Experimental Study On Runoff-producing And Flow Concentration Characteristics Of Typical Underlying Surface In Handan

Based on the rainfall runoff test site of Hebei University of Engineering as the experimental base,according to the rainfall and daily rainfall data at the Linmingguan hydrological station in Handan for 11 years,the rainfall characteristics of Handan were analyzed,and the long-term,short-duration,long-term rainfall data from Handan collected at various rainfall stations were used as the design basis for artificial rainfall simulation.Through fitting the water level flow relationship of different specifications of thin wall triangle weir through the runoff test field,we can know that the relation formula of the water level flow of the simulated river and the middle flow soil 1 is:f?x?=0.0045136h^2.3968,R2=0.99;the relation formula of the water level and flow of the surface runoff is:f?x?=0.00784h^2.2845,R2=0.99,and the relation formula of the water level and flow of the middle flow soil 2 is:f?x?=0.01562h^2.1545,R2=0.99,water and flow relation of the formula has great significance for calculating runoff and runoff coefficient of each soil layer.First,the confluence characteristics of typical underlying surfaces are analyzed.Through three kinds of actual rainfall intensity of 0.35mm/min,0.68mm/min and1.52mm/min,the flow rate of surface runoff was changed from small to constant,and the influence of rain intensity on the water curve of surface runoff was studied.It is found that rainfall intensity has little effect on the duration of water withdrawal,and has great influence on runoff generation time and runoff collection time.With the increase of rainfall intensity,the gathering time decreases and the runoff time increases.The influence of rainfall duration on runoff coefficient is studied.When rainfall duration is 45min,55min,85min,120min and 180min,rainfall intensity is designed to be 0.5mm/min.It is found that the runoff coefficient increases with the increase of rainfall duration.The polynomial regression analysis is made for rainfall duration and runoff coefficient,and the fitting formula is y=-5E-06x²+0.0019x+0.2581,R²=0.9968.The influence of rainfall intensity on runoff coefficient is studied.The duration of rainfall is 67min.When the actual rain intensity range is 0.35mm/min¹.52mm/min,the fluctuation range of runoff coefficient is 0.31⁰.54.The rainstorm intensity and runoff coefficient are polynomial regression analysis,and the fitting formula is y=-0.0769x²+0.3389x+0.202,R²=0.9989.Secondly,sampling different soil layers of typical underlying surface with soil ring knife,the actual volume water content of different soil layers was measured by drying method,and compared with the soil moisture data of rainfall runoff test site,the ratio of conversion coefficient between measured value and monitoring value was defined,and the conversion coefficients of different monitoring layers were 1,1.03,1.02,0.87,1.27 and 1.26 respectively.Finally,based on the layering design of the typical underlying surface of the rainfall runoff experimental field,the water balance is analyzed and calculated.When the design rainfall is 106min and the actual rainfall intensity is 57.6mm/h,the actual rainfall is 78.36m³,the total amount of runoff is 41.50m³,and the total volume change of soil water volume is 35.81m³,and the total amount of evaporation is about 0.27m³.Then the amount of water filling and the other losses are about 0.78m³.The amount of runoff accounted for 52.96%of the total rainfall,and the increase of soil water accounted for 45.70%of the total rainfall,and the evapotranspiration and the amount of loss accounted for 1.34%of the total rainfall.The runoff coefficient of the typical rainfall experiment is 0.45,and the formula of water balance is basically established,conforming to the tentative plan of the test.