Desired profile
Each section defines the target cross-section shape of the waterway after dredging — the minimum depth and slope angles (or a custom drawn profile). The desired depth at any point across the channel is computed by interpolating between the two bank endpoints along the section line.
Comparison grid
The measured bathymetry is interpolated onto a regular 300 × 300 grid that covers the full survey extent. Each square cell represents an equal portion of the riverbed — its side length is simply the survey width or height divided by 300 (e.g. a 300 m wide survey gives 1 m × 1 m cells; a 60 m wide survey gives 0.2 m × 0.2 m cells). For every cell that lies within the plan area the algorithm compares the interpolated bed elevation to the desired profile depth at that position.
To dredge (red)
Where the measured bed is shallower than the desired depth, material must be removed. The volume to dredge equals the depth deficit of each such cell multiplied by its area, summed across all cells that need work. The cross-section area shown in the slice view is the same calculation in 2-D (depth deficit × bin width along the section line).
Adequate (green)
Where the measured bed is already at or deeper than the desired depth, no work is needed. The "adequate" figure is the complementary area/volume.
Dredge area
The number of grid cells that need dredging, multiplied by the cell area in m².
Average dredge depth
Total dredge volume divided by dredge area — the mean thickness of material to remove across the sections that require work.