Numerical models have
a valuable role to play in the sustainable management of coastal waters but accurate
simulation of land-sea interactions, particularly in areas of complex
coastlines, requires the use of high spatial resolutions. As a result, the
computational cost of such models can become quite prohibitive. Nesting
techniques offer a cost-effective solution to the spatial resolution problem by
allowing specification of high spatial resolutions in limited areas, i.e. selective
down-scaling. A one-way nested model was developed for simulation of tidal
hydraulics in coastal waters. The nesting procedure was developed to reduce
errors in the nested domain generated by the treatment of the nested open
boundaries. Such 'boundary errors' are primarily caused by loss of mass and
momentum due to non-conservative boundary schemes and/or inaccurate boundary
data due to unsuitable nested boundary locations. In the first instance, high
levels of conservation of mass and momentum are achieved by the use of a Dirichlet
boundary condition and linear interpolation scheme for specification of nested
boundary data, and by a nested boundary configuration incorporating ghost cells
which, in effect, allows the formulation of open boundaries as 'internal
boundaries'. In the second instance, a procedure for identification of suitable
nested boundary locations ensures the level of error passed from the low
resolution solution to the nested solution via the boundary prescription is low.
Nested model functionality was verified for both experimental and natural test conditions.
The nesting procedure was found to reduce boundary errors and produce highly
accurate solutions for a fraction of the computational cost of high resolution
single grid models.