GI Leadership Exchange: A National Collaborative Study to Distill Modeling and Monitoring Lessons Learned
The Green Infrastructure Leadership Exchange (giexchange.org) is a nonprofit that is connecting stormwater agencies from across the country to share knowledge and resources with the aim of expanding and improving sustainable stormwater management. This presentation focuses on one of the Exchange’s first ever grant-funded collaborative studies. The study was led by San Francisco and brought together several major stormwater programs to share knowledge and lessons learned in the fields of GI modeling and monitoring. The purpose of the study was to progress national standardization in these areas, while creating peer-reviewed guidance that can provide refined direction to existing GI programs and jumpstart development of more nascent municipal GI programs.
The goals of this presentation are to:
- Make GI practitioners aware of the resources and collaborative efforts being developed by the Exchange;
- Summarize the results of one the first collaborative studies supported by the Exchange, which synthesized lessons learned from across the country to advance the standardization of GI modeling and monitoring;
- Encourage feedback and expanded cross-pollination of ideas from conference attendees to improve study recommendations and expedite nationwide learning curves.
The study, entitled Standardizing GI Modeling and Building Cost-Effective Monitoring Programs, resulted in active collaboration and data sharing across several major GI programs. The San Francisco Public Utilities Commission and Lotus Water led the study in partnership with New York City, Washington D.C., Philadelphia, King County, and Vancouver. Results were summarized into two memoranda and webinars to share study outcomes.
The modeling portion of the study focused on what was determined to be the most implemented GI type of the collaborators—bioretention—and the most used modeling platform—EPA SWMM. Existing bioretention modeling parameters, soil specifications, and design standards were synthesized from the collaborators and additional industry sources and then compared to existing default SWMM parameters to develop revised recommended default modeling parameters for bioretention.
After establishing recommended bioretention modeling parameters, these parameters were then used to evaluate runoff reduction performance from different regions of the country. A total of 480 SWMM model runs were conducted to analyze 20 different sizing ratios and four different soil types across six cities in the U.S. Each model run simulated 30 years of performance using rainfall data from the municipality’s local rain gauge. The model output clearly demonstrated how bioretention performance varies across the different climatological regions of the country.
These results set up the second piece of the study, comparing model-predicted bioretention performance to monitoring results. Monitoring data, as well as lessons learned and recommendations regarding monitoring approaches and equipment, was compiled from the collaborating cities. The data indicated that these cities have refined their monitoring strategies over time and come to similar conclusions about which approaches are most effective. These lessons were distilled into monitoring equipment and configuration recommendations customized to the scale of the monitored area. Lastly, the monitoring data was used to evaluate performance in different regions of the county, that was compared to the model-predicted performance developed earlier. The results display how GI is performing across the country and enable programs to assess if their default modeling parameters are overly conservative. Presenting this feedback loop between modeling and monitoring is a critical component of developing more cost-effective GI programs. Most importantly, the study outcomes connect the dots by creating shared recommendations that can help jumpstart newer GI programs while providing refined direction to ongoing programs.
Scott Durbin founded Sustainable Watershed Designs in 2007 to create an engineering company focused on full water cycle design and treating stormwater as a resource. The company, now doing business as Lotus Water, implements water resources and civil engineering projects that emphasize integrated water management solutions. Scott's background includes leading multi-benefit stormwater management and flood reduction capital planning for the City of San Francisco and developing the City’s stormwater compliance guidance tools. Scott’s current projects include leading technical analyses for Phase 2 of GI implementation in San Francisco, developing the GI Plan for the City of San Jose and the stormwater resource plan for Santa Clara County.