Spatial variation in physio-chemistry in a small river estuary

Understanding of riverine and estuarine mixing processes remains limited, and predictions are highly sensitive to specific features of natural systems. One reason for this is the very complex variations of hydrodynamic and physio-chemical properties with the tidal phase. This study presents the results of two field works during which a range of flow and chemical parameters were recorded simultaneously at several locations along a small sub-tropical estuary. The studies were conducted in contrasting (wet and dry) conditions. Field measurements indicated that the hydrodynamics and water conductivity were dominated by tidal forcing and, to a lesser extent, by freshwater inputs. There were generally significantly greater differences between longitudinal sites than between vertical depths, although some marked differences were observed between the upper and lower estuarine zones. The comparative results between wet and dry field studies illustrated some marked stratification in wet weather along the whole of the estuary, implying that the surface samples were not representative of the average water column properties. Overall, the complexity of the hydrodynamics and water quality has some impact on water quality modelling of the system.