Surface Water Design Manual and Low Impact Development

The City adopts the 2021 King County Surface Water Design Manual, along with our City Surface Water Design Manual Addendum

The City adopted code amendments that encourage low impact development (LID) principles to minimize the loss of native vegetation and reduce runoff from developed sites. The 2021 KCSWDM requires onsite flow control best management practices (BMPs) to mitigate the impacts of storm and surface water runoff generated by new impervious surfaces, new pervious surfaces, existing impervious surfaces, and replaces impervious surfaces. Flow control BMPs are methods to disperse, infiltrate, or otherwise reduce or prevent development related increases in runoff at or near the sources of those increases. The 2021 KCSWDM provides specific design guidance for implementation of the LID measures encouraged in the City's development code. As a result, the 2021 KCSWDM and the City development code complement each other. 

Development Review
The City provides stormwater development review for development and redevelopment in Newcastle. As per the City’s NPDES permit, we are required to adopt updated surface water design standards that guide stormwater design within Newcastle.

Construction and Stormwater

All development projects in Newcastle require erosion control and an Erosion and Sediment Control (ESC) plan and must be submitted to the City for review. Some projects (>1 acre) need a Construction Stormwater General Permit (CSWGP), issued through the Washington State Department of Ecology.

Who needs a CSWGP? 

1. Does your construction project disturb one or more acres of land through clearing, grading, excavating, or stockpiling of fill material?

Remember to count the cumulative acreage of the entire project, whether in a single or in a multiphase project. This applies even if you are responsible for only a small portion [less than one acre] of the larger project planned over time. 

2. Is there any possibility that stormwater could run off your site during construction and into surface waters or conveyance systems leading to surface waters of the state?

In almost every case, the answer to this question is yes. However, if the topography and location of your site is such that there is no possibility that rainfall or snowmelt could leave the site or enter a waterway, you do not need permit coverage. 

If you answered "yes" to both of these questions, your construction site needs a permit. Construction site operators must apply for a permit 60 days prior to discharging stormwater. As part of a CSWGP, the Permittee must develop a Construction Stormwater Pollution Prevention Plan (SWPPP). 
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