Influence Of Geological Conditions On Gully Distribution In The Yuanmou Dry-Hot Valley,SW China

The Dry-hot Valley of Yuanmou is a serious region of soil erosion in China.Due to the unique terrain and climate conditions,it has semi-arid climate characteristics,with sparse vegetation,loose soil,soil erosion and gully development,which not only poses a serious threat to the local ecological environment,but also affects people’s production and living activities.Geological condition is an important factor affecting the development of gully erosion,but it is usually used as the background value of gully erosion research.At present,it is not clear how and to what extent geological conditions affect the spatial distribution of gullies.Therefore,in order to explore the quantitative relationship between geological conditions and spatial distribution of gullies at regional scale,as well as the influence mechanism of geological conditions on spatial distribution of gullies.This paper took the gully in dry-hot valley of Yuanmou as the research object,selected lithology and fault as geological conditions,and built GIS database of gully;based on kernel density evaluation,spatial autocorrelation and correlation ratio analysis,the index of spatial distribution of gullies was established,the spatial distribution pattern of gully and regional geological characteristics were analyzed,the relationship between geological conditions and spatial distribution of gullies was revealed,and the influence of geological conditions on spatial distribution of gullies was clarified.The main conclusions were as follows:(1)Gullies had spatial clustering characteristics.Based on spatial autocorrelation analysis,and results showed that Moran’s I was 0.89(p<0.01),indicating that the kernel density with clustering distribution pattern of spatial differentiation characteristics.It was observed that the gully was mainly characterized by low clustering(0～1.96 km/km~2),followed by medium clustering(1.96～3.91 km/km~2),while high clustering(3.91～5.87km/km~2)were small and concentrated in the western region.The eastern Dongshan was mainly characterized by medium clustering of north-south zonal distribution.Yuanmou Basin was mainly characterized by low clustering of north-south zonal distribution.The clustering distribution of gullies in the west of Yuanmou Basin and south of Laocheng Basin was complex,which was characterized by low clustering,and mosaic distribution of medium clustering and high clustering with small distribution area.In the north of the Wumao Basin and Qingling River,the low clustering was the main feature,followed by the medium clustering,which showed that the low clustering was distributed around the medium clustering,and the medium clustering was distributed in the west.(2)There was a strong correlation between lithology and clustering degree of gully.The gully cluster degree of the seven lithologic types were as follows:the first type(loose Quaternary sediments,mudstones and siltstones,sandstones,schist and phyllite)>the second type(conglomerate,marble and quartzite,granite).It was observed that there was a negative correlation between the resistance of lithology and the development degree of gullies.The sandstones,the combination of mudstones and siltstones,loose Quaternary sediment,the combination of phyllite and schist were more conducive to the development of gullies.However,the granite,conglomerate,the combination of marble and quartzite may lead to a lower gully clustering.(3)There was no correlation between faults and clustering degree of gully,but faults had a certain influence on the development of gullies.Faults had a controlling effect on topography,thus affecting the topographic relief and hydrodynamic conditions of gully erosion.At the same time,it also affected the sedimentation-erosion process of stratum and magmatism,and controlled the spatial distribution pattern of lithology to a certain extent.(4)The superposition of topography,land use and lithology made the influence of lithology on the clustering characteristics of gully more significant.There was a moderate correlation between slope and clustering degree of gully.Gentle slope(0-5°)could better reflect the influence of lithology on clustering characteristics of gully,and the increase of slope may weaken the influence of lithology on gullies.There was a moderate correlation between the relative height difference and the clustering degree of gully.When the relative height difference was less than 700 m,the lithology had a more obvious influence on the clustering characteristics of gully.There was a strong correlation between land use type and clustering degree of gully,and the clustering degree of gully was shrub>forestland>grassland>cultivated land.In cultivated land and grassland area,lithology had more obvious effect on clustering characteristics of gully.