Determination of peak design flows of highway bridges and culverts with geographical information systems

Today, geographic information systems (GIS) are an integral part of hydrological basin modeling. Hydrological parameters such as the drainage area and drainage network of the basin, soil structure and vegetation, average slope, concentration time, etc. can be determined more quickly and accurately using GIS programs. These hydrological parameters are then used as inputs in hydrological modeling programs to obtain peak flow rates used in the design of engineering structures. In this study, by using the Python programming language, a plug-in called QSCS was developed for an open-source GIS software QGIS, which allows the automatic determination of the hydrological characteristics of any basin. QSCS, which basically delineates the basin according to a certain outlet point with the curve number data set and elevation raster selected as input, prepares a template for the hydrological simulation program called HEC-HMS after running some algorithms. Using this plugin, the characteristics of two different basins with form factors of 0.15 and 0.36 were determined. These determined features were transferred to the HEC-HMS program and the peak flow rates observed at both basin outlets were estimated as 20.1 and 38.2 m3/s, respectively. In addition, a culvert were planned at the exit of one of the basins in order to give a practical aspect to the thesis study. In this context, a design was made with the HY-8 computer program and it was decided to choose a box culvert with 3x3 dimensions. As a result of the study, it was seen that it is extremely important to divide the basins into sub-basins appropriately in the correct estimation of the peak flow rates. It was observed that the sub-basins selected in very small sizes predicted the peak flow approximately twice as wrong. However, it was seen that choosing the basin area too large increased the calculation time in an impractical way. In addition, in a basin that is divided into many sub-catchments, it has been seen that a flow routing method whose parameters are chosen mostly based on previous observations should be selected and applied correctly.