黄土丘陵沟壑区有无水保措施对NRCS-CN模型参数的影响研究

对水土流失区进行综合治理的同时改变了流域水分循环,为了进行水土保持措施对流域产流规律的影响研究,利用王家沟对比观测小流域的降雨径流资料,将降雨划分为A、B、C、D、E 5种类型,采用NRCS-CN模型进行径流模拟,确定出两个流域不同雨型相应的参数取值。结果表明:进行流域综合治理后模型参数取值总体减小,羊道沟初损率值介于0.05~0.2,CN值介于40.72~92.00;插财主沟初损率适宜取值为0.01,CN值的取值范围集中在20~50。插财主沟中B和E型降雨径流深减少率与CN值减少率呈正相关关系,与初损率减少率呈负相关关系,A和D型降雨则呈相反规律,但C型降雨无此规律。

Incorporating a rainfall intensity modification factorγinto the I a-S Relationship in the NRCS-CN method

The Natural Resources Conservation Service runoff curve number(NRCS-CN)method is widely used to simulate direct runoff,but the impact of rainfall intensity has not been considered.In this study,a rainfall intensity modification factor(γ)was incorporated into the Ia-S relationship of the NRCS-CN method,and the modified method(NRCS-CN-γ)was compared with the NRCS-CN method withλ=0.2 andλ=0.05 in three watersheds of the Walnut Gulch Experimental Watershed(WGEW).The results showed that for 2016-2018 period,the simulation performance of the NRCS-CN-γmethod was close to the NRCS-CN(λ=0.05)method and better than the NRCS-CN(λ=0.2)method.When the new data(2009 data with high variance)was added,the significant improvement was observed by NRCS-CN-γmethod with all the evaluation parameters being the best in the three watersheds,indicating a more adapted capa-bility of the modified method with highly uneven rainfall intensities.The covariance between rainfall intensity and the simulated runoff were 19.01,15.14,and 16.35 for the three methods,respectively.When the optimal CN changed,the relative errors representing CN sensitivity were 6.25,6.49 and 17.39 for the methods,respectively.It is suggested that the NRCS-CN-γmethod outperformed the other two methods and could contribute to a more accurate estimation of direct runoff where rainfall intensity greatly varied,especially in monsoon region or under the context of climate change.

An improved method that incorporates the estimated runoff for peak discharge prediction on the Chinese Loess Plateau

An accurate prediction of peak discharge in watersheds is critical not only for water resource manage-ment,but also for understanding the complex relationships of hydrological processes.In this study,a modified peak discharge formula based on the Chemicals,Runoff,and Erosion from Agricultural Man-agement Systems(CREAMS)model was developed by introducing rainfall intensity and soil moisture factors.The reliability of the proposed method was tested with data from 1464 storm events in 41 watersheds and was applied to 256 storm events in five remaining typical watersheds using the opti-mized parameters.The results indicate that the proposed method is highly accurate in terms of model efficiency,as determined by Nash-Sutcliffe efficiencies(NSEs)of 88.60%,74.04%,and 90.12%during the calibration,validation,and application cases,respectively.Furthermore,it performed better than the original and modified CREAMS methods.Subsequently,using the parameters derived from the initial 41 watersheds and the runoff estimated using the modified Soil Conservation Service curve number(SCS-CN)method,the proposed method was used to predict the peak discharge from the last five typical watersheds.Large NSE(63.88-80.83%)and low root mean square error(RMSE)values(0.31-35.93 m^(3)s^(-1))were obtained for the five watersheds.Overall,the proposed peak discharge model,combined with the modified SCS-CN method,may accurately predict event-based peak discharge and runoff for general applications under various hydrological and geomorphic conditions in the Loess Plateau region.