Bioretention hydrologic performance studies

Use of bioretention is widespread in the Puget Sound region and expected to increase as a preferred means for stormwater flow control and reducing pollution.

State and local governments are eager to evaluate and ensure that bioretention facilities constructed under Ecology’s Stormwater Management Manual for Western Washington attain the desired performance.

Studies measuring hydrologic control of stormwater

Two projects (phases) of a similar design are currently active to evaluate bioretention facilities built to two different design standards.

Phase I: The early bioretention facilities in western Washington were designed prior to the 2012 stormwater management manual for Western Washington. The City of Bellingham led the first project.
Phase II of the project is led by the City of Olympia to evaluate facilities built using the 2012 bioretention design standard.

Both projects will assess performance of the facilities to capture, infiltrate stormwater runoff. Results will be compared to model predictions. The findings will provide feedback on design, construction, maintenance, or modeling that impact the hydrologic performance of bioretention facilities.

Pre-2012 Bioretention Hydrology Performance Study

Study questions

Are bioretention facilities being built across Western Washington as designed?
Once built, are bioretention facilities performing hydrologically as modeled by the Western Washington Hydrology Model (WWHM)?

Study findings

The City of Bellingham led a study to evaluate pre-2012 designed bioretention facilities to evaluate performance against the WWHM model predictions. Ten sites were monitored in the winter of 2016-2017, and represent real-world early design bioretention facilities and conditions.The results evaluate overall hydrologic performance to control stormwater flows, design constraints, and modeled expectations. The report summarizes the findings, provides reasons and data for observed differences in performance and expectations, and makes recommendations for engineers, jurisdictions, and model development..

Key project documents

Current Design Bioretention Hydrology Performance Study

Study question

Are bioretention facilities being built across Western Washington as designed?
Once built, are bioretention facilities performing hydrologically as modeled by the Western Washington Hydrology Model?

Study goal

This study led by the City of Olympia will select 10 new bioretention sites that were built to the 2012 or later manual design.

Results of the project will provide data to evaluate design and performance, and confidence in how the the 2012 (current) bioretention design performs hydrologically.

Project tasks and deliverables

Scope of work

Tasks

Task 1: Project Management

D1.1 Quarterly Progress Reports
- 2017: Quarter 4
- 2018: Quarter 1 & 2, Quarter 3 & 4
- 2019: 2018: Quarter 1 & 2, Quarter 3 & 4

Task 2: Site Selection and Preparation

Task 3: Develop Quality Assurance Project Plan (QAPP)

D3.1 Draft QAPP
D3.2 Final QAPP

Task 4: Study Monitoring

D4.1 Equipment list for purchasing
D4.2 Memo on geotechnical results for each site
D4.3 Memo on hydrologic design for each site
D4.4 Memo on vegetative investigation for each site

Task 5: Data Analysis and Modeling

D5.1 Meeting with SWG
D5.2 Technical memo on models for each site
D5.3 WWHM model of each site
D5.4 Memo of interim findings for SWG
D5.5 Meeting with SWG on interim findings

Task 6: Report & Findings Communications

D6.1 Draft report for review
D6.2 Presentation
D6.3 Final report
D6.4 Fact Sheet
D6.5 Presentations to counties and cities (to be decided- ideas below)
- north, south, central, east or west sound locations
- southwest WA
- local conferences

Contact information

Brandi Lubliner
Stormwater Action Monitoring Coordinator
brandi.lubliner@ecy.wa.gov
360-407-7140