I wrote before about the completion of the pond digging and since then I’ve begun work on the first test pump for the wetland filtration system. Sourcing the washed gravel and sand to use as a growing medium for the plants in the biofilter has turned out to be a bit difficult, so I am still working that out.

But now, the rainy season is upon us and there has been flooding in Bangkok several days this past week. Here is a picture of the pond with about 20-30cm of water in the bottom now:

(For reference, the near and far sections are “pond”, and the middle section is shallower and will be filled in with sand and gravel and plants.)

The bad news is that I won’t have a chance to consider options for liners on the bottom of the pond any more unless I am willing to pump out the water. And I’d rather not do that since the rainwater is relatively clean (compared with the canal water I might use instead) and I’d like to fill up the pond with rainwater as quickly as possible.

The good news is that the clarity of water without any liner at all is far better than I had expected. Here is a wider and narrower picture of the deeper side of the pond:

The water is tinted green from the algae that is growing in it. But that is normal in standing water, and should go away once the biofilter and pumps are installed and operational. What is more interesting is how clear the water is. The most recent big rain was less than 12 hours ago, and the water is about 30cm deep here, so I would have expected the rain to stir up the clay bottom making the water turbid. But you can clearly see the ruts in the bottom caused by the digging equipment when it was digging, with almost no cloudiness in the water at all.

Based on this, I am starting to conclude that I can get away with no liner on the bottom of the pond. The natural clay soil seems to hold the water just fine, and it appears to be clean enough that the water stays clear, even after a rain.

Very interesting!

Now I just have to find a source for the washed gravel and sand before the pond fills up to that level