Typical small shovel logging system, using manual felling and extraction by small crawler excavator with grapple and crawler carriers, is the predominant logging method in the Republic of Korea, due to the associated high productivity. The trails with ground pressure and one more passes of the shovel and carriers may lead to soil compaction. However, impacts of these bunching-extraction technologies on physical and hydrological properties of soils are not well known. The main objectives of this study were to: (1) determine the bulk density, porosity, and saturated hydraulic conductivity of soils in logging operation areas with three different disturbance types (i.e., undisturbed areas [UAs], bladed trails [BTs], and skid trails [STs]), and (2) compare soil compaction between these disturbance types. The most intense compaction occurred within BTs and STs, with increased bulk density and reduced porosity and hydraulic conductivity. Soil bulk density increased by 27-53% at all depths in BTs and STs compared to UAs, while porosity decreased by 23-49%. On average, saturated hydraulic conductivity at depths of 0-20 cm decreased from 337.5 mm h-1 to 30.5 mm h-1 in the most compacted sections of BTs and STs. Skid trails, which are characterized by trail construction and frequent vehicle movement, also caused greater impacts on soil compaction than BTs. This study provides useful insights to aid forest consultants and field managers in planning more environmentally sound mechanized logging operations.

Soil erosion control dams are widely used as part of measures to reduce damage caused by debris flow all over the world. Engineering considerations are needed for proper design of erosion control dams, but in the Republic of Korea, the impact force of debris flow is not fully reflected in the current design criteria of the dam. Against this backdrop, this study was conducted to estimate the impact force of debris flow for the practical purpose of designing erosion control dam. Simulated flume experiments were performed to develop the relationship to estimate the flow velocity as well as the impact force of debris flow. Experimental results showed that increases both in sediment mixture volume and flume slope gradient led to an increase in flow velocity. Especially, it was found that as clay content increased gradually, the flume slope gradient had greater impact on the increase of flow velocity. Also, it was proved that the impact force of debris flow was well fitted to the hydrodynamic model as it showed linear correlation with the flow velocity. Then, the debris‐flow velocity model was established based on the factor related to the debris‐flow velocity. Finally, the dynamic model to estimate the impact force of debris flow was introduced utilizing correlations between the established debris‐flow velocity model and Froude number. Both models which were developed with using statistically significant watershed characteristics succeeded in explaining the experiment results in a more accurate way compared to existing models. Therefore, it is highly expected that these models can be fully utilized to estimate impact force of debris flow which will be required to design erosion control dams in practical use through overcoming their identified limitations.

Landslides are major forest disasters in the Republic of Korea that result in significant loss of life and property damage. Since the 1980s, the National Institute of Forest Science has conducted various studies on nonstructural landslide mitigation, including early warning systems and susceptibility mapping, to reduce damage induced by landslides. A landslide early warning system based on the TANK model was developed and used for decision-making on the preparedness level and for ordering evacuations for local people. A nationwide 5-level landslide susceptibility map was developed based on logistic regression in the 2010s, considering geological, geographical, and forest characteristics. In addition, we provide primary data for determining evacuation priorities by developing debris-flow hazard zonation and societal vulnerability assessments in that area. For public awareness, all of this information is provided through the WebGIS platform “Landslide Information System.”

Debris flows, consisting of water–sediment mixtures that travel rapidly along channels, often carry materials ranging from fine sediments, such as clay or silt, to large boulders, resulting in significant impacts on lives and infrastructure. Accurate estimation of the debris-flow behavior is crucial for establishing effective debris-flow mitigation strategies. However, the dynamic entrainment process complicates simulations because it significantly affects flow characteristics, including velocity, depth, and sediment concentration. In this study, we analyzed the effects of entrainment on debris flow simulations using two one-dimensional models for a debris-flow event that occurred in 2011 in Seoul, Republic of Korea. The results show that including entrainment improves the accuracy of the debris-flow simulation. Moreover, a scheme dealing with entrained sediment in the governing equations is important for reproducing debris-flow characteristics. These findings highlight the necessity of entrainment models for effective debris-flow simulation, with implications for enhancing debris-flow hazard mitigation strategies.

Rainfall-induced landslide early warning systems require reliable estimation of soil moisture conditions. This study proposes a Soil Water Index (SWI) framework based on a three-stage TANK model. Through GLUE (Generalized Likelihood Uncertainty Estimation)-based behavioral parameter sampling and K-means clustering, SWI response characteristics were classified into two representative scenarios: slow drainage (Scenario 1) and fast drainage (Scenario 2). Two-stage thresholds—Watch (α = 0.40 × SWI_peak) and Warning (β = 0.70 × SWI_peak)—were established from SWI rise profile analysis at 500 m and 5 km resolutions, providing 20–27 and 4–5 h of lead time, respectively. Verification against the July 2025 heavy rainfall event across multiple resolutions and spatial extents yielded Hit Rates of 0.984–1.000, while FAR (False Alarm Ratio) remained structurally high (0.607–0.648 for grids sharing the rainfall field with occurrence sites). These findings confirm that SWI serves as an effective regional-scale necessary condition indicator for landslide-triggering moisture, but FAR reduction requires integration with slope susceptibility information.