Flash flood mitigation modeling — case study small Carpathians

Flash floods are becoming a phenomenon that troubles people more and more often in many Slovak under-mountain regions and society needs to deal with these extreme natural events. This article is showing an example of mathematical modeling of flood protection measures in Small Carpathians region. To secure flood protection, detention reservoirs have been proposed, because of their automatic function that is important due to rapid progress of flash floods. As a base for this project a previous work that attempted to reconstruct the flood has been used. HEC-RAS 4.1.0 software package was used for numerical modeling, which includes flood mitigation calculation. Six variants of proposed detention reservoirs were created and checked by a design flood wave that was created according to rainfall with recurrence period of 100 years. All of the proposed detention reservoirs have exact proportions needed to secure flood protection including height of the dam, length of the dam in crest, type and dimension of outlet and dimensions of emergency spillways. The modeling included flood wave passing during several situations - normal function of detention reservoirs, blocked outlet and dam break. This study should be considered as a base for future flood protection project. An extensive terrain survey has been performed in frame of this project