Abstract:
This study investigates gully expansion and quantifies soil erosion and sedimentation in the Dashte Jeyhoon watershed, Bandar Khamir County. The analysis utilized aerial photographs from 1967 and 1994, historical Google Earth images from 2012, and UAV imagery from 2023 to assess gully growth. Surface erosion was estimated using the WaTEM/SEDEM and RUSLE models. UAV imaging, with a ground sampling distance (GSD) of 3 cm, was conducted to map gully expansion and measure morphometric characteristics, providing an estimate of soil loss due to gully erosion. The findings indicate that the gully area increased from 132.64 hectares in 1967 to 326.39 hectares in 2023, with an expansion rate of 3.46 hectares per year. Detailed measurements were taken at 481 points using a digital elevation model (DEM) with a 6 cm accuracy, derived from UAV data. The average gully depth was found to be 1.01 meters, suggesting that the gullies in the study area are generally small to medium in size. The ratio of top width to depth exceeding 1 highlights significant implications for the destruction of agricultural lands and infrastructure. Flooding and water flow into the gullies were identified as the primary drivers of gully expansion in the watershed. The study estimated that average soil erosion from surface processes was approximately 3.40 tons per hectare per year, while total soil loss from gully erosion was around 52,000 tons per year. Over a 56-year period (1967-2023), the average soil loss due to gully erosion was calculated to be approximately 12 tons per hectare per year. The total annual soil loss from all erosion types in the Dashte Jeyhoon watershed was estimated at 15.4 tons per hectare per year.