Time scales in Galveston Bay: An unsteady estuary

Abstract

Estuarine time scales including the turnover, particle e‐folding time, the age (calculated with a passive tracer), and residence time (calculated with Lagrangian particles) were computed using a three‐dimensional hydrodynamic model of Galveston Bay, a low‐flow, partially stratified estuary. Time scales were computed during a time period when river flow varied by several orders of magnitude and all time scales therefore exhibited significant temporal variability because of the unsteadiness of the system. The spatial distributions of age and residence time were qualitatively similar and increased from 15 days in a shipping channel to >45 days in the upper estuary. Volume‐averaged age and residence time decreased during high‐flow conditions. Bulk time scales, including the freshwater and salinity turnover times, were far more variable due to the changing river discharge and salt flux through the estuary mouth. A criterion for calculating a suitable averaging time is discussed to satisfy a steady state assumption and to estimate a more representative bulk time scale. When scaled with a freshwater advective time, all time scales were approximately equal to the advective time scale during high‐flow conditions and many times higher during low‐flow conditions. The mean age, Lagrangian residence, and flushing times exhibited a relationship that was weakly dependent on the freshwater advective time scale demonstrating predictability even in an unsteady, realistic estuary.

The Use of Stable Isotope-Based Water Age to Evaluate a Hydrodynamic Model

“…The hydrodynamic model predicted stage, flow and salinity accurately at the majority of stations in the model domain ( Table 2). The target diagrams in Figure 3 show less normalized bias and similar normalized unbiased RMSE (unRMSE) in flow and similar normalized bias in water level relative to [31]. However, our results had larger normalized bias in water level with our results tending to underpredict mean water level in the Delta.…”

Role of Baroclinic Processes on Flushing Characteristics in a Highly Stratified Estuarine System, Mobile Bay, Alabama

“…These timescales have been widely used in applications in a variety of estuaries (Abdelrhman, ; Du & Shen, , ; Sheldon & Alber, ; Shen & Haas, ; Viero & Defina, ). Flushing time, the average time of materials to stay within a system before being flushed out, is a bulk or integrative parameter that describes the overall renewal capability of a waterbody and it establishes the time scale for physical transport of river‐borne material, such as nutrients, organic matter, and suspended sediment (Dyer, ; Geyer et al, ; Officer, ; Oliveira & Baptista, ; Rayson et al, ). It can thus be compared against the time scales of relevant biogeochemical processes to determine whether transformations are occurring in estuaries (Alber & Sheldon, ).…”

Water renewal in semi‐enclosed basins: A high resolution Lagrangian approach with application to the Bay of Algeciras, Strait of Gibraltar

“…It is strictly defined as the ratio of volume of water to the volume transport across the basin open boundaries (Zimmerman ). However, in the hypothesis of the continuous stirring tank reactor (Monsen et al ; Rayson et al ) where any insertion of mass in the domain is assumed to be instantaneously and homogeneously mixed, it can be estimated from the tracking of mass concentration over the time. In a Lagrangian framework, such concentration is represented by particles abundance inside the dock, varying according to trajectories evolution, and can be least‐squares fitted by an exponential function as follows: …”

“…Here is the percentage of particle at time and is the e ‐folding time, the time required to reduce the number of particle inside the study area by a factor of . The ‐folding flushing time, as defined by Monsen et al (), is widely used in environmental science (Sánchez Garrido et al ; Rayson et al ; Viero and Defina and references therein) and it is actually recommended by the Bay of Algeciras Port Authority (Juanes et al ).…”

“…The green lines indicate the release times of the experiments carried out to assess the effect of the AJ on the renewal efficiency of the Bay. Rayson et al 2016; Viero and Defina 2016 and references therein) and it is actually recommended by the Bay of Algeciras Port Authority (Juanes et al 2013).…”