Spatial variation in physio-chemistry in a small river estuary

The understanding of riverine and estuarine mixing processes remains limited, and the predictions are highly sensitive to specific features of the natural system. One reason 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 contrasted conditions: wet and dry conditions. The field measurements indicated that the hydrodynamics and water conductivity were dominated by the tidal forcing, and to a lesser extent by the 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 all 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 the water quality modelling of the system