This Architectural Drawing is of Tunnel portal Section drawing. An irrigation canal or lateral is constructed to convey water from the source of supply to one or more farms. PRACTICE INFORMATION. The purpose of this practice is to deliver water to the farm irrigation system (s). Tunneling is a protocol that allows for the secure movement of data from one network to another. Tunneling involves allowing private network communications to be sent across a public network, such as the Internet, through a process called encapsulation. For more details and information download the drawing file.