Certain aspects of Green element computational model for BOD–DO interaction

The physical laws governing the interaction of biochemical oxygen demand (BOD), and dissolved oxygen (DO) in a water body are expressed as coupled one-dimensional, transient partial differential equations and solved by the Green element method (GEM). The GEM has been developed as a flexible, hybrid numerical approach, that utilizes the finite element methodology to achieve optimum, inter-nodal connectivity in the problem domain, while at the same time retaining the elegant second order accurate formulation of the boundary element method (BEM). While overcoming some of the limitations of classical boundary element approach, GEM guarantees a sparsely populated coefficient matrix, which is easy to handle numerically. We test the reliability of GEM by solving a one-dimensional mass transport model that simulates BOD–DO dynamics in a stream. The results compare favorably with those obtained analytically, and by the finite element method (FEM) Galerkin procedure.