Abstract
The study was aimed to synthesize drainage morphology of tectonic watershed in upper Ing Watershed in Phayao province, northern Thailand. The morphometric analysis of 12 sub-watersheds was carried out using Geographic Information System (GIS) software-ArcGIS 9.3 for analysing drainage pattern and calculating the 16 theoretical values of drainage morphometric parameters in 3 aspects including linear aspect, areal aspect and relief aspect. The geologic formation and structure are also overlain on drainage morphological map to determine their influence on drainage patterns. The results showed that most areas were dendritic drainage pattern, while rectangular drainage pattern occurs relative to the direction of the fault. Trellis drainage pattern shown on the northeast of the watershed in Mae Puem sub-watershed which the rock layers bend or tilt in syncline structural geology. The upper Ing watershed was classified as a third to fifth order streams, which controlled by physiographic and structural conditions. The tectonic force formed a graben basin which Kwan Phayao wetland is the lowest area of this graben while the high mountain ranges in the western area. As a result, the river is flowing from western highland to lowland quickly especially in the western sub-watershed, this result affecting low permeability, high discharge of runoff and intensity of erosion processes which the calculated drainage morphometric parameters showed the results according to their appearance. It could be said that the drainage patterns in this area is influenced by tectonic structure rather than geologic formation. This study provided more understanding in drainage morphological characteristics of the upper Ing watershed for planning sustainable management of the Kwan Phayao wetland.
Highlights
Upper Ing watershed lay on the north of Phi Pun Nam ranges, situated in the southern of Phayao-Chiang Rai basin, which is a part of Mekong watershed
2) Synthesizing Drainage Morphology Calculating the 16 theoretical value of drainage morphometric parameters including (a) linear aspects like stream order, stream number, stream length, mean stream length, stream length ratio, bifurcation ratio, mean bifurcation ratio (b) areal aspects like drainage density, drainage texture, stream frequency, form factor, elongation ratio, circularity ratio, length of overlandflow and (c) relief aspects like watershed relief, relief ratio, ruggedness number (Table 1) and using geographic information system (GIS) for overlay the geologic formation and tectonic structure maps on drainage morphological map in order to determine their influence on drainage patterns
According to the result of this study, it was demonstrated that the drainage patterns correlated to geological structures and directions of fault
Summary
Upper Ing watershed lay on the north of Phi Pun Nam ranges, situated in the southern of Phayao-Chiang Rai basin, which is a part of Mekong watershed. The watershed was affected from tectonic forces that formed a graben along the fault. Kwan Phayao is the lowest area of this graben which accumulated water, sediments, nutrients, and poisonous substances. Morphometric analysis provides quantitative description of the basin geometry to understand initial slope or inequalities in the rock hardness, structural controls, recent diastrophism, geological and geomorphic history of drainage basin (Strahler, 1964). This study aimed to understand the drainage morphology in upper Ing watershed. The 16 value of drainage morphometric parameters were calculated in 3 aspects include linear aspect, areal aspect, and relief aspect. The knowledge of this study will be beneficial to management of Kwan Phayao wetlands
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