| Culverts are commonly installed wherever roads cross small streams. Hanging culverts, those with elevated outfalls, are upstream movement barriers for fishes and cause watershed fragmentation. Half (50%) of industrial road culverts surveyed in four northern Alberta watersheds were hanging. Hanging culverts developed over time, at a rate regulated by landscape gradient. I developed HANGFRAG, a simulation model to compare stream fragmentation and infrastructure costs resulting from alternate road management strategies for simulated high and low gradient watersheds, at high and low levels of initial road development, for low and high degrees of management intervention. In both areas, low intervention was achieved cost-effectively by hanging culvert replacement, combined with road build rate reduction and stream crossing avoidance. For high intervention, greatest cost-effectiveness was achieved through the alternative use of temporary bridges, more so in steep landscapes. I placed watershed fragmentation in the context of island biogeography theory and constructed a conceptual watershed-scale strategic planning model for remediation of fragmentation. |
