The Mapping of Floodplains With Four Probabilities of Exceeding and the Highlighting of Floodable Land Areas for the Bistrita Valley Middle Mountain Area, Between the Broșteni and Poiana Teiului Localities

Abstract

An ample flood risk mapping campaign has been carried out at a national level, at the suggestion of the European Union. Considering the fact that the project has been realized at a 1:25,000 scale and that 1,549 rivers were mapped, totalling to approximately 33.478 km of water course length, ANAR shows that the presented maps are of general interest, with an informative purpose that can help promote investing, (land) design, and more., etc. It is also noted that once every 6 years or whenever it is needed, the hazard maps and floodplains must be remade. Therefore, the present study aims to create new floodplains with the topographic numerical model of the current terrain, with a better resolution and a clearer emphasis on morphological details. The vector layers (the river valley, the minor bed, the major bed, the cross-sectional profiles and the land usage) required for flood simulations were created using the LIDAR topographic support (5 m pixel resolution) and satellite imagery from 2012. The programs that were used to create the vector layers and to simulate the flooding are: ArcGIS, Hec-Ras and Hec-Georas. The flooding simulation was realized for four occurrence probabilities: 1%, 2%, 5%, and 10%. To calculate the probabilities and to evaluate the hydrological regime of the Bistrita River, the flows and the daily levels from two stations located on the analysed river sector (upstream-Broșteni, the middle of the sector-Frumosu) were obtained from the Siret River Basin Administration, from the year 1968 until 2016. As a result of the intersection of the floodplains obtained with the land usage data, the land use categories that may be affected by floods were observed. The arable land, situated in the proximity of the minor river bed, in the slope sector favouring the practice of agriculture, represents the most vulnerable area for all the probabilities of exceeding. The total number of constructions that can be affected at a 1% probability is of 4.544, and at a 10% probability of 2.376. By comparing the intersected surfaces of the flood bands obtained from the ABA Siret with the current flood bands, significant differences can be observed regarding the number of affected constructions as well as regarding the other categories of use. For a more accurate estimation of the risk degree and of the possible damages caused by flooding, it was necessary to study in detail all the factors involved in the hydrological risk phenomenon. In order to best manage the emergencies arising because of the hydro-geomorphological phenomena, it is necessary to map out the floodplains after any major hydrological event that contributes to the changing of the current parameters.