Spatial Distribution And Influencing Factors Of Gullies In Small Watershed Of Loess Plateau In Northern Shaanxi Province

Gully is a serious ditch erosion in soil erosion.Gully distribution characteristics are the external manifestation of the interaction of environmental factors.Studying the distribution characteristics and influencing factors of gully in small watershed can reveal the evolution mechanism of gully landscape pattern,and can also guide the gully erosion control.Based on Quickbird image（0.6 m）and DEM（5 m）,six small watersheds were selected in Suide County,Shaanxi Province.The information of 352 gullies were extracted by visual interpretation method.The regression model of fractal dimension and length-width ratio was established,and the influence factors of the distribution characteristics of gully morphological parameters were discussed.Secondly,987 gullies were extracted from30 Small Watersheds based on visual interpretation method,and the spatial distribution characteristics of gully density were analyzed from three aspects of slope,slope direction and elevation.A BP neural network model for predicting trench density based on average slope and area was established,and the influencing factors of the distribution characteristics of trench density were discussed.The main conclusions are as follows:（1）The length,width,area,length-width ratio and fractal dimension of gullies are mainly distributed in the range of 6 m-40 m,5 m-18 m,27 m²-800 m²,0.5-3.5 and0.97-1.15,with the average values of 31.42 m,14.42 m,519.52 m²,2.29 and 1.03,respectively;the functional relationship between fractal dimension and length-width ratio is R²=0.64.（2）The morphological parameters and quantity of gullies increased first and then decreased on the slope,and they were concentrated in the range of 20 degrees to 50 degrees,accounting for 83.5%of the total number of trenches,and the shape parameters of gullies were the largest in the range of 30 degrees to 40 degrees;the shape parameters of gullies were larger on the negative slope than on the positive slope,and the number of gullies was larger on the slope.The distribution of quantity on the slope is that the positive slope surface is larger than the negative slope surface;according to the area size,the gullies are divided into large gullies,medium gullies and small gullies.（3）The study on the gully density showed that the gully was most easily formed on the slope of 25-40 degrees,and the gully density increased first and then decreased with the increase of the slope.The gully density is the highest on the East and West slopes.The gully density in the southwest direction bounded by the northwest-southeast direction is generally higher than that in the Northeast direction.The difference of gully density at elevation is that the gully density below 900 m increases with the increase of elevation,and that above 900 m decreases with the increase of elevation.（4）Based on BP neural network,the average error of prediction results is 4.04 m·hm^-2,the range is 12.3 m·hm^-2,and the standard deviation is 3.30.This indicates that the prediction precision of gully density in small watershed is high,and the error dispersion is small.This model can reduce the workload for the calculation of gully density in small watershed.