Longitudinal river profiles are among the most widely used approaches for analyzing short‑term landscape responses. Compared to conventional longitudinal profiles, normalized longitudinal profiles provide enhanced interpretability and more effectively highlight slope breaks. This study investigates the geomorphic response patterns of streams within selected basins located in the Makran Accretionary Prism, using DEM derived normalized longitudinal profiles generated by the NProfiler plugin. A total of 37 streams, including five main channels and 32 tributaries, were selected and analyzed. The results indicate that all main channels and most tributaries exhibit concave longitudinal profiles, as reflected by positive concavity parameter (CT) values. The CT values for the main channels range from 29.89% to 52.47%, whereas those for the tributaries vary between 1.38% and 64.39%. Among the main channels, the maximum and minimum CT values correspond to the Kahir and Jagin rivers, respectively, while among the tributaries they are associated with B6 and J1. The most linear and most convex longitudinal profiles in the study area are observed in the J1 (CT = 1.38%) and B7 (CT = −11.36%) channels, respectively. The dominance of concave profiles suggests an erosion‑dominated landscape in a state of relative dynamic equilibrium. Only two profiles display negative concavity values, indicating a tendency toward convexity. These convex profiles are primarily associated with small sub‑basins, headwater reaches, and intensely faulted zones in the northern Makran highlands within the Bahukalat and Jagin basins, reflecting a transient landscape state likely linked to localized tectonic uplift.
Introduction
Early morphometric methods from the 1980s (Pérez-Peña et al., 2017) presented computational challenges for large-scale analyses, limiting investigations to localized areas with restricted datasets (e.g., Mackin, 1948; Hack, 1957; Seeber & Gornitz, 1983; Merrits & Vincent, 1989). However, in recent times, there have been significant advances in the scientific discussion over the suitability and meaning of some of these topographic parameters (Keller & Pinter, 2012; Wobus et al., 2006a; Goldrick & Bishop, 2007; Pérez-Peña, Azañón & Azor, 2009a; Kirby & Whipple, 2012; Royden & Taylor Perron, 2013). The advancement of ArcGIS software and the widespread availability of digital elevation models (DEMs) with varying spatial resolutions have significantly transformed and evolved spatial analysis methodologies for geomorphic landscapes. As highlighted by several researchers (Kirby & Whipple, 2001; Grohmann et al., 2007; Zang et al., 2011; Pérez-Peña et al., 2017), the aforementioned factors facilitate the analysis of remote regions exhibiting significant geological and tectonic importance. Consequently, they contribute to a more comprehensive understanding of the dynamic processes operating within these areas.
The drainage pattern of rivers contains unique information about the past and present tectonic regime. The longitudinal profile of a river is sensitive to the ongoing process of uplift and can be used to recognize active structures (Seeber & Gornitz, 1983). The extraction and analysis of longitudinal river profiles from digital elevation models has become a prevalent methodology in contemporary tectonic geomorphology. This approach facilitates the evaluation of drainage network dynamics to a range of environmental controlling factors. In recent years, geoscientists have increasingly employed topographic and drainage network analyses as effective tools within the field of tectonic geomorphology (e.g., Pérez-Peña et al., 2009a; 2009b; 2010; Kirby and Whipple, 2012; Giaconia et al., 2012; Royden and Taylor Perron, 2013; Willet et al., 2014; Pérez-Peña et al., 2017). Longitudinal profiles are a standard tool used by geoscientists to analyze drainage network patterns. This is predicated on the understanding that, within a stable system, erosion occurs in equilibrium with uplift (Seeber & Gornitz, 1983), and that rivers continuously adjust their longitudinal profiles in response to the climatic, lithological, and tectonic characteristics of their respective regions. Alterations in topographic and drainage network configurations can serve as indicators of shifts in underlying controlling factors (e.g., Seeber & Gornitz, 1983; Rigon et al., 1996; Jackson et al., 1996; Brookfield, 1998; Pérez-Peña et al., 2009a, 2010; Kirby & Whipple, 2012; Giaconia et al., 2012). In this context, the comparison of normalized longitudinal river profiles can elucidate variations in river gradients, which are typically governed by the aforementioned factors. River gradients, which govern the rate of erosion, are generally adjusted to correlate varying discharge rates with corresponding erosion rates. Consequently, significant slope alterations in river profiles may suggest the presence of active faults intersecting these rivers (Seeber & Gornitz, 1983). Longitudinal river profiles (Pérez-Peña et al., 2017) are now recognized as a highly effective method for analyzing the short-term responses of geomorphic landscapes to recent active geological, lithological, and climate change processes. Therefore, drainage network patterns can be utilized to infer the initial phases of landscape evolution and their corresponding responses.
Material and Methods
This research aims to investigate and assess the geomorphic response patterns of rivers within select basins Bahukalat, Kahir, Sedich, Gabrik and Jagin situated in the Iranian sector of the Makran Accretionary Prism (MAP). The study will analyze these patterns in relation to environmental controlling factors, employing normalized longitudinal river profile extraction (Pérez-Peña et al., 2017) via the NProfiler plugin, which utilizes DEM data. Furthermore, topographic and geological data were sourced from topographic maps (scales of 1:250,000 and 1:50,000) and geological maps (scales of 1:100,000 and 1:250,000), respectively. The NProfiler plugin for ArcGIS offers researchers a streamlined and efficient implementation. This plugin enables the extraction of key information from longitudinal profiles within the ArcGIS environment, significantly enhancing their subsequent analysis and interpretation (Pérez-Peña et al., 2017). The NProfiler Add-In facilitates the visualization of normalized longitudinal river profiles, along with their associated morphometric indices, including normalized concavity (CT), maximum concavity (Cmax), and length of maximum concavity (Lmax). This extension facilitates spatial analysis of drainage networks within the ArcMap environment.
Results and Discussion
In this study, 37 streams were selected and evaluated, comprising 5 main and 32 secondary streams. The longitudinal profiles exhibit notable characteristics. The data indicate that the main streams, along with many secondary streams, display high CT values. This means that most of the normalized longitudinal profiles have a concave shape. The results of this study underscore the significant influence of multiple active faults exhibiting both normal and reverse mechanisms (including the Chah Khan, Ghasr Ghand, and Bashagard Thrust) on the longitudinal profiles analyzed. As demonstrated by these profiles, the impact of these faults is readily apparent in the development of knickpoints and alterations in the longitudinal gradient of the rivers examined. The CT parameter variation for main streams ranges between 29.89% and 52.47%, while for secondary streams, it ranges from 1.38% to 64.39%. Furthermore, the maximum and minimum CT values observed in the main streams were associated with Kahir and Jagin, respectively. Among the secondary streams, the highest and lowest CT values were found in B6 and J1, respectively. The J1 (CT = 1.38%) and B7 (CT = -11.36%) streams exhibit the most linear and most convex longitudinal profiles within the region, respectively. The prevalence of concave profiles in the examined streams suggests a state of relative dynamic equilibrium in their longitudinal profiles, indicative of an eroded landscape. Moreover, the concavity value only becomes negative in two profiles, indicating a tendency towards convexity in the curve.
Conclusion
Normalized longitudinal river profiles facilitate the comparison of gradient variations across different rivers, potentially influenced by climatic, lithological, or tectonic factors. Normalized profiles offer enhanced interpretability compared to traditional longitudinal profiles, effectively highlighting knickpoints. The normalized longitudinal profiles of the main streams (Figure 8) and the majority of secondary streams profiles (Figure 10) exhibit a pronounced degree of concavity. This characteristic suggests a landscape subject to significant erosion. Specifically, concave normalized longitudinal profiles are indicative of a state of relative equilibrium within the river systems. Furthermore, analysis of the drawn profiles indicated that relatively linear, straight, and even convex profiles are associated with streams situated in the headwater regions of the basins. Although these profiles are found in limited areas in the region, they show the connection and influence of small sub-basins with low area with abundant faults (especially main thrusts) in the region, as well as the lithological diversity of the Makran highlands. This demonstrates that the streams in these areas (the upstream areas of Bahukalat and Jagin) are in a transient state.