Quantifying Landslide Activity in Response to Anthropogenic Drainage Reorganization in a Steep Mountain Basin, Dump Creek, Idaho, USA.

Abstract:

Drainage reorganization, where one watershed joins a different one, is an important process that has occurred throughout geologic time. The incision that occurs due to a capture event can steepen local hillslopes, generating a pulse of landslide activity; yet the rarity of such events has led to a paucity of data measuring the hillslope response to localized drainage reorganization. Dump Creek, in Idaho, provides a natural experiment to constrain such data. Dump Creek was historically a small stream, but placer mining activity in the area caused an adjacent creek, Moose Creek, to divert into Dump Creek around 1897. Moose Creek, above the point of contact, has a drainage area of more than 76 km², whereas Dump Creek had a basin of around 21 km². As a result, Dump Creek experienced historically intense flow rates from the increased snowmelt from higher elevations. Between the Salmon and the diversion point, hillslopes became unstable along all 4.8 miles of Dump Creek’s drainage, and the effects of this diversion are still correcting 40 years after Moose Creek was restored to its original stream path. This project is ongoing and uses Google Earth, stitched aerial photos, and LiDAR data to quantify hillslope processes between 1979 and 2019. We use the Topographic Analysis Kit for Matlab to model fluvial processes and reconstruct historical basins. Using aerial imagery and LiDAR, we map and quantify landslides along Dump Creek. The data allows us to estimate the erosion that has occurred after restoration and assess the health and stability of the hillslopes on Dump Creek between the Salmon and restoration project. We present the magnitude and frequency of mapped landslide processes and compare these hillslope processes to the pattern of incision quantified by extending relict landforms back to the valley center. The intense change in geomorphic rates and processes highlights the long-lasting impact of a sudden drainage change on landscape evolution and further underscores the impact of human activities on natural systems.

Figure: LIDAR image of canyon at headwaters of historical Dump Creek; this canyon is around 40 meters at its deepest and 500 meters at its widest.