Influence Of Spatial Pattern Of Erosion Gullies On Sediment Connectivity In Small Watershed Of Loess Region In Northwest Hebei Province

The connectivity under the influence of spatial pattern of erosion gully can effectively express the ecological geomorphic process at different scales,which is crucial to the prediction of gully erosion process and sediment transport.Eroded gullies in small watersheds in the intermountain basin area of northwest Hebei are widely distributed and evolving,forming a unique erosion environment,which has become the main sediment source in the region.Exploring the impact of spatial pattern of erosion gullies on sediment connectivity is helpful to understand the interaction between erosion development and hydrological and geomorphic processes,and also provides theoretical basis and scientific methods for erosion gully management.In this paper,20 small watersheds in Dongcheng Town,northwest loess region of Hebei Province,are taken as research objects.Based on high-resolution remote sensing images(0.8m resolution)and high-precision DEM(0.8m resolution)data,morphological parameters of erosion gullies are extracted,morphological characteristics of erosion gullies are analyzed,and their spatial patterns are discussed;The influence of DEM with different resolutions on sediment connectivity index is compared and analyzed,and the sediment connectivity characterization model suitable for this area is determined;Finally,the influence of spatial pattern of erosion gully on sediment connectivity in small watershed is analyzed.The main conclusions are as follows:(1)Erosion gullies in small watershed are clustered,and the erosion degree of gullies is uneven;The erosion gullies are mainly micro gullies(with a length of less than 0.2 km)and small gullies(with a length of 0.2～0.5 km);The average erosion gully density and fissure degree of small watershed are 15.41 km/km2 and 0.0722km2/km2 respectively,Erosion gully intensity is mainly severe and intense.The average value of spatial pattern index increases with the increase of gully level,and the erosion degree also increases with the increase of gully level.(2)The sediment connectivity index is calculated based on DEM with different resolutions.The results show that the sediment connectivity increases with the decrease of DEM resolution,but the overall connectivity trend within the basin remains unchanged.Therefore,when analyzing the overall sediment connectivity structure and trend of small watershed,if considering the reduction of research cost and computational complexity,a slightly lower resolution DEM can be selected to replace the high-resolution DEM for analysis.(3)Based on the spatial differentiation characteristics of small watershed,spatial autocorrelation distribution characteristics of erosion gullies and morphological characteristics of gullies,the impact of spatial pattern of erosion gullies on sediment connectivity is analyzed.The correlation analysis shows that with the increase of spatial pattern index,the erosion intensity of the basin increases,and the sediment connectivity increases.Spatial autocorrelation analysis shows that erosion gullies are clustered in small watersheds,and the degree of sediment connectivity aggregation is positively correlated with the degree of erosion gullies aggregation.According to the channel distribution,the spatial pattern index and sediment connectivity index increase with the increase of channel level.