Not all leaky tanks are good

Maybe that’s just me. Can any leaky tank be good?

Well, for many years, starting with the Little Stringybark Creek Project, we have been promoting tanks that leak for passive irrigation, as a good stormwater management solution. A well-designed leak (to an adequate garden space) does little to alter the reliability of supply, while increasing the retention capacity of the tank next time it rains, and potentially providing some restoration of lost base flows (e.g. Burns et al., 2015: also an encouraged option in our environmental benefit calculator).

Nevertheless, I was less than happy to discover last September that my 5-year-old slimline steel tank in our back yard had sprung multiple leaks (the back yard is a confined space surrounded by buildings and other constructions: not a place that we want to encourage excessive infiltration into the ground).

Spot the leaks: along the seam…

 

Disappointingly, there were multiple slow leaks along the horizontal seam half-way up the tank. After a lot of thought, and advice, and waiting for the tank to empty below the seam, I opted for using a sealant to seal along the seam from the outside. Once the tank had emptied and dried sufficiently, I used Selley’s SMP high-performance sealant to add an external seal along the length of the seam, having been advised that I shouldn’t use a silicon-based sealant. I was expecting that the pressure from within would make this solution not work, but I was pleasantly surprised to find, next time it rained, that it worked. When the tank filled again, there was no sign of the leaks.

Now, I’m not 100% sure that there are no leaks on the other side of the tank (which is hard up against the fence), but, as far as I can see, there aren’t. Perhaps the sealant along the seam inside the tank perished along this side because it was subject to the hot afternoon sun. Nevertheless, it is disappointing to find a high-end tank like this springing leaks after 5 years.

If we had to replace the tank, it would be something of a logistical nightmare. (I have thought through our options and none of them are easy. The most likely option would be using a lift over the back fence through the neighbour’s property. Almost certainly a replacement tank would require cutting into our decking, which was built around the tank. Luckily, it seems we have deferred this decision for some time.)

This small hiccough aside*, the raingarden and tank system continue to work well, and keep us happy in many ways. For more information check out My Raingarden Diary.

*and the pump problem noted in my previous post…just catching up on the parts of our system that haven’t gone as well as planned, in the name of full disclosure that it is not a perfect world.

References

Burns, M.J., Fletcher, T.D., Ladson, A.R. & Walsh, C.J. (2015) Flow-regime management at the urban land-parcel scale: a test of feasibility. Journal of Hydrological Engineering, DOI: 10.1061/(ASCE)HE.1943–5584.0001002.

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