Minecraft wiki entry for Underwater_home, associated text: Sugar cane blocks water, but not movement, ‌[Java Edition only] so you can use them as air-to-water doors. However, placement is restricted: Just like on dry land, the bottom block must be placed on sand or dirt, with a water block next to, and one level below, the placed cane. Also, sugar cane is fragile, and if any cane is broken, all the canes above it will break too.
If Ice can form over the surface of the water above your base you need to ensure that you have a way to get out from under it.
If building an underwater tunnel to access your base, remember that still water will allow you to pass in both directions at the same rate, but flowing water works better for one-way paths.