YIELD — (1) The quantity of water expressed either as a continuous rate of flow (e.g., cubic feet per second — cfs) or as a volume per unit of time (e.g., acre-feet per year — AFY) which can be collected for a given use or uses from surface- or ground-water sources on a watershed. The yield may vary with the use proposed, with the plan of development, and also with economic considerations. (2) Total runoff. (3) The streamflow in a given interval of time derived from a unit area of watershed. It is determined by dividing the observed streamflow at a given location by the drainage area above that location and is usually expressed in cubic feet per second per square mile.

YIELD, AVERAGE ANNUAL — The average annual supply of water produced by a given stream or water development.

YIELD, FIRM — The maximum annual supply of a given water development that is expected to be available on demand, with the understanding that lower yields will occur in accordance with a predetermined schedule or probability. Sometimes referred to as Dependable Yield.

YIELD, PERENNIAL — The amount of usable water of a ground-water reservoir that can be economically withdrawn and consumed each year for an indefinite period of time. It cannot exceed the sum of the Natural Recharge, the Artificial (or Induced) Recharge, and the Incidental Recharge without causing depletion of the groundwater reservoir.

YIELD, SAFE — With reference to either a surface- or ground-water supply, the rate of diversion or extraction for Consumptive Use which can be maintained indefinitely, within the limits of economic feasibility, under specified conditions of water-supply development.