A New Method Of Calculation For The Hydrological Design To Small Bridge And Culvert Of Highway In Central Area Of Sichuan

Culvert and small bridge are the main part of high-grade highway such as expressway. Quickly and accurately hydrological design to culvert and small bridge is an important work for ensuring highway safety and reducing cost. Based on the observed runoff data, more accurate designed flow to a culvert or a small bridge may be obtained by curve fitting on frequency curve of Pearson type III distribution. However, it lacks runoff data in absolutely most areas where culvert and small bridge locate. Some traditional design method, such as the methods of statistic zone parameter, modification by catchment area, rainfall-runoff, reasoning formula and empiric equation et al, are used to estimate flood flow through culvert or bridge. With low precision, these methods are troublesome to calculation and give overestimation of flood flow so that waste money to culvert or bridge engineering occurs as overestimation of span for these engineering. Based on theory of water travel in catchment and reasoning formula, a new calculation model for flood flow design of culvert and small bridge in Sichuan hilly area where is no runoff data is derived in the paper. There are only four parameters i.e. C, e, b and Ap in the model. C, e and b relate to storm rainfall while Ap is correcting coefficient to design frequency. As a test place, contour charts of C, b and e in Sichuan hilly area, which area is 75000km2, are plotted as standard chart for flood flow design. Ap is rated by regression based on several regions where is longer runoff data. When catchment area, average channel gradient and catchment shape factor of designed culvert or bridge are known, a user can be convenient to get local parameters C, e and b from standard contour charts and easy to calculate flood flow just by a calculator. Design period of flood flow is enormously shortened as well as a high precision. Estimated flood flow through culvert or small bridge by new calculation model is generally less than by traditional methods, so that much cost is cut down as reducing the span ofculvert or small bridge.