average Component Acceleration method with longitudinal distribution of the average component term for fast flood flow simulations under various downstream conditions

The trade-off problem in numerical simulations for flood forecasting is defined by an increased computational load with increasing resolution of the calculation, which improves accuracy. The Average Component Acceleration (ACA) method addresses this issue by proposing a new axis for acceleration calculation. In the ACA method, to compensate for the shortening of the time scale of the discharge hydrographs, the temporal change in water depth is divided into average and local components, amplifying only the average component. However, the ACA method has not yet been applied to several downstream conditions. This study proposes a novel evaluation method for the average component term and applies it to several downstream conditions with various calculation domain length to flood wavelength ratios. The accuracy of the previous ACA method decreased with the ratio of the channel domain length to the wavelength. The enhanced ACA method, employing a quadratic curve for the average component, efficiently reproduced the temporal variations in water surface distributions with the original analysis under several downstream conditions.