Watershed management of thoppiayar upper basin using remotesensing and gis

The study area is one of the watersheds of Thoppaiyar River. Covering an area of 269sq.km.and lies between 11050’00’’N - 12002’00’’N latitude and 780 02’00’’E – 78018’00’’E Longitude In south of shervaroyan mountains northern part of the Salem district and Southern part of the Dharmapuri district. The study area is mainly covered by red soil and black cotton soil to the minor extent. The infiltration capacity is moderate to poor. The entire study area is occupied by the Precambrian crystalline rocks. The recent formation is marked by river alluvium and soil. Thoppaiyar upper basin is divided into twenty mini-watersheds. As a whole Thoppaiyar upper basin having five orders of stream. But the mini-watershed differs in the ordering system. The first order streams are numerous in the mini-watershed 1, 2 and 3. These are due to highly elevated portions of Shevaroy Mountains. Particularly in Lokur and Mulivi the drainage are in the slopes of Shevaroy Mountains. So the entire study area has been further divided into 20 mini-watersheds named mw1 to mw20. ranging in geographical area 269sqkm and has been taken up for prioritization based on morphometric analyzing using GIS and Remote sensing techniques. The drainage density varies between 1.15 and 10.92 indicating low drainage density. In the study area, the low drainage density indicates the region has highly permeable subsoil and thick vegetative cover. The elongation ratio vary from 0.6 to 1.0 over a wide variety of climatic and geologic types. Values close to 1.0 are typical of regions of very low relief, whereas values in the range 0.6 – 0.8 are usually associated with high relief and steep ground slope (Strahler, 1964). These values can be grouped into four categories namely (a) circular (>0.9), (b) oval (0.9 to 0.8), (c) Less elongated (<0.7). The Re of mini-watershed of the study area varies from 0.47 to 0.84. The circularity ratio (Rc) is influenced by the length and frequency of streams, geological structures, land use/land cover, climate, relief and slope of the basin. The circulatory ratio range between 0.28 to 0.61.The compound parameter values are calculated and the mini watershed with the lowest compound parameter is given the highest priority. The mini watershed has a minimum compound parameter value is likely to be subjected to maximum soil erosion and susceptible to natural hazards. Hence it should be provide with immediate soil conversion measures.