Approximation of the Effects of Subgrid Variations in Geometry in a Regional Ocean Model

Accounting for the effects of subgrid features in a numerical model is a longstanding problem in surface water hydrodynamics. This problem arises in several ways: in many cases, objects in the flow are too small in scale to consider resolving, and in other cases, there can be tremendous savings in computer resources by limiting the resolution. At least two approaches can be used for estimating these effects. In a general method using double-averaging techniques, volume averages are calculated and include terms that arise from the stresses exerted by the subgrid objects. In another method primarily used to account for subgrid topographic variations, the subgrid data is incorporated directly into the model. The first method leads to the inclusion of form drag and is illustrated by studies of flow through vegetation on a river floodplain and tidal power potential of turbines placed in Minas Passage in the Bay of Fundy. The second method is illustrated by a study of tsunami runup on the west coast of Vancouver Island.