The paper shows in detail the case of delineation of risk area in the village of Log pod Mangartom in the Koritnica River valley due to possible debris flows that might in future be triggered on the Stoze slope above the Mangart Mountain pasture. On the basis of field and laboratory investigations of the debris flow of November 17, 2000, that devastated the Koritnica River valley, the possible scenarios of triggering new debris flows on the Stoze slope were investigated. For the determination of debris flow hazard area in the Koritnica River valley, the results of one- and two-dimensional modelling of selected debris flows of known magnitudes and different viscosities were applied. For the determination of risk area, the existing and the possible new infrastructures were taken into account, and the risk area was divided into 3 zones. The paper presents the expert bases summarised by the legislator in the relevant decree issued by the Government of the Republic of Slovenia on the conditions and limitations governing the construction in the debris-flow risk area of Log pod Mangartom. This regulation is the first of its kind in Slovenia.