Objective: Prevent Impacts from New Development on a Site-Specific Scale

New development needs to be conducted in a fashion which preserves natural hydrologic processes and otherwise prevents the generation of stormwater to the greatest extent feasible.  This can be accomplished through the use of low impact development techniques.  New development is defined here as all new construction as well as grading and clearing projects on undeveloped sites.

All new development should be designed to prevent the generation of stormwater. New development should be required to maintain or restore natural hydrologic condition of the site.  In all but rare instances, sites in the Puget Sound region will be able to achieve zero overland flow of stormwater by utilizing low impact development strategies. If a site is such that it cannot be developed utilizing low impact development techniques, then it should be considered “un-buildable” and set aside.  Scientific research on the ecological impacts of stormwater indicate that, in conducting new development, we should maintain or restore 65% of the site in sizeable, native evergreen trees.  Development should be dispersed within the wooded area, with no stormwater runoff allowed from the site.  In addition, to minimize impacts, the site should contain zero effective impervious surfaces and no more than 10% total impervious surfaces.  The 65 10-0 standard of development (65% forested; 10 max impervious; zero overland flow) can and should be implemented in a way that maximizes density requirements under the state Growth Management Act.  In order to achieve this goal, high density residential housing should be expanded and new development should be encouraged or required to utilize a smaller footprint where necessary to meet these goals.

Recent research indicates that new development in the Puget Sound region can, in all but rare instances, achieve a standard of zero overland flow for the site.  Methods for eliminating runoff from developed surfaces include (but are not limited to) using pervious paving materials, routing runoff from impervious area to bioretention facilities, the use of “green” roofs or cisterns, and by reducing impervious areas to functional minimums.  Codes should be changed to require that new paving and roofing be constructed using materials and practices that prevent them from generating runoff to surface water.  Water that is collected on site should be utilized on site to the greatest extent feasible.

In the rare cases in which it can be demonstrated that low impact development is not possible on a given site, then fully mitigate and apply best management practices discussed in Sections D and E below.  Low impact development should be considered “possible” if soil amendments or project design changes make it possible to proceed with low impact approach.

Require jurisdictions to adopt a “fix-it first” approach to growth.  Allow the expansion of urban growth boundaries only when the local jurisdictions have adopted and are successfully implementing programs to reduce sprawl and the “retrofit program” outlined below (see D, bullet 3).

Preserve Natural Hydrological Processes on a Landscape or Watershed Level

Source Control

Restore Hydrologic Processes and Water Quality in areas Where Development has Caused Harm

Mitigate Fully for Any Loss of Hydrologic Functions which Result from New Development

After Maximizing Prevention and Source Control Strategies, Use Best Management Practices to Reduce Impacts Until Restoration is Possible

Overarching Mechanisms to Achieve Objectives

To comment or for more information, contact Bruce Wishart, (360) 754-9177.