PATTERNS OF DEPOSITION AND LANDSLIDES IN VERMONT STREAMS IN TROPICAL STORM IRENE

Tropical Storm Irene brought heavy precipitation and flooding, often exceeding the 100-year recurrence interval flow event, which resulted in large and frequent landslides and depositional features along riverways in Vermont. Although the geomorphic effects were widespread, the spatial distribution was not uniform. Moreover, the geomorphic effects did not follow a simple pattern of landslides focused in the upland headwaters and deposition focused in the downstream reaches. For example, only some headwater reaches of the White River exhibited landslides, while lower in the watershed there were groups of landslides separated by long reaches without landslides. On the Saxtons River, deposition exhibited an intermittent pattern, with floodplain deposits concentrated in distinct reaches separated by reaches of little to no near-bank deposition. Here we explore how the gradient in total stream power affects the spatial distribution of landslides and deposition. We find that reaches of increasing stream power are more susceptible to landslides and less likely to accumulate floodplain deposits. In contrast, reaches of decreasing stream power coincide with accumulation of floodplain deposits. We attribute the focal points of floodplain deposition to the decreasing total transport capacity of the river. These results can help prioritize stream repair efforts following future large floods, and improve basic understanding of how mountainous watersheds are affected by extreme events.