BOSS International

RMA11 Features


RMA11 is a finite element water quality model for simulation of three-dimensional estuaries, bays, lakes and rivers. It is also capable of simulating one and two dimensional approximations to systems either separately or in combined form. It is designed to accept input of velocities and depths, either from an ASCII data file or from binary results files produced by the two-dimensional hydrodynamic model, RMA2, or the three-dimensional stratified flow model, RMA10. Results in the form of velocities and depth from the hydrodynamic models are used in the solution of the advection diffusion constituent transport equations.

Governing Equation

The two/three-dimensional advection diffusion equations are simulated for conservative and decaying constituents.


The equations are solved by the finite element method. The prototype system is represented by a network of triangles and quadrilaterals / cubes and prisms that may have curved sides if desired. Within each element the model uses quadratic approximations for water quality constituents. A fully implicit solution scheme is used for solution of time dependent problems.


  • Temperature with a full atmospheric heat budget at the water surface
  • Dissolved Oxygen
  • The nitrogen cycle (including organic nitrogen, ammonia, nitrite and nitrates)
  • The phosphorous cycle (including organic phosphorous and phosphates)
  • Alogia growth and decay
  • Cohesive suspended sediment
  • Non-cohesive suspended sediment such as sand
  • Conservative constituents

In addition the model may be configured for other simpler constituents such as tracers and E-coli.


The primary features of RMA11 are as follows.

  • RMA11 shares many of the same capabilities of the RMA2/RMA10 hydrodynamics models including irregular boundary configurations, variable element size, one-dimensional elements, and the wetting and drying of shallow portions of the modeled region.
  • RMA11 may be executed in steady-state or dynamic mode. The velocities supplied may be constant or interpolated from an input file (This may be RMA2 or RMA10 output).
  • Source pollutants loads may be input to the system either at discrete points, over elements, or as fixed boundary values.
  • In formulating the element equations, the element coordinate system is realigned with the local flow direction.  This permits the longitudinal and transverse diffusion terms to be separated, with the net effect being to limit excessive constituent dispersion in the direction transverse to flow.
  • For increased computational efficiency, up to fifteen constituents may be modeled at one time, each with separately defined loading, decay and initial conditions.
  • The model may be use to simulate temperature with a full heat exchange with the atmosphere, nitrogen and phosphorous nutrient cycles, BOD-DO, algae, cohesive or non-cohesive suspended sediments and other non conservative constituents.
  • A multi-layer bed model for the cohesive sediment transport constituent keeps track of thickness and consolidation of each layer.