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Oak Shor

Corte Madera, California

Stormwater Treatment/Bioretention






Nunley Engineering


February 2023

Technical Description:

  • (3) Filterra Peak Diversion 
  • (2) Filterra Bioscape Vault 
Located on the Ring Mountain Preserve, Oak Shor is a single family development located between San Francisco Bay and the vibrant Corte Madera neighborhood in Marin County, California. 

Traditional bioretention was infeasible due to topography. After a meeting with the engineer introducing them to Filterra, and showing how it could be used in such an application, it was a clear choice to save valuable space on this hillside development. The California Water Resources Control Board allowed Filterra to be used on this project as it met all four bioretention equivalent effectiveness measures. These include an equal or greater amount of runoff is infiltrated or evapotranspired, equal or lower pollutant concentrations than what is in runoff discharged after biotreatment, there is an equal or greater protection against shock loadings and spills, and there is an equal or greater accessibility and ease of inspection and maintenance.  

The engineer specified five Filterra bioretention systems of various configurations throughout the site. Three of the five units had high peak flow rates, which required the use of the Filterra peak diversion configuration that provides treatment and high flow bypass in one structure, eliminating the need for an external bypass structure. These units also have open media bays providing improved aesthetics. 

The remaining two Filterra systems were Filterra Bioscape Vaults, which utilize an open-top configuration to integrate the vegetation into the surrounding landscaping. They also have have an internal bypass pipe to handle peak flows internally. 

The project was built into the side of a hill, so the site was tight, and access was a challenge, so a Contech Field Consultant was on site to assist the contractor with the installation, which went off with perfect execution. Once the site is stabilized, plants will be added, and the systems will be activated. 

Technical Description:

  • (3) Filterra Peak Diversion 
  • (2) Filterra Bioscape Vault 

800-338-1122 |
Project #: 649,960


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