Hydrodynamic modelling in support of flash flood warning

Abstract

A new approach is proposed to determine the distributed threshold rainfall for flash flooding to support practical flood warning. It is built upon a two-dimensional full hydrodynamic model incorporating rainfall, infiltration loss and boundary resistance. Numerical solution of the governing equations of the model is achieved under an operator-splitting framework, the second-order total-variation-diminishing version of the weighted-average-flux method along with the Harten-Lax–van Leer contact wave (HLLC) approximate Riemann solver for the homogeneous equations, and a Runge–Kutta scheme for the ordinary differential equations of the source terms. The applicability of the new approach is demonstrated as applied to real flash flooding-prone areas in Hunan Province, China. The threshold rainfall for flash flooding, resulting from rainfall of durations from 1 h to 6 h, is found to be locally less than 100 mm or even 50 mm. This means a high risk of flash flooding in the local areas, and therefore effective measures are necessary to avoid loss of property and life. The present work should find general application in support of practical flash flood warning in catchments with the necessary topography and soil and geological data available.