DEVELOPMENT OF A METHOD TO ESTIMATE THE RETENTION TIME OF SALT WATER IN RIVERINE ESTUARIES

Abstract

We have developed a numerical model to elucidate the retention feature of salinity in riverine estuaries. The model has a feature to partition a physically conservative water quality index variable (e.g. salinity) into several components and calculate concentration change of each component by mass balance model which is consistent with conventional water quality model. Using this model, we have estimated the spatial distribution of the age of salinity that penetrated into an estuary from the mouth of a river. Also estimated was the residence time of salinity which was present inside of the estuary at a certain time. Simulation results have shown that the age is highly heterogeneous within the estuary spatially implying that morphology is important in estimating the salinity retention in estuaries. This model has a good potential in assessing the impact of physical alternation such as flow change and excavation on the salinity retention which often control the occurrence of bottom anoxia in riverine estuaries.