Building a Living Model – Quantifying Stormwater Capture and Pollutant Load Reduction Directly from a Water Quality Asset Inventory
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Stormwater permittees in Orange County have built an open-source, cloud-based platform to quantify stormwater capture and pollutant load reduction directly from their Best Management Practices (BMPs) asset management inventory.

The system serves as a living, up-to-date, model of BMP performance and pollutant load reduction that is tightly coupled with their asset inventory. Model results can support maintenance prioritization, regulatory reporting, and adaptive management. This presentation will provide an overview of the system, how it is being used by Permittees in Orange County, and how it could be applied to other jurisdictions with similar objectives.

In 2018, Orange County Public Works launched the initial version of the OC Stormwater Tools web application to provide a consistent framework to inventory, inspect, and maintain county-wide structural BMPs. The modular platform has been instrumental in building and maintaining consistent BMP asset inventories across jurisdictions in the county. In 2019, a Trash Module and supporting delineation workflows were added to the web application to address statewide trash requirements, including trash capture systems and on-land visual trash assessment (OVTA). Earlier this year, the platform was expanded with a new Modeling Module to quantify stormwater capture and pollutant load reduction associated with inventoried BMPs and Priority Development Project sites. With this new module, MS4 permittees can utilize the OC Stormwater Tools to view calculated reductions for multiple regulated stormwater pollutants including bacteria, metals, TSS, and nutrients as well as the quantity of urban runoff captured during dry and wet weather.

Three core elements support the functionality of the Modeling Module:
=> BMP inventory workflows support permittees in populating the inventory with enough information to model the performance of BMPs. Mapping interfaces in the application allow permittees to visualize where their assets appear in the network and propose changes to the County GIS staff to improve the stormwater network and regional watershed delineations over time.
=> The OC Stormwater Tools web application includes automated data synchronization with Orange County's enterprise GIS resources to gather additional inputs to support the modeling calculation engine. Leveraging centralized GIS resources supports consistent county-wide calculations and enables datasets to be updated and improved over time.
=> The cloud-based modeling calculation engine uses the OC Stormwater Tools asset inventory and County GIS resource inputs to provide real-time quantification of performance. The modeling engine maintains a network connectivity graph to recalculate results in near-real-time when users update an asset inventory. This approach also accounts for the cumulative benefit of nested stormwater BMPs.

MS4 permittees can view results for their structural BMPs within the web application or use web services provided by the application to create their own reports in external software products such as Tableau or PowerBI.

As part of this presentation, we will demonstrate the application of the Modeling Module for a case study watershed in South Orange County. Attendees will learn first-hand how Orange County permittees are benefiting from having all their Treatment BMPs and Water Quality Management Plans located in a centralized tool and learn about transferrable elements of this system.

Publication Summary

  • Geosyntec Authors: Austin Orr
  • All Authors: Eric Rademacher, County of Orange; Austin Orr, Geosyntec Consultants
  • Title: California Stormwater Quality Association (CASQA) 2020 Virtual Conference
  • Event or Publication: Event
  • Practice Areas: Urban Stormwater Management Planning and Design, Water and Natural Resources
  • Citation: Several Geosyntec staff members will present at the California Stormwater Quality Association (CASQA) 2020 Virtual Conference on September 15 and 16, 2020.
  • Date: September 15 and 16, 2020
  • Location: Online
  • Publication Type: Platform Presentation