The computer program FourPt (Version 95.01), a model for simulating one-dimensional, unsteady, open-channel flow

Abstract

FourPt is a computer program capable of computing unsteady one-dimensional flow in networks of open-channels. Optionally, governing equations may represent dynamic-wave, diffusion-wave, or kinematic-wave equations and may include variable channel sinuosity and variable water density. If density is allowed to vary, density values must be supplied by the user as this version of FourPt does not currently compute transport or heat flow. Governing equations are converted to a set of linearized equations using a four-point-implicit finite-difference method with Newton-Raphson iteration. The resulting set of simultaneous equations are solved directly by Gaussian elimination. Optional boundary conditions include known flow, water-surface elevation, water-surface slope, and three-parameter ratings. Additionally, a facility exists for users to program their own boundary constraints. Logarithmic and semi-logarithmic stage-discharge relations and dam-break functions also may be used as boundary constraints and are included in the program code as examples of user-programmed boundary constraints. Channel cross sections may be represented by rectangular, trapezoidal, or irregular geometry, depending on which geometry routines are linked with the program code. Spacing of user-supplied channel cross sections is independent of the selection of spatial discretization for numerical solution. FourPt is written in FORTRAN 77 using a data-encapsulation programming paradigm. This report describes data input and output and demonstrates selected model capabilities with examples.