ANALYSIS OF RAINFALL THRESHOLDS OF DEBRIS FLOWS ON THE SMEDAVSKA HORA MT., JIZERSKE HORY MTS., CZECH REPUBLIC

In August 2010 extreme rainfall affected the north of the Czech Republic and caused regional floods and landslides. Three torrential debris flows originated in the Jizerské hory Mts., close to Bílý Potok on the north slope of the Smědavská hora Mt. The rainfall situation which triggered the debris flow was analysed and compared with the rainfall situation in 1958 when a debris flow occurred in the same area. The rainfall data were obtained from rain gauges of the Czech Hydrometeorological Institute. Four rain gauges were chosen close to the Smědavská hora Mt. with data of daily amounts from 1983 to 2013 and 10-minute intensity or hourly amounts from the specific period. The data from 1958 were available from three different rain gauges (only daily amounts). The data series were not complete so linear regression was applied to interpolate them. A number of analyses were carried out including daily rainfall, two-day/three-day moving values, antecedent precipitation index (API) of 5/10/30 days, 10-minute intensity, hourly amounts, etc., and the trigger factor of the debris flow in the study area was also investigated. It was determined that for the triggering of debris flows both high API values as well as high intensity-short duration rainfall is needed. It was documented that in cases of solely high API indices or high intensity-short duration rainfalls no debris flows were initiated.