The Khoramroud River has undergone significant morphological changes with diverse consequences over the past few decades. Therefore, this study aims to investigate and analyze evolutionary trends, assess the changes that have occurred, and determine the relationship between these trends and their controlling factors across four time periods (2006–2025). The objective is to facilitate effective river management and mitigate adverse impacts in two distinct reaches: the first reach spans 16,700 meters and is divided into six sub-reaches (17 cross-sections), while the second reach extends 17,212 meters and is subdivided into seven sub-reaches (18 cross-sections). For this study, hydrometric data from two stations Bahram Jo (Section 1) and Cham Anjir (Section 2) were used, along with topographic maps, Google Earth satellite imagery, field observations, and surveys conducted in these sections to analyze channel dynamics and planform changes. The results indicated that the highest average periodic variations in centerline and channel displacement for both sections occurred during the second time interval (2017–2019). The findings from the first section (2006–2025) revealed a reduction in channel width due to river erosion, whereas the second section exhibited not only erosion but also bank erosion, leading to floodplain formation and subsequent river widening. A comparative analysis of the two sections demonstrated varying degrees of vulnerability in agricultural lands and rural settlements along both river segments. However, the vulnerability level in the first section was significantly higher and more pronounced than in the southern portion of the study area, primarily due to the downstream location of Khorramabad City.
Introduction
The exploitation of environmental resources necessitates a conscientious and protective approach, one that pursues development and sustainability concurrently. Alluvial rivers are dynamic landscape components that react to alterations in flow, sediment, vegetation cover, and climatic conditions. Fundamentally, channel dynamics govern the structure and function of river and floodplain ecosystems. In recent decades, intensified human activities and modified hydrological regimes have driven significant transformations in river systems worldwide. While natural fluvial variability is essential for ecological balance, a pronounced increase in anthropogenic interventions has extensively altered natural river courses. Consequently, many rivers are now experiencing substantial adjustments in width and depth. These changes present considerable challenges for nations worldwide, impacting policymakers, resource managers, and communities reliant on these aquatic systems. The long- and short-term consequences of river system alterations are particularly acute in densely populated mountainous regions, where land scarcity and high population density amplify risks. Thus, this issue remains a persistent and critical challenge in environmental management discourse.
As a mountain river, the Khoramroud River has undergone significant morphological changes in recent decades, each with distinct environmental and societal implications. To date, no comprehensive study has quantified the scope and drivers of these changes. This research therefore aims to (1) examine evolutionary trends, (2) quantify the magnitude of morphological change, and (3) identify the relationship between these trends and their controlling factors from 2006 to 2025. The findings are intended to inform improved river management strategies and mitigate adverse impacts.
Material and Methods
Study Area: The study area encompasses a 34-km segment of the Khorramrod River, located within and adjacent to the city of Khorramabad. It is divided into two sections: a northern segment (Reaches 1–7) and a southern segment (Reaches 8–13). The northern section, extending approximately 16,700 m, runs parallel to the Khorramabad–Kermanshah road from Darhoz Village to the Falak al-Din Martyrs Bridge. The southern section spans approximately 17,250 m, from the Yadgar Imam Bridge at the city’s downstream limit to the Kesht e Sanat Complex Bridge.
Based on data from the Bahram Jo and Cham Anjir hydrometric stations (2004–2024), the river’s average discharge is 2.02 m³/s and 7.87 m³/s, respectively. Geologically, the area lies within the Lorestan region of the Zagros folded thrust belt, northwest of the Dezful depression. The oldest exposed formation in the core of the Khorramabad anticline is the Gro formation.
Climatic data from the Khorramabad meteorological station show a mean annual precipitation of 517 mm and a mean annual temperature of 16.8 °C. According to the De Martonne aridity index, the regional climate is classified as semiarid (Mediterranean type).
Data Collection: This study investigated morphological changes in the Khorramrod River channel between 2006 and 2025. Data were collected through field surveys, direct observations, and physical measurements. Spatial data were processed and digitized using ArcGIS software.
Given the river’s length and the central position of Khorramabad city, the study area was divided into northern and southern sections. Following the reach scale analysis framework of Rinaldi (2013), the northern section was further subdivided into six reaches (containing 17 cross sections), and the southern section into seven reaches (containing 18 cross sections). Detailed maps for each section and reach were produced in ArcGIS.
Morphological Change Analysis: Bankline and channel adjustments were assessed using multi temporal satellite imagery and field verification. To quantify planform change, the left and right banks of each reach were delineated for each study year. Superimposing these banklines allowed calculation of the displaced area, from which rates of erosion and accretion per reach were derived using the River Network Change Index (RNCI). A positive RNCI value indicates net erosion dominance, while a negative value indicates net sedimentation.
Channel dynamics were analyzed by digitizing the channel centerline for each reach and year. Aggregating these centerline shifts yielded the total area of channel displacement, providing a measure of interannual channel mobility.
All quantitative data were processed in Microsoft Excel to generate summary tables and graphs. Finally, spatiotemporal patterns of riverbank change and channel dynamics were compared between the northern and southern sections across the study period, and an integrated analysis of channel variation was conducted.
Results and Discussion
Analysis of channel dynamics across four distinct time periods in the first study section revealed the intervals with the highest rates of change. These were interval 5 in the first period (2006–2017), interval 2 in the second (2017–2019), interval 2 in the third (2019–2025), and interval 6 in the composite fourth period (2006–2025). The highest average rate of change for this section occurred during the second time period, at 2.82 m per year. In the second study section, the highest centerline dynamics were observed in interval 1 of the first period, interval 4 of the second, interval 7 of the third, and interval 7 of the fourth period. Here, the highest average dynamics also occurred during the second time period, at 2.92 m per year.
An assessment of river planform changes in the first section showed that the right and left banks were entirely compact in type during the first, second, and fourth time periods. In contrast, all banks were erosive in type during the third period. The greatest average periodic changes in this section were recorded during the second time period, measuring 1.38 m on the right bank and 5.46 m on the left bank. For the second study section, bank types varied temporally: in the first period, right banks were compact while left banks were erosive; in the second and fourth periods, all banks were compact; and in the third period, all banks were erosive. The highest average periodic changes in this section also occurred during the second time period, reaching 2.24 m on the right bank and 5.09 m on the left bank.
In the first study section, multi-temporal imagery and field observations over the 20-year study period (2006–2025) revealed extensive and significant changes in the river reaches. Prior to major flood events, these reaches experienced erosion accompanied by a notable reduction in channel width. Following flood events, however, a sudden increase in sediment supply and the presence of highly erodible banks triggered substantial lateral expansion in addition to continued bed erosion. A comparative temporal analysis indicated that the six examined reaches underwent not only bed erosion but also a reduction in channel width of up to ten meters.
In the second section, the river exhibited different behavioral patterns. Before major floods, reaches experienced only minor erosion with negligible widening. In the post-flood period, a combination of increased sediment supply, removal and thinning of riparian vegetation, and bed erosion led to significant channel expansion. Temporal comparison showed that the seven studied reaches in this section were subject to both bed erosion and a cumulative channel widening of eight meters.
Conclusion
Although channel banks particularly in alluvial rivers are rarely stable and naturally fluctuate over time due to compaction and erosion, the magnitude of change observed in the study reaches during the investigation period suggests an unnatural river condition. Lateral channel migration is a critical process that sustains river ecosystems and forms an integral part of natural river dynamics; the deviations observed here, however, imply potential anthropogenic influences or altered hydrological regimes.
Given the high land value in this mountainous region, flooding can lead to the loss of agricultural land and damage to infrastructure and residential areas. In addition to affecting agriculture and rural settlements along both river sections, the extent of this vulnerability is significantly greater and more severe in the northern section than in the southern part of the study area. This disparity is largely attributable to the downstream location of the city of Khorramabad. Therefore, to enable more effective and efficient river management in this section, it is essential to identify and regulate areas prone to severe channel adjustment.