Answer:
a) horizontally
Explanation:
If the sewage sludge is disposed of into the deep water , then the density gradient separates the surface water from the deep water,
the internal waves transport wastes horizontally .
When the transport of the particles is dominated by the tides ,wind and the density gradients, the movement is essentially in horizontal direction whereas the vertical transport of the particles is mainly driven by gravity and also by some other processes that occur at the sediment-water interface.
