Erosion risk modelling
Issue
- The proportion of harvesting on steep terrain will increase significantly as the plantings of the early 1990’s mature.
- Shallow landslides can trigger debris flows that cause huge damage to the environment, infrastructure and put at risk the industry’s licence to operate.
- There is no standard objective erosion risk assessment that can guide investment decisions in harvesting, engineering and afforestation decisions.
Potential cost
The cost of erosion is potentially large in terms of lost soil productivity, damage to the environment and infrastructure, or loss of human life.
The possible loss of the industry’s licence to operate in erodible hill country or increasing compliance costs imposed by regulators has the potential to impact on the viability of the industry in many regions.
Research
Researchers have tested two modelling approaches for predicting erosion events.
Both models use detailed information including LiDAR data to create Digital Elevation Models (DEM) for the two test catchments used in the study.
Both models predicted over 70% of slips in at-risk areas with one accurately predicting the likelihood of slipping.
The work also showed that increasing the DEM resolution, from 20 m to 1 m, increased the accuracy of slip prediction.
Outcomes
The work has resulted in a significant advance in assessing erosion susceptibility at a local property scale compared to the generalised subjective approach (1:50,000) used in the proposed National Environmental Standard for Forestry.
Conclusion
Based on the results of this work it is now possible to develop a standard methodology for erosion risk assessment on steep slopes for use by both harvesting and afforestation planners and council planners.
The benefits for the industry, if this could be achieved, would be continued licence to operate on steeplands and stemming the flow-on negativity to all hill country harvesting.
