In order to represent many of the fine channel features of the Delta we have developed 10-meter horizontal resolution grid. While the underlying data is very dense in some areas (over 130 soundings per hectare near Roe Island) in most of the Delta a 10 m resolution grid requires interpolation and extrapolation over tens of cells. Simple interpolation techniques produce grossly inaccurate bathymetry models. The web of interlocking channels and varying sounding densities produce unusable results when simple interpolation or distance-weighted gridding techniques are used. See how poorly the bathymetry grids in figure 10(a) and 10(b) agree with the shore outlined channel.

Figure 9 shows example input data (soundings, shoreline, and contours) for a complex channel. In figure 10, we compare results for a simple linear interpolation with a distance-weighted interpolation. The resulting grids are fragmented. Although they correlate well with individual soundings, they do not maintain channel integrity.

We can evaluate the accuracy of the depth model by comparing the grid cell value with the underlying soundings. Differences are computed only for those cells where soundings exist. The table below summarizes this comparison.