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USGS hydrologic technician Erik Ohlson measures the discharge of the Suwannee River floodwaters coming over US highway 90 near Ellaville, Florida. (Saturday, April 11, 2009)

Benthic Flux and Submarine Groundwater Discharge

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Benthic Flux and Submarine Groundwater Discharge Calculators

King et al. (2009) define benthic flux qbf as "the rate of flow of some property across the bed of a water body, per unit area of bed, with no limitation on the type of water body or the direction of flow. Benthic flux is a vector quantity, where the vector is normal to the bed. Benthic discharge flux qbd is oriented from the geologic domain to the surface water domain, and benthic recharge flux qbr is oriented from the surface water domain to the geologic domain. The units of qbf are a function of the property under consideration. For example, the units of a benthic volume flux are [L3 T-1 L-2 ] = [L T-1], where [L] is a length dimension and [T] is a time dimension." Submarine groundwater discharge (SGD) is a benthic water discharge flux to a marine water body.

The following web tools calculate qbf and SGD generated by surface gravity waves on a plane bed composed of a homogeneous, isotropic porous medium with the following stratigraphy:





 Two-dimensional, vertically oriented cross sections

Figure 1. Two-dimensional, vertically oriented cross sections, in x and z dimensions, of wave-forced benthic recharge flux qbr.w and wave-forced benthic discharge flux qbd.w, with a water surface at z = η oscillating about a still water surface at z = 0. The bed of the water body is located at z = -h;. The following domain geometry is used to solve two-dimensional boundary value problems in King et al. (2009): (A) Case I, hydrogeologic unit of infinite thickness; (B) Case II, hydrogeologic unit of finite thickness; and (C) Case III, dual-unit system, which consists of a unit of finite thickness over a unit of infinite thickness. The wave-forced velocity field transports constituents within the porous domain, over -h > z > -h - ζ



King et al. (2009) state that a "model of a natural system is usually an abstraction of a more complex prototype, with a soluble system of less complexity," and that the "abstraction process requires assumptions, which can lead to limitations." SGD and qbf characterized by these models are only one component of an array of SGD and qbf forcing mechanisms, which may exist in a natural system.

The U.S. Geological Survey hosts the following sites related to benthic flux and SGD:


Reference

King, J. N., A. J. Mehta, and R. G. Dean (2009), Generalized analytical model for benthic water flux forced by surface gravity waves, J. Geophys. Res., 114, C04004, doi:10.1029/2008JC005116.


Contact: jking@usgs.gov

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