The Study Of Topographic Feature Authenticity Base On The Water-Soil Retaining Measures In The Loess Plateau

The development,change and evolution of geomorphology has always been one of the cores of geographical research,and the influence and role of biological and abiotic forces in reshaping the earth's surface is also a topic of wide discussion in the scientific community.As a very important part of biological forces,human activities have greatly altered the geomorphologic shape,leaving a mark that is uniquely human.However,there is still a lack of a multiple quantitative evaluation index system for the quantitative research on the human impact on geomorphologic shape.In this paper,the concept model of topographic shape authenticity is put forward.Three loess watershed are selected,the natural topographic shape of the sample areas and the water-soil retaining measures in these watershed are studied.With the help of digital terrain analysis(DTA)theory and methods,the influence of check-dams and terraces on the topographic shape are quantified;characteristics and differences of these two typical water-soil retaining measures on reshaping topographic shape are studied.This study aims to supplement and improve the quantitative index system of the degree of topographic shape transformation caused by human activities,and support further explore on the internal mechanism and laws of topographic shape transformation caused by human beings.The main contents and conclusions are as follows:1.Concept and scientific cognition of topographic shape authenticityThe concept model of topographic shape authenticity is put forward.In this paper,topographic shape authenticity means: the similarity of the topographic shape under the specific human impact is compared to that before human interrupted.In the Loess Plateau,the research on the topographic shape authenticity of loess watershed is to study the similarity of topographic shape after the reconstruction of typical water-soil retaining measures,especially check-dams and terraces.The characteristics of regional difference,genetic complexity and scale dependence of the topographic shape authenticity are summarized.2.The construction of the quantification index system of topographic shape authenticity and the extraction method of indexOn the basis of the scientific cognition of topographic shape authenticity,a quantification index system of topographic shape authenticity is constructed.The index system includes three aspects of indices: area index,volume index and morphological texture indices.The area index reflects the ratio of the area of soil-water retaining measures to the regional area,which is the most basic and intuitive description of the change degree of topographic shape.The volume index mainly reflects the material migration amount changed before and after the construction of soil-water retaining measures,which is a three-dimensional description of the influence degree of artificial appearance on the surface.Morphological texture indices are sensitive to directional information and material density.They can identify the changes caused by human activities to the overall shape,direction,and continuity of the original natural texture of landform,which is an important index to measure the topographic shape authenticity from the microscopic perspective of graphics.The index system includes the ratio of artificial appearance to total area,earth volume per unit area,second-order angular distance(energy),inverse difference moment,and information entropy of texture.The extraction and calculation methods of the above indices are clarified and the index values are obtained.Based on entropy weight method and normalized statistics,the contribution weights of each index to the topographic shape authenticity in the sample area are determined,and the evaluation scores of topographic shape authenticity are calculated to represent the influence of construction of water-soil retaining measures in the region.3.Study and analysis on the effect of water-soil retaining measures on topographic shape based on topographic shape authenticityThe check-dam area and the terrace area in the small loess watershed are extracted respectively.For the check-dam and its siltation area,the extraction is based on the method of object-based image analysis(OBIA).For the terrace area,the extraction is comprehensively considering the high-resolution remote sensing image and the regional topographic information,and the terrace information in the DEM is enhanced based on the morphological characteristics and parameters of the terrace ridges.Due to the lack of DEM data of the sample area before the construction of check-dams and terraces,the topographic shape information before check-dam and terrace construction are restored,and the DEMs without the influence of water-soil retaining measures are constructed.For Wangmaogou watershed,the effect of water-soil retaining measures on topographic shape is evaluated by using the quantification model of topographic shape authenticity.The evaluation results can reflect the impact degree of water-soil retaining measures construction on geomorphic morphological transformation.For Guandigou and Zhifanggou watershed,this paper reflects the different attributes,characteristics,and distribution pattern of check-dam and terrace,which are two typical kinds of water-soil retaining measures.These differences lead to the diversity of the reconstruction mode of landform and the different value of the topographic shape authenticity.Check-dams mainly affect the natural surface through the volume transformation caused by siltation,while terraces are more closely related to the area index and the surface morphology.Overall,area index is still the most influential factor with the highest weight in the evaluation formula of topographic shape authenticity.This study puts forward the concept of topographic shape authenticity and its index system.On the basis of typical loess watershed with water-soil retaining measures,the influence of the artificial appearance construction impact on the morphology of the internal mechanism and rule are explored.The impact of human activities on the natural surface is more comprehensive understood.