澜沧江糯扎渡水库消落带土壤侵蚀特征研究

Study on soil erosion characteristics of water level fluctuating zone in the Nuozhadu Reservoir,Lancang River

澜沧江干流梯级水电开发形成大面积的水库消落带,该区土壤侵蚀极其严重,对水库安全运行构成严重威胁.文章利用ArcGIS空间分析功能,结合遥感影像判识、野外调查及侵蚀针技术等,查明澜沧江流域规模最大的糯扎渡水库消落带空间分布特征和土壤侵蚀过程的关键驱动因子.结果表明:(1)糯扎渡水库消落带总面积129.95 km^(2),其中干流57.29 km^(2)、支流72.66 km^(2);消落带面积随高程的降低逐渐减小;不同坡度消落带面积分布不均,15°~25°坡度上分布最广,大于35°的急陡边坡分布最少.(2)糯扎渡水库消落带土壤侵蚀营力多样,最常见的侵蚀形式为涌浪侵蚀和崩塌,涌浪侵蚀是消落带特有的水力侵蚀形式.(3)糯扎渡水库消落带土壤侵蚀异常强烈.2016—2018年干流消落带平均土壤侵蚀速率38.50 mm/a,而库湾平均土壤侵蚀速率17.00 mm/a,干流消落带土壤侵蚀速率是库湾的2.30倍.(4)消落带坡度、植被和土壤水分变化对土壤侵蚀的影响显著.坡度与消落带年均侵蚀深度呈现显著的线性相关;植被可以减缓消落带土壤侵蚀;随着土壤含水率的增加,土壤抗剪强度随之降低,土壤侵蚀加剧.

The cascade hydropower development on the main stream of the Lancang River forms a large-scale of riparian zone(also called water level fluctuation zone,WLFZ).The comprehensive action of periodical submerged-exposed and storm runoff causes severe soil erosion in the WLFZ,which threatens the safe operation of Nuozhadu Reservoir(NZDR)as well as the safety of lives and property around the reservoir.In this study,the area of WLFZ in NZDR involving different counties,elevations and slopes was investigated based on the ASTERG DEM V230 m data,together with GF-1,the Google Earth image,and erosion needle technology,so as to observe the soil erosion intensity in the riparian zone under different underlying surface conditions in NZDR.The results show that:(1)The total area of WLFZ in NZDR is 129.95 km^(2),with 57.29 km^(2) in the Lancang River and 72.66 km^(2) in its tributaries.The area of WLFZ gradually decreases along with elevation reduction.The distribution areas of WLFZ in different slopes are not uniform,with the widest area on the slopes of 15°~25°,while the WLFZ areas of steep slopes greater than 35°are very few.(2)The driving factors of soil erosion in WLFZ include rainfall,runoff,wind wave,ship traveling wave,gravity and so on.And the most common erosion types are surge erosion and collapse.(3)Soil erosion monitoring from 2016 to 2018 showed that the average soil erosion intensity in the mainstream of the Lancang River was 38.5 mm/a,while in its tributaries,it was 17.00 mm/a.Besides,the depth of soil erosion in the main stream fluctuating zone was 2.3 times that of the reservoir bay.(4)The changes of slopes,vegetation,and soil moisture in the WLFZ have significant effects on soil erosion.Furthermore,the slope has a significant linear correlation with the annual average erosion depth,and vegetation can significantly reduce soil erosion in WLFZ.Additionally,the alternation of drying and wetting has a significant effect on the soil water content in WLFZ,which in turn changes the soil shear strength.The present study indicates that the soil shear strength decreases significantly with the increasing of soil moisture content.