Estimating Spatially Varying Transport Times in a Shallow Water Environment Using a Numerical Hydrodynamic Model

A recently developed age concept is capable of quantifying transport characteristics of dissolved substances over a Eulerian coordinate framework. This allows for the estimation of transport time to be presented as a spatial variable and reveals detailed transit time information for transport both within a basin and to reach its exterior. This paper outlines the calculation of spatial distribution of age-of-water within coastal embayments by using a high-resolution numerical hydrodynamic model. The Lynnhaven River, located in Virginia Beach, Virginia, is used for the case study. The surface elevation, current velocity, and salinity were calibrated using the UnTRIM model. Implementing the age-of-water calculation into a calibrated hydrodynamic model, one can account for the localized effects of tide and river discharge. To quantify transport properties in the context of transport timescales, flushing time, residence time, turnover time, and age-of-water have often been used to determine water contamination, nutrient retention, and biochemical processes in estuaries. First-order timescale (integrated) calculations have been traditionally used for shallow water coastal embayments, assuming a completely mixed waterbody. This may not be the best approach for complex coastal embayments, even if they are "small".