Build the simplified iAVs Percolation Rate Tester
iAVs-suitable sand should be three things. It should be inert. It should be free of silt and clay. It must drain effectively.
We measure the sand’s ability to drain by measuring how quickly water travels through the sand. This measurement is known as the hydraulic conductivity…or percolation rate.
In this presentation, we show you how to build a simple test rig – and how to use it to determine the percolation rate.
The iAVs Sand Tester consists of a 500mm (18″) section of 100mm (4″) PVC pipe – to which an end cap is attached.
I chose this length because it allows for 15″ of sand with sufficient space left to pour the water.
I tend to over-engineer things, so here’s another way to attach a handle to the test rig…
…and here’s an even simpler way.
Drill enough holes in the end cap to allow water to drain freely.
These holes are about 5mm (5/16″).
Cut a couple of swatches of shadecloth. These are placed against the inside of the end cap…to hold the sand in place.
To do the testing, you’ll need a jug…or a drink bottle of a known volume…and a bucket to catch the water as it drains from the test rig.
You’ll also need a means of measuring the time that it takes for the water to percolate through the sand.
Use a pencil to mark the sand level inside the test rig.
We’ll use this line to measure how much the sand settles.
Significant ‘slumping’ of the sand may indicate the presence of fine sand in the sample.
Suspend the test rig over the bucket so that you can capture the water as it drains.
Take a measured quantity of water (I used one litre) – pour it into the top of the test rig.
This initial flooding is just to wet the sand and to settle it.
Check the distance that the sand has settled (or slumped) in the tester. This is an indicator of the amount of fine material in the sample.
Refill your jug or bottle…and repeat the test.
Repeat the test…as often as you need to confirm that there is no further settling (slumping) of the sand… and that you are getting a consistent percolation rate (time).
What's the Ideal Percolation Rate?
The better question is likely to be…”What works?”
The consequences of getting it wrong differ – based on the scale of the unit. Putting the wrong sand into a backyard system is inconvenient …but a bad choice for a commercial project may be catastrophic.
When I did this test, the water drained through the sand sample and into the bucket in 2m 30s.
Several subsequent tests confirmed the percolation rate…so this sand is suitable for use in an iAVs.