Significant Human Modification of the Lower Arkansas River Sediment Budget

Abstract

Large river systems provide many services, including water resources, barge transport, and sand and gravel (S&G) for mining. However, unlike damming, the impacts of channel dredging and S&G mining are poorly monitored. We quantify these impacts on the Lower Arkansas River, U.S.A., where anthropogenic processes are well documented. The construction of dams caused a 98% reduction in suspended sediment discharge (Qss). Since dam construction, fluvially-transported Qss and suspended sand discharge (Q sand ) varied on the decadal scale, but the average of Qss (4.4 ± 0.5 Mtyr -1 ) and Q sand (1.1 ± 0.1 Mtyr -1 ) at Van Buren are of the same order as sediment removal rates by dredging (1.2 ± 0.1 Mtyr -1 ) and S&G mining (1.7 ± 0.1 Mtyr -1 ). During 1975-2019, the cumulative sediment deficit caused by dredging and S&G mining (1.7 Mtyr -1 ) outpaced the cumulative post-dam fluvial sediment deficit (0.7 Mtyr -1 ), indicating sediment extractions are now essential parts of rivers' sediment balance.

Significant Human Modification of the Lower Arkansas River Sediment Budget

“…Based on the BQART model (Syvitski & Milliman, 2007), we assumed the Q ss is simply proportional to the square root of the drainage basin area. Thus, sediment data from Lee Creek enable a first-order Q ss estimation for all tributaries in Ozark and Ouachita Mountains at 0.39 Mtyr −1 (refer to Chen et al, 2022). Reservoirs were built on these tributaries, and thus we assume the LAR received negligible Q sand from these tributaries.…”

“…The total wing-dike field area is ∼110 km 2 and with an average thickness of about 1.5 m, the accommodation of wing-dike fields is ∼165 Mm 3 (refer to Chen et al, 2022). The median wing-dike field filling ratio in 1969, 1994, and 2017 is about 0%, 16%, and 30%, respectively (Figure 3c), indicating that between 1969 and 2017, the annual averaged filling ratio of wing-dike fields is about 0.63%/year.…”

“…The drainage basin area of Lee Creek is about 1,200 km 2 and the total drainage basin area of the Ozark and Ouachita Mountains is about 20,300 km 2 (see details in Chen et al, 2022). Based on the BQART model (Syvitski & Milliman, 2007), we assumed the Q ss is simply proportional to the square root of the drainage basin area.…”

“…S&G mining data were compiled from mining companies along the LAR between 2011 and 2019 and archived by the Arkansas Commissioner for State Lands (records before 2011 are no longer archived). Additionally, a longer record of Arkansas statewide S&G mining data were compiled from the USGS National Minerals Information Center (NMIC) (refer to Chen et al, 2022). Between 2012 and 2018, the S&G mining contribution ratio from the LAR relative to statewide is averaged at 0.176 ± 0.019.…”

“…Sand and gravel mining data were compiled from mining industries along the Lower Arkansas River and the USGS National Minerals Information Center (NMIC) which is accessible at https://www.usgs.gov/centers/nmic/state-minerals-statistics-and-information. The sediment data, MKARNS dredging summary, wing-dike and bar areas, USGS aggregates sand mining data, and suspended sediment and sand deficit data are openly available in the Figshare repository associated with this work (Chen et al, 2022): https://doi.org/10.6084/m9.figshare.19706704.…”