Submarine groundwater discharge can be a significant source of dissolved solutes to coastal environments. Complex systems like tidal rivers can be biogeochemical hotspots for groundwater processes. However, confining groundwater exchange and groundwater-driven nutrient cycling has seldom been done in continuums like tidal freshwater zones (TFZ). To date, few studies have highlighted the importance of tidal dynamics in altering groundwater flux and nutrient transformations before entering surface waters, and many are spatially limited. Here, we quantify groundwater discharge over 80 km of the Hawkesbury River TFZ using high spatiotemporal resolution 222Rn measurements. Three campaigns were conducted in varying hydrologic and seasonal conditions along four reaches with differing land use and geomorphology. Preliminary results show heterogeneous surface water 222Rn activities across the reaches and wet-dry periods. Groundwater activities are up to one order of magnitude higher. Surveys reveal higher 222Rn activity upstream, suggesting higher groundwater discharge, concentrated inputs from tributaries, or lower mixing rates upstream. To discern between these and determine the contribution of groundwater, we employ a 222Rn mass balance model. This model will provide a crucial understanding of groundwater dynamics in the catchment to best inform water resource management strategies for the planned expansion of Greater Western Sydney.