A Simple Tool to Understand the Impacts of River Flow on Estuarine Salinity
Joan Sheldon and Merryl
Alber (Dept of Marine Sciences, Univ of Georgia, Athens, GA, USA)
Nature Conservancy, Georgia Coastal Management Program, National Science Foundation
SqueezeBox is a desktop modeling tool developed by Merryl Alber and Joan Sheldon at the University of Georgia that can be used to evaluate the effects of freshwater inflow on the salinity distribution and mixing time scales of riverine estuaries. Salinity is a master variable that affects many estuarine characteristics and is important to estuarine organisms. Mixing time scales, such as residence time and flushing time, provide information on water movement that can be compared with the rates of processes that may act upon materials (such as nutrients or pollutants) as they are carried through the estuary.
SqueezeBox is useful for evaluating water quality questions because it can be used to determine how long it will take to reduce an initial pulse of a dissolved substance, such as a water-borne pollutant, to a percentage of its original concentration or to a specified standard. The model can also be used to predict the expected distribution of the substance after a given amount of time.
SqueezeBox generates 1-dimensional, tidally averaged box models with structures scalable for different river flows. It is designed to be flexible and easily adaptable to different estuaries with minimal data requirements. The application is a compiled Microsoft Visual Basic program that runs under Microsoft Windows versions 95-XP (not tested on Vista), but the end user does not need Visual Basic. Estuary module development requires bathymetry, freshwater input rates, and salinity observations throughout the estuary at a range of freshwater flows. These data are used to develop descriptive equations of the along-channel variation in cross-sectional area and the response of the net up-estuary flow of seawater to freshwater inflow changes. These equations constitute an estuary module, which is supplied as text files read by application. Simple mixing equations are used to predict the salinity distribution for a chosen river flow, and the application generates a conventional box model with suitable box sizes and time step for stable numerical simulations. The user then specifies an initial distribution and optional sources of a simulated tracer, which could represent many dissolved substances. The tracer can be inert, or a first-order reaction rate can be specified for each box. Preset tracer distributions can be used to calculate several mixing time scales such as average residence time and turnover time.
SqueezeBox and modules for the Altamaha River estuary (GA) and the Ogeechee River estuary (GA) have been developed with funds from The Nature Conservancy, the Georgia Coastal Ecosystems LTER program (NSF), and the Georgia Dept. of Natural Resources Coastal Incentive Grant program (NOAA).
SqueezeBox is constantly being upgraded as new features are desired for ongoing research, and it is not yet packaged for wide distribution with integrated help functions, but the initial application and module development have been described in the following publications:
Sheldon, J. E. and M. Alber. 2002. A comparison of
residence time calculations using simple compartment models of the Altamaha
River estuary, Georgia. Estuaries 25:1304-1317.
Sheldon, J. E.
and M. Alber. 2003. Simulating
material movement through the lower Altamaha River estuary using a 1-D box model.
In K. J. Hatcher (ed.) Proceedings of the 2003 Georgia Water Resources Conference.
Institute of Ecology, University of Georgia, Athens, Georgia. (Link
opens in new window, PDF)
Sheldon, J. E. and M. Alber. 2005. Comparing transport times through salinity zones in the Ogeechee and Altamaha River estuaries using SqueezeBox. In K. J. Hatcher (ed.) Proceedings of the 2005 Georgia Water Resources Conference. Institute of Ecology, University of Georgia, Athens, Georgia. (Link
opens in new window, PDF)
To see an application of SqueezeBox, see Joan Sheldon's presentation
from the 2001 Estuarine Research Federation Meeting, Any
way you slice it: a comparison of residence time calculations using simple compartment
models of the Altamaha River Estuary. (PDF -- opens in new window)