Landslide erosion risk to New Zealand pastoral steeplands productivity
✍ Scribed by P. G. Luckman; R. D. Gibson; R. C. Derose
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 235 KB
- Volume
- 10
- Category
- Article
- ISSN
- 1085-3278
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✦ Synopsis
Pastoral land use in New Zealand's North Island hill terrain has led to high rates of rainstorm-induced landslide erosion higher than existed under the indigenous forest regime, with consequent soil productivity declines in the long term. To assist extrapolation of research results to other areas, and to shed light on long-term erosion risks, a simple model was developed that simulates the evolution of hillslope soil productivity, taking into account the eect of slope, rainstorm magnitude±frequency relations and soil recovery rates. Risks are evaluated by Monte Carlo simulation, and re¯ect parameter uncertainty as well as the natural randomness associated with climatic events. A sensitivity analysis showed that landslide risk was most aected by the rainfall threshold for landsliding, the mean of the extreme value distribution for annual maximum storm rainfall, and the maximum degree of recovery of pasture productivity following landsliding. Simulations suggest productivity stabilizes at a reduced level well before all steep terrain is aected by landsliding, and that subsequent expected landslide-induced productivity declines are too slow to provide sucient economic motivation for measures to prevent landslide damage. A re®ned model showed that long-term average rates of productivity decline are sensitive to changes in recovery rates resulting from progressive removal of the soil resource. Charts summarizing simulation results can be used to estimate long-term productivity declines.