The objective of this paper is to develop a model to estimate soil erosion based on data from natural rainstorms on the hillslopes of burnt mountains. For this research, 52 plots were established on mountain slopes in the eastern coastal region of South Korea and operated for 6 years after the fire. Runoff and soil erosion were influenced greatly by rainfall and vegetation factors, respectively. The vegetation index that reflects the structure of vegetation recovered after the forest fire and the soil index that reflects soil characteristics in burnt forest lands showed higher correlations than factors of the revised universal soil loss equation (RUSLE). Sediment yield decreased generally with increasing slope steepness and length because of the effects of depression storage and flow interception by stems and litter on forest lands. The Soil Erosion Model for Mountain Areas in Korea (SEMMA), used to compute sediment yield from hillslopes, is a statistical model composed of four variables: rainfall, vegeta...

The second-largest wildfire in the history of South Korea occurred in 2022 due to strong winds and dry climates. Quantitative evaluation of soil erosion is necessary to prevent subsequent sediment disasters in the wildfire areas. The erosion rates in two watersheds affected by the wildfires were assessed using the revised universal soil loss equation (RUSLE), a globally popular model, and the soil erosion model for mountain areas (SEMMA) developed in South Korea. The GIS-based models required the integration of maps of the erosivity factor, erodibility factor, length and slope factors, and cover and practice factors. The rainfall erosivity factor considering the 50-year and 80-year probability of rainfall increased from coastal to mountainous areas. For the LS factors, the traditional version (TV) was initially used, and the flow accumulation version (FAV) was additionally considered. The cover factor of the RUSLE and the vegetation index of the SEMMA were calculated using the normalized difference vegetation index (NDVI) extracted from Sentinel-2 images acquired before and after the wildfire. After one year following the wildfire, the NDVI increased compared to during the year of the wildfire. Although the RUSLE considered a low value of the P factor (0.28) for post-fire watersheds, it overestimated the erosion rate by from 3 to 15 times compared to the SEMMA. The erosion risk with the SEMMA simulation decreased with the elapsed time via the vegetation recovery and stabilization of topsoil. While the FAV of RUSLE oversimulated by 1.65~2.31 times compared to the TV, the FAV of SEMMA only increased by 1.03~1.19 times compared to the TV. The heavy rainfall of the 50-year probability due to Typhoon Khanun in 2023 generated rill and gully erosions, landslides, and sediment damage in the post-fire watershed on forest roads for transmission tower construction or logging. Both the RUSLE and SEMMA for the TV and FAV predicted high erosion risks for disturbed hillslopes; however, their accuracy varied in terms of the intensity and extent. According to a comparative analysis of the simulation results of the two models and the actual erosion situations caused by heavy rain, the FAV of SEMMA was found to simulate spatial heterogeneity and a reasonable erosion rate.

Studies of sediment transport problems in mountainous rivers with steep slopes are difficult due to rapid variations in flow regimes, abrupt changes in topography, etc. Sediment transport in mountainous rivers with steep slopes is a complicated subject because bed materials in mountainous rivers are often heterogeneous and contain a wide range of bed material sizes, such as gravel, cobbles, boulders, etc. This paper presents a numerical model that was developed to simulate the river morphology in mountainous rivers where the maximum bed material size is in the range of cobbles. The governing equations were discretized using a finite difference method. In addition, an empirical bed load formula was established to calculate the bed load transport rate. The flow and sediment transport modules were constructed in a decoupled manner. The developed model was tested to simulate the river morphology in an artificial channel and in the Asungjun River section of the mountainous Yangyang Namdae River (South Korea). The simulation results exhibited good agreement with field data.

A large wildfire occurred due to strong winds and dry climates in the Gangwon province of South Korea. Thereafter, floods and sediment damage were caused by Typhoon Mitag in the burned areas. This study was an attempt to quantitatively evaluate the risk of soil erosion in wildfire areas using the Soil Erosion Model for Mountain Areas (SEMMA) based on GIS, which was developed in South Korea. The model required the integration of maps of the main factors involved, i.e., rainfall erosivity, vegetation index, soil erodibility, and slope length and steepness. According to the model simulation results, high erosion rates of over 100 t/ha were concentrated within the wildfire areas. Sediment yields from the study watershed, including the wildfire areas, were estimated to be 40.33 t/ha for the 30-year frequency of rainfall, which is similar to those of the typhoon. The high risk of erosion was predominantly observed in the upper mountains, which are characterized by steep slopes, silt loam, and shallow soil depths within the wildfire areas. Urgent and excessive logging of burned trees further increased the risk of erosion. However, various treatment strategies were implemented to control soil erosion and sediment transport from the post-fire watershed. This study confirmed that temporal and spatial BMPs should be selected and enforced to reduce sediment disasters in wildfire areas.

Hydraulic characteristics of rill incipience on steep slopes with sandy soils are different from those of gentle slopes in the mountainous watersheds. In other to better understand the processes of the incision and expansion of rill, rainfall simulations were conducted in a laboratory soil box with an inflow device installed at the top of the steep slope. The location and shape of the rill incision were tested with respect to different slopes (20, 24, and 28°), rainfall intensity (80 and 100 mm/h), and segment distances with various inflow rates (0.0, 8.8, 17.5, and 26.3 ml/s). The result showed that rills with heatcut were mostly incised on the 2.4 m segments and progressively moved upslope on the 3.2 m segments. The steps of rill evolution with increase of inflow are identified as four stages; (1) sheet flow with impact of raindrops, (2) overland flow with flowpaths, (3) microrill with headcut incision, and (4) rill enhanced by headcut expansion. It appears that incision and headcut of rill is prevalent when the Froude number (Fr) changes from subcritical flow to supercritical flow and the maximum velocity of rill reaches over 0.065 m/s. Unit stream power using the maximum velocity of rill was the best parameter for estimating rill erosion as rill evolution greatly depends on maximum velocity of the local flow enhanced by rill incision and expansion As a result, it was found that critical conditions for rill incipient of sandy soils on steep slope are observed greater than those of loamy soils or gentle slopes.

This article presents that deicers such as calcium chloride (CaCl₂) and EFDs (Eco-Friendly Deicers) composed with organic acids affect germination of seeds buried in old-field soil. CaCl₂, one of a commonly used deicer in the world, have shown an inhibitory effect on the germination of the buried seeds. Species richness, species diversity, and total biomass of the plant community after germinating were greatly decreased with increase of CaCl₂ concentration. The germination of buried seeds was inhibited seriously by CaCl₂, but the degree of its varied significantly with plant species. EFD1 manufactured from organic chemicals showed the higher inhibition on germination than CaCl₂. However, EFD2 composed with organic acids of food waste didn’t have an inhibitory effect on the species richness after germination and rather enhanced the germination and initial growth of the seedlings. The positive effect was evaluated that EFD2 caused to supply nutrition on germination or growth of buried seeds. The deicers may change dynamically the plant community of the roadside because the response of germination and growth by deicers differ from plant species.