Orifice control of bioretention

Washington State University - Puyallup will be evaluating a water flow rate controlling outlet (called an orifice) which is part of a bioretention underdrain system. The project will be studying bioretention facilities with smaller orifices controlling the water flow rate and evaluating both water quality and water quantity performance improvements.


Study Questions

  • What is the water quality treatment performance of bioretention with the smaller outlet-control as compared to the traditional media-controlled configuration?
  • How does outlet-control vs. media-control effect the residence time and residence time distribution of water in the bioretention mesocosm?
  • Are any differences in plant health and vigor notable at a mesocosm scale between outlet-controlled and media-controlled designs?
  • Does a small orifice pose notable operations and maintenance issues compared to standard bioretention BMPs without underdrain outlet controls?
  • How are the hydraulic conditions (i.e., stage-discharge relationships) of the compared systems different? Any impacts to modeling?
  • How do hydraulic conditions vary over time and between replicate mesocosms?

Study findings

This study is on-going until April 2022.

Project tasks and deliverables

Scope of Work

Task 1: Project planning and QAPP development

  • Deliverable 1.1 Meeting notes from project Kickoff meeting with TAC
  • Deliverable 1.2 Draft Quality Assurance Project Plan (QAPP)
  • Deliverable 1.3 Final QAPP

Task 2: Installation and startup

  • Deliverable 2.1 Table of equipment purchases, and dates received
  • Deliverable 2.2 Installation photolog
  • Deliverable 2.3 Installation and Startup Report

Task 3: Monitoring study implementation

  • Deliverable 3.1 Progress Report #1 summarizing vegetation establishment, water quality event #1, special testing event #1, and O&M observations
  • Deliverable 3.2 Progress Report #2 summarizing water quality event #2 and O&M observations
  • Deliverable 3.3 Progress Report #3 summarizing water quality event #3, special testing event #2, and O&M observations

Task 4: Modeling study (to be added to scope of work via amendment)

Task 5: Reporting and communication of findings

  • Deliverable 5.1 Interim presentation to TAC of draft findings
  • Deliverable 5.2 Revised analysis report for TAC

Task 6: Communication (to be added to scope of work via amendment)