| With the mid-20 th century,the progress of scientific revolutions,the trend of geomorphology research has gradually transformed from the qualitative description advocated by Davis to the quantitative analysis based on the process.In particular,the law of the number of rivers,the law of length and the law of area created a mathematical geomorphology study of Horton,which has become a standard for the quantitative analysis of water system and landform,and has opened up a new horizon for the study of river basin topography and water system development.In the past 30 years,the rapid development of computer technology and the emergence of high-precision digital elevation model have provided great benefit to the quantification of geomorphic analysis.It has become an important method and necessary means for the analysis and process research of river basin topography.The continued uplift of the Tibetan Plateau since the Late Cenozoic Era,the northeastern part of the plateau is one of the most active areas of tectonic activity,and the area is located in the intersection of the three natural areas of China,climate change is remarkable,under the combined action of structure,climate and denudation,the landform is complex and diverse.In the process of crushing deformation and uplift of the mountain,the change of drainage structure and watershed topography of the area to the external variables such as tectonics,climate and so on is very apparent.At the same time,multi-level planation surfaces and partial peneplains are formed in the process of long-scale mountain evolution.Quantitative research on these drainage structures,geomorphology and barbed features can provide in-depth understanding of the evolutionary history of watershed geomorphology and its theoretical understanding of tectonic activity and climate change response.In this paper,based on DEM,in the ArcGIS environment,study of the drainage network parameters,geomorphic parameters,longitudinal profiles and planation surfaces digital geomorphic features were studied quantitatively of the Taohe.Some important findings are drawn as follows:(1)The Taohe streams were extracted by using hydrology-based algorithms with the catchment area threshold of 10 km2,according to the Strahler classification system for classification of network,the statistics of the number?length?area.The results show that the river in the Taohe is divided into five grades.The Bifurcation ratio is between 4-9,average length ratio is between 1.1and 20.8,and the average area ratio is between 2.9-19.2.The network of the 5 rivers compared with the Horton's Law,the streams are resented by the Horton Laws for the streams from the first to fourth orders but deviated dramatically at the hightest order.Indicating that the drainage pattern for this tectonic,climate and other external factors in the cumulative effect of large scale performance are more obvious.(2)Hypsometric integral(HI),drainage basin asymmetry(AF),drainage basin shape(BS),and Valley floor width-valley height ratio(VF)was calculated in ArcGIS based SRTM DEM.The results show that these geomorphologic indices has an great difference in space,the HI between 0.26-0.59,HI of the basin upstream the Yemuhe outlet is generally higher(0.32-0.59),and mostly are of S-shape HC,exclude the Yemuhe who's HC is convex,indicated that the uplift rate is slight higher than the erosion rate,but much higher than the erosion rate in the Yemuhe,due to intense active of the north frontal fault zone of the West Qinling Mountains and the granite rock leads to low erosion rates.HI of the basin downstream of the Yemuhe is lower(0.26-0.29)and the HC is concave,which indicates the down-cutting erosion dominated.The AF is between 19.01 and 91.82,mostly distribution between 35 to 65,indicating the tectonic tilting had little influence on the basin.The BS is between 0.52 and 5.27,indicating the basin shape is almost round,the tectonic active is lower.The VF is between 0.52 and 5.27,most of the tributaries of the VF value is relatively low(less than 1),represented V-shape valley,in the lower reaches of the western tributaries of the VF value are relatively large(3-5),were broad valleys,indicating that the watershed is dominated by the down-cutting.Based on these geomorphologic indices,we think that the Taohe with a rapid overall uniform uplift and strong river vertical down-cutting the dominated.(3).Based on the Taohe 19 tributaries of the longitudinal profiles,concavity index,steepness index and knickpoint analysis.It is found that the rivers(the main stream and the tributaries)of the upper reaches of the Yemuhe knickpoint are not related to lithology and tectonics.Above the Knickpoint is gentle and the ksn is distributed at 22.8-60 m0.9,under the knickpoint,the ksn distribution between 70-466 m0.9,showing a significant Topographic unconformities,indicating that the river is also responding to changes in boundary conditions,did not reach equilibrium,the general remnants of the palaeosurface.In the downstream of the Yemuhe(main stream and tributary),most of them show typical smooth and concave characteristics.The concavity index is between 0.57 and 0.89,and ksn is between 28.4 and 105 m0.9,indicating that most of the rivers have reached equilibrium.The obvious difference of the longitudinal profile of the downstream and upstream of the river,may be reflection of the difference between the tectonic uplift and climate differences.(4).Based on the fuzzy logic,in the ArcGIS by the SRTM DEM with 90 m resolutions,slope,curvature,terrain rougness index and relative height of the 4 geomorphic indices were extracted.And compared with other typical landform units,the fuzzy logic threshold was determined,and the membership function of the plane is established.Among them,the higher degree of membership is mainly located in the river watershed,wide valley above the flat highlands and modern valley valleys,for the potential distribution of the flat area.We selected the membership in more than 80% of the region to represent the distribution of the planation surface,and the smaller area(0.2 km2 below)and accumulation of the cause of the polygon removed.The results show that there is altogether 3,700 polygon,with an area of 0.2-593.46km2,with a total area of 2660.99 km2,accounting for 10.4% of the total area of the basin.In the large area,the elevation frequency distributions and the topographic profile show that the altitudinal plane is mainly distributed in the three elevation ranges of 3200-4300 m,2700-3200 m and 1950-2700 m.The average elevation is cut from the southwest to the northeast,Northeast,may be the result of a unified flattening of the area.In the district,in the Taohe,under the main plane and the modern valley may also be developed above the 1-2 level partial peneplains.Indicating that the area has experienced many times the construction of the uplift-erosion and leveling process,Taohe modern drainage pattern and river valley system formed after the dismantling of the planation surface. |
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