Skip to main content
Website Home

Turner Court Green Infrastructure Demonstration Project

From Gray to Green

Construction site with cement truck pouring concrete for a new projectYoung tree with fall colors on sidewalk, wood fence background.
Turner Court, Hayward - Parking lot during conversion (top) and installed permeable pavement and tree wells (bottom)

Spearheaded by the District, 951 Turner Court is a demonstration project with low-impact development (LID) techniques that showcase next-generation green stormwater infrastructure. Industry professionals can now visit Turner Court to learn about LID infrastructure, which uses flowthrough planters, permeable pavers, bioretention tree wells, and other best practices to filter and slow urban runoff. Turner Court is also open to the public for on-site workshops and self-guided tours developed by Alameda County’s Clean Water Program.

This project is a collaboration of the Public Works Agency and the Alameda County Flood Control & Water Conservation District (the District), with funding provided in part by the California State Water Resources Control Board.

The Turner Court Monitoring Project

The District monitored the Turner Court Demonstration Project to measure the reduction in stormwater runoff and pollutants after the LID features were installed.

Key findings include:

  • The new LID pavement resulted in a 52 percent decrease in stormwater runoff, compared to the old impervious pavement.
  • Sediment and sediment-associated analytes (inorganic parameters) showed high removal efficiencies, as did petroleum hydrocarbons and oil & grease. There were notable mass load reductions for all analytes in the solids, conventionals, and synthetic organics groups, some of the nutrients, and total iron.

Turner Court Receives a CASQA Award

In 2019, the Alameda County Public Works Agency (ACPWA), with the support of the District, converted two agency-owned parking lots at Turner Court in Hayward into a Green Infrastructure Demonstration Project. The District and Turner Court Project were recognized for their excellence by the California Stormwater Quality Association (CASQA).

Click the links below for more information

concrete vault connected to the catch basin with manhole and curb inlet
The concrete vault is connected to the catch basin with manhole and curb inlet.

Horizontal Flow Biofiltration

Horizontal flow biofiltration systems, often referred to as “modular wetlands,” treat high flow rates in a small footprint. After passing through a trash screen, stormwater flows into the void space within the vault perimeter. Moving horizontally, the stormwater filters through biotreatment soil media, and then enters the storm drain system through the underdrain.

flow-through planter in use next to a building
Flow-through planters can be used to treat stormwater where infiltration is not desired, such as next to buildings.

Flow-Through Planter

Flow-through planters are self-contained systems that collect roof runoff and filter it as it percolates through the biotreatment soil media and permeable material below. Water not used by the plants enters the storm drain system through a perforated pipe at the bottom of the planter. Flow-through planters can be used to treat stormwater where infiltration is not desired, such as next to buildings, or where it is not possible due to poorly draining soils and steep slopes.

Worker amending the soil with compost improving soil health and saving water
A diversity of plants that are adapted to the site’s microclimate helps resist diseases and pests. Amending the soil with compost improves soil health and saves water.

Bay-Friendly Principles

The Green Infrastructure Demonstration Project at Turner Court is a Bay-Friendly landscape, which means it reduces waste, protects watersheds, and enhances community livability. The seven Bay-Friendly Principles are:

  • Landscape locally
  • Landscape for less to the landfill
  • Nurture the soil
  • Conserve water
  • Conserve energy
  • Protect water and air quality
  • Create wildlife habitat
Using plants suitable for bioretention areas
Plants suitable for use in bioretention areas include those tolerant of both dry and wet conditions such as California Gray Rush (Juncus patens).

Bioretention Area

Bioretention areas use plants and soil to slow and filter stormwater. Mimicking a natural process, bioretention areas allow for ponding of stormwater, filtering it through the planted area and through biotreatment soil media. The filtered water then percolates into the ground where it can replenish groundwater. Where site conditions don’t allow for this infiltration, a perforated underdrain sends the treated water to the storm drain system.

Permeable pavers used as surface covering for parking spaces.
Permeable pavers used as surface covering for parking spaces.

Permeable Pavers

Permeable pavers are concrete pavers installed with wider-than-normal joints to let stormwater pass through the joints between the pavers. Below the surface, permeable layers capture pollutants and store stormwater. Stormwater percolates into the ground, and excess flows into the storm drain system through a perforated underdrain. Permeable and pervious pavers appear to be similar, but the difference between them is that the joints between permeable pavers are wider and the water does not pass through the paver.

Pervious pavers in use
Joints between pervious pavers are no wider than traditional concrete pavers since water can pass through the pavers.

Pervious Pavers

Pervious pavers allow stormwater to pass through the paver as well as the around it, unlike traditional concrete pavers where the water runs off into the storm drain system. Below the surface, permeable layers capture pollutants and store stormwater. Stormwater percolates into the ground, and excess water flows into the storm drain system through a perforated underdrain.

Underground structural cells installation
Medium permeable stone is tamped down before the structural cells are placed.

Underground Structural Cells

With underground structural cells, biotreatment soil medium can be placed under paved surfaces that are designed for pedestrians and vehicles. This allows tree roots to grow without damaging the pavement, while filtering and taking up stormwater. Stormwater not used by the trees percolates into the ground or enters the storm drain system through the underdrain.

Bioretention tree well in use
A louvered screen keeps trash and plant debris out of the tree well. Access for cleanout is through the grate.

Bioretention Tree Well with Trash Capture

Developed by the city of Fremont, bioretention tree wells with integrated trash capture provide stormwater collection and treatment where space is limited and pedestrian access needs to be maintained. Stormwater enters through the trash capture inlet where debris is removed before a biotreatment soil medium in the bioretention area filters out pollutants. Stormwater not used by the tree percolates into the ground or enters the storm drain system through a perforated underdrain.

Tree well being installed
The tree well before the sidewalk surface around it is completed.

High Flow Rate Tree Well

High flow rate tree wells offer stormwater capture and treatment in locations where space is limited. The tree well filters consist of premanufactured concrete boxes filled with proprietary high flow rate media. Stormwater enters through the curb inlet and is filtered by the media and tree roots. Stormwater not used by the tree enters the storm drain system through a perforated underdrain.

Workers lay down porous asphalt
During a rain event, water passes through the porous asphalt shown in front. It does not pass through the traditional asphalt shown in back.

Porous Asphalt

Porous asphalt allows stormwater to pass through the pavement, unlike traditional asphalt pavement where it runs off into the storm drain system. Below the surface, permeable layers capture pollutants and store stormwater. Stormwater percolates into the ground, and excess flows into the storm drain system through a perforated underdrain.

Water deposit
Rainwater tank

Rainwater Harvesting

Rainwater harvesting reduces runoff and allows for the beneficial use of rainwater, conserving water. Rain barrels and tanks capture rainwater from rooftops and store it for nonpotable uses later, like landscape irrigation. Built-in screens exclude mosquitos from the system.

Articulated concrete block pavement used for a parking lot.
Articulated concrete block pavement used for a parking lot.

Articulated Concrete Blocks

Articulated concrete blocks are a pavement solution for areas with high runoff rates that prevents flooding by providing temporary water storage. The pavers are spaced so that stormwater can enter and accumulate inside the pavers’ arched chambers and in the permeable stone layer below where angular rocks create void spaces. The stored water percolates into the underlying soil or enters the storm drain system through a perforated underdrain.

Worker pouring pervious concrete
Compared to traditional concrete, pervious concrete contains less sand and water and contains more pea gravel. This results in a more porous material with 15-22% void space compared to 3-5% in traditional concrete.

Pervious Concrete

Unlike traditional concrete, pervious concrete allows stormwater to pass through pavement and run off into the storm drain system. Below the surface, permeable rock captures pollutants and stores stormwater.
Stormwater percolates into the ground and excess flows into the storm drain system through a perforated underdrain.

Full Trash Capture Device
Overflow openings at the top of the device prevent flooding during heavy storms.

Full Trash Capture Device

Full trash capture devices are tools for trash load reduction. They can be installed in existing and new catch basins to keep litter and other debris carried by stormwater from entering the storm drain system and flowing to creeks and the Bay.
Access to the device for regular maintenance is through the grate. Trash and debris are removed with a vacuum truck.