2024 Stormwater Master Plan

This 2024 Stormwater Master Plan (SMP) identifies and prioritizes projects and programs to increase system capacity, address infrastructure and maintenance needs, add or enhance water quality treatment, address natural system deficiencies, and proactively plan for future growth. The SMP development process includes the:

• Evaluation of project needs and system improvements as identified by City staff.
• Development of validated hydrologic and hydraulic (H/H) model to confirm capacity issues and to assess anticipated flooding frequency and severity.
•  Assessment of stormwater system retrofit opportunities for water quality treatment and/or flow control.
• Assessment of the natural (stream) system to identify risks to infrastructure and stream stability.
• Identification of programmatic opportunities to address recurring maintenance needs and water quality issues at a citywide scale.
• Development of a comprehensive, prioritized CP list and associated costs.
• Analysis of staffing levels to meet deferred and future maintenance and regulatory requirements.

Master Plan Technical Analyses

The following technical analyses were conducted to evaluate stormwater system deficiencies and define project and program needs in support of SMP development.

Project Needs Identification: Project needs were initially identified through the distribution of surveys to City staff and the public, a literature-based and Geographic Information System (GIS) data review, and site visits and staff interviews. Information collected helped to create a robust inventory of the stormwater collection system features and problem areas related to capacity, maintenance, system condition, and infrastructure needs. Locations warranting additional analyses via hydraulic modeling and/or stream assessment were defined based on results of this effort.

Stormwater Retrofit Analysis: A stormwater retrofit analysis was completed to inform potential locations for water quality improvements, erosion prevention/natural resource enhancement, and/or flow mitigation in the city. Based on the site characteristics, the continued applicability of water quality projects not implemented from the 2012 SMP, and the ability to integrate water quality into other project needs, CP and program needs were identified to expand and enhance stormwater treatment throughout the city.

Stream Assessment: A stream assessment was conducted on select reaches of Boeckman, Meridian, Arrowhead, Newland, and the unnamed tributary to the Willamette River at SW Kruse Rd. (thereby referred to as Kruse Creek for this SMP) to inform locations where stream morphology may be or is currently impacted by changes to upstream land use, and in response to changes in flow, infrastructure, and sediment supply. The assessment included a desktop GIS analysis and stream walk (field observations) to inform capital project and ongoing monitoring needs.

Stormwater System Capacity Evaluation: The stormwater hydrologic and hydraulic (H/H) model developed for the 2012 SMP was updated to reflect changes in land use and impervious coverage and additional City-owned (public) storm pipe, culverts, and detention facilities constructed since 2012. CPs installed since 2012 were also incorporated into the H/H model, and the model was used to simulate rainfall and runoff characteristics and identify capacity limitations under both current and projected future development conditions.

Maintenance and Staffing Evaluation: Operational activities were assessed to identify staffing level needs and constraints. Information on current maintenance activities, regulatory needs, and anticipated engineering activities associated with implementation of this SMP, as well as compensation rates, were incorporated into staffing recommendations for both Public Works and Community Development/Engineering.

Project/Program Development and Prioritization: Project opportunities from the various technical evaluations were consolidated and developed into CPs and programs. CP development included conceptual design, facility sizing, and cost estimation. CPs were prioritized based on multiple criteria including system operations (capacity, recurring maintenance, safety); system condition; regulatory compliance (water quality, natural system condition, instream erosion); and other needs including project concurrence/scheduling, development drivers, and contributing drainage area. Project scoring and ranking helped designate high, medium, and lower priority projects for use in project scheduling and future stormwater funding evaluations.

ADDITIONAL INFORMATION

If you have any questions about the master plan, please contact Natural Resources Program Manager Kerry Rappold at 503-570-1570.