A hydraulic and water quality simulation model was used to analyze the hydraulic and water quality variation in estuarine reservoirs constructed during tidal land reclamation, considering seawater circulation with drainage gate operations for water quality management during farmland development before reservoir desalination. The applicability of the model assessed after calibration and verification by comparison with field data that had been collected in the Saemangeum tidal land reclamation project area where seawater circulates through the gates after final closure of the sea dike.