Orange County Stormwater Tools: Development of an Open Source Web Platform for Stormwater Asset Management and Modeling

Municipal stormwater permittees in Orange County are implementing watershed management programs to meet MS4 Permit requirements. As part of these programs, Permittees are responsible for inventorying and inspecting private and public stormwater assets as well as reporting on progress toward watershed planning goals and regulatory requirements. To help address these requirements, the Permittees, Geosyntec Consultants, and Sitka Technology Group worked together over the last three years to develop an open-source web platform for stormwater asset management — OC Stormwater Tools (www.ocstormwatertools.org). This platform is intended to help manage and report on existing assets and plan for future assets (Figure 1). The tool caters to many user roles, from field crew to jurisdictional managers, across several modules. The Inventory Module maintains consistent BMP asset inventories across jurisdictions in the County. Geosyntec worked with early adopters to onboard their data and tailor the system to user needs. The Inventory Module supports mobile data entry, rapid condition assessment and maintenance tracking. It also allows users to inventory development sites and associated private BMPs. It now contains over 11,000 structural BMPs across 18 jurisdictions and is growing (Figure 2). The Trash Module supports Permittees in complying with statewide trash requirements. It also supports mobile visual surveys of the effectiveness of measures to reduce trash loading. Based on the inventoried trash BMPs, the tool calculates quantitative progress toward goals (Figures 3 and 4). The Modeling Module calculates the water balance and pollutant load reduction of inventoried BMPs for both dry and wet weather conditions (Figure 5). To do this, it runs algorithms in near-real-time as information about BMPs and their drainage areas is added. This is also supported by GIS resources and geoprocessing services provided by the OC GIS department. Although the network of BMPs in the County is complex, the algorithm recalculates the long-term stormwater capture efficiency, volume reduction, and treatment performance much faster than a continuous-simulation model. This presentation will provide an overview of the tool, key takeaways from the process, and a discussion of how this will support more streamlined reporting and planning in the future. We also hope to engage in an audience discussion about how this open-source code could benefit other stormwater and watershed managers.