Analysis Of Hydrologic Frequency In The Halaqin Small Catchment Based On Inconsistency And Characteristic Parameter Verification For Halaqin Reservoir

Climate change and human activities have been influencing catchment hydrological characteristics to some extent in the most continental areas on the earth.Especially some projects constructed in the catchments like dams,water and soil conservancy constructions have significantly impacted catchment hydrological characteristics.The consistency of the natural hydrological time series in the catchments has been affected to different degrees.As a result,the hydrologic characteristics calculated by the traditional hydrologic frequency analysis methods could not reflect the hydrologic regulations.Design flood calculation and reservoir routing with respect to the changing environment have more and more been focused on in recent years.Halaqin Reservoir was built in 2002 based on the hydrologic series data that had been observed since 1956.Since then,the hydrological underlying surface conditions in the upper reaches of the reservoir have changed significantly.Whether the designed reservoir characteristic parameters could be safely used for the reservoir management has been becoming one of the key issues.It is urgent to carry out engineering hydrologic calculation and analysis to verify the characteristic parameters.The field investigation in the catchment was carried and the current operation situation of the reservoir was analyzed.The hydrological data series was extended to 2016.The process line method,moving average method,and the Hurst coefficient method were applied to analyze the hydrological sequence inconsistency and diagnose its change point.The results showed that the hydrological sequences represented jumping mutation.The optimum fitting distribution of the hydrological sequences was determined according to ABS,OLS,and WLS criteria.The flood hydrograph and the flood design characteristic parameters with inconsistency were worked out through the same frequency amplification method.Compared with the designed parameters in 2002 the and traditional P-? distributions synthesis that did not involve the variation,there were significant differences between them.As a result of this,the flood regulation calculation of inlet flood with inconsistency was carried out.The reservoir characteristic parameters of under the variation conditions was determined.This would provide guidance for the management and operation of Halaqin Reservoir.The main results are as follows:(1)The hydrological sequence of Halaqin Reservoir presented jumping variation.The variation points of annual flood peak occurred in 2003.The variation points of annual inlet,annual maximum 1d flood,annual maximum 3d flood,and annual maximum 7d flood were all occurred in 1962.(2)The reservoir design flood peak and 1d maximum inlet flood by optimum fitting distribution with inconsistency were about 30%-40%and 40%less than that designed in 2002 respectively.The reservoir design flood peak and Id maximum inlet flood by optimum fitting distribution with inconsistency were 31%and 26%less than that determined by P-? Curve which did not involve the variations.(3)Under the influence of the change of the underlying surface in the catchment,the inlet flood peak by the inconsistency optimal distribution method was slightly less than that of the designed,but its stagger time was somewhat longer.The suggested results of the reservoir characteristic parameters by hydrologic frequency analysis with inconsistency were that the top level of flood control,design level of flood,and check flood level were 0.4m,2.41m and 3.02m respectively lower than that of the designed ones.