Evaluation of the Effectiveness of Trail Repair Works Based on Three-Dimensional Monitoring around Mount Kurodake, Daisetsuzan National Park, Japan

Abstract

Many mountainous, protected areas, such as national parks worldwide, face trail erosion; stakeholders have made significant efforts to manage eroded trails. However, their effectiveness has not been evaluated. This study aimed to (1) create digital elevation models of an eroded trail using structure-from-motion and multi-view-stereo photogrammetry in Daisetsuzan National Park, northern Japan; (2) conduct a six-year monitoring of the trails repaired by volunteers to reveal trail surface changes; and (3) discuss the effectiveness of the repair works. Palm-fiber bags were used on the trail section to stop the movement of the eroded soil. The results of the three-dimensional analysis identified a certain effectiveness of the repair work during 2017–2022. However, the effectiveness lasted for only approximately three years and was not permanent. Therefore, regular maintenance is necessary to ensure trail sustainability. In addition, the soil erosion rate calculated using the maximum erosion depth has increased from 0.52 mm y−1 (1923–1990) to 44.4 mm y−1 (2013–2022), suggesting the need for frequent observations. Trail maintenance through a combination of monitoring and repair work is vital, and the role of hikers/trekkers is becoming increasingly important.