Why Sediment Matters to Archeology

Sediment plays an important role in river systems, from building fish habitat to affecting the chemical composition of water. In this project, I’m focusing on sediment dynamics at areas along the river, such as sandbars or river terraces, that are home to archaeological sites. Although there is little sediment deposition in this stretch of the river corridor, water and wind are still causing erosion. Erosion is a natural process, but without the deposition needed to counterbalance the amount of erosion happening, these sites are losing material. Thus, many of the sites are vulnerable to being washed away by the river without the sediment to stabilize them.

One way to increase sediment supply is with the High Flow Experiments (HFEs) conducted by the dam, which is operated by the Bureau of Reclamation (BOR). If river conditions meet specific criteria, the dam will release water at extremely high rates (almost 40000 cfs!) to push sediment through the dam to replenish this stretch. These HFEs are conducted as part of the Long Term Experimental and Management Plan (LTEMP), a collaboration between the BOR and NPS.

Imagery collected before and after the HFEs reveals where new sediment is being deposited and thus how effective they are. Aerial photos of several archaeological sites have been collected over the past five years, and my job is to analyze this data! Photogrammetry is the science (or art?) of stitching images together, and from these images I can make a 3D model. By comparing 3D models from different years, I can quantify how much erosion has occurred at a site over time. In addition to analyzing existing imagery, I will be taking new imagery of a few sites! On my second day of work, I visited some of these sites to see the erosion firsthand. The sites in this stretch are only accessible by boat and when we passed through Horseshoe Bend, I could just make out the tiny figures of people standing at the observation point on the canyon rim!