【作者】 王雪；

【导师】 宋孝玉； 李怀有；

【作者基本信息】 西安理工大学 ， 土木水利（专业学位）， 2025， 硕士

【摘要】 自1999年开展退耕还林还草、封山禁牧工程措施以来,黄土高原沟壑区植被条件改善明显,加之极端气候增多的影响,该地区径流量显著减少,部分小流域暴雨洪水灾害严重。因此探究典型流域产汇流特征对气候和下垫面条件变化的响应规律可为流域治理、水资源有效管理和洪水灾害防御提供科学依据。本文以黄土高原沟壑区南小河沟流域为研究区域,基于流域下垫面遥感影像数据及降雨洪水资料,采用数理统计学方法和ArcGIS分析流域下垫面和降雨特征的时空变化特征,结合水文学原理和流域产汇流理论对基准期和变化期黄土高原沟壑区典型场次降雨洪水的产汇流特征值及产流模式进行辨析,根据流域特征构建HEC-HMS模型,验证其在黄土高原沟壑区的适用性,并运用模型探究基准期、变化期和未来土地利用条件下流域设计暴雨洪水的产汇流特征对降雨和下垫面条件变化的响应规律,主要研究结果如下:(1)1980—2020年南小河沟流域土地利用类型主要以耕地和草地为主,其面积占比为78.41%-84.30%,各类土地利用面积变化主要表现为耕地和林地分别减少了1.72km~2,0.41km~2,草地和建设用地分别增加了0.04km~2,1.96km~2,耕地减少部分主要转向了草地和建设用地,林地减少部分主要转向了草地。1986—2022年流域植被覆盖度时间上呈上升趋势,空间分布上呈现东北低西南高的特征,主要以中高等和高等为主,其面积占比最大为67.69%,出现在2021年,从1986年到2022年FVC改善区面积达55%,径流深与植被覆盖度呈负相关关系,植被覆盖度增加会增大降雨损失量,导致径流深减少。(2)1981—2022年流域汛期降雨量和次降雨量上升趋势均不显著,分别以每年1.27mm,0.06mm的速率上升,空间上分布不均匀;汛期径流深和次径流深呈下降趋势,分别以每年0.61mm,0.04mm的速率下降,其中,汛期径流深趋势显著,发生突变的年份为2002年。年最大洪峰流量和洪量呈下降趋势,最大雨强与洪峰流量、降雨量与洪量的相关性较好,相关系数分别为0.613,0.467,相似最大雨强条件下,洪峰流量衰减率在54.25%-95.12%之间,衰减率均值为71.92%,当雨强为4-8mm/h时,衰减率在80%以上;相似降雨量条件下,洪量衰减率在48.29%-92.22%之间,衰减率均值为67.57%,当降雨量大于30mm时,洪量衰减率达80%以上。土地利用类型之间的转换和植被覆盖度的增加会影响产汇流过程,导致洪峰和洪量衰减。(3)流域典型场次洪水对应的降雨以大雨和暴雨为主,占比达85.7%,变化期降雨量、降雨历时、平均雨强、最大雨强、洪水历时、峰现时间和前期影响雨量均值较基准期增大,其中峰现时间和洪水历时增加最为明显,增长率分别达225.94%和153.93%,而径流深均值减小。基于流域产汇流特征值、洪水过程线及退水曲线判别典型场次洪水的产流模式,从基准期到变化期超渗产流占比由61.90%降至28.57%,蓄满和混合产流占比分别由23.81%和14.29%上升至33.33%、38.10%,但整个时期仍以超渗产流为主,其占比为45.24%。在此基础上结合产流模式判别指标体系综合辨析表明,基准期南小河沟流域呈现超渗产流为主导的混合产流模式,在变化期主要以混合产流为主,下垫面条件对径流深减少的贡献率达71.71%,是产流模式发生变化的主要因素。(4)构建研究区HEC-HMS模型进行场次洪水模拟,合格率达90%,10场洪水中有9场洪水的确定性系数在0.7以上,其洪峰流量相对误差小于11%,径流深相对误差小于12%,峰现时间差不超过2h,模型精度可达乙级,该模型可用于黄土高原沟壑区典型小流域场次洪水模拟。采用适线法推求基准期和变化期5年、10年、20年和50年一遇的设计暴雨过程,结果显示,重现期越小,设计暴雨量越小,在相同重现期内,变化期的设计暴雨量均大于基准期。运用模型模拟基准期、变化期和未来利用条件下流域设计暴雨洪水过程,结果表明,基准期洪峰和洪量较变化期分别减小了47.52%-128.74%,52.26%-263.16%,峰现时间增加了47.92%-364.91%,流域下垫面变化会消减洪峰流量,减小径流深,延长峰现时间。在未来建设用地面积增加,林草植被面积减少条件下,流域径流深会有所增加,但同时洪峰流量也会升高,且峰现时间前移。更多还原

【Abstract】 Since the implementation of engineering measures such as the"Conversion of Cropland to Forest and Grassland"project and the"Closing Hillsides to Facilitate Afforestation and Ban Grazing"initiative in 1999,there has been a marked improvement in vegetation conditions in the gully regions of the Loess Plateau.Coupled with the impact of increasing extreme weather events,runoff in this area has decreased significantly,and some small watersheds have experienced severe rainstorm-induced flood disasters.Therefore,exploring the response laws of the generation and convergence characteristics of typical river basins to changes in climate and underlying surface conditions can provide a scientific basis for river basin governance,effective water resources management and flood disaster prevention.This paper takes the Nanxiaohegou watershed in the gully region of the Loess Plateau as the study area.Based on the remote sensing image data of the underlying surface of the basin and the rainfall and flood data,mathematical statistics methods and ArcGIS are used to analyze the spatio-temporal variation characteristics of the underlying surface and rainfall characteristics of the basin.Using hydrological principles and basin runoff theory,we discern the characteristic values and runoff generation patterns of typical rainfall-flood events in the Loess Plateau gully region during baseline and variation periods.The HEC-HMS model was constructed based on the basin characteristics to verify its applicability in the gully area of the Loess Plateau.The model was used to explore the response laws of the generation and convergence characteristics of rainstorm and flood in the basin design under the base period,variation period and future land use conditions to the changes of rainfall and underlying surface conditions.The main research results are as follows:(1)From 1980 to 2020,cultivated land and grassland were the dominant land use types in the Nanxiaohegou watershed,accounting for 78.41%-84.30%of the total area.The changes in land use areas were primarily characterized by a decrease of 1.72 km~2 in cultivated land and 0.41km~2 in woodland,while grassland and construction land increased by 0.04 km~2 and 1.96 km~2,respectively.The reduction in cultivated land was mainly converted into grassland and construction land,and the decrease in woodland was predominantly transformed into grassland.From 1986 to 2022,the vegetation coverage in the basin showed an upward trend in time.In terms of spatial distribution,it presented the characteristics of low in the northeast and high in the southwest,mainly medium and high levels.Its area proportion was the largest,reaching67.69%,which occurred in 2021.From 1986 to 2022,the area of the FVC improvement zone reached 55%.The depth of runoff was negatively correlated with the vegetation coverage.An increase in vegetation coverage will increase the amount of rainfall loss,resulting in a reduction in runoff depth.(2)From 1981 to 2022,the upward trends of rainfall during the flood season and secondary rainfall in the basin were not significant.They increased at rates of 1.27mm and 0.06mm respectively per year,and the spatial distribution was uneven.The runoff depth and secondary runoff depth during the flood season showed a downward trend,decreasing at rates of 0.61mm and 0.04mm per year respectively.Among them,the trend of runoff depth during the flood season was significant,and the year with the sudden change was 2002.The annual maximum peak flood flow and flood volume show a downward trend.The correlations between the maximum rain intensity and the peak flood flow,as well as between the rainfall and the flood volume,are good,with the correlation coefficients being 0.613 and 0.467 respectively.Under similar maximum rain intensity conditions,the attenuation rate of the peak flood flow is between 54.25%and 95.12%,and the average attenuation rate is 71.92%.When the rain intensity is 4-8mm/h,The attenuation rate is above 80%.Under similar rainfall conditions,the attenuation rate of flood volume ranges from 48.29%to 92.22%,with an average attenuation rate of 67.57%.When the rainfall is greater than 30mm,the attenuation rate of flood volume reaches more than 80%.The conversion between land use types and the increase in vegetation coverage will affect the confluence process,resulting in the attenuation of flood peaks and flood volumes.(3)The rainfall corresponding to typical flood events in the basin was mainly heavy rain and torrential rain,accounting for 85.7%.The average rainfall during the variation period,rainfall duration,average rainfall intensity,maximum rainfall intensity,flood duration,peak-occurrence time and the average rainfall affected in the early stage increased compared with the base period.Among them,the peak-occurrence time and flood duration increased most significantly,with growth rates reaching 225.94%and 153.93%respectively.However,the mean depth of runoff decreases.Based on the characteristic values of runoff generation and convergence in the basin,the flood process line and the drainage curve,the runoff generation patterns of typical flood events were identified.From the base period to the variation period,the proportion of superpermeation runoff decreased from 61.90%to 28.57%,while the proportions of storage and mixed runoff increased from 23.81%and 14.29%to 33.33%and 38.10%respectively.However,during the entire period,superosmotic flow production was still dominant,accounting for 45.24%.Based on this,a comprehensive analysis combined with the index system for discriminating runoff generation patterns shows that during the base period,the Nanxiaohegou Basin presented a mixed runoff generation pattern dominated by superosmotic runoff generation.During the change period,it was mainly mixed runoff generation.The contribution rate of the underlying surface conditions to the reduction of runoff depth reached 71.71%,which was the main factor for the change in the runoff generation pattern.(4)Constructing the HEC-HMS model for flood simulation in the research area,with a pass rate of 90%,9 out of 10 floods have a certainty coefficient of 0.7 or above,a relative error of less than 11%for peak flow rate,less than 12%for runoff depth,and a peak appearance time difference of no more than 2 hours.The model accuracy can reach level B.This model can be used for simulating floods in typical small watersheds in the gully region of the Loess Plateau.The line fitting method is used to calculate the design rainstorm process with 5-year,10-year,20-year and 50-year return periods.The results show that the smaller the return period,the smaller the design rainstorm volume.In the same return period,the design rainstorm volume in the change period is greater than the reference period.The model is used to simulate the basin design rainstorm flood process under the base period,change period and future utilization conditions.The results show that the peak and flood volume in the base period are reduced by 47.52%-128.74%,52.26%-263.16%respectively compared with the change period,and the peak time increases by 47.92%-364.91%.The change of the underlying surface of the basin will reduce the peak flow,reduce the runoff depth,and extend the peak time.Under the conditions of increasing construction land area and decreasing forest and grass vegetation area in the future,the runoff depth of the watershed will increase,but at the same time,the peak flow will also increase,and the peak time will move forward.更多还原