基于经验单位线的丰乐河流域洪水预报

Flood Forecasting of Fengle River Basin on Unit Hydrograph Method

摘要: 经验单位线法是洪水模拟与预报中推求地面净雨汇流过程常用的方法之一。以丰乐河流域为研究区域，基于该流域1984年至2013年的降雨、径流和蒸发资料，选取了30场洪水，采用三水源新安江模型进行次洪的产流与分水源计算，以地面径流与壤中流作为直接径流，利用经验单位线法和线性水库法分别模拟直接径流和地下径流的汇流过程，通过合成直接径流与地下径流，构建了丰乐河流域洪水模拟模型。以新安江模型计算的14场率定洪水的径流深与实测径流深平均误差最小化为目标，采用遗传算法确定了新安江模型的参数。采用分析与试错相结合的方法推求了直接径流的汇流经验单位线。采用大洪水推求的单位线(980915场次)对30场洪水进行模拟，得14场率定洪水的径流深平均相对误差为7%、平均洪峰误差为8%、平均峰现误差为2.57h，合格率分别为93%、93%和86%，平均确定性系数为0.91；16场检验洪水的径流深、洪峰和峰现的误差分别为8%、9%和3.38h，合格率分别为88%、94%和88%，平均确定性系数为0.89。表明基于新安江模型与经验单位线所构建的模型可用于该流域的洪水预报，计算精度较高。采用基于大洪水推求的单位线进行中小洪水汇流计算时的精度较低，反之亦然。推求了相应于大、中小洪水的经验单位线对大、中小洪水分别进行汇流计算，可获得较高的模拟精度。建议在该流域根据形成次洪的降水量的大小，采用不同的经验单位线对洪水进行预报，以提高预报精度。

Abstract: To calculate ground net rainfall runoff, unit hydrograph method is one of the common methods for flood simulation and prediction. Taking Fengle River basin as a study case, 30 floods were selected based on data of its rainfall, flow and evaporation from 1984 to 2013. The Xinanjiang model was used to calculate the runoff and the separate water sources. Considering surface runoff and interflow as the direct runoff, unit hydrograph and the linear reservoir methods were adopted to simulate the confluence process of the direct runoff and underground runoff respectively. Then flood forecasting model for Fengle River basin was established. With the goal of minimizing the average absolute error between the calculated runoff depths with Xinanjiang model and the observed runoff depths of 14 floods as calibrated samples, the genetic algorithm was adopted to calibrate the parameters of Xinanjiang model. The unit hydrograph of flood confluence of direct runoff was quantified by the method based on the combination of analytical and trial and error approaches. Then 30 floods were simulated with the unit hydrograph acquired through flood data of No. 980915. According to the results, the average relative error of the runoff depth, the error of average flood peak and the peak time of 14 calibrated floods are 7%, 8% and 2.57 h respectively, with the qualification rate are 93%, 93% and 86% respectively, and the average deterministic coefficient is 0.91. The error of the runoff depth, flood peak and the peak time of the 16 validated floods are 8%, 9% and 3.38 h respectively, with the qualification rate are 88%, 94% and 88% respectively, and the average deterministic coefficient is 0.89. Practical applications of the flood forecasting for Fengle River water- shed show that, the model based on the Xinanjiang model and the unit hydrograph can be used to forecast the flood occurred within the watershed, and reaches to a high accuracy. However, the accuracy of concentration calculation of small floods with the unit hydrograph acquired through big flood data usually is lower than those big floods, and vice versa. So unit hydrograph should be calibrated with different rainfall intensities, then using different unit hydrograph to forecast flood processes according to their corresponding precipitation amounts.