Hydrological Frequency Calculation And Research Based On Genetic Algorithm

Chinese floods is mainly by storm floods,china was endangered by storm floods from year to year, Dam-break by storm floods were frequently occurs. In the 1970s of china, Storm floods cauce reservoirs of BanQiao and Shi ManTan dam-collapse, and the reason is the data of design flood is too low, so the design of flood is low. Reservoir flood control is one of purposes of hydro project construction, and the primary task is hydrological analysis; P-ⅢDistribution was used in rainfall frequency analysis in china, and the curve shape depends on the hydrological characteristic parameter: (x|-),C_v,C_s, the fiist thing of hydrology frequency calculation is to calculate the estimated value of (x|-),C_v,C_s, Traditional algorithm is directly using line fitting method or a single parameters estimation method(moment method,probability weighted moment method , etc.) to estimate parameters,then draw the P-ⅢDistribution curve of rainfall distribution. Traditional calculation methods have the advantage of the formula can be applied, but have drawbacks. For example, the moment method for third-order moments of the estimated C_s have a greater error; Probability weights moment method used only three first-order moments ,the sensitivity is not inadequate, etc.This paper studies the optimization of P-ⅢDistribution curve's three parameters based on Genetic Algorithm("GA" for short),Specific work is Application of GA in the hydrological frequency calculation. This paper also Collectes each of the largest 24-hour rainfall from 1966 to 2005 of DaRen Reservoir TengXian WuZhou Guangxi Zhuang Autonomous Region. Using P-Ⅲdistribution to Calculat the rainfall frequency curve, The first, using traditional methods(moment method,probability weighted moment method,single-weight function method and Double-Weights function method)to estimate the three parameters in advance,and then use GA to Optimal parameters. Use (x|-),C_v,C_s as decision variables of GA. According to the results of the traditional methods, Minimum value of (x|-) is 122.98, The Max is 125.94; Minimum value of C_v is 0.5, The Max is 0.6; Minimum value of C_s is 1.5, The Max is 2.5, After appropriate adjustments,the decision variables of GA is: C_v∈[ 0.4,0.6], C_s∈[1 .5,2.6], (x|-)∈[1 22.98,125.94].GA's Operator includes select operator,crossover operator and mutation operator, select the Roulette Wheel Selection,Single-point Crossover and Basic Bit Mutation. According to the experience, establish 12 groups operating parameters for program testing, Adjusting and defining the GA's operation parameters from the result figures, finally, operating GA. The result figures of 100-year design flood show that, the design flood which calculated by traditional method is not high accuracy, optimization of P-Ⅲdistribution three parameters by GA has more higher than that was calculated by Double-Weights function method. In addition, Compared to the recheck results of YuLin Water Resources and Hydropower Design Institute of GuangXi in 2005, the design flood that calculated by Design Institute is too large.