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Guiding Growth - Healthy Watersheds: Science to Local Policy

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What is a watershed?

A watershed is the area of land that drains downslope until it reaches a common body of water, either a river or lake, or Puget Sound. This includes water that flows over the land as streams and rivers as well as water that moves through the land as groundwater. One way to picture a watershed is as a giant funnel that catches and directs all of the water that falls into it towards the bottom.

Watershed Diagram

We all live in watersheds. As you read this webpage, you are standing or sitting within a watershed that is shared by fellow neighbors and neighborhoods. Watersheds follow natural boundaries determined by the shape of the land, rather than political boundaries, and there are several watersheds within Thurston County, including large watersheds that follow the Nisqually, Deschutes, and Chehalis Rivers, as well as smaller watersheds such as those that drain into Totten, Eld, Budd, and Henderson Inlets. A single watershed may be divided into smaller drainage areas, called sub-watersheds or basins.

How does development impact watershed health?

As more people move into an area, more land is covered by hard, impermeable surfaces such as roofs, roads, and sidewalks. In these developed areas less rainwater is able to soak into the soil and slowly filter back to waterways. Instead, the water rushes along hard surfaces and pours directly into rivers and streams, carrying pollution and causing erosion and flooding. Local research shows that streams may be impacted when as little as 10 percent of a watershed (1 acre in 10) is impermeable.  Just a little additional development in some healthy watersheds could tip them over the edge to being unhealthy.

Damage to watersheds from growth often results in environmental and human health problems. These problems can be unpleasant to live with and costly to fix. For example, rural growth around Henderson Inlet caused water quality problems that led to shellfish harvest closures. As a result, a new septic maintenance program for homeowners was created to improve water quality. While this program has been a success, it has created an additional expense for rural homeowners and businesses.

What can be done to limit the impact of development on watershed health?

Preventing damage to our watersheds while they are still healthy is less expensive than paying to restore watershed health after it has been damaged. Communities have many tools at their disposal to direct growth away from areas where it can do harm and to minimize the impact of development where it does occur. These tools include changing development and zoning regulations, encouraging the transfer or purchase of development rights, implementing low-impact development, or purchasing sensitive lands.

We have local examples of how proactive land-use planning can help maintain watershed health. In 1999, the City of Olympia found the Green Cove Basin watershed to be sensitive to the impacts of growth. While still in good condition, it was facing the threat of immediate development pressure. In order to protect the health of the basin, the City of Olympia and Thurston County changed the zoning, development standards, and tree retention standards there. These measures have kept Green Cove Creek healthy and averted what could have been serious harm to the environment and the community.


For more information on watersheds and watershed planning, visit the following links:


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