Aiwa canal
The Ndak had a few early engineering achievements, most notable of which was a canal (the name of which is no longer remembered) from a branch of the lower Aiwa twenty miles to the nearest arm of the sea. It was dug over the course of a generation by slave labor, building on the previous aborted attempts by the Ngauro to do the same. it did not actually connect to the Aiwa at the upper end; instead, a long ramp rose out of the end of the canal and descended into the Aiwa on the other side, with ships being pulled across the ramps over log rollers by - you guessed it - up to several hundred slaves pulling ropes tied to the ship.
The original canal did not include the ramp, the waterway opening directly into the Aiwa, but this arrangement caused most of the river to divert down the narrow canal in a torrent sufficient to prevent upstream travel.
The canal was necessary for ships to get from the river to the sea or vice versa; the Aiwa does not empty into the sea by a single channel, but instead splits and splits again into a thousand small and shallow channels winding though the flat, swampy delta, which change course every time the river floods.
See also