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Partially Blocking: means that the mask blocks partly the movement of water in the water column. Masks can be fixed in place so that only water can only flow through specific cells vertically and horizontally despite changes in water levels. Alternatively, the masks can be on a floating object, so that water can still move under the mask. And this changes depending on the water level, e.g., a floating bridge. Figure Grid Masks (1) provides a schematic of the components of a partially blocking mask.
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