Recurrence of hyper-concentration flows on the orogenic, subtropical island of Taiwan

The combination of abundant precipitation and frequent earthquakes in Taiwan, an orogenic, subtropical island, results in huge amounts of sediment discharge delivered into river channels and provides high potential for turbidity current, a kind of extreme hydro-phenomenon characterized by high turbidity and flow velocity. This study collected hydrometric data from 11 rivers around Taiwan, and applied statistical methods to estimate the recurrence interval (RI) of hyper-concentration flow. Analysis results revealed that RI of hyper-concentration flow was dominated mainly by the magnitude of the drainage area and the geological environment within the catchments. The catchments in southwestern Taiwan with relatively larger areas and/or frequent landsliding have comparatively shorter RIs of <10 years. Comparing the RI of daily rainfall with the RI of hyper-concentration flow reveals the possible rainfall threshold for hyper-concentration flow, and the application of rainfall threshold for hyper-concentration flow is well demonstrated in the catchments. The average rainfall threshold for the whole of Taiwan is 510 mm/day, and is positively related with geomaterial properties within the catchments.