Author(s): Rodhrai Crowley; Joe Harrington; Leonard O' Driscoll; Bidroha Basu; Juan Tomas Garcia; Juan Manuel Garcia-Guerrero

Linked Author(s): Rodhraí Crowley, joe harrington

Keywords: Hydrological modelling; HEC-HMS; SWAT; Discharge; Suspended sediment

Abstract: 43% of Ireland’s rivers have been designated as having ‘unsatisfactory’ water quality, and the proportion of high ecological status rivers in Ireland continues to decline (Environmental Protection Agency, 2021). Fine sediment is widely recognised as a primary pressure on water quality in Ireland (Environmental Protection Agency, 2019). Thus, the study of fine sediment transport in Irish catchments is important from a water quality perspective. In-situ sediment monitoring is an important component of sediment management, but there are limitations associated with the cost and spatial representation of this approach. Integrated hydrological and sediment transport modelling is an important tool for sediment management and can contribute to more spatially targeted measures for the protection and improvement of water quality at catchment scale. In this paper, HEC-HMS (USACE, 2021) and QSWAT+ (Dile, 2021) models are applied for continuous daily simulation of river discharge and sediment yield in the Owenabue catchment, County Cork, Ireland. Soil erosion in both HEC-HMS and QSWAT+ is estimated based on the Modified Universal Soil Loss Equation (MUSLE) (Williams, 1975) generating sediment yield estimates at different temporal scales within these hydrologic models. The Owenabue catchment is relatively small in an Irish context, with a total catchment area of approximately 117 km². A long-term monitoring station is located at Upper Ballea Bridge immediately upstream of the tidal intrusion limit. The station provides continuous records of river flow and turbidity-based suspended sediment (SS) data, allowing for modelled discharge and SS yield to be validated against observed data. The 2018-19 and 2019-20 hydrologic years were selected for river flow model calibration and validation, respectively. The catchment model is composed of 69 sub-basins and 34 reaches. Sensitivity analysis was performed to identify the most sensitive model parameters. Ongoing work includes modelling of soil erosion and sediment transport in HEC-HMS in addition to application of QSWAT+ for the same purpose. Model results confirm that HEC-HMS is suitable for continuous hydrologic simulation in the Owenabue catchment, with ‘satisfactory’ to ‘good’ model performance observed during both the calibration and validation periods based on different model performance evaluation criteria (Moriasi et al., 2015). The model calibration results were: R² = 0.79, NSE = 0.78 and PBIAS = -12.71%; model validation results were: R² = 0.84, NSE = 0.78 and PBIAS = -7.76%. The model showed some tendency to underpredict discharge during low flow conditions. Overall, the simulated river discharge was generally in agreement with the observed flow data at Upper Ballea Bridge and effectively captured many of the flow events during the simulation period (including high flow events). This has provided a reliable basis for simulating soil erosion and fine sediment transport in the catchment.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221495

Year: 2022