Calculation Based On Curve Fitting Unit Hydrograph Both In Bridges Hydrological

There are a lot of middle-small-scale bridges in the railway and highway engineering. Many of these bridges are never installed with gauging station, and some rarely have flood marks on them, so it is difficult to get historical flood flow using morphological investigation method.Moreover, the maximum floods of some small watersheds mostly are formed by rainstorms, and these small watersheds have the features of abrupt slope, short flow concentration time, and floods rised up and down sharply. All of these features can easily cause dangers. Currently, the flood discharge capacity and the security of these bridges have already influenced the safety of the traffic and engineering. However, the flood calculation of the middle-small-scale bridges in watersheds without flow data is one of the difficulties in forecasting water disaster. A curve fitting unit hydrograph method was put forward in this article on the basis of traditional unit hydrograph method. Based on the observed water levels and the rainfalls in history, a more precise fitted curve of time-and-level is fixed by this method.Then the crest stage and flood concentration time can be got through the fitted curve of time-and-level.So it makes reasonable arrangements of flood fighting as well as emergency treatments for some dangerous bridges before flood comes possible.It has great significance to guarantee the vehicle's traveling safety so as to achieve great victory in the fight against floods.In previous methods, only the least square method of time-and-flow or time-and-level was studied. Thus,the time-and-flow or time-and-level results were not continuous.Problems such as large time-interval and the probability of missing the crest stage still exist, and they can have a great influence on water hazard prewarning. This article has presented a curve fitting method to fix functional curve, which is a clear concept of unit hydrograph method.Using the functional curve to predict the crest stage and flood concentration time would be more effective.This is meaningful for the water hazard prewarning.The forecasting method presented in this paper can greatly reduce the workload of field reconnaissance and make the flood prediction of middle-small-scale bridges easier and more effective.Especially, it offers practical applied value to the hydrological forecasting of those watersheds without data.