Loree Estates Outfall Diversion

🌧️ Loree Estates Outfall Diversion

Project Number: SW-610Improving Stormwater Resilience through Outfall Relocation

💡 Project Purpose

The Loree Estates Outfall Diversion project aims to resolve slope instability and improve stormwater management in Sammamish. The City is relocating an existing outfall originally discharging to a tributary of Kanim Creek. The proposed alternative routes stormwater to a more stable location within the City right-of-way near SE 19th Street.

The project reduces erosion risks, enhances public safety, and supports long-term infrastructure resilience by finding a preferred alternative for relocating the outfall from a narrow 23-foot drainage easement between private properties.

🌿 Project Background

In 2019, a slope failure downstream of the current outfall raised concerns about infrastructure stability and stream erosion. The outfall from stormwater facility D90112 is located between two homes, discharging into an unstable tributary of Kanim Creek. This analysis explores rerouting stormwater conveyance to discharge closer to SE 19th Street at a culvert crossing, leveraging City-owned right-of-way.

Hydrologic and hydraulic modeling (MGSFlood and FlowMaster), informed by the 2019 Kanim Creek Tributary Analysis, supports this effort. The outcome will reduce flooding risks, minimize utility conflicts, and support environmental goals.

📍 Project Location

Loree Estates Neighborhood
Tributary to Kanim Creek, Sammamish, WA
Near SE 19th Street

Embed vicinity map of outfall and potential discharge realignment.

📅 Project Timeline

💰 Project Budget

• Here is the link to 2025-2026 Budgeted Projects file 

🧰 Project Scope

The project includes:

• Environmental permitting (SEPA, HPA, SWPPP)

• Geotechnical analysis and design support

• Final PS&E bid-ready design packages

• Stakeholder engagement and coordination

• Optional construction support (RFI review, field visits)

• Construction of new flow control and outfall system

🤝 Partners & Stakeholders

• City of Sammamish Public Works

• Osborn Consulting, Inc. (design & permitting)

• Regulatory Agencies: WDFW, Ecology, King County

• Local Residents and Property Owners

• Utility Providers

⚠️ Key Risks & Constraints

• Slope instability near SE 19th Street

• Utility conflicts and complex retrofits

• Permitting delays (SEPA, HPA)

• Construction disruption and traffic impacts

• Unforeseen subsurface/geotechnical issues

📢 Community Engagement

• Bi-weekly internal team meetings

• Targeted outreach to affected property owners

• Permit coordination with WDFW and Ecology

• Project updates shared via web, email, and public briefings

Stakeholder input and regulatory alignment are essential to ensure smooth delivery and broad community benefit.

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