Installing Infiltration Chimneys @ Lafayette Oaks Bioswale (April 2016)
Problem: Prolonged Ponding.
As discussed on the Slow Draining Evaluation Page it was discovered that a low permeability clay lens lies 1-2 feet beneath the bioswales which restricts vertical infiltration of ponded water. Hand augers further found that the clay lens is only 1-2 feet thick with more permeable soils beneath. |
Solution:
Infiltration Chimneys were installed in both Lafayette Oaks Bioswales on April 9, 2016. The concept of the infiltration chimney is to allow a path for ponded water at the surface to bypass the clay lens and soak into more permeable soils beneath the lens. The tools and materials are relatively simple and cheap: shovel, post hole digger, corrugated pipe (WITH Slit Openings for Drainage!), pipe sock, dome grate, sand (NOT UNWASHED playsand), clippers/knife. |
SAFETY FIRST: Call Before You Dig. Make sure utilities are located before you begin digging.
Step 1: Dig oversized top opening. This will make it easier to flex the post hole diggers at greater depths. Also allows large zone of sand for surface infiltration into the pipe. |
Step 2: Use Post Hole Diggers to complete hole. Be sure to remove all unwanted soil materials from the hole (such as clay).
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Step 5: Place filter sock around pipe. This helps keep fine soils from entering the pipe. Sock at the top also prevents mosquitoes from breeding inside the pipe (the pipe will hold water longer than the surrounding bioswales).
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Step 6: Insert wrapped pipe into hole. Note the sock is closed at the top to stop mosquitoes.
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Step 8: Install Dome Grate cap. The cap helps prevent large material from entering the pipe. I prefer dome grates as they are less prone to clogging from mulch. Mulch will easily cover the top of a flat grate; however a flat grate is less of a tripping hazard. Since our chimney pipes are in non-pedestrian areas surrounded by mulch, the dome grate was the way to go.
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Step 9: Apply mulch and otherwise blend into the landscape.
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Install Complete!
Some Additional Info:
Time: It took about 45-60 minutes to install each chimney which included time to take photos & drink water.
Machine Auger: Renting a machine to dig the holes can save a lot of time and energy ... but you miss out on the cardiovascular exercise and team building ;)
Cost: ~$30 (not including tools like shovel and post hole diggers)
The No Pipe Option: As an alternative, the dug holes can be filled directly with sand without using a pipe. Water should still be able to move rapidly through the sand and you do not have to worry about mosquitoes breeding in a pipe. With a pipe; however, you can observe the water table if you want which was a desired feature in our little project showcase.
Grate Tops: Securing the grate tops to the pipe can be tricky. You may need to use zip ties or string.
Monitoring: Of course we will be monitoring the bioswales and we will post how the chimneys are holding up and working over time.
Machine Auger: Renting a machine to dig the holes can save a lot of time and energy ... but you miss out on the cardiovascular exercise and team building ;)
Cost: ~$30 (not including tools like shovel and post hole diggers)
The No Pipe Option: As an alternative, the dug holes can be filled directly with sand without using a pipe. Water should still be able to move rapidly through the sand and you do not have to worry about mosquitoes breeding in a pipe. With a pipe; however, you can observe the water table if you want which was a desired feature in our little project showcase.
Grate Tops: Securing the grate tops to the pipe can be tricky. You may need to use zip ties or string.
Monitoring: Of course we will be monitoring the bioswales and we will post how the chimneys are holding up and working over time.