Remote Sensing of Alluvial Fan Erosion and Deposition In Thurgood Canyon

The Thurgood Canyon alluvial fan, located on White Sands Missile Range (WSMR), is bisected by a primary installation road and is in the proximity of sensitive fish habitats. The intense, high energy flow events from arid mountainous environments and resulting large sediment loads create scour and deposition that can negatively impact drainage structures, the roads they protect, and local sensitive habitats and their species, especially those present on or near alluvial fans. This project was initiated to determine if/how sensitive fish habitats at the base of the Thurgood Canyon alluvial fan are impacted by the existing drainage infrastructure and to assess the condition and sustainability of the existing transportation infrastructure. Analysis of remotely sensed data was a primary method of assessing current conditions and historic changes of the alluvial fan due to the remoteness of the study sites and frequent inability to access the site due to military testing restrictions in the area. Using locally collected LiDAR data and aerial images from the USGS National Agricultural Imagery Program (NAIP), flow impacts and sediment depositions were mapped to determine current infrastructure conditions and develop more sustainable designs or management approaches. The location and pattern of sediment deposition, erosion, and channel formation over time along the lower reaches of the fan were also mapped to determine if the current drainage infrastructure or proposed changes to drainage infrastructure may increase (or mitigate) potential overland flow impacts to the sensitive habitat downstream. Findings show that the current drainage infrastructure maintains flow energy and sediment carrying capacity further down the fan than would occur in its absence. However, frequent to moderately rare (small to medium) flood events dissipate over 2 km from sensitive habitat and overland flow and sediment do not reach the base of the fan. Controlled flow diversion is recommended upstream of the primary installation road to mitigate both infrastructure and habitat impacts during very rare (very large) flood events.