title: SEDIMENT TRANSPORT INVESTIGATION IN A KARST BASIN DEFINES GOVERNING TRANSPORT PROCESSES AND EXPLAINS HYSTERESIS PATTERNS
Creators: name: Bettel, Leonie
Publisher: name: University of Kentucky Libraries
Year: 2021
Subjects: subject: FOS: Civil engineering
valueUri: http://www.oecd.org/science/inno/38235147.pdf

description: Water resources researchers have advanced our understanding of sediment transport in karst aquifers and cave systems in recent years. However, we find knowledge gaps for sediment transport in karst including knowledge of processes controlling sediment hysteresis patterns from sensor datasets, and knowledge of dominant sediment transport processes that lead to sediment transport formulas for prediction. To address these gaps, we analyze a new suspended sediment, electrical conductivity and water flowrate datasets from sinking streams and a phreatic cave system for an epigenetic karst basin in the inner bluegrass region of Kentucky USA.

Three sediment patterns are common including: pulses of sediment arriving before or after water flowrate peaks indicating hysteresis; a direct and near linear dependence of sediment concentration as a function water flowrate; and an order of magnitude shift in sediment transport flux and time lags during spring 2018. The hysteresis patterns occur from external sediment entering the cave from the sinking streams. Variability of hysteresis reflect the time-varying sediment concentration of water entering via the sinking streams and pre-event water storage in the karst aquifer. Sediment pulses from the sinking streams are attenuated as they arrive at the cave’s spring. The effect is evidenced from clockwise Q-TSS patterns in the sinking streams shifting to linear and counterclockwise patterns in the cave, clockwise EC-TSS patterns for all sites, and clockwise Q-TSS patterns for all sites when surface water is isolated via mixing models and used in the analyses. The effect is further evidenced with statistical moments of hysteresis indices and numerical modelling of sediment transport, which are novel features of this contribution. The timing of the sediment peak relative to the water flowrate peak at the cave’s spring agrees well with pre-event water storage in the karst aquifer. The magnitude of pre-event water storage can cause clockwise or counterclockwise hysteresis as evidenced by both data and numerical modelling results. Findings are contrary to interpretation of hysteresis in previous karst studies where researchers suggest resuspension of internal cave sediment cause hysteresis. We find no sediment mechanics available to predict such interpretation.

The direct and near linear dependence of sediment concentration as a function water flowrate (i.e., no hysteresis) reflects resuspension of internal cave sediment. Sediment pulses out of phase with water flowrate do not occur from this process. Rather, the system is monotonic with water discharge and is evidenced by the fact that it is well described by the fluvial sediment transport rate formula of Partheniades.

Sediment hysteresis results in the cave are also indicative of disturbances across the landscape surface. We find a six-month time period of very high disturbance in the basin increases sediment loads by one order of magnitude at the cave’s spring, shifts hysteresis patterns to highly influenced by streambank erosion, and require shifting the sediment storage parameter in the Partheniades formula.
description: © 2021 Leonie Bettel