The activation of ephemeral streams in karst catchments of semi-arid regions

Ephemeral streams are morphological elements of karstic low-relief areas, characterized by relatively large and flat transects, which occasionally drain runoff, in particular when generated by extraordinary or extreme rainfall events. The main problem related to this streams and affecting the analysis and prediction of flood events in karst semi-arid regions is the almost complete absence of discharge time series. Floods are relatively rare events for semi-arid karst regions; however, they can be really severe and disruptive, causing serious damages to people and infrastructures.This work presents an analysis of the response to rainfall of ephemeral streams in a karst semi-arid regions of southeast of Italy by an innovative approach. The analysis is based on a 2D simulation model of the behavior of a network of ephemeral streams. The used approach integrates the hydrological and hydraulic models in order to account first for the dynamic of catchment response to rainfall and activation of the streams, and then for the hydraulic behavior of the streams. Results show the slow response of ephemeral streams to the rainfall, whereas more extreme rainfall events generate quick and high discharge responses of the ephemeral streams. In addition, modeling results emphasize the non-linearity of runoff generation, in particular for some flow paths, which are biased by the local morphology as well as by the intensity of the rainfall event.

► Activation of ephemeral streams in a Mediterranean karst region is investigated. ► A historical analysis of ephemeral stream activation is introduced. ► An integrated 2D simulator models the behavior of ungauged catchments. ► Geomorphological information significantly affects runoff dynamics modeling. ► Just extreme rainfall events generate discharges through the ephemeral streams.