Piracy on the Niobrara : A Geomorphic Examination of Waterway Banditry

Abstract

Our research is focused on the geomorphic history of the Niobrara River, located in northern Nebraska. This river exhibits noteworthy landforms, including a large number of terraces. The goal is to determine what event(s) may have taken place to cause these formations. Through analyzing the terraces, it’s apparent that it has drastically aggraded and degraded to form a complex series of terraces. The Niobrara is located just north of the Nebraska Sand Hills, which is a crucial aspect of the landscape that contributes to the river’s geologic history. To understand what happened, we mapped all the terraces within the Niobrara Scenic River Corridor. We utilized ArcGIS Pro to digitize each terrace, then calculated their average height above the river. Once completed, we classified the terrace heights into categories to reveal geographic patterns. We hypothesize that there was a river piracy event that caused the Niobrara to reroute towards the Keya Paha River, a tributary to the Niobrara, and abandon the ancestral course that is now the Elkhorn River. A possible explanation includes the transport of sediment from the Sand Hills to create a sand dam on the river, which would have formed an overflowing lake, spilling over the dam boundaries.