<p>Saltwater intrusion poses a significant threat to the security of freshwater resources in the Zhujiang (Pearl) River Delta, a region of immense economic and social importance. Effective water resource management requires predictive tools that are both accurate and practical. This study validates a one-dimensional analytical model for saltwater intrusion in the Modaomen Estuary, the primary distributary of the Zhujiang River. The model is tested against a comprehensive dataset covering ten tidal events during the 2025 dry season, a period of high intrusion risk. By assuming a Van der Burgh’s coefficient (<i>K</i>) of 0.5, a value appropriate for partially mixed estuaries, the model is simplified to require the calibration of only a single parameter: the longitudinal dispersion coefficient at the inflection point (<i>D</i>₀). The results demonstrate an excellent agreement between the simulated and observed longitudinal salinity profiles under high water slack and low water slack conditions, confirming the model’s applicability. Based on the calibrated <i>D</i>₀ values from the ten events, a new site-specific predictive equation for the dispersion coefficient is developed. Furthermore, sensitivity analyses indicate that the predictive framework is relatively insensitive to moderate uncertainties in tidal excursion length and freshwater discharge inputs. This validated analytical model, combined with the site-specific predictive equation, provides a simple yet practical tool for forecasting saltwater intrusion, offering crucial support for water resource management decisions, such as regulating freshwater releases and planning water intake locations in the Modaomen Estuary.</p>