INSIGHTS ON COARSE SEDIMENT ROUTING IN TRIBUTARIES OF THE BUFFALO NATIONAL RIVER, AR

Bed load is a principal transport mechanism in gravel mantled bedrock streams, but there are few in situ studies of gravel movement at the reach to watershed scale. Thus, this research focuses on the variability in caliber and provenance of gravel in major tributaries of the Buffalo National River (BNR) in order to better understand gravel routing within the watershed. Pebble counts and provenance sampling have taken place along gravel bars on four tributaries at least one stream bend up from the confluence with the BNR. Data collection is ongoing and will be compared to previously collected data on the main stem of the Buffalo. Preliminary provenance data suggests that Calf Creek gravel input has a measurable influence on BNR gravel. While only 33/60 (55%) samples analyzed on a BNR gravel bar just upstream of the confluence were identified as Boone Formation limestone or chert, 50/60 (83.33%) of those sampled on Calf Creek and 51/60 (85%) from a BNR bar below the confluence are from the Boone. Since Calf Creek incises the Boone almost exclusively, this increase in relative Boone gravel after the confluence can likely be attributed to sediment inputs from Calf Creek. As we build our data set, we hope to determine which tributaries and lithologies within the watershed are influencing sediment loads in the BNR.

Additionally, this project will track gravel movement at the reach scale using innovative radio-frequency identification (RFID) technology. For this portion of the study, additional cross-channel gravel counts were conducted at the top and bottom of two riffle sequences on Beech Creek. For the upstream riffle sequence, gravel size distribution percentiles changed from D50 = 65mm, D90 = 117mm to D50 = 92mm, D90 = >256mm from the top to the bottom of the sequence. For the lower sequence, the percentiles changed from D50 = 82mm, D90 = 200mm to D50 = 116mm, D90 = >256mm. At this location, cobbles are generally larger at the bottom of riffle sequences than the top, and size generally increases from one riffle sequence to the next. Although the significance of these results is not clear, we expect to better understand bed load dynamics in this tributary as we track gravel movement over the next water year.