SATELLITE IMAGERY ANALYSIS OF SEDIMENTATION IN THE SAN GABRIEL RESERVOIR, LOS ANGELES, CALIFORNIA

The San Gabriel Reservoir regulates the San Gabriel River that runs through Los Angeles, a highly developed city that lacks abundant permeable surfaces. Prolonged reservoir sedimentation can influence flood devastation in the urban landscape by reducing basin water holding capacity. In this study, we quantified sedimentation in the San Gabriel Reservoir using satellite images of suspended sediment. We analyzed reservoir trapping efficiency in the San Gabriel Reservoir using suspended sediment concentration estimated from Landsat satellite images from 2014 to 2024. Suspended sediment concentrations from two locations, the upstream San Gabriel Reservoir and the downstream Morris Reservoir, were compared to calculate trapping efficiency.

These analyses reveal that the average trapping efficiency of suspended sediment in the San Gabriel Reservoir is 72% for the entirety of the sample years. In 2022, the upstream suspended sediment count was an average of 189.1 mg/L with a trapping efficiency of 95%. In 2023, the suspended sediment count was an average of 85.8 mg/L with a trapping efficiency of 70%. The study revealed that higher levels of suspended sediment result in higher trapping efficiency rates. These results suggest that the dam is capable of trapping the majority of sediment that moves through the San Gabriel River, regardless of the amount of suspended sediment. Overall, the study revealed that the San Gabriel Reservoir is an effective sediment trap.

Further investigation will examine a correlation between river discharge and the trapping efficiency of suspended sediment in the San Gabriel Reservoir. Additionally, large events that overwhelm the infrastructure and carry large amounts of sediment will be analyzed. These analyses will contribute to a better understanding of the future efficiency and stability of reservoirs in order to create strategies to maximize water holding capacity of our current infrastructure.