By Steven Schauer, Deputy Executive Director

When the historic storms and flooding hit King County last December, you may have heard unfamiliar words and phrases for the first time, including words and phrases like Flood Phase, river gage, levee breach, and more. Understanding what these terms mean can make a real difference in how people prepare, respond, and stay safe before, during, and after flooding.

At the King County Flood Control District (KCFCD), our mission is to implement flood risk reduction policies and projects to protect life and property while advancing various benefits including equity and social justice, sustainable livelihoods, habitat protection, salmon recovery, recreation, and resilient communities. But flood risk reduction isn’t just about engineering projects and emergency response. It’s also about making sure people have clear, accessible information when it matters most.

That’s why we created this Flood Terms 101 guide. This blog is designed to be a simple, plain-language primer for King County residents, no technical background required. Whether you lived through the December flooding, are new to the area, or just want to feel more prepared for future storms, this glossary will help you better understand flood-related language.

When we all speak the same language about flooding, we’re better equipped to protect ourselves, our neighbors, and our communities.

Flood Terms 101

All definitions below are used by the KCFCD and are defined as such by the KCFCD unless otherwise indicated at the end of the definition. The sources of other definitions in the list below include the Federal Emergency Management Agency (FEMA), King County, National Weather Service (NWS), University of Washington Climate Impacts Group (CIG), and U.S. Geological Survey (USGS).

Please note, the definitions from King County come from the 2006 King County Flood Hazard Management Plan, which is the planning document that formed the basis for the creation of the KCFCD in 2007.

Armor

To protect fill slopes, such as the sides of a levee, by covering them with erosion-resistant materials such as rock or concrete. (As defined by FEMA)

Backfill

To fill in a hole with the soil removed from it or with other material, such as soil, gravel, or stone. (As defined by FEMA)

Base Flood

The base flood is a flood having a one percent chance of being equaled or exceeded in any given year, often referred to as the “100-year flood.” (As defined by 2006 King County Flood Hazard Management Plan)

Base Flood Elevation (BFE)

Elevation of the 100-year flood. The BFE is determined by statistical analysis for each local area and is designated on the FIRMs. This elevation is the basis of the insurance and floodplain management requirements of the NFIP. (As defined by FEMA)

Basin

A basin is a geographic area that contains and drains to a stream named and noted on common maps or a geographic area that drains to a non-flowing water body, such as a lake or marine area, named and noted on common maps. (As defined by 2006 King County Flood Hazard Management Plan)

Breach

Flood facilities are built along rivers to contain floodwater and reduce the frequency of flooding in nearby communities. Sometimes a flood facility, like a levee, can breach, or fail, if floodwater gets too high or part of the flood facility breaks. A breach is rare but can be dangerous and very damaging.

Capital Improvement Program (CIP)

A multi-year plan intended to reduce flood risk for communities throughout King County. The KCFCD Capital Improvement Program (CIP) is typically 6-years in length, outlines and prioritizes capital improvement projects (and occasionally programmatic actions) based on funding availability and risk, severity, and consequence, includes estimated time to complete projects identified for funding, and is approved annually by the KCFCD’s Board of Supervisors. The approved CIP, as part of the annual budget, forms the basis for the KCFCD’s annual work plan, which is implemented by the KCFCD through Interlocal Agreements (ILA) and contracts between the KCFCD and its service providers.

Capital Improvement Project

A flood risk reduction project planned as a large-scale investment, creating or significantly enhancing durable assets (e.g., flood facilities) to systematically address and lessen the impacts of flooding within a community. Projects are typically characterized by their substantial financial investment and the implementation of infrastructure or measures which are expected to last for many years. This may include, but not limited to, construction of new, or improvements to existing, physical infrastructure such as levees, revetments, floodwalls, and pump stations. Non-structural solutions may also be considered as a capital improvement project, such as the acquisition and removal of flood-prone properties (buyouts), elevation of existing homes, or the development of green infrastructure like vegetated detention basins, constructed wetlands, and bioswales, which can also provide environmental co-benefits.

Capital Investment Strategy (CIS)

A proposed sequence of coordinated capital improvement projects intended to upgrade and modernize King County’s aging flood risk reduction facilities to meet current and future demands. The strategies, organized by river basin, suggest potential near-term, medium-term, and long-term capital improvement projects that were identified during an assessment of key problem areas and potential solutions. The KCFCD directs the development of Capital Investment Strategies (CIS), which are completed by the KCFCD’s service providers, with input provided by Tribes, federal, state, and local governmental partners, interested parties, and the public. Programmatic activities may occasionally be included as suggested actions in the strategies with the approval of the KCFCD. The final strategies are approved as policy guidance by the KCFCD’s Board of Supervisors, and projects and actions identified within each approved CIS may then be considered for inclusion in the KCFCDs annual CIP.

Channel Migration

The movement of a river or stream channel across a landscape through erosion, which can happen gradually over time or abruptly. Both gradual and abrupt migration present risks, and abrupt migration, called an avulsion, can pose especially dangerous risks to people and property.

Channel Migration Zone

An area the width of the floodplain where a river or stream channel naturally moves sideways over time (see Channel Migration) driven by erosion on outer banks and deposition on inner banks and is subject to risk due to bank destabilization, rapid incision, bank erosion, and shifts in the location of channels. The channel migration zone is shown on King County’s Channel Migration Zone Maps, which are created by the KCFCD and King County, as service provider to the KCFCD. These maps are used by King County and other jurisdictions when making land use regulations.

Climate Change

The gradual warming of our planet caused by human activities. Manufacturing and industrial processes, driving gas-powered cars or flying in an airplane, and generating electricity all release greenhouse gases — including carbon dioxide — into the air. Though greenhouse gases are a normal part of our atmosphere and help keep Earth habitable for humans and other life, the excess greenhouse gases released by humans are trapping extra heat near the Earth’s surface. This is causing global temperatures to rise. Climate change stands to have profound impacts on water, ecosystems, forests, coasts and oceans and human health and society. (As defined by CIG)

Confluence

The junction of two rivers.

Consequence

The potential outcomes of a flood event, including threats to public safety, damage to infrastructure and property, economic disruptions, environmental degradation, and disproportionate impacts on vulnerable populations.

Critical Facility or Critical Infrastructure

A facility (or infrastructure) necessary to protect the public health, safety, and welfare. (As defined by 2006 King County Flood Hazard Management Plan)

Debris

Materials carried by floodwaters, including objects of various sizes and suspended soils. (As defined by FEMA)

Environmental Justice

All people, regardless of race, color, national origin, or income (historically disadvantaged populations), enjoy the same degree of protection from environmental and health hazards.

Environmental Stewardship

The responsible management and protection of natural resources and ecosystems to ensure their sustainability for present and future generations. It involves proactive efforts to conserve, restore, and enhance the environment through practices that minimize human impact, promote biodiversity, and support ecological balance. Environmental stewardship can be carried out by individuals, communities, organizations, and governments through policies, conservation initiatives, sustainable land and water management, and advocacy for environmental justice.

Equity

Ensuring fair treatment and meaningful involvement of all people, regardless of race, color, ethnicity, religion, income, or education by providing resources to community members that are proportionate to what they need to thrive.

Erosion

The wearing away of soil by moving water. (As defined by FEMA)

Flash Flood Warning

A Flash Flood Warning is issued by the NWS when a flash flood is imminent or occurring. If you are in a flood prone area move immediately to high ground. (As defined by NWS)

Flash Flooding

A rapid and extreme flow of high water into a normally dry area, or a rapid water level rise in a stream or creek above a predetermined flood level, beginning within six hours of the causative event (i.e., intense rainfall, dam failure, ice jam). (As defined by NWS)

Flood or Flooding

A general and temporary condition of partial or complete inundation of normally dry land areas from the overflow of inland or tidal waters or the unusual and rapid accumulation of runoff of surface waters from any source. (As defined by 2006 King County Flood Hazard Management Plan)

Flood Advisory

A Flood Advisory is issued by the NWS when a specific weather event that is forecast to occur may become a nuisance. A Flood Advisory is issued when flooding is not expected to be bad enough to issue a warning. However, it may cause significant inconvenience, and if caution is not exercised, it could lead to situations that may threaten life and/or property. (As defined by NWS)

Flood Alert

An automated system created by the KCFCD and operated by King County which sends customized alerts of potential flooding on King County’s major river systems. Notifications about pending high water and flood phases can be received via email, text, or voicemail.

Flood Depth

Height of flood waters above the surface of the ground at a given point. (As defined by FEMA)

Flood Facility or Flood Protection Facility

Physical structural works which have been constructed specifically to modify flooding to reduce the extent of the areas within a community subject to flooding and the depths of associated flooding. Includes, but not limited to, dams, reservoirs, levees, or floodwalls.

Flood Insurance Rate Map (FIRM)

The official map of a community prepared by FEMA that shows the BFE, along with the special flood hazard areas and the risk premium zones for flood insurance purposes. Once it has been accepted, the community is part of the regular phase of the NFIP. (As defined by FEMA)

Flood Phase

Flood phases reflect river flood conditions. The higher the phase, the more water flows in our rivers, and the greater the likelihood of flooding. These phases (0 – 4) are based on historical flood conditions unique to each river basin, helping emergency managers, public agencies, and residents understand the severity of an event.

Flood Risk Reduction

An action taken to decrease exposure of people and property to flood or channel migration hazards. (As defined by 2006 King County Flood Hazard Management Plan)

Flood Warning

A Flood Warning is issued by the NWS when the hazardous weather event is imminent or already happening. A Flood Warning is issued when flooding is imminent or occurring. (As defined by NWS)

Flood Warning App or Flood Warning Mobile App

The app, created by the KCFCD and operated by King County, provides current river flows, real-time flood phase information, and gage data trends and forecasts. Data is downloaded every ten minutes from U.S. Geological Survey and the National Weather Service’s Northwest River Forecast Center with the most current information.

Flood Watch

A Flood Watch is issued by the NWS when conditions are favorable for a specific hazardous weather event to occur. A Flood Watch is issued when conditions are favorable for flooding. It does not mean flooding will occur, but it is possible. (As defined by NWS)

Floodplain

The floodplain is the total area subject to inundation by the base flood. (As defined by 2006 King County Flood Hazard Management Plan)

Floodplain Management

A community-based effort to prevent or reduce the risk of flooding, resulting in a more resilient community. (As defined by FEMA)

Floodwall

Flood barrier constructed of manmade materials, such as concrete or masonry. (As defined by FEMA)

Flow or Flood Flow or Flow Velocity

Speed at which water moves during a flood. Velocities usually vary across the floodplain. They are usually greatest near the channel and lowest near the edges of the floodplain. (As defined by FEMA)

Habitat Protection and Salmon Recovery

Restore and protect riparian and in-stream habitats to benefit fish and aquatic organisms and to support long-range recovery goals for Endangered Species Act (ESA)-listed Chinook and steelhead.

Hazard Mitigation

Action taken to reduce or eliminate long-term risk to people and property from hazards such as floods, earthquakes, and fires. (As defined by FEMA)

Jobs and Sustainable Livelihoods

Diversity and number of jobs that are retained and increased in areas suitable for development that support residents and employees.

Levee

A manmade structure, usually an earthen embankment, designed and constructed to contain, control, or divert the flow of water so as to provide protection from temporary flooding. (As defined by 2006 King County Flood Hazard Management Plan)

National Flood Insurance Program (NFIP)

The Federal program, created by an act of Congress in 1968, that makes flood insurance available in communities that enact satisfactory floodplain management regulations. (As defined by FEMA)

Open Space Conservation

Retain priority open space in the floodplains and advance regional conservation plans. The U.S. Forest Service defines open space as land that is valued for natural processes and wildlife, agricultural and forest production, aesthetic beauty, active and passive recreation, and other public benefits. Locally based, long-term open space conservation plans help communities protect their environment, improve quality of life, and preserve critical elements of the local heritage, culture, and economy.

Production and Viable Agriculture

Create, support, and implement policies and actions that support continued production of crops and livestock on the remaining farmland.

Pump Station

A pump station is a public infrastructure facility with pumps and controls that moves water (typically floodwater) from one place to another, especially against gravity. For example, the Black River Pump Station serves as part of the levee containment that holds Green River floodwaters out of Renton, Kent, and Tukwila by pumping the Springbrook Creek drainage from the valley floor into the river, which is usually higher.

Recreation and Other Opportunities to Connect People with Nature

Leverage existing plans and fill known gap areas in recreation in an equitable manner.

Regulatory Floodplain

Flood hazard area within which a community regulates development, including new construction, the repair of substantially damaged buildings, and substantial improvements to existing buildings. In communities participating in the NFIP, the regulatory floodplain must include at least the area inundated by the base flood. (As defined by FEMA)

Repetitive Loss Area

A defined area that includes identified repetitive loss properties and other properties not listed as repetitive loss that are subject to the same flooding conditions. (As defined by 2006 King County Flood Hazard Management Plan)

Repetitive Loss Property

A repetitive loss property is any NFIP-insured property that, since 1978 and regardless of any change(s) of ownership during that period, has experienced any of the following:

• Four or more paid flood losses exceeding $1,000 each
• Two paid flood losses exceeding $1,000 each within any 10-year period since 1978
• Three or more paid losses that equal or exceed the current value of the insured property

(As defined by 2006 King County Flood Hazard Management Plan)

Resilience or Flood Resilience

The ability of communities, ecosystems, and infrastructure to recover quickly and effectively from flooding events while adapting to changing conditions over time.

Resilient Communities and Ecosystems

Create, support, and implement policies and actions that reduce climate change vulnerabilities equitably and increase the resilience of communities, natural systems, and the built environment.

Revetment

A facing of stone, broken rock, or other material placed on a streambank or slope to minimize erosion by moving water. (As defined by 2006 King County Flood Hazard Management Plan)

Risk

The estimated impact that a hazard would have on people, services, facilities, and structures in a community. Risk measures the likelihood of a hazard occurring and resulting in an adverse condition that causes injury or damage. Risk is often expressed in relative terms such as a high, moderate, or low likelihood of sustaining damage above a particular threshold due to occurrence of a specific type of hazard. Risk also can be expressed in terms of potential monetary losses associated with the intensity of the hazard. Synonymous with urgency.

River Gage or Stream Gage or Gage or USGS Gage

Per USGS, a gage is a scientific instrument that frequently collects data about the conditions of a river or stream. Commonly collected data includes river height and flow. Some gages collect water temperature, pH levels, salinity, turbidity, dissolved oxygen, precipitation, and more. Note: the USGS spells “gage” without the “u.” (As defined by USGS)

Severity

The potential magnitude of flood impacts, including the depth and velocity of floodwaters, the extent of inundation, the duration of flooding, and the resilience of the affected community, acknowledging historically underserved communities may have limited resilience. Severity is typically identified by river basin in terms of phases based on historical flood events.

Social Justice

Ensuring fair treatment and meaningful involvement of historically repressed people who have disproportionately faced institutional discrimination or systemic racism.

Sustainability

The capacity to meet present flood protection needs without compromising the ability of future generations to address their own needs, emphasizing long-term ecological health, community well-being, and climate adaptability.

Sustainable and Clean Water

Create, support, or implement policies and actions to improve water quality (temperature and chemistry).

Sustainable Development

A development pattern that recognizes ecosystem values, is resilient to climate change and natural hazards, sustains a viable economy, creates livable communities, and advances equity. Economic development conducted without depletion of natural resources. It is an organizing principle for meeting human development goals while sustaining the ability of natural systems to provide the natural resources and ecosystem services on which the economy and society depend. It can also be defined as meeting the needs of the present without compromising the ability of future generations to meet their own needs.

Watershed

An area of land that drains into a single outlet and is separated from other drainage basins by a divide. (As defined by 2006 King County Flood Hazard Management Plan)

Be Flood Ready

Flooding is a natural part of living in a river-rich place like King County, but confusion about what’s happening doesn’t have to be. Knowing the meaning behind common flood-related words and terms helps turn uncertainty into awareness, and awareness into action.

We hope this Flood Terms 101 guide helps you feel more confident when you hear a flood watch has been issued, read flood alerts, or follow emergency instructions. Understanding the language of flooding makes it easier to know when to prepare, when to move to higher ground, and how to protect what matters most.

While the KCFCD continues to invest in levees and revetments, floodplain restoration, warning systems, and long-term solutions to reduce flood risk, individual preparedness remains a critical part of community safety. Floodwaters can rise quickly, emergency services can become stretched, and every household plays a role in staying ready.

We encourage you to Be Flood Ready by visiting our flood resources page to learn more about flood alerts, flood preparedness tips, evacuation planning, and how to protect your home and family.

Together, through smart public investments, strong partnerships, and informed residents, we can continue building a King County where thriving communities and healthy rivers coexist, even in the face of a changing climate and more extreme storms.