Instream Flow Glossary

Note: These definitions are provided to help readers understand water management terms.  They are not intended to be legal definitions.  Definitions in individual rules may vary.

Closure: Closing a specified water body to new uses, based on a finding that water is not available.  Closures protect streams, as well as existing water users, from being affected by new uses.

Consumptive use: A use of water that diminishes the water source.

Groundwater: Water located under the ground.

Hydrograph: A graph of the flow level in a stream over a period of time.

Instream flow: A specific stream flow level (measured in cubic feet per second, cfs) at a specific location on a given stream.  Instream flow is a range (a “regime”), usually changing month-to-month, instead of a single number.  It is a water right to protect a quantity of stream flows for instream resources.

Instream resources and values: As defined in state law, includes fish and wildlife, aesthetics, water quality, navigation, livestock watering and recreation.

Mitigation: Measures that offset potential adverse effects on a water source, from a proposed water use.  For more information read the WRP Policy Evaluating Mitigation Plans

Permit-exempt groundwater withdrawals: In the state Ground Water Code, the “groundwater permit exemption” (RCW 90.44.050) allows for certain amounts and uses of groundwater without obtaining a water permit from Ecology.  While exempt from the permitting process, these withdrawals are still subject to all other state water laws.  Also referred to as “permit-exempt wells. Find out if your project is exempt from a water right permit.

Priority date: The effective date of a water right. Washington State water law is based on the prior appropriation doctrine, often characterized as “first in time, first in right.” (RCW 90.03.010)  The priority date of a water right determines one’s access to water. In times of water shortage, older (more senior) water right holders have their water needs satisfied first.

Reservation: A reservation, or reserve, of water is a one-time, finite amount of water set aside for specific future uses.  These uses may often continue even when stream flows fall below established instream flow levels.  Reserves usually have conditions of use that must be met to access them.

Rule: An administrative rule or regulation.  Under state law, Ecology and other executive branch agencies may write administrative rules or regulations, to implement state law.  Once adopted, these rules become part of the Washington Administrative Code (WAC).

Stream flow: The amount of water flowing in a stream or river.  See also "instream flow".

Water right: A water right is a legal authorization to use a certain amount of public water for a designated purpose, at a certain place and during a certain period of time.  The water must be put to “beneficial use” which refers a use of water without waste, to uses such as irrigation, domestic water supply, and industry and power generation.