Support

RAFT Technical Documents

RAFT Typical Application

This image shows a typical urban streetscape where a series of RAFT units are deployed to support existing storm sewer infrastructure and improve the health of nearby streams and rivers. This is an example of how RAFT can be used to retrofit existing cities and towns and create a viable Best Management Practice (BMP).

During a rain event, the RAFT units intercept runoff and filter pollutants before entering the storm sewer. This also serves as temporary storage that regulates the rate of runoff and helps prevent the existing infrastructure from being overwhelmed in a cloudburst event. Urban bioretention is designed to occupy a small surface area in relative to the contributing drainage area and should be implemented in a series for best effect.

The intent for these interventions is to support the existing stormwater infrastructure that is unable to handle the current runoff capacity rather than replace entire sections of underground storm sewer infrastructure.

Determine the desired
treatment area

Of that area, determine what percentage is impervious

Determine the designed storm event and duration to treat

For high watertables, check whether the groundwater elevation conflicts with the BMP

Determine the adjacent slopes along the BMP

Check whether it is a manageable grade for the matching BMP and whether check dams or weirs are necessary

Locate all utilities both overhead and below ground

Check whether utilities conflict with the BMP and whether protective sleeving is needed

Determine the runoff rates for PRE & POST development

Check what POST-development rates are necessary for the development to meet local runoff requirements

Designing for Stormwater Management

RAFT Assembly Overview

Step 1

Excavate area per the design drawings

Step 4

Set the inlets and pretreatment devices into place and backfill

Step 2

Spread base layer aggregate and set the FRP assembly frames in place

Step 5

Layer the designer specified BMP soil media mixture in specified lift depths

Step 3

Starting at one end, begin sliding the panels into the frames until complete

Step 6

Install the specified vegetation and top dressing mulch cover

QUICK FAQ

Why aren’t you on the DEQ BMP Clearinghouse website RAFT is the "container" for urban bioretention and other Best Management Practices to be held within. RAFT by itself is not a BMP product that can be approved for the DEQ BMP Clearinghouse. It is, however, capable of holding a range of DEQ BMP Clearinghouse approved soil mixes and was designed to be functionally equivalent to a BMP "bioretention planter" or "planter box" when used for treating stormwater.

If RAFT is just the container, then what defines the BMP within The BMP within RAFT should be defined by a licensed professional in accordance with local guidelines. RAFT is designed to comply with the 2019 Washington State Department of Ecology Stormwater Management Manual, but a range of complimentary products may be used.

Why is the post and panel assembly so important The largest cost for urban bioretention is the container holding the BMP. This is due to material, equipment, and labor costs. The post and panel system is the key to simplifying component parts (lower material cost), reducing weight for small equipment use (lower equipment cost), and slashing installation time (lower labor costs). The system does not require mechanical fasteners or special equipment to assemble. Using the preassembled FRP frames allows panels to slide into place and interlock. Think of building blocks linking together to create a strong end unit.

Read the Full FAQ Here