Spencer Dam filled with sand within a couple decades of construction int he 1920s. After that, it flushed sediment twice a year to make room for hydropower operations. Dr. Paul Boyd recorded a time lapse video of the first day of the flush in 2014.

We talk about this operation on season 2 of the RSM River Mechanics Podcast, which is dedicated to Reservoir Sediment Management:

https://www.hec.usace.army.mil/conflu...

Apple: https://podcasts.apple.com/us/podcast...

We also measured and modeled this event and documented it in a paper:
Gibson, S. and Boyd, P. (2016) "Monitoring, Measuring, and Modeling a Reservoir Flush on the Niobrara River in the Sandhills of Nebraska," River Flow Proceedings of the International Conference on Fluvial Hydraulics, RIVER FLOW 2016 pp. 14481455.

https://rsm.usace.army.mil/pubs/pdfs/...