Mechanism of Salt Transport in the Upper Delaware River

Transport processes controlling the salinity distribution in estuaries are determined by river discharge, bathymetry, and tidal motion. While most of our understanding of estuarine transport processes is derived from studies in the central region (i.e., mesohaline), the oligohaline reach – characterized by salinity levels between 0.5 and 5 psu– remains largely unexplored. This region is known to be the landward limit of salt intrusion and exhibits distinct physical characteristics, such as constricted channel geometry and bathymetric complexity, both of which are important to tidal dispersion. This study investigates transport processes in the oligohaline region of the Delaware River using field measurements, including moored acoustic Doppler current profiler (ADCP) and conductivity, temperature, depth, and pressure sensor (CTD) data during an extended drought period in 2024. With this data, we assess the salt flux mechanism by decomposing the spatial and temporal variability of the velocity and salinity distributions, separating salt flux due to tides, river discharge, and “steady” exchange flow. We also examine how variation in discharge and spring/neap variability modulate salt transport and vertical stratification. Preliminary findings highlight the influence of strong tidal amplitude during low-flow conditions on salinity gradients, stratification, and mixing processes. This knowledge enhances our understanding of salinity intrusion dynamics and is significant for water resource management.