A morphodynamic model to evaluate long-term sandbar rebuilding using controlled floods in the Grand Canyon

Controlled floods released from dams have become a common restoration strategy in river systems worldwide. Here we present a morphodynamic model of sandbar volume change for a subset of sandbars of the Colorado River in Grand Canyon National Park, where controlled floods are part of a management strategy focused on sandbar maintenance. We simulate sandbars as a triangular wedge, where deposition and erosion are modeled using physically based approaches that are driven by nearly continuous observations of flow and suspended sand concentration. We optimize an eddy exchange coefficient and erosion rate parameter by comparing model predictions to measured bar volumes. The model captures most of the variability in observed volume changes, and demonstrates the importance of flood frequency and sand concentration on average bar size. The model is easily implemented and adaptable, providing a means for predicting the future behavior of sandbars under a variety of streamflow and sediment supply scenarios.