Transport and Dispersion of a Conservative Tracer in Coastal Waters with Large Intertidal Areas

Abstract

In late December 1991, an accidental release of 5,700 CI of tritiated water (HTO) from the Savannah River Site was transported via site streams into the Savannah River where it was carried downstream to the coastal zone. HTO released into a semitropical Georgia estuary was forced into the tidal marshes surrounding the estuary as well as discharged directly into the Atlantic Ocean. The spreading of HTO was studied with a 3D hydrodynamic model (ALGE) that includes flooding and draining of intertidal areas. Comparisons of model simulations to measured HTO concentration showed that ALGE simulated well the general increase and decrease of HTO as its plume passed a given area. The "sheet flow" approximation for marsh and small tidal creek flow largely compensated for lack of model resolution and accurate bathymetry in areas with numerous small to medium-sized tidal creeks. The water volume of the unresolved tidal creeks had to be accounted for in the simulations by increasing the initial water depth over the marshes. ALGE and a simple box model both reproduced the trapping of HTO in intertidal areas. The time scale over which intertidal areas import and export HTO back to the tidal channels varies between 10 and 30 days.

Spatial and temporal variation in the hydrodynamic landscape in intertidal salt marsh systems

“…A number of studies have, for example, examined turbulent flow characteristics in small‐channel estuaries (Bell et al 1997; Collins et al 1998; Chanson et al 2005) or explored how processes like tidal forcing (Chanson et al 2012), wind generation of currents (Jones and Monismith 2008; Lentz and Fewings 2012), and turbulence (Trevethan et al 2008) interact to affect large‐scale estuarine dynamics, as well as sediment entrainment and deposition processes (Green et al 1997; Christiansen et al 2000). Conversely, general circulation models and estuary‐scale modeling can provide information on the large‐scale patterns of water flow essential to predict the transport of pollutants from a point release or estimate water particle residence times within estuaries (Fortunato et al 1997; Blanton et al 2009; Blanton et al 2010). Such models can also provide information about currents that could influence ecological processes, but they are limited to spatial scales on the order of 200–500 m (Janin et al 1997; Stanev et al 2007; Blanton et al 2009).…”

“…Conversely, general circulation models and estuary‐scale modeling can provide information on the large‐scale patterns of water flow essential to predict the transport of pollutants from a point release or estimate water particle residence times within estuaries (Fortunato et al 1997; Blanton et al 2009; Blanton et al 2010). Such models can also provide information about currents that could influence ecological processes, but they are limited to spatial scales on the order of 200–500 m (Janin et al 1997; Stanev et al 2007; Blanton et al 2009). Model accuracy may be limited by a number of variables, including topography or bathymetry (Gross and Werner 1997; Fortunato et al 1997), whether the model incorporates flooding and drying (Stanev et al 2007), model resolution, or values of friction coefficients (e.g., when a three‐dimensional structure such as marsh grass is included; Blanton et al 2010).…”

A case study of chlorine transport and fate following a large accidental release

“…ALGE includes a freesurface simulator, first-order chemical reactions, tracer transport, particle transport deposition/resuspension, and distribution coefficient-based modeling of chemical adsorption/desorption to particles. The model has been extensively used to simulate sediment and pollutant transport and thermal stratification in large lakes and estuaries (Garrett et al, 2005;Li et al, 2007;Blanton et al, 2009). ALGE is also used to compute transport, diffusion and deposition of aqueous tracers and has been validated against a unique radioactive tracer database (Blanton et al, 2009).…”

“…Absorption of the chlorine vapor by these waters, and the subsequent dilution and transport of the absorbed chlorine (as hydrochloric acid) were modeled with the Savannah River National Laboratory's ALGE model (Garrett et al, 2005;Blanton et al, 2009). Chlorine absorption rates were calculated using a Henry's Law approach modified for reactive chemicals.…”

Thermodynamics of partially frozen cooling lakes

“…ALGE has been used to simulate power plant cooling lakes, pollutant discharges to rivers, ocean discharges, radioactivity fate and transport in estuaries and sediment transport in large lakes 2,3,4,5,6 . In this project, SRNL added a one-dimensional ice simulation model 7 to the ALGE code and developed the logic required to integrate the ice model into a 3-D hydrodynamic code.…”