Exposed of Tower Intake gatehouse or tower structures are generally used for large projects on rivers or reservoirs with large water-level fluctuations. They may be built either sufficiently near the shore to be connected by a bridge walkway or at such distance that they can be reached only by boat. Gate-controlled openings (also called ports) are generally provided at several levels in order to permit selection of the best-quality water. There are two major types of exposed of tower intakes: wet-intakes tower, and dry-intake towers.