What is a watershed?

A watershed is an area of land -- regardless of size -- where snowmelt and rainwater drain from higher areas into lower lying areas and then into a single water body; such as a wetland, stream, river, lake or ocean. Watersheds are separated from each other by elevated features such as ridge tops, hills, or roads. When precipitation increases rapidly and surface water flows across flat or impervious areas, it can cross over watershed boundaries. For example, if the upper Sammamish River Valley experienced a 100-year storm, stormwater runoff would most likely flow across the boundaries of the City's smaller watersheds and flood areas of the Sammamish Valley floor.

Interesting Facts About Redmond's Watersheds

  • The City of Redmond has designated approximately 87 different watersheds, either wholly or partly included within city limits.
  • The smallest of these watersheds is 1.6 acres; the largest is 1,685 acres.
  • The majority of the city watersheds (approximately 66) occupy less than 200 acres; another 13 occupy between 200-400 acres; and only eight watersheds are larger than 400 acres in size.
  • Total Impervious Surface (TIS) as a percentage of total watershed area, varies among these watersheds from a low of 2% to a high of 89%.
  • Only two of the 87 watersheds have less than 10% TIS. Twenty-seven watersheds have 10-40% TIS; and the remaining 58 watersheds have impervious surfaces exceeding 40%.
(Large-scale land cover data is available for all of Redmond's watersheds on King County's website: King County Land Cover 2001)

Why Focus on Watershed Management?

In the past, project development and land management decisions have often been approved project-by-project, jurisdiction-by-jurisdiction and regulation-by-regulation. This singular approach does not identify the significant cumulative impacts to watershed functions and processes when viewed as small, seemingly harmless, projects.

What happens when, instead, you look at things from a watershed perspective? Because so many watershed functions and processes are closely interrelated, it becomes harder to look at a single project or management issue in isolation. Landscape linkages become more obvious and several issues can be dealt with together--cumulative impacts to a wider area become clearer and may be addressed in a more equitable and cost efficient manner.

Adopting a broader watershed perspective encourages the development of solutions to environmental issues that can satisfy several regulatory requirements simultaneously. For example, compliance with the Clean Water Act, Endangered Species Act, or possible hazardous waste and toxics cleanup. Watershed plans will also enable us to make better choices about how to plan, maintain, and construct our drainage systems so they can better meet the community's many needs.

Watershed management solutions can only be effective with support from policymakers, elected officials, and the public. These groups are encouraged to adopt a long-term, broad-based watershed perspective.

What does stormwater have to do with watersheds?

As urban areas grow, we dramatically alter the way water flows through developed areas. As natural vegetation is replaced with impervious surfaces (roads, parking lots, buildings, and rooftops), runoff from rainfall increases, flushing sediment and pollutants into nearby wetlands, streams, and lakes. This in turn impacts our surface water quality--one of the toughest environmental challenges facing all cities. Redmond has adopted a watershed management approach to address these environmental challenges.

Using the watershed as our vantage point, we can craft better stormwater management techniques and meet the needs of businesses, residents, and wildlife.

What watersheds does Redmond manage?

Historically the US Geological Survey, Washington Department of Ecology, and King County have monitored the larger main-stem rivers and streams in Redmond (Sammamish River, Bear and Evans Creeks), as well as Lake Sammamish. When Redmond started its water quality monitoring program in 1995, it focused on the smaller streams and watersheds that drain into these larger water bodies.

Redmond's Watershed Map

Watershed Map

The Watershed Map provided above identifies the 20 watersheds, and associated water bodies, within Redmond’s city limits. Each watershed is color coded based on the strategy needed to restore a healthy water body in each watershed. Green color coded watersheds are in good shape, yellow watersheds are the most likely to become healthy with investment (programs and projects), orange watersheds are likely to become healthy with investment over a longer period of time, and red watersheds are heavily impacted and will take substantial time and investment to become healthy. No water body will be allowed to get worst, but improvements to existing impacts will be focused as much as possible in the yellow color coded watersheds.