Over the last half-century, the Nakdong and Yeongsan Estuaries of the Republic of Korea (S. Korea) have experienced a wide range of engineered coastal modifications including construction of seawalls, extensive land reclamation, and installation of estuarine dams. Combined, these alterations have considerably modulated the timing and intensity of river discharge, appreciably reduced the tidal prism, prevented natural tidal exchange, modified the shoreline profile, and altered the transport of sediment and organic matter within the coastal zone. Additionally, chronologic reconstructions suggest that rapid industrialization of the region has resulted in a pronounced increase in anthropogenic mercury. In order to assess the sedimentary impacts of these modifications, cores were investigated using 210Pb, 7Be, and 137Cs radioisotope geochronology, laser diffraction particle size analyses, δ13C and δ15N isotope ratio mass spectrometry, total mercury concentration, and X-radiography. Bathymetric, CHIRP seismic, and side-scan sonar data were also utilized to evaluate the spatial distribution of sediments and determine average Holocene sediment accumulation rates. Overall, observations record a shift in depositional environments as a response to an extensive array of anthropogenic alterations. Ultimately, land reclamation and dam construction have severely altered the fate and transport of sediment within these estuarine systems. As a consequence, sedimentation rates have increased dramatically and depositional events occur episodically corresponding to high discharge dam releases.