Comparative Study On Erosion Gully Development In Different Seasons In Black Soil Area Of Northeast China

The black soil area in northeast China belongs to the seasonal snow area,and the soil and water loss caused by the seasonal change is more serious.Erosion ditch is one of the important forms of soil and water loss.The development of erosion ditch seriously affects the agricultural development and threatens the food security of China.At present,the research on the morphological characteristics and mechanism of erosion gully is relatively weak.Therefore,this article selects four typical small watershed in the northeast black earth area 10 erosion gully as the research object,using carrier phase difference technology in May and October each year on selected erosion gully,incorporating the visual features of Arc GIS software for the spatial analytics,obtaining rainfall and snowmelt erosion gully shape parameter values,to explore the erosion gully development regularity in different season.Based on field observation of the changes of erosion gully bank,gully bottom and erosion materials during rainfall and snowmelt,combined with the effects of indoor freezing-thawing cycle on soil physical and mechanical properties,the differences of erosion gully development in different seasons were analyzed from the mechanism.Based on the analysis of the growth rates of erosive gullies in four typical small watersheds in different seasons,it is found that the growth rates of length,area and volume of erosive gullies in rainfall period are higher than that in snowmelt period,and the growth rates of treated gullies are much lower than that of untreated gullies.The development rates of erosive gullies have significant seasonal differences.In order to further explore the differences in morphological development of erosion gullies in different seasons,three erosion gullies in Guangrong Small Watershed were selected as research objects for in-depth analysis.The results show that the cross section of erosion gully changes from "gully head" to "gully middle" to "gully tail",and the erosion gully area increases mainly at the gully head during rainfall period,while the erosion gully area also develops strongly in the middle of the gully during snowmelt period.The increase of length and area of erosion gully caused by gully head collapse and gully tail receding in rainfall period is greater than that caused by gully head collapse and gully bank melting and sliding,gully wall melting and gully slope melting and shrinking in snowmelt period.The erosion degree of runoff generated by rainfall is greater than that in snowmelt period,which leads to the increase of erosion ditch volume in rainfall period than that in snowmelt period.In order to clarify the development mechanism of erosion gully in different seasons,an erosion gully in Guangrong Basin was selected to study,and the difference of development of erosion gully in different periods was analyzed from the mechanism combined with indoor freezing-thawing cycle simulation test.The results show that there are great differences in soil properties,fissure generation mechanism and runoff scour of gully bottom in different periods.Raindrop strikes and destroys soil structure,compacts soil and is more conducive to the formation of surface runoff.The crack produced by local stress caused by the uneven change of water content in the gully bank becomes the preferential channel for runoff infiltration,which makes the gully bank prone to instability and collapse and increases the area of erosion gully.The soil at the bottom of gully is more erodible than other positions in the gully,and the slope runoff flows into the erosion gully from the gully head.The potential energy of runoff is large,and the erosion ability of gully bottom is enhanced,and the volume increase is large.Freezing-thawing changes soil physical properties and increases soil erodibility during snowmelt.The freezing degree of gully bank is intensified by the action of double cold fronts,and the soil expands and deforms to crack.The erosion of gully bank collapse,gully slope melting slide and gully wall melting collapse occur frequently,and the erosion area of gully increases.The erosion material formed by gully bank accumulates in gully bottom and gully slope,hinders runoff cutting down,and increases the volume of gully erosion less.The innovation of this paper lies in the in-depth analysis of the causes and mechanisms of the development of erosion gullies in different seasons through the observation of the differences in the morphological development of erosion gullies in different seasons,which is of great significance for the in-depth understanding of soil erosion in black soil areas of China.