About the Division

The Surface Water Management (SWM) Division works to protect Newcastle’s natural waterways and reduce flooding. Rain and melting snow that runs off rooftops, roads, and other hard surfaces can pick up pollutants before entering the stormwater system and flowing into creeks, lakes, and wetlands. The division manages this runoff, known as stormwater, to prevent damage to people and property and to keep local water resources healthy.

Natural Waterways and Drainage Basins

Newcastle is part of three major watersheds – Coal Creek, East Lake Washington, and May Creek – each with smaller drainage basins that guide water flow. Local waterways include Lake Boren, China Creek, Boren Creek, Newport Hills Creek, Gypsy Creek, May Creek, and surrounding wetlands. Understanding these systems helps staff identify areas at risk for flooding or pollution and make informed decisions to protect our waterways.

Understanding Stormwater

Stormwater is rain or melting snow that flows over hard surfaces instead of soaking into the ground. As it moves, runoff can pick up pollutants and carry them through storm drains into creeks, wetlands, and Lake Boren. During heavy rain, stormwater can overwhelm drainage systems and cause flooding that affects homes, roads, and natural habitats. Managing stormwater helps protect water quality, reduce flooding, and keep our environment healthy.

Newcastle’s Stormwater System

Because all stormwater eventually flows into local creeks, wetlands, and Lake Boren, the city relies on a complex system to manage it safely. Newcastle’s stormwater system includes nearly 50 miles of pipes, more than 3,400 storm drains, over 150 facilities like ponds and tanks, and 38 low-impact development sites. Regular maintenance ensures these systems function properly, protecting local waterways and minimizing flooding.

Comprehensive Surface Water Management Plan

The City repairs and upgrades stormwater facilities and builds new ones to improve water quality and reduce flooding. The Comprehensive Surface Water Management Plan guides these efforts by setting priorities based on waterway health, maintenance needs, and system modeling. Together, the plan and its capital projects help safeguard creeks, wetlands, and Lake Boren while keeping Newcastle’s stormwater system strong.

View the Comprehensive Surface Water Management Plan in the Document Center.

Learn about current capital projects on the Capital Improvements page.

How We Serve the Community

Using knowledge of watersheds, drainage basins, and stormwater systems, the SWM Division protects Newcastle’s waterways by reviewing new developments, maintaining public stormwater systems, inspecting private systems, and monitoring local creeks, wetlands, and Lake Boren. Staff also provide education and outreach to help the community reduce pollution and keep waterways clean, safe, and resilient.