Speaker
Description
Forest road infrastructure plays a multifunctional role in mountain forest management, with a focus on enabling efficient forest management while potentially altering catchment hydrology and flood response. Despite their importance, the quantitative hydrological effects of forest road networks under varying maintenance conditions are not well understood, which limits evidence-based planning and prioritisation of infrastructure investments. This study combines a comprehensive digital road network assessment with hydrological scenario modelling to quantify the influence of forest road condition and drainage functionality on runoff dynamics in the Rindbach catchment in the Northern Limestone Alps in Austria.
First, the entire network of forest roads accessible to trucks within the catchment area was digitally recorded. Then, selected sections were inspected through systematic on-site surveys. These surveys included a detailed assessment of culverts, the condition of the road surface, longitudinal drainage systems and the load-bearing capacity in both dry and wet conditions. The results revealed significant deficiencies in the infrastructure. For instance, only 59% of culverts were fully functional, while 22% were non-functional and just 18.2% of longitudinal drainage systems were operating at full capacity. However, the load-bearing capacity remained adequate, even in wet conditions (an average of 72.7–73.9 MN/m²), indicating the prevailing geology (limestone). This suggests that weather-related usage restrictions are primarily due to drainage deficiencies rather than structural deficiencies.
Hydrological simulations were then performed using NASIM a deterministic precipitation-runoff simulation tool to evaluate three infrastructure scenarios: (i) the natural state without roads; (ii) the optimal state with fully functional drainage; and (iii) the actual state with documented deficiencies. These simulations were conducted under a 10-year, 12-hour design precipitation of 118 mm. In the sub-catchment areas, peak discharge (Q_max) decreased from 8.90 m³/s in the natural state, to 7.50 m³/s with optimal drainage infrastructure, and to 6.80 m³/s in the actual state. This demonstrates that functional drainage systems could act as effective buffers, flattening hydrographs and reducing flashiness indices. Deficient structures prolonged concentration phases and increased baseflow duration through uncontrolled retention effects. These findings challenge the conventional assumption that forest roads universally accelerate runoff, revealing that properly designed and maintained drainage infrastructure could mitigate rather than exacerbate flood risk.
The practical implications emphasize the targeted improvement of culverts and drainage ditches, the strategic closure of little-used roads to restore retention areas, and the implementation of decentralized water retention measures such as retention ditches and infiltration zones. The digital road network provides a solid basis for maintenance planning in line with requirements, hazard assessment, and prioritization of forest road infrastructure investments. This integrated approach demonstrates that hydrologically sensitive forest road planning, combining regular functional monitoring and maintenance with strategic design, improves both operational stability and flood protection at the watershed level in mountainous regions.
| Keywords | Runoff; Drainage; Maintenance; Hydrology |
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