About OTIS

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OTIS is a mathematical simulation model used to characterize the fate and transport of water-borne solutes in streams and rivers. The governing equation underlying the model is the advection-dispersion equation with additional terms to account for transient storage, lateral inflow, first-order decay and sorption. This equation and the associated equations describing transient storage and sorption are solved using a Crank-Nicolson finite difference solution.

OTIS may be used in conjunction with data from field-scale tracer experiments to quantify the hydrologic parameters affecting solute transport. This application typically involves a trial-and-error approach wherein parameter estimates are adjusted to obtain an acceptable match between simulated and measured tracer concentrations. Additional applications include analyses of nonconservative solutes that are subject to sorption processes and/or first-order decay.

A modified version of OTIS, OTIS-P, couples the solution of the governing equation with a nonlinear regression package. OTIS-P determines an 'optimal' set of parameter estimates that minimize the squared differences between the simulated and measured concentrations, thereby automating the parameter estimation process.

The OTIS solute transport model and related materials (data and documentation) are made available by the U.S. Geological Survey (USGS) to be used in the public interest and the advancement of science. You may, without any fee or cost, use, copy, modify, or distribute this software, and any derivative works thereof, and its supporting documentation, subject to the USGS software User's Rights Notice.

Funding for software development was provided by the USGS Toxic Substances Hydrology Program and the USGS Office of Water Quality.