Introduction to Instream Flows and Instream Flow Rules

Introduction to Instream Flows and Instream Flow Rules  

This web page has answers to basic questions about instream flows and instream flow rules.

Terms in green are linked to a glossary.


What is an instream flow? Answer...

An instream flow is a water right for the stream and the resources that depend on it. It has a priority date like any other water right.  Instream flows are the stream flow levels that will protect and preserve instream resources and values.

The term “instream flow” identifies a specific stream flow level (measured in cubic feet per second, cfs) at a specific location on a given stream. The weather causes natural flow variations throughout the year so an instream flow is a range (a “regime”), usually changing month-to-month, instead of a single number.

Instream flows do not affect existing (senior) water rights, rather, they protect the river from future withdrawals.

Setting instream flows does not put water in streams.

In state law, the terms “base flow” and “minimum instream flow” have the same meaning as “instream flow.”

  Example of an instream flow: Instream flows set on the Kalama River in southwest Washington are measured at River Mile 2.8. The flows range from 1050 cfs in December to 900 cfs in June and 400 cfs from August 16-31. (WAC 173-527)  
Hide this content.

Why are stream flows important? Answer...

Stream flows are important for many reasons, including:

Hide this content.

What is an “instream flow rule”? Answer...

An instream flow rule is a stream flow regime set in a state regulation. The Legislature has directed Ecology through state law to protect and preserve instream resources. One of the ways Ecology fulfills this mandate is to set instream flows in rule.

Instream flow and water management rules

The instream flow rules developed since 2000 are much more complex and comprehensive than their counterparts in the 1970’s and early 1980’s. While we still tend to refer to the more recent regulations by the shorthand “instream flow rules,” these rules are more accurately called “instream flow and water management rules,” or “water resources management programs.”

In addition to setting flows, typical instream flow rules now include broader water management strategies. Current rules are intended to help protect existing water rights and instream resources, while providing water for future urban and rural needs. Today's rules include:

Hide this content.

Are there instream flows set in my watershed? Answer...

Instream flows are generally set on a watershed-by-watershed basis.  For management purposes in Washington, we have divided the state into 62 Water Resource Inventory Areas (WRIAs, or watersheds).  Instream flows have been set in 26 watersheds, see the Instream Flow Rule status map, and are being developed in several others.  The intent is to set instream flows throughout the state. View existing rule texts by WRIA.

Hide this content.

How could setting instream flows affect me? Answer...

Instream flow/water management rules only affect water right decisions made after the adoption date of the rule.  Therefore such rules will not affect use of:

Water rights secured after the rule adoption date will be “junior” to the instream flows.  If you start a new water use, or make a change to an existing water right, after the effective date of the rule, you will be subject to any water management strategies and requirements specified in the rule.  For example, water for new year-round household uses may come from a water reservation with certain conditions, or new water uses may require mitigation to offset the impacts on local streams.  For more information on any requirements in your area, you can contact your local building permit office or one of Ecology’s regional offices.

  Washington State water law is based on the prior appropriation doctrine, often characterized as “first in time, first in right.”  Water rights have an effective or “priority” date which determines one’s access to water.  In times of water shortage, older (more senior) water right holders have their water needs satisfied first.  
Hide this content.

Are instream flows all about protecting fish? What about people? Answer...

Washington state law requires that instream resources, including fish, have adequate flow levels to protect and preserve them.

When setting flows, a lot of discussion centers around fish needs because fish are considered an “indicator species” – setting instream flow levels adequate for fish generally provides flows adequate for other instream resources. And fish needs can be more easily quantified by existing methods than other instream values.  This is why fish studies are usually the basis for determining instream flow numbers.

Adequate stream flows are important for instream resources and values that directly impact people, including water quality, recreational activities like fishing, boating and swimming, and the scenic and aesthetic qualities of natural settings that Washington State is famous for. (Also see the question Why are stream flows important?)

When making decisions about water right permits, it is necessary to know how much is needed and how much is available.  Adopting instream flow rules help Ecology determine whether there is enough water for additional out-of-stream uses and support local communities in managing their current and future water needs.

  Isn't instream flow really an issue of “water for fish” vs. “water for people”?  Aren't people more important than fish?

There is no question that people are more important than fish.  However, fish (for consumption, sport/recreaton, and as an essential part of the overall food chain) are an important and interconnected part of Washington's quality of life and diverse economy.   In adddition, while fish are just one of many organisms that live in streams but they often offer a gauge of the overall environmental health of a stream or river.

Instream flow is an issue of water and river management - seeking ways to maintain healthy, diverse ecosystems that contribute to Washington's high quality of life while sustaining our basic life functions and economies.  Accomplishing this goal is never easy, as it involves integration of scientific knowledge and societal demands within a set of legal limitations.

Overall, having informed and effective instream flow management should afford a healthy, enjoyable existence for people while maintaining healthy, diverse aquatic resources.  

   Instream Flow Council
Hide this content.

How are instream flow numbers determined? Answer...

Fish studies (see previous question) and hydrographs are usually the basis for determining instream flow numbers. While everyone agrees fish need water to survive, not everyone agrees on how much. Fortunately, there are ways to answer the question scientifically. The first step is to calculate the stream flows needed to protect fish spawning and rearing: a fish habitat study. (“Habitat” simply refers to the environment that fish live in.)

The most commonly used methods by Ecology and the Washington Department of Fish and Wildlife for studying fish habitat are Toe-width” and the “Instream Flow Incremental Methodology” (IFIM). (see The Science Behind the Flows webpage.)

So how much water do fish need? That depends on the type of fish, its life stage and the time of year. To address the needs of the many different species that depend on adequate stream flows, water managers try to ensure there is sufficient water in the stream at different times of year. State law is clear that instream flows must be set at levels that protect and preserve fish and other instream values over the long-term. Some years of higher flows are necessary to support healthy fish runs, so instream flows establish month-by-month levels that include these higher flows.

But a fish habitat study cannot by itself determine instream flows. Instream flows are based on the best available science in the fields of biology and hydrology, and by professional judgment. Data from the studies are integrated with an understanding of the stream flow needs of fish and other instream values, and, where possible, balanced with the water needs of people.

Hide this content.

Why are instream flows sometimes higher than the flow in the stream? Answer...

While the amount of water in the stream is considered when determining instream flow numbers, they cannot be based solely on existing levels (see next question).

State law is clear that instream flows must be set at levels that protect and preserve fish and instream resources over the long-term.  The instream flows reflect levels that would be beneficial for fish if those flows were present in the stream.

Actual stream flow levels naturally vary throughout the year due to seasonal changes and water use.  So the differences between the actual stream flows and instream flows will also vary throughout the year.

If the instream flow number is high relative to the average stream flow in the stream in the summer, this does not mean that the instream flow number is wrong.  Rather it means that the stream will provide more fish habitat in wet years than in dry ones.  Protecting the occasional “good water year” is needed to preserve a healthy population of fish.  If we want to protect the habitat available in those good wet years, then the instream flow needs to be set at that higher flow level.

Hide this content.

Why not set flow levels lower than the existing flows in the stream? Answer...

An instream flow is not the lowest amount of water that has occurred in the stream according to stream flow records.  State law is clear that instream flows are to protect and preserve fish and other instream resources over the long-term.

If an instream flow is set at an extremely low number so it can always be achieved during the summer, then we can expect:

Eventually the fish population would collapse.

If the instream flow number is high relative to the average stream flow in the summer, this does not mean that the instream flow number is wrong.  Rather it is a red flag that signals the fish have barely enough water to survive, and no surplus water is available for new water rights if fish and instream resources are to be protected.

Hide this content.

What are the laws that allow Ecology to set flows by rule? Answer...

The legal authority to set instream flows by rule comes from laws passed by the state legislature, including:

Hide this content.