Hydrological analysis of floods for the Savinja River watershed

Najrazličnejše poplave predstavljajo tako v Sloveniji, kot tudi drugod po svetu eno izmed hujših naravnih nesreč. Povzročajo ogromno škode in ogrožajo življenja številnih ljudi. V zadnjih nekaj letih ponovno opažamo porast trenda poplav. To gre večinoma na račun sprememb podnebja, kar se odraža v spremembah pretokov rek in pretočnih režimih. S svojo nepremišljeno gradnjo in urbanizacijo pa je velikokrat za škodo ob poplavah kriv človek sam. Poplava je namreč naravni pojav, ki predstavlja nevarnost in tveganje le ob bližnji prisotnosti človeka. Izredni pomen ima tako spremljanje in opozarjanje pred poplavami, s čimer lahko ljudi pripravimo na najhujše in s tem bistveno zmanjšamo njihovo ogroženost in povzročeno škodo. Da pa je opozarjanje čim boljše in pravočasno je potrebno poplave natančno analizirati in ugotoviti povezave med padavinami, odtokom in pretokom v strugi vodotoka. To je bil tudi glavni cilj magistrske naloge. In sicer smo analizirali večje poplavne dogodke ter ekstremne pretoke na porečju Savinje. Porečje Savinje velja zaradi relativno velike poseljenosti poplavnih območij za bolj problematično v Sloveniji. Izrazit hudourniški značaj reke Savinje in njenih pritokov pa problematiko poplavljanja na tem območju le še povečuje. Močnejše padavine povzročijo izredno hitre poraste pretokov. Do razlivanja vodotokov lahko pride v zelo kratkem času od nastopa padavin praktično na celotnem območju porečja. Najbolj problematični sta mesti Celje in Laško ter manjši kraji v zgornjem delu porečja, kjer pridejo do izraza tudi manjši hudourniški vodotoki. V analizah smo ugotovili, da poplave povzročijo predvsem močne in intenzivne padavine. Velik vpliv ima tudi predhodna namočenost, ki močno zmanjša sposobnost zadrževanja padavin na porečju in s tem poveča površinski odtok padavin. Trajanje poplavnih valov je kratko. Konica je običajno dosežena znotraj enega dne ali še prej. Preko analiz mesečnih ekstremov je bilo tudi ugotovljeno, da lahko največ poplavnih dogodkov pričakujemo v mesecih novembru in septembru.Various flooding present one of the most severe natural disasters in Slovenia and all over the world. Floods can cause a huge material damage and are a threat to many human lives. In recent years we have witnessed increasing trends in flooding. Most of them are the result of climate variability, which is reflected also in discharge and flow regimes changes. Humans can also be the guilty part of it, with reckless building and urbanization in flooding areas. Flooding is a natural phenomenon, which represent a danger and risk only if it’s close to the population. Monitoring and alerting before the flooding have a significant impact, as with it we can prepare people for the worst and minimize the threat and damage. In order to achieve alerting as precise as possible and timely, the floods have to be accurately analyzed and the connections between rainfall, discharge and runoff in the watershed have to be determined. This was also the main aim of this master thesis. We analyzed larger flood events and extreme flows of the Savinja River basin. Because of dense populations of the flood area the watershed of the Savinja River is one of the most problematic watersheds in Slovenia. Prevailing torrent character of the Savinjaa River and its tributaries increasing the flooding issues in this area. Heavy rainfall can cause incredibly fast increase in flow. The overflow can be very shortly after the rainfall practically all over the watershed. The most problematic places are towns of Celje and Laško, and some smaller towns and villages in the upper part of the watershed, where smaller torrents come to an expression. Analysis showed that flooding is caused mainly by heavy rainfall. Great influence has also antecedent soil moisture, which greatly decreases the ability of retention of the rainfall in the watershed and with it increases the runoff. The duration of the flood waves is short. The peak discharge is usually achieved in the timeframe of a day or even earlier. Analysis of the monthly extremes showed that flood events can be expected mostly in months of November and September