Lower Perennial - Water velocity slow, but some water flows throughout the year. Gradient is low. The substrate consists of sand and mud. Oxygen deficits may occur. Upper Perennial - Gradient high, water velocity fast.
Water flows throughout the year.
Substrate consists of rock, cobble, gravel, and sand. Dissolved oxygen content high. Intermittent - Flowing water present only part of the year. When water is not flowing, it may remain in isolated pools or surface water may be present. Flowing water present all year.