Hydropower plants that depend on river flows without a large reservoir are called a diversion or run-of-the-river facility. These hydropower facilities funnel a portion of the water flow either through a pipe called a penstock or through a canal. Diversion facilities may or may not use a dam to direct the water. They may have a small amount of storage, called pondage, but the storage capability is much less than an impoundment facility. In most definitions for diversion or run-of-the-river facilities, storage is limited to daily or weekly fluctuations in water flow and does not materially alter downstream river flows.