Author(s): Kwan Tun Lee; Yi-Ru Chung
Linked Author(s):
Keywords: Overbank flooding time forecasting; Probabilistic-based rainfall forecasting; Quasi-steady-flow routing; HEC-RAS; Kinematic-wave-based GIUH model
Abstract: A simple method for overbank flooding time forecasting is proposed in this study as an alternative of using currently sophisticated models. To alleviate the requisition of real-time hydro-metrological data obtained from weather radars, a probabilistic-based rainfall forecasting model was developed to forecast incoming rainfall intensities by analyzing historical rainstorm records. To avoid numerical instability in performing an unsteady-flow routing algorithm for rapid rising flow cases, a quasi-steady-flow routing method associated with a geomorphologic IUH model were developed to simulate the propagation of flood wave in the stream. The proposed simple method was applied to Keelung River Watershed in northern Taiwan. Hydrological records from two severe typhoons were used to demonstrate the applicability of the proposed methodology for flood forecasting. The maximum water stages generated by using the quasi-steady-flow model were verified using high water marks only with negligible differences, and these differences could be minimized by using a shorter reach length in performing the quasi-steady-flow routing. Acceptable results were also found for the overbank flooding time forecasting for 1- to 5-hour lead time while an adequate exceedance probability of rainfall was employed to estimate the incoming rainstorm hyetograph and then linked to the watershed runoff model associated with the quasi-steady-flow routing model for runoff forecasting.
Year: 2007