Essential hydrologic functions
Essential hydrologic functions means the role of an alluvial valley floor in collecting, storing, regulating, and making the natural flow of surface or ground water, or both, usefully available for agricultural activities by reason of the valley floor's topographic position, the landscape, and the physical properties of its underlying materials. A combination of these functions provides a water supply during extended periods of low precipitation.
30 CFR § 701.5
As used in this chapter, the following terms have the specified meanings, except where otherwise indicated: