Monitoring of Debris-glacial floods by radar interferometry (case study: Debris-glacial flood of 2022 in Oshtorankuh East Lorestan)

A B S T R A C T
Monitoring the performance and environmental changes caused by deposited floods play an important role in land planning and management. Monson's rains in summer 1401 occurred in large areas of Iran, which in the Astran Mountain created a flood of deposits. It also had significant morphological changes to the most important river in the area  and damaged the water transfer facilities of the cities of Azna and Aligudarz . Nowadays, radar methods are effective in studying qualitative and quantitative dimensions of deposited flows, with high accuracy and low cost, and this study is also for tracking the origin of deposits-ally from radar and Sentinel-1 and index data (NDSI) to evaluate the impact of sudden snow melting. Used in snowmelts in the area. The results indicated the sudden melting of snowmelts in the area due to Monson's rainfall, which played an important role in the creation of a deposited-water flood. The flow through the glacier valleys of the area, the plant's sediments and remnants of the area were transferred to water transfer facilities and caused a lot of damage to them. Radar analysis of water zones also showed that the Kamandan Dam before the flooding phase has prevented more serious damage to the downstream
Extended Abstract
Introduction
Natural hazards can affect living beings and especially humans in various scales. Also, geomorphological hazards are considered one of its most important sub-sections. Also, it is necessary to record information such as: magnitude, frequency, extent of the area, speed of onset, spatial distribution and time interval for each of the geomorphic hazards. Every year debris floods cause great damages to humans and significant geomorphic changes in the mountaneous basins. Debris floods carry a lot of sediments along with the remains of plants, trees and large boulders for a long distance and in a short time, they have the ability to cause significant human and financial losses in the downstream areas. In general, a flash flood phenomenon has three parts: 1- source area, 2- transfer area, and 3- accumulation area. Monitoring and environmental changes caused by debris floods play an important role in planning and managing land use. ongoing land use and climate changes increases the frequency of debris floods. Due to complexity of flood debris occurance mechanism, it attract many researchers attentions.Since, the debris floods in mountainous areas, contain glacial sediments, it also called debris-glacial floods. The researchers identify the heavy rains that happened in a short period of time and the melting of snowdrifts and the sudden increase in air temperature in the mountainous areas as the main driving factors for the occurrence of devastating debris floods. Tracing the origin of glacial sediment production in flood in different parts of a mountain can help us in the implementation of protection plans to identify sediment production areas and prevent their transfer in subsequent floods to the downstream areas. One of the technologies for tracking and monitoring debris-glacial floods is the use of interferometric radar. One of the techniques used in interferometric radar is the use of offset tracking, that its efficienvy is proven in the studies related to monitoring glaciers, landslides, and moving dunes. Monsoon rains in the summer of 1401 occurred in large areas of Iran, which caused avalanche-glacial floods in Oshtorankuh. In this study, the interferometric method was used to trace the origin of the debris flood event occur at july 2022 in Oshtorankuh area located in eastern Lorestan.
 
Materials and methods
The type of this sudy is applied-developmental research and its method is analytical-field. The input data used for this research is Sentinel 1A_IW-GRDH data in two ascending and descending orbits for use in offset tracking and McVitie techniques and Sentinel-2A data for use in the NDSI index. The offset tracking technique was used to determine the places in the Oshtorankuh with the most sediment mass displacement. This method is based on the calculation of the displacement in the pixel unit using the optimization of the mutual correlation between the pair of images resulting from the phase intensity of the SAR data. Also, the Normalized-Difference Snow Index (NDSI) was used to monitor the condition of the snow reserves of Oshtorankuh before and after the monsoon rains. This index is based on low reflectance in the mid-infrared and high reflectance in the visible region, which can distinguish snow-covered areas from non-snowy and cloudy areas. McVittie technique was used to determine the situation and prepare a flood map downstream of the Kamandan basin.
 
Result and discussion
By using the offset tracking technique, the soil masses displacemant after the northeast monsoon rains of Oshtorankuh (Kamandan) in two descending orbits and ascending orbits were identified and analyzed. The results show that the highest recorded values are due to displacement tracking belonging to the cirques, snowdrifts, and glacial deposits of Oshtorankuh. Also, the highest displacement and speed of movement related to the sediments of Kol-e Geno Cirque and Aznadar glacial deposits are located in and at the lower levels of the sediments in Kol Jeno and Aznader glacial valleys. From this event, the V shape (interglacial period) was in the U-shaped bed (glacial period), it has given its place again to the U shape (caused by the sediments carried by the debris flow). Also, the changes in snow cover before and after the monsoon rains were poreover, the results revealed melting of all the snowfields located around the cirques and glacier valleys of Kol-e Geno and Eznader ranges in the period. Also, the morphological responses of the waterways to the debris-glacial flood event were not the identical, and some responded by digging or filling. Another point is that the degree of sphericity and poor compaction of the sediments transported by the debris flood shows that there are few channel erosions in them and most of them are from the glacial sedimentary deposits of this mountain such as the end parts of the cirques and moraines. This dangerous event also caused a lot of damage to the water conceyancy structures and canals from this region to Aliguderz and Azna. The condition of the downstream basin and the recently drained Kamdan Dam showed the retention effect of this structure on preventing the flooding of the downstream parts.
 
Conclusion
Nowadays, the use of interferometric radar in monitoring environmental changes has become a popular and practical tool. In this research, it was found that it is possible to evaluate and identify the displacement and origin of sediment deposits, as well, quantify their speed and movement patterns using interferometric radar and the Offset tracking technique. The monsoon event occurred at July 2022 leads to sudden melting of the snowfields in Oshtorankuh played and a flash floods along with glacial deposits. But field evidence showed that waterway responses to this event is not identical. Considering that this region plays an important role in supplying water to its neighboring cities and some regions of central Iran, the results of this research can be used in the management and supply of water resources and the management of torrential floods to reduce possible damages to water transmission channels. The evaluation of the floodplains in the lower basin shows that the dams can be at risk of being filled with deposited sediments. Therefore, it is requested that the potential of a deposited flood be taken into account in the location stage. Although Kamandan reservoir stored a significant part of the flood and prevented damage to the residential and agricultural areas downstream of the dam.
 
Funding
There is no funding support.
 
Authors’ Contribution
All of the authors approved thecontent of the manuscript and agreed on all aspects of the work.
 
Conflict of Interest
Authors declared no conflict of interest.
 
Acknowledgments
We are grateful to all the scientific consultants of this paper.