The phrase "form a system of drainage" refers to the process of designing and implementing a network of channels, pipes, and other structures intended to direct the flow of water away from a particular area. There are many synonyms for this term, such as "construct a drainage system," "establish a drainage infrastructure," or "create a system for managing water runoff." Other options might include "develop a network of water channels," "install a series of drainage features," or "engineer a drainage plan." Regardless of the specific wording used, the goal is always the same: to create an efficient and effective system for managing water and preventing flooding or erosion.