The New Experimental Research For Sharp-crested Weir Formula

Flood disaster is one of the most serious natural disasters in the world,and it is often distributed in areas with a dense population,high degree of agricultural reclamation,concentrated distribution of rivers and lakes and abundant rainfall,such as warm temperate zone of the Northern Hemisphere and subtropical zone.China and Bangladesh are the areas in which flood occurs most frequently in the world,and the situations of flood disaster in America,Japan,India and Europe are also relatively serious.China has a vast territory,complex terrain and a significant monsoon climate,and it is one of the countries in which flood occurs frequently and affects widely in the world.About 35% of arable land,40% of population and 70% of industrial and agricultural production all over the country are threatened by the river flood,and the property loss due to flood disaster ranks first among various disasters.From the perspective of generative mechanism of flood disaster,it has the characteristics of obvious seasonality,regionality and repeatability.Generally speaking,the flood disaster in our country occurs during April to September.During the flood disaster in July 2016,1192 counties of 26 provinces(autonomous regions and municipalities)were threatened by the flood disaster,the affected area of crops was about 2.942 million hectares,the flood-hit population was 32.82 million and 1.48 million people were relocated.186 people were died and 45 were missing due to the disaster.56 thousand houses were collapsed,and the direct economic losses stood at about RMB 50.6 billion.It can be seen from the affected area that the urban area was hit particularly hard with the maximal direct economic losses.Therefore,urban flood protection is another important issue.In the modern urban flood control system,flood discharge measurement is extremely important and weir is a significant hydraulic structure for discharge measurement.Therefore,this thesis discusses the function of sharp-crested weir on the flood control,and emphasizes relative calculation formula of free fall flow sharp-crested weir.According to the problems existed in the previous calculation formula,based on the momentum theorem,we analyze the relationship between upstream head and critical head,Reynolds number and upstream head.And also combine with the least square method and figures as well as analysis of variance to get the new free fall flow formula.Finally we concludes that,from the perspective of calculation formula of flow coefficients,the applicability of the calculation formula of newtheory is higher than that of previous theory,therefore the latter is more adaptable for calculating the free outflow of sharp-crested weir under extreme atmosphere.