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[Display omitted] • Optimal flow process can maximize the denitrification capacity of riparian zones downstream of reservoirs. • Denitrification is reaction- instead of transport-limited when the hydrograph wave amplitude/duration ratio is high. • Riparian nitrogen removal has a strongly positive correlation to return/infiltration time ratio of solutes. Flood waves generated by reservoir discharge play a crucial role in the potential for riparian denitrification downstream. The efficiency of nitrogen (N) removal from river water by riparian zones is typically enhanced with greater wave amplitude (A) and duration (T). However, a knowledge gap exists with respect to the impact of flood waves on N removal when considering a fixed-value integral over time of flood waves (IOFW). This study explored N transport and transformation in the riparian zone downstream of the dammed Inbuk River, Korea under various wave conditions with a fixed IOFW. The results revealed a logarithmic enhancement in solute infiltration into the riverbank with an increasing wave amplitude/duration ratio (A / T ratio). The solute residence time within the riparian zone displays an initial increase followed by a decrease with the increment in the A/T ratio. We identified a threshold for the wave A/T ratio that maximizes riverine N removal by the riparian zone, a phenomenon observed across various dammed rivers. Our findings indicated that riparian denitrification is reaction time-limited when the wave A/T ratio exceeds the threshold; contrarily, it becomes transport capacity-limited. Additionally, we observed a significant relationship between the net nitrate removal and the return/infiltration time ratio of water (r2 = 0.93, p < 0.05). The research results contribute to a better understanding of the impact of water level fluctuations on the N cycle in riparian zones, and provide valuable insights for developing sustainable reservoir operation strategies. [ABSTRACT FROM AUTHOR]

Highlights: [•] Numerical method to delineate hyporheic zone depth using CAD analysis was proposed. [•] To evaluate adequacy of the proposed method, sensitivity analysis was performed. [•] The hyporheic zone depth was little influenced by hyporheic water flux shapes. [•] Estimated hyporheic zone depth of the method is comparable with that of tracer test. [•] The proposed method has an advantage even when hyporheic flux shape is ambiguous. [Copyright &y& Elsevier]

Summary: The Korean Ministry of Construction and Transportation (MOCT) and the Korean Ministry of Environment (MOE) manage the National Groundwater Monitoring Stations (NGMS) and the Groundwater Quality Monitoring Stations (GQMS) under Article 17 of the Groundwater Act. Under the same legislation, local government will install or designate an additional 10,000 monitoring wells as Subsidiary Groundwater Monitoring Stations (SGMS) by 2011. However, a standard for the installation and management of the SGMSs has not yet been developed. This study focuses on the development of a model for the determination of optimal monitoring frequencies during the manual measurement of the SGMSs. The groundwater level time series for the 81 deep and shallow monitoring wells making up the NGMSs were analyzed using an AR(p) model, and a harmonic series model was then made for the determination of groundwater level sampling frequency in the SGMSs. The result showed that the average sampling frequency necessary for groundwater level monitoring is about once every 8.9 days. Moreover, it indicates that water level sampling needs to be performed more frequently in steeply inclined sites, deep wells, and in monitoring wells belonging to an AR(2) rather than an AR(1) model. [Copyright &y& Elsevier]