@2024 Afarand., IRAN

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ISSN: 2538-4384    Geographical Researches 2021;36(2):205-216

Background
As the hidden active fault of Khorram Abad is located in Khorram Abad plain, this region is highly influenced by the neo-tectonic activities of the fault.
Previous Studies
Rivers' system reaction to the neo-tectonic activities, land-use changes, and climate changes are among the most important geomorphology studies. Geomorphological changes caused by geological activities are not specific to the unhidden faults and hidden ones' activity can have a great impact on the region [Bonforte et al., 2012; Rezauki et al. 2020, Aliyannezhadi et al., 2020; Bottari et al., 2020]. Hidden faults activity in Kumroj in the Kamchatka peninsula of Russia had increased the river width and depth [Cevera, 2013].
Aim(s)
This study aimed to evaluate the geological activities of the hidden fault of Khorram Abad in the formation of the geomorphological characteristics of the Khorram Abad river.
Research type
The current research is an empirical study in terms of its purpose.
Research society, place and time
The current research is carried out along the Khorram Abad river
Sampling method and number
The sampling method and the number of samples are not mentioned.
Used devices&materials
Aerial images of 1955 and Google earth images of 2016 in the GIS environment, as well as the field studies, were used in this study.
Findings by Text
Stream length-gradient index (SL) The analysis of the SL index shows that the amount of this index varies in different parts of the river. The lowest and highest values of the SL index are recorded in zone number 2 and 4, respectively (Graph 1). Decreasing SL in zones 2 and 5 show the gentle slope of the river in these zones. Figure 3 shows two main reasons for this issue. Lithological combination of the rivers' bedrock in different times is the most common explanation for the vulnerable rivers' bedrock. However, this bedrock lithological combination is almost the same along the river. Hence, lithology does not have a considerable impact. Khorram Abad, on the other hand, is an alluvial river that minimizes lithological impact on rivers' behavior. Zone 2 is located in the upper parts of the fault's anticline while zone 5 is in the lower parts. It explains the reason for the smaller SL in zone 5. There is a rise in the amount of SL in zone 3 and 4. Increased SL in zone 4 is mainly because it is located adjacent to the main axis of evolution. Increased SL in zone 3 is because of tilting to the back of the eastern edge of the anticline. Maunders and sinuosity amounts in various zones of the Khorram Abad river The minimum and the maximum number of the maunders both in 1955 and 2016 are detected in zones 1 and 5, respectively (Table 1). Fewer changes in the number of the maunders in zone 1 are because of its stone bedrock. While maunders are more abundant in zone 5 because this zone is located in the lower parts of the evolution axis of the hidden fault of Khorram Abad and the vertical movements of the fault increased the overall slope of the river. The river stroke a balance by creating new waves. The fewer number of the maunders in zones 3 and 4 that are located in the upper parts of the evolution axis is because of two reasons: the movements of the hidden thrust fault of Khorram Abad, human activities such as the construction of the walls in the riverbank, dredging, flattering the bedrock, and constructions near the river. The evaluation of the sinuosity amounts in different zones of Khorram Abad river in 1955 and 2016 shows that zone 1 in the first period had the lowest values which are mainly because the river is surrounded by strong stone walls. Hence, zone 2 and zones 5 have the lowest and highest sinuosity, respectively in the alluvial part of the river. A comparison between the S value in the first and second period shows that the S value has been almost consistent but had increased insignificantly in zone 2 and considerably in zone 5. S value had decreased in zones 3 and 4 (Figure 4). Khorram Abad river longitudinal profile According to the river's profile, the river has a concave profile. The transformation seen between 18 and 29 km from the beginning of the river's route shows turbulence in the river's bedrock (Graph 2). Mentioned turbulence made the river flow much faster and turbulent in comparison to the upstream and downstream of the river. The average speed of the river flow is 1.6 m/s in the middle of the river which is much faster than upperparts with 0.8m/s and lower parts with 0.56 m/s. Fluvial terraces near the river Some spots in the upper parts (anticline), middle parts, and lower parts of the Khorram Abad river were selected to analyze the fluvial terraces (Figure 5). For the estimation of the relative age of these terraces, geomorphological features, sequences, sedimentological features, and stratigraphic connections were used. Three types of old, middle-aged, and new terraces can be seen in the lower parts of the river. Figure 6 shows the alluvial terraces in Khorram Abad river. Differences in the height of the terraces in different parts of a river, similar to that of the Khorram Abad river, approves the tectonic activities such as Khorram Abad's hidden thrust fault activities (Table 2).
Main comparison to the similar studies
Human activities in the Khorram Abad river have increased the overall slope of the river and consequently sinuosity coefficient and formation of the new maunders. Other researchers such as Silva et al. (2003) in the southern parts of Spain, Malik et al. (2014) along the Aegean coast, and Ramesht et al. (2012) in the Jajrood basin used this index (SL) to evaluate the impact of neo-tectonic activities in the formation of the geomorphological features of the river.
Suggestions
There is no suggestion reported.
Limitations
There is no limitation reported.
Conclusions
Among three main factors of tectonic, water flow rate, and sediment flow rate, tectonic plays the most important role in the geomorphological features of the Khorram Abad river in the last decades. Since the flow rate and sediment flow rate in the Khorram Abad river have been decreasing but such changes just occur when the trend is increasing. Then, the hidden thrust fault of the Khorram Abad is the main factor changing the morphological features of Khorram Abad river in the studied period.
Acknowledgments
We thank Razi University, the Iranian geological organization, and the regional water company in Lorestan that provided needed information for the researchers.
Conflict of interest
None.
Ethical Permissions
None.
Funding Sources
This study is carried out on Razi University of Kermanshah expense.

TABLES and CHARTS

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