金沙江干热河谷冲沟形态发育特征及其侵蚀速率估算

Morphological characteristics and erosion rate estimation of gully in Hot-Dry Valley of Jinsha River of China

冲沟侵蚀是金沙江干热河谷土壤流失的重要原因,造成严重的土地退化,威胁区域农业发展和粮食安全。探究冲沟的形态发育特征明确其侵蚀速率,对于冲沟侵蚀量化评估和土地保护等具有重要意义。为摸清冲沟发育演变规律,该研究选取元谋干热河谷金雷国家水土保持科技示范园区附近沟谷地貌流域为研究区,选择35条冲沟,通过无人机遥感影像提取冲沟形态参数,分析形态特征,并结合高分遥感影像计算冲沟侵蚀速率。结果表明:1)研究区冲沟直线长度、顶宽、底宽、深度的范围分别为25.21~180.43、10.76~51.76、3.56~26.85、1.22~11.92 m;面积、体积的范围分别为257.50~8987.88 m^(2)、142.64~19479.25 m^(3)。冲沟形态参数差异性较大,长度在发育过程中受坡面限制小于其他地区。2)冲沟底部宽度和顶部宽度比值(BW/TW)的范围为0.24~0.59,冲沟主要为“V型”和“V~U型”;冲沟顶部宽度和深度比值(TW/D)的范围为2.56~26.29,均值为6.04,横向侵蚀速率远大于下切侵蚀速率。3)2015—2022年间,35条冲沟中,19条长度明显增长,冲沟溯源侵蚀速率为0.02~1.10 m/a(均值0.34 m/a);27条宽度明显增长,冲沟横向侵蚀速率为0.07~1.10m/a(均值0.36 m/a);29条面积和体积明显增长,冲沟面积增长速率为1.64~105.40 m^(2)/a(均值23.44 m^(2)/a);冲沟体积侵蚀速率为1.26~339.42 m^(3)/a(均值51.21 m^(3)/a)。冲沟横向侵蚀速率大于溯源侵蚀速率,在面积和体积增长中贡献较大。研究结果可为金沙江干热河谷地区大尺度冲沟的发育演变规律和侵蚀定量评估提供方法和依据。

Gully erosion is one of the most important indicators of soil loss in the dry-hot valley of the Jinsha River.Serious land degradation has threatened regional agriculture and food security.It is of great significance for the quantitative evaluation of gully erosion and land protection.In this study,the erosion rate was determined from the morphology evolution and development of the gully.The research area was selected as the gully geomorphic watershed near Jinlei National Soil and Water Conservation Science and Technology Demonstration Zone in Yuanmou Dry-Hot Valley.35 gullies were selected to extract the gully shape parameters from the remote sensing images of unmanned aerial vehicles(UAV).Morphological characteristics were analyzed to calculate the gully erosion rate combined with high-resolution remote sensing images from 2015 to 2022.The results show that:1)The straight length,curve length,top width,bottom width,depth,area and volume of gully in the study area were 25.21-180.43 m,25.73-203.01 m,10.76-51.76 m,3.56-26.85 m,1.22-11.92 m,257.50-8987.88 m^(2) and 142.64-19479.25 m^(3),respectively.There was a great variation in the morphological parameters of the gully.The length of the gully was less restricted by slope than other areas during development.2)The ratio of length to top width of gully(L/TW)ranged from 1.35 to 6.38,with an average value of 2.78.There was no significant gully narrowness.The strong lateral erosion occurred at the same time as retrogressive erosion.The ratio of the bottom width to the top width of the gully(BW/TW)ranged from 0.24 to 0.59.The flushing channels were mainly in the"V"and"V-U"shape.The ratio of top width to depth of gully(TW/D)ranged from 2.56 to 26.29,with an average value of 6.04.The lateral erosion rate was much higher than that of the downward.There was a great difference in the cross section of the gully from gully head to mouth.The tortuosity index of gully(TI)ranged from 1 to 1.13,with an average value of 1.05.There was a small bending degree of the gully.3)54.29%of the 35 gullies experienced an increase in length,where the retrogressive erosion rate of the gully was 0.02-1.10 m/a(average 0.34 m/a).77.14%of the gullies experienced an increase in width,where the lateral erosion rate ranged from 0.07 to 1.10m/a(average 0.36m/a).80.56%of the gullies experienced an increase in area,and the growth rate of the gully area was 1.64-105.40m^(2)/a(average 23.44m^(2)/a).The optimal fitting was obtained for the power function of 35 gullies area and volume:V=0.0584A1.405,with R2=0.9461.The volume of the gully was calculated to combine the gully area from the GF-2 remote sensing image.The volume erosion rate of the gully ranged from 1.26 to 339.42 m^(3)/a(average 51.21 m^(3)/a).Both the number and rate of lateral erosion gullies were greater than those of retrogressive erosion gullies.Lateral erosion greatly contributed to the growth of the gully area and volume.The findings can provide a strong reference for the development and evolution of large-scale gullies,in order to quantitatively evaluate the erosion in the Dry-Hot Valley of Jinsha River.