FLASH FLOOD FORECASTING IN KARSTIC BASINS

The height of and celerity of flash floods in subterranean streams are poorly understood and rarely studied. Yet, flash floods occur as frequently in subterranean streams as flash flood occur in rivers and result in the erosion and transportation of the streambed sediment and of sediment-associated microbes and contaminants. In addition, visitors (cavers) to subterranean streams can be caught off guard by these flash floods and this infrequently, yet tragically, can result in death by drowning. Hydrologists need to understand the physical processes that control the height of and celerity of a flash flood as a flood surge travels through subterranean streams. This research will test the applicability of the linear diffusion wave equation to predict the height and celerity of flood surges in subterranean streams and will compare those predictions to observations.

The well-known, nonlinear, St. Venant equations provide the basis for understanding the celerity and height of flash flood in rivers and likely in subterranean streams as well. The linear diffusion wave equation (a simplification of the St. Venant equations framed for wide, open channels with no lateral inflows) is well known and relates the height of the wave to the kinematic wave celerity [(gy0)0.5], D is the noninertia diffusion coefficient [v0y0/2S0], the depth (y0) and velocity (v0) of steady uniform flow in the channel, and the channel bed slope (S0). Based on analyses of seven storms in a subterranean stream, D = 0.2 ± 0.2 m2s-1 and ck = 1.4 ± 0.2 ms-1. Based on these values and the solution equation, predictions of the movement of flash floods through the subterranean stream can be made.