The ditches of Sung-Shu and Erh-Lung were partially filled.
The main ditches, or canals, afterwards also serve as a means of navigation.
The ditches may be filled in one or other of several different ways.
In the case of small plantations the difficulties of adjusting a right-of-way for outlet ditches have interfered seriously with this plan.
To increase the reservoir capacity of the polder, as well as to conduct the water to the windmills or engines, it is intersected by a network of ditches cut at right angles to each other, the amount of ditching required being usually one-twelfth of the area to be drained.