Untangling Geomorphic Processes in the Grand Canyon with Topographic Time Series from Hybrid Surveys

Sandbars along the Colorado River in the Grand Canyon are a fundamental part of the landscape – creating habitat for native plants and animals, providing camping beaches, and supplying sediment needed to protect archaeological resources. The Glen Canyon Dam just upstream of the Grand Canyon reduces the amount of sediment available for sandbars and the flows available to deliver sediment. Decades of intensive monitoring and research have been conducted to better understand the altered sediment budget of the Colorado River, particularly the erosion and restoration of sandbars. To make management decisions that aid in sandbar retention it is important to understand the sediment budget, specifically the fluxes and changes in storage. Recently, the explosion of different methods for collecting high-resolution repeat topographic datasets in rivers has led to the ability to monitor longer reaches and build topographic spatiotemporal time-series of river reaches. Unfortunately, no single data collection method works everywhere and many methods have been combined to build a representation of the Colorado River. For nearly two decades, over 30 miles of river and over 60 discrete sandbar sites along the Colorado River below Glen Canyon Dam have been surveyed repeatedly with a combination of multi-beam SONAR, single-beam SONAR, photogrammetry, LiDaR and total station surveys. Survey data has been analyzed to explore how experimental flood releases, timed with natural sediment inputs, alter landforms downstream of the dam. However, current monitoring efforts do not and cannot produce a complete (spatial) sample of all the change in storage throughout the Canyon. Here we present results of analyses using a new version of the Geomorphic Change Detection software. A budget segregation feature is exploited to decompose the budget by specific geomorphic mechanisms of change. We explore whether changes in storage can be explained by geomorphic, hydrologic, and vegetative metrics collected through topographic surveys and existing discharge data. By utilizing a hybrid of available datasets for estimating changes in storage, we gain insight into how different eddybar - fan complexes are evolving through time in response to a highly regulated flow regime and experimental flood releases