Modeling solute transport and geochemistry in streams and rivers using OTIS and OTEQ

by
Robert L. Runkel, Kenneth E. Bencala and Briant A. Kimball

U.S. Geological Survey

Abstract

Solute transport in streams is governed by a suite of hydrologic and geochemical processes. Interactions between hydrologic processes and chemical reactions may be quantified through a combination of field-scale experimentation and simulation modeling. Two mathematical models that are used to simulate solute transport in streams are presented here. A model that considers One-dimensional Transport with Inflow and Storage (OTIS) may be used in conjunction with tracer-dilution methods to quantify hydrologic transport processes (advection, dispersion, and transient storage). Additional applications of OTIS include analyses of nonconservative solutes that are subject to sorption processes and (or) first-order decay. A second model, OTEQ (One-dimensional Transport with EQulibrium chemistry), combines the transport mechanisms in OTIS with a chemical equilibrium submodel that considers complexation, precipitation/dissolution, and sorption. OTEQ may be used to quantify the geochemical processes affecting trace metals.