Version: 1.0 (February 1994)
Order No: FOS 77
Price: Contact for more info

The program 'SHARP' is a quasi-three dimensional finite difference model for simulating freshwater and saltwater flow, separated by a sharp interface in layered coastal aquifers. The model accommodates multiple aquifers, separated by confining layers. The uppermost aquifer can be confined, semi-confined or unconfined with areally distributed recharge. Temporal variations in recharge and pumping are accounted for by introducing multiple pumping periods. The boundary conditions which can be modeled include prescribed flux boundaries, constant freshwater/and or saltwater head boundaries, mixed type boundary conditions (e.g. induced recharge from streams). Aquifer properties can be both heterogeneous and anisotropic (hydraulic conductivity tensor aligned with Cartesian coordinate axes). The model can be used for both areal (horizontal) and cross-sectional (profile) studies.

For each aquifer the vertically integrated freshwater and saltwater equations are solved. These two equations are coupled by the boundary condition at the interface. Leakage between the aquifers is calculated applying Darcy's law. The resulting system of nonlinear partial differential equations is discretized using an implicit finite difference scheme. The discretized system of equations is solved using the strongly implicit procedure (SIP).

The position of the interface tip and toe, within the discretized finite difference blocks, are tracked using linear extrapolation of the interface elevations calculated at grid points. Steady-state results are obtained by running a transient simulation until it achieves steady-state. The model supports variable grid block lengths in the X-, and Y- or Z-direction.

The public domain SHARP program runs in batch mode. Example data sets are provided, which can be copied and edited with a text editor to create the input file for new problems. The program results are saved in text files. Distribution of SHARP includes source code, executable image, example data sets, and the USGS user's manual.


Intel 80386/80486 based computer (i486 recommended), at least 6 Mb RAM, DOS 5.0 or higher; runs as a DOS application under MS Windows 3.1; math coprocessor optional.

Author: H.I. Essaid (U.S. Geological Survey).