Risk analysis of the Vidaa River System
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The main goal of this hydraulic study is the asses of flooding in the Vidaa River system. In order to realize a complete assessment, the main water contributions to the river system have been included in the flood analysis. Three kind of software have been used: • Flooding simulation (MIKE11). • Stochastic weather generator (RainSim). • Extreme value analysis (EVA tool from MIKE11). Mike11 offers the possibility of based upon twenty years observed rainfall data (main head catchments) and water levels data of the Vidaa River mouth dam, setting up a model to auto calibrate and evaluate the Manning Coefficients (M) and the water levels around the Vidaa course. To estimate flood, stochastic weather generator is going to be used. Through observed rainfall time series, RainSim will analyse, fit, and simulate to obtain synthetic rainfalls time series with different time periods. These time series will have the same characteristics as observed rainfall data (the precipitation occurrence process will be exactly the same). The synthetic rainfall time series, and the auto calibrated Manning values will be introduce in the flood model as a new Boundary Conditions to simulate our river and extract a new water level time series for each rainfall time period. Thanks to these new water levels time series, and using the Extreme Value Analysis (EVA) tool from MIKE11, an engineer can obtain the extreme events for different return periods (10, 25, 50, 100, 200, 500 years) and evaluate if floods in order to get the higher and more dangerous data from our system. Return periods of 50, 100, and 200 years have been used to simulate floods in three different point along Vidaa River (WL1 – Upstream, WL4-Middle stream, and WL5-Downstream) The results show that Tønder (WL1, the biggest town in the area) will be safe from extreme flood events. In the Middle- and Down- Stream, the flow will exceed Vidaa River banks, flooding surrounding farm lands.