BASMAA Green Infrastructure Facility Sizing Criteria

BASMAA is an organization of stormwater agencies in the San Francisco Bay Area that shares planning and regulatory strategies and develops technical best practices. BASMAA’s current stormwater permit requires each agency to prepare a Green Infrastructure plan to guide the implementation of stormwater projects in streets and other public areas. In evaluating green infrastructure projects, BASMAA members face a challenge common among urban and suburban communities: a) how to assess the potential benefits of stormwater retrofits and b) how the prioritize opportunities and select projects to implement. 

Dubin Environmental conducted an HSPF modeling analysis for BASMAA that estimates annual stormwater treatment volumes, based on project location and bioretention configuration. The analysis involved HSPF modeling for 10 different rain gauges, computing detailed hydraulics in the surface reservoir, soil media, gravel layer and underdrain, and then computing the annual fraction of water treated. Dubin Environmental used automated processes to create HSPF models and evaluate their output. Results for more than 1,300 scenarios were synthesized to create simple nomographs that designers and reviewers can use to estimate treatment fractions across a broad variety of bioretention projects. The modeling team also addressed specific “what if” questions asked by the BASMAA development committee. For example, the modeling analysis was extended to assess a) the effectiveness of bioretention facilities without an underdrain and b) how reducing the percolation capacity of engineered soil media (for specific plant palettes) affects bioretention hydraulics. BASMAA members integrated the project results into their Green Infrastructure manuals and to assist in negotiations with regulatory agencies.

Services: Modeling, LID/GSI