Geomorphic change detection on the upper Verde river using historical plots and terrestrial lidar

Abstract

The Upper Verde River in northern Arizona, one of the last free-flowing perennial rivers in Arizona, is a vital resource for the wildlife and humans that rely on it. This study combines historical United States Forest Service (USFS) single-line transect cross-section data with high resolution terrestrial laser scanner (TLS) data to quantify geomorphic changes along the Upper Verde River between 2009 and 2021-2022. Seventeen plots along the Upper Verde River were surveyed with the TLS and the data were registered together with a Root Mean Square Error of <0.03m among scan positions within individual plots. Digital Elevation Models (DEM) were derived for each plot from the TLS data at 10cm resolution and compared to the 2009 USFS cross-section data to quantify elevation changes. Empirical Cumulative Distribution Function (ECDF) analysis was used to determine the probability of true changes versus changes that could be attributed to errors in the datasets. All elevation changes with a p-value <= 0.05 were retained as true changes. The observed mean absolute change was +0.30m with a maximum erosion of -0.37m and maximum deposition of +0.97m. While deposition and erosion were documented at different locations in the study area, the results indicate deposition predominated within the flood-prone areas outside of the river channel over the last 13 years. Furthermore, greater deposition occurred in the lower reach of the river compared to the upper reach of the river. This study also demonstrates development of a new method that integrates historical single-line cross-section data with contemporary lidar data to quantify geomorphic change over time. This approach integrates traditional field-based survey methods and with newly available technology, which can be broadly implemented across a wide range of natural resource management applications