Dynamic river model for dissolved oxygen, pH, temperature and biomass solved by orthogonal collocation
by
Richard Jordan
Christchurch Polytechnic

This mathematical model dynamically simulates the dissolved oxygen concentration, pH, temperature and biomass growth of a river. The orthogonal collocation method was used to solve a set of partial differential equations to calculate depth, longitudinal and time dependent temperature and concentration profiles. The model considers photosynthesis to occur as a two step reversible reaction. Oxygen transfer processes include oxygen interchange at the water surface and an effective vertical diffusivity. Insolation, surface heat transfer and conduction model the diurnal temperature variation. The model takes 12 seconds to run on a 120MHz pentium computer for 48 time steps of one hour with two 5.5km steps axially along the river. As the algorithm is very stable, large time and axial distance steps can be made resulting in a hig hly accurate dynamic mathematical model of a complex system. The parameters of the model have been manually varied to fit hourly data from the Ohau River for a 48 hour period.

Date received: June 24, 1999

Copyright © 1999 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cacc-58.