The Morphological Relationship Between Gully Systems And Watersheds In Yuanmou Dry-hot Valley

The study of morphological relationship between gully systems and watersheds is the important area in gully geomorphology,which has significance for the understanding of the process of gully development and the predicting of the trend of gully evolution.In natural factors of influencing gully development,the most influential non-zonal factors for gullies development speed,scale,number and total length are watershed morphology,geological structure,river valley,cutting degree.Watershed morphology not only is the object of soil erosion,but also the result,influences the process of soil erosion in turn.From the last century,the morphological relationship between gully systems and watersheds has always been a research hotspot for soil and water conservation and soil erosion.However,it mainly concentrates on debris flow gully research generally,and research on erosion gully needs to be further studied.In recent years,for the study of gully,the scholars tend to study relatively single channel or small gully system,while it is still rare to study the large-scale gully system.In the study,the Yuanmou dry hot valley as the research object,where ravines and gullies criss-cross and the development of gullies is typical.We selected the morphology relationship between gully systems and watersheds as the research content.Based on the method of visually interpreting the gully system and the SWAT model to determine the threshold value,the basin was divided into the small watersheds.According to the calculation results,the characteristics and relationship between gully systems and watershed are discussed.The results are expected to enrich the study of geomorphology in this area in theory,which are helpful to the mechanism of the hedge erosion,and provide theoretical support for the prevention and control of engineering geological disasters and the treatment of soil erosion in practice.The conclusions are as follows:(1)The total area of research area is 1141.66km~2,the slope is 13.57°.We divided into 42 watersheds by the SWAT model,the range of watershed area is0.39~96.43km~2,the dominant type of watershed topographic texture ratio is fine texture.The watershed fluctuation is large,the range of slope is 4.76~21.88°,which is8~15°as a focus,the relief ratio is 0.1~0.19,the surface cutting depth is 0.10~7.33,the area elevation integral is 0.21~0.61,when the geomorphological development stages of watershed at the haste.The watershed shapes are long bars,the number of watershed is the most,the range of circularity ratio is 0.30~0.83.On the whole,there is a large difference in the watershed morphology of the Yuanmou dry-hot valley.(2)In the study area,the total length of gullies is 5252.72km,the average of gully density is 4.29km/km2.The range of gully length is 0.72~439.84km,the gully density is 0.54~6.98km/km2,the number is most when the gully density is 3~7km/km2,the gully density is uneven in the area,the occurrence degree of gully erosion is dominated by strong and extremely strong,the development intensity of gully erosion is dominated by intense and moderate,the gully frequency is 1.82~36.6gullies/km2,the main gully length is 0.38~19.93km,the dominant range of the coefficient of main and branch gullies is 0~0.16,the type of gully system is branch-leading.The range of branch ratio and length ratio is 4~6 and 2~4.(3)From the development of mountainous large-scale gully systems,the top of the valley is very close to the watershed,the extension of the gully system is controlled by the watershed,so the watershed scale influences the scale and development potential of gully system.There is significant relationship between characteristic of watershed fluctuation and gully system morphology.The slope with main gully length,gully density,relief ratio,coefficient of main and branch gullies are closely related.The surface cutting depth with main gully length,gully length are closely related.The area elevation integral with main gully length are closely related.The variation of surface fluctuation is one of the main causes of surface heterogeneity,The degree of fluctuation determines the dynamic difference of water flow,resulting in the formation of gully system of different sizes.The watershed shape has no obvious influence on the development process of gully system.It is because of the circularity ratio and length-width ratio as the reflection of the contour of the basin,not only the influence of lithology,but also the total slope of the region.In the case of low lithology,circularity ratio and length-width ratio are easy to maintain a constant state.(4)By nonlinear regression analysis,we calculated the relationship model between gully length and watershed area,watershed topographic texture ratio:L=0.036A2+5.736T+0.748,.And the relationship model between gully number and watershed area,watershed topographic texture ratio is N=0.097A2+25.694T-72.211.The decision coefficients are R2=0.919 and R2=0.950 respectively,and through the test of measured value and predicted value,the models have good effect.On the whole,gully system is reflected by watershed morphology properly,the result could be used to establish a wide application of the model of gully system and watershed.