Double Flow Installation
The Double Flow system uses two perforated pipes in one trench, with catch basins positioned between them to handle larger volumes of water. Below is the proper process for a successful install.
Step 1: Confirm Utilities
Ensure 811 has been called and all utility markings have been identified before digging.
Step 2: Excavate the Trench
Dig a trench with a minimum of 1% slope, with a flat and compacted trench floor. Widen the trench in areas where catch basins will be installed by 4-6" on each side to allow proper fit and spacing.
Step 3: Lay Filter Fabric
Lay filter fabric across the trench, securing it with landscape pins. Keep the base of the trench smooth during this process.
Step 4: Install First Perforated Pipe
Place the first perforated pipe along one side of the trench. Make sure connections are tight, and lay tracer wire laid at this time.
Step 5: Install Second Perforated Pipe
Lay the second perforated pipe parallel to the first, but cut the pipe and leave 2 foot long gaps where the catch basins will be installed. Check with the foreman for correctly placement. Cap the ends of this second perforated pipe during install to prevent gravel from entering the line,, you do not need to tape these connections. These two pipes should fully cover the trench bottom.
Step 6: Install Catch Basins
Set each catch basin into the marked gap between the perforated pipes. The top of the basin should sit 1–1.5" below natural soil grade. If the basin sits too low, backfill with gravel to raise it. Follow the standard catch basin procedure, like drilling holes in the bottome, installing locking rings, and using solid blue pipe.
Step 7: Secure Basin Lids
Place the lids on each basin and screw them in using the hardware that came with the locking rings. Do not overtighten. If gravel is being installed around the lid, cover it temporarily with 4" pipe tape to keep the basin clean during backfill.
Step 8: Add Gravel
Fill the trench with gravel until it's about 4–6" from the surface. Hold the solid blue catch basin pipes to one side of the trench while pouring gravel, so it lays on top of one of the perforated pipes. If the blue pipe fall between the perforated pipes, a low spot may form and reduce performance.
Step 9: Wrap the Fabric
Fold the excess filter fabric over the gravel. Trim overlaps exceeding 2". Cut around the basin tops so the lids will sit flush, and secure the fabric with landscape pins.
Step 10: Backfill
Add the final 4–6" of soil above the wrapped gravel. Compact the dirt using methods outlined in the backfill procedures.