Erosion and Erodibility from Off Highway Vehicle Trails in Alberta's Southern Rocky Mountains
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Abstract
Runoff, sediment production, and erodibility from off highway vehicle (OHV) trails was studied using rainfall simulation experiments and natural rainfall observations in Alberta’s south-west Rocky Mountains to evaluate the suitability of models such as Universal Soil Loss Equation (USLE) to support management of OHV trails networks by identifying problem areas for mitigation. Sediment production from rainfall simulation on small 1 m2 plots (< 2 yr. return period 20 min. precipitation of 22.5 mm hr-1) ranged from 0.01-6.4 tonnes ha-1 of trail surface while natural storms on larger trail segments produced 0.9-43.3 tonnes ha-1 from larger storm events ranging from 35.6-146.3 mm (peak 30 min. intensity 4.6-24.4 mm hr-1). Both studies showed that trail use intensity was a chief factor governing both runoff and erosion with greater erosion from trails with greater OHV intense use. Rainfall simulations showed that usage rates, reflected in trail organic matter content, affect runoff pathways through compaction and reduction of infiltration on high use trails, and through greater surface roughness, and increased infiltration on low use trails. Natural rainfall observations likewise showed variable patterns of erosion, reflecting variable physical trail characteristics and use rate intensity with trails receiving greater use producing greater rates of erosion than current models such as USLE predict. While, sediment availability and erodibility were strongly affected by OHV use, soil properties commonly used to predict erodibility and required to model erosion using a broad suite of erosion models, substantially under-predicted erodibility on higher use trails. However, natural rainfall observations also showed a simple linear response between erosion and event precipitation for high use trails, suggesting that regionally specific precipitation-erosion relationships may offer an interim solution to erosion prediction from OHV trail networks.