QUANTIFYING SEDIMENTATION DYNAMICS OF REGULATED RIVER BACKWATER CONFLUENCES WITH LOW-ORDER TRIBUTARIES

Sediment dynamics in backwater confluences of regulated rivers have received limited study, despite being recognized as hotspots for sedimentation and nutrient attenuation. Development of management and restoration strategies in these landscapes require improved understanding of fluvial geomorphology and sediment transport dynamics due to the alterations in hydraulic regimes and sediment inputs associated with riverine backwaters. The objective of this study was to couple remote sensing, high frequency sensing, and numerical modeling to quantify drivers of erosion and deposition dynamics within regulated river backwater tributary confluences. To meet the objective of this study, data was collected and analyzed from the Fourpole Creek confluence with the Ohio River in Huntington, WV, USA. A change detection analysis of land surface elevation data was performed over an eight-year period using LiDAR data in ArcGIS Pro 3.1.0. A change detection analysis showed variable channel erosion/deposition patterns from upstream to downstream portion of the confluence floodplain, with outer-bend erosion of banks upstream, inner-bend erosion in middle portions, and minimal bank erosion downstream. Regarding the floodplain, deposition was greatest in upper portions of the floodplain (furthest from the Ohio River source) and decreased towards the Ohio River. Further, a 2-D HEC-RAS model of the confluence was used to evaluate hydraulic conditions resulting in the erosion and deposition dynamics highlighted in the change detection analysis. Additionally, the 2-D HEC-RAS model was used to evaluate transient sediment storage within the Fourpole Creek floodplains and the Ohio River channel under calibrated conditions. Model scenario analysis was used to evaluate the influence of tributary sediment, main-stem Ohio River flow, and Ohio River sediments on transient sediment storage dynamics. For this size confluence, main channel flow and sediment loading were observed to govern sediment deposition in the main channel and confluence area while having an influence in the backwater floodplains.Sediment dynamics in backwater confluences of regulated rivers have received limited study, despite being recognized as hotspots for sedimentation and nutrient attenuation. Development of management and restoration strategies in these landscapes require improved understanding of fluvial geomorphology and sediment transport dynamics due to the alterations in hydraulic regimes and sediment inputs associated with riverine backwaters. The objective of this study was to couple remote sensing, high frequency sensing, and numerical modeling to quantify drivers of erosion and deposition dynamics within regulated river backwater tributary confluences. To meet the objective of this study, data was collected and analyzed from the Fourpole Creek confluence with the Ohio River in Huntington, WV, USA. A change detection analysis of land surface elevation data was performed over an eight-year period using LiDAR data in ArcGIS Pro 3.1.0. A change detection analysis showed variable channel erosion/deposition patterns from upstream to downstream portion of the confluence floodplain, with outer-bend erosion of banks upstream, inner-bend erosion in middle portions, and minimal bank erosion downstream. Regarding the floodplain, deposition was greatest in upper portions of the floodplain (furthest from the Ohio River source) and decreased towards the Ohio River. Further, a 2-D HEC-RAS model of the confluence was used to evaluate hydraulic conditions resulting in the erosion and deposition dynamics highlighted in the change detection analysis. Additionally, the 2-D HEC-RAS model was used to evaluate transient sediment storage within the Fourpole Creek floodplains and the Ohio River channel under calibrated conditions. Model scenario analysis was used to evaluate the influence of tributary sediment, main-stem Ohio River flow, and Ohio River sediments on transient sediment storage dynamics. For this size confluence, main channel flow and sediment loading were observed to govern sediment deposition in the main channel and confluence area while having an influence in the backwater floodplains.