River profile modeling and fluvial geomorphological evaluation of Thoppaiyar sub-basin using Geoinformatics technology
KAVITHA G1, JOTHIBASU A1, and ANBAZHAGAN S1
1Centre for Geoinformatics and Planetary Studies, Periyar University, Salem ‘ 636 011
Corresponding author Email: gkavitha782@gmail.com
The curvature of river profiles has long been taken to be a fundamental indicator of the underlying processes governing fluvial erosion and thereby of landscape evolution. Longitudinal profile is a graph of distance verses elevation is an x-y plot showing bed elevation as a function of downstream distance. Due to the plate movement is considerably slow, the human history record is too short to register landscape change for such a long time scale. In the present study, an attempt has been made the quantitative analysis of geomorphic indices coupled with some mathematical models for the Thoppaiyar sub-basin and its 16 micro-basins, including the gradient index (SL), normalized gradient index (SL/k), Profile complexity index (PCI) and slope’area relationship (Slr). Based on quantitative results of these geomorphology indices, this study suggests that the important factor influencing landscape of the Thoppaiyar sub-basin. Topographic map, IRS P6 LISS III satellite data, 10m contour interval, SRTM data and ArcGIS 9.3 software were utilized. The contour lines of topographic maps of the main river and 14 micro basins are digitized as control points. Models of the longitudinal profiles using simple mathematical functions were made considering four functions for describing the form of longitudinal profiles. The abnormally high SL and SL/k values indicated that a decreasing trend from lower to mid-stream areas and the result of slope’area relationship also indicated that the regression line of the upper and lower steam exhibit an obvious right-shift could be explained by geodynamic models of active deformation in Thoppaiyar sub-basin.
Keywords: River profile, gradient index, mid-stream, fluvial geomorphology, thoppaiyar
1. Introduction
Longitudinal river profile can display watershed landscape characteristics (Lee and Tsai, 2010). Drainage network has geometric properties that can be quantitatively described (Leopold et al., 1964). Analysis of the river morphologies from longitudinal profiles of bedrock rivers (e.g., rivers of the study area) has been widely used to determine incision and uplift rates in tectonically active landscapes (Snyder et al. 2000; Kirby and Whipple 2001; Kirby et al. 2003; Schoenbohm et al. 2004; Whipple 2004; Clark et al. 2005; Harkins et al. 2007). This quantitative relationship has been widely applied for channels in steady-state condition with a balance between incision and uplift (Lague and Davy 2003). For tectonically active landscapes, i.e., landscapes adjusting to changes in tectonic forcing (cf., Safran et al. 2005; Stock et al. 2005), base-level fall (Anderson et al. 2006; Berlin and Anderson 2007), climate change, and drainage reorganization (Clark et al. 2004), a systematic exploitation of the above indices can extract valuable information for transient rivers. Depending on retreat rate, knick points (sharp change in channel slope if river) may be preserved in present day longitudinal river profiles, providing information on past uplift events (Jakica et al., 2011, Quigley et al., 2010, and Flament et al., 2014). The geomorphic indices are important indicators capable of decoding landform responses to active deformation processes and have been widely used as a reconnaissance tool to differentiate zones deformed by active tectonics (Keller and Pinter, 2002; Chen et al., 2003).The stream gradient index proposed by Hack (1973) allows the identification of anomalies in the longitudinal profile of a river. In mountain ranges, recent and active tectonics can be viewed as the main factor contributing to rock uplift, their present-day topography being the result of the competition between tectonic and erosional processes (Andermann and Gloaguen, 2009; Perez- Pena et al., 2009; Guedes, 2008; Fujita, 2009), tectonic activity (Etchebehere, 2000),. Many researches in previous decades employed numerical modeling to characterize longitudinal river profiles and quantitatively used geomorphic indices to evaluate landscape evolution (Keller and Pinter 1996; Douglas and Robert 2001). Regression including factors linear, exponential, logarithmic and power, and the quantifying approximation relationship between internal and river longitudinal profile can be established. Long profile anomalies have been quantified using the SL/k index. Also, it is important to recognize that within the fluvial slope-area scaling regime, knickpoints may separate channel reaches with distinct steepness and concavity indices, depending on the spatial distribution of substrate properties, spatial and temporal rock uplift and climatic patterns, and transitions from bedrock to alluvial channel types (VanLaningham 2003, Wobus et al. 2003). Still, given the present uncertainty, landscape evolution models (Tucker & Bras 1998) and Roe et al. (2002) that use fluvial process in tectonically active regions, the bedrock channel network dictates critical relationships among relief and elevation, (Howard et al., 1994). Consequently, analysis of the longitudinal profiles of channels provides a promising avenue of exploration of these relationships (Hack, 1957), and much recent research has focused on the quantitative description of bedrock channel forms and processes. For both the basin-wide and main-channel slope-area data sets, the technique of averaging the slopes in logarithmic bins of drainage area was used, similar to other studies (Tarboton et al., 1991; Montgomery and Foufoula-Georgiou, 1993).
2. Study area
Thoppaiyar sub-basin located in Dharmapuri and Salem districts respectively northern and southern part of the basin and the river act as boundary for both districts (Fig.1). The sub basin area is bounded between northern latitudes 11”51’47’ – 11”59’56’ and eastern longitudes 77”53’5′ – 78”18’2′. The highest elevation in the sub-basin is 1600m above mean sea level (amsl) in upstream at near muluvi and lowest elevation 240m amsl in downstream at vellar. The area is well connected by north-south NH-7 National highways and railway line. The total aerial coverage of the sub basin is 462 Sq.km. The average annual rainfall of Thoppaiyar sub-basin is 708 mm. The climate in the sub-basin is generally warm. The sub-basin is mostly covered by Precambrian crystalline rocks and recent alluvium along the river course
3. Methodology
Due to the plate movement is considerably slow; the human history record is too short to register landscape change for such a long time scale. However, longitudinal river profile can display watershed landscape characteristics (Lee and Tsai, 2010). The present study, an attempt has been made the quantitative analysis of geomorphic indices coupled with some mathematical models for the Thoppiayar sub-basin and its 16 micro basins, including the gradient index (SL), normalized gradient index (SL/k) and slope’area relationship (Slr). Based on quantitative results of these geomorphology indices, this study suggests that the important factor influencing landscape typeset of the Thoppaiyar sub-basin.
The survey of India (SOI) toposheet, IRS P6 LISS III satellite data, 10m contour interval, SRTM data and ArcGIS 9.3 software were utilized. Based on the micro watershed and drainage pattern the 16 micro basins are digitized as control points. The work obtained elevation of each contour (vertical data) and distance from the source (horizontal data) to draw a longitudinal river profile (Fig.1).