Torrential flow is the highest velocity flow that can occur in a given reach of a natural channel, when slope is higher than a given value, (close to 0.001). Such flows occur in mountain streams, and in streams in the piedmont areas, dominated by alluvial cone depositional geo forms. The aggressivity of these flows is such that they often result in debris flows and avalanches where the sediment concentration in the waters far exceeds normal hydrologic concentrations, reaching values as high as 65% at the source and in the order of 35% to 50% at piedmont alluvial cones.

Disasters from Torrential floods turned into debris flows have recently become a major source of loss of lives and goods in many countries, particularly in tropical piedmont areas. Just in Colombia, over 5000 lives have been lost to torrential floods in less than 10 events between 2015 and 2018. The treat becomes more dangerous due to the lack of knowledge regarding the characteristics of these types of floods, which greatly depart from similar events in Plain Rivers, where flow behavior and flood consequences are very different.

This article presents some of the basic differences between floods of torrential and non-torrential nature, in order to generate some understanding on the behavior of these types of floods, and explore some of the hydrodynamic characteristics of torrential flow, to foster ways to understand and prevent or mitigate the effects of these events.

HEY WORDS

Torrential Flow, Avalanches, Debris flows