三峡库区喀斯特洼地小流域产沙强度WaTEM/SEDEM模拟——以巫山县常家洼洼地流域为例

Modeling sediment yield using WaTEM/SEDEM for a small catchment of karst depression in the Three Gorges Reservoir region:A case study of the Changjiawa depression catchment of Wushan county

三峡库区喀斯特广布,人类扰动强烈,石漠化问题日趋凸显,获取可靠的小流域产沙数据是认识石漠化过程的基本依据。以WaTEM/SEDEM模型模拟三峡库区典型喀斯特洼地流域即常家洼小流域的产沙强度,以^(137)Cs进行洼地沉积物定年得到流域产沙模数,用以模型参数校正,并用已报道喀斯特流域侵蚀产沙数据验证。结果表明:1963—2017年常家洼洼地流域产沙模数为122.91 t/(km^(2)·a);泥沙输移系数KTc最佳组合为18和7,此时有效系数c_(NS)达到峰值0.79;流域产沙模数和产沙量的模拟结果与实测值相关系数较高,分别为0.93和0.94,WaTEM/SEDEM模型模拟数据较为可靠。因此核示踪定年技术与WaTEM/SEDEM模型相结合获取峰丛洼地小流域侵蚀产沙强度,在缺乏监测数据的喀斯特地区有一定借鉴意义,未来对该地区的水土保持研究可选用WaTEM/SEDEM模型作为评估土壤侵蚀情况的有效工具。

[Background]In karst area,the soil formation rate is low,and soil layer is thin and shows great spatial heterogeneity.The Three Gorges Reservoir region is the ecological security barrier in the middle and upper reaches of the Yangtze River.Karst landscape is wide in this region.In general,the karst land has complex terrain,and is subjected to intensive human disturbance and increasing rocky desertification.Reliable data of specific sediment yield(SSY)from small catchment is essential to our understanding of the process of rocky desertification.[Methods]The WaTEM/SEDEM was used to analyze the effects of multiple factors on soil erosion,to simulate the interception of sediment by water bodies such as reservoirs,ponds,dams and river sections in the southwest karst area.The WaTEM/SEDEM model was used to assess the SSY of Changjiawa catchment,a typical karst depression catchment in the Three Gorges Reservoir region.The SSY was determined by ^(137)Cs dating to calibrate the model parameters and verified by the reported data of SSY from karst catchment.[Results]1)The sedimentation rate in the Changjiawa depression was 0.27 cm/a,and the SSY was 155 t/(km^(2)·a).The simulation results were corrected using the SSY determined by ^(137)Cs dating in the depression,and the optimal combination of the minimum and maximum K_(TC) values of WaTEM/SEDEM were 18 and 7,with the highest c_(NS)(Nash-Sutcliffe coefficient)of 0.79,it showed that the model simulation effect was the best.2)Using the WaTEM/SEDEM model,the total sediment deposition and SSY of Changjiawa small catchment since 1963 were 557 t and 122.91 t/(km^(2)·a),which was higher than that in most karst catchments,which was mainly related to the lithology of the basin and the intense human activities.3)WaTEM/SEDEM model simulation results were verified by published erosion and sediment modulus data.The correlation coefficients of the simulation results of SSY and sediment yield(SY)were 0.93 and 0.94,implying the simulated data reflected the actual erosion and sediment modulus situation in this area,and ^(137)Cs data had good correction effect on WaTEM/SEDEM model parameters.[Conclusions]The combination of nuclear tracer dating technology and the WaTEM/SEDEM model may produce reliable SSY from small catchment of peak cluster depression,which is useful in karst areas lacking monitoring data.In the future,the WaTEM/SEDEM model may be used to assess sediment yield at the scale of depression catchment in this region.