Sadašnji propis o određivanju posljedica u slučaju rušenja velikih brana izrađen je 1975. godine. U međuvremenu je došlo do novih spoznaja o mehanizmima formiranja otvora u  nasutim branama i značajnog napretka u metodama modeliranja rušenja brane  i propagacije poplavnog vala.  Trenutno se ulažu veliki napori u izradu novog pravilnika koji će osigurati realnije opisivanje mehanizama rušenja brane, propagacije poplavnog vala i štete koje takav događaj može izazvati, radi povećanja sigurnosti brana i racionalnijeg iskorištavanja zemljišta u plavljenom području. U ovom su radu prikazane neke novosti vezane za modeliranje poplavnog vala predložene za novi pravilnik te zapažanja proistekla analizom rezultata u modeliranju propagacije poplavnog vala na primjeru modeliranja rušenja retencije Lipovečka gradna. Opisani su rezultati modeliranja prve faze rušenja brane i vjerojatnost ispiranja nizvodne – potporne zone. Izračunat je utjecaj brzine formiranja otvora i njegove veličine na hidrauličke parametre poplavnog vala..; The existing regulation on the determination of consequences in case of a large dam breach was developed in 1975. In the meantime, new insights have been gained into the mechanisms of formation of openings in earthen dams while methods of modelling of dam breaches and floodwave propagation have been significant advanced.  At present, great efforts are being made on the development of the new regulation which should ensure a more realistic description of the dam breach mechanism, floodwave propagation and damages that such event can cause, which are aimed at improving dam safety and at a more rational land use in the flooded area. This paper presents some novelties related to flood wave modelling proposed in the new regulation as well as observations derived from the analysis of results of floodwave propagation modelling as exemplified by the modelling of a breach in the retention storage Lipovečka gradna. The results of modelling for the first phase of dam breach are described as well as the probability of washing out of the downstream retention zone. The impacts of how quickly the opening is formed as well as its size on the hydraulic parameters of the flood wave have been calculated.