an ocean
A waterway deep and wide enough for a vessel is called navigable.
channel
canal
navigable river
The adjective navigable is a word used to describe a body of water as deep and wide enough to provide passage to ships.
Because the St Lawrence river, the St Lawrence seaway as it is known, is wide & deep enough for ships to navigate the waterway.
They can be 'navigated'
Some just wide enough for 2 soldiers to pass by each other and others smaller
Capable of being navigated; deep enough and wide enough to afford passage to vessels; as, a navigable river.
Not deep enough, not wide enough, doesn't run through any major freight hubs.
If it is an exterior shed type storage room you can go as deep and wide as you want. If it is part of a home and attached it should be 12 inches wide and deep enough to get below the frost or freeze depth in your area. If freezing ground is not a problem than 12 inches deep should be fine.