Benthic Flux and Submarine Groundwater Discharge

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• Calculators:
  • Wave-forced q_bf and SGD component on a single-unit medium of infinite thickness
  • Wave-forced q_bf and SGD component on a single-unit medium of finite thickness
  • Wave-forced q_bf and SGD component on a dual-unit system

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Benthic Flux and Submarine Groundwater Discharge Calculators

King et al. (2009) define benthic flux q_bf 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 q_bd is oriented from the geologic domain to the surface water domain, and benthic recharge flux q_br is oriented from the surface water domain to the geologic domain. The units of q_bf 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 q_bf and SGD generated by surface gravity waves on a plane bed composed of a homogeneous, isotropic porous medium with the following stratigraphy:

• a single-unit medium of infinite thickness (Figure 1A)
• a single-unit medium of finite thickness (Figure 1B)
• a dual-unit system, which consists of a unit of finite thickness over a unit of infinite thickness (Figure 1C)

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 q_bf characterized by these models are only one component of an array of SGD and q_bf forcing mechanisms, which may exist in a natural system.

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

• Benthic Flux and the U.S. Geological Survey Toxic Substances Hydrology Program
• Submarine Groundwater Discharge: An Introduction
• Submarine Groundwater Discharge and Its Influence on Coastal Processes and Ecosystems

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