In message , Michael
Kilpatrick writes
Three years ago when we had the extension built, I had also had a
rainwater harvester put under the ground in front of the house. It's
6.5m^3 and feeds the toilets, waters the garden and keeps the pond
topped. It takes 90% of the rainwater from the roof of the house.

If the harvester runs dry, I have an automatic system to top up the
toilet header tank with mains water.

The harvester has an overflow in the form of a u-band in the turret of
the tank which exits via 110mm drainage pipes into a 3-metre soakaway.
The level of the overflow is approx 70cm below ground level.

So, guess what? After over 2 years of lovely rain collection and
hassle-free use, what has happened? Well, it has rained *so* much this
year that the ground water table appears to have risen to approximately
70cm below ground level and has been sitting there for weeks. The
soakaway is therefore completely useless.

Which means that water is actually pumping back up from the soakaway
through the 110mm pipes, round the u-bend, and trickling slowly into
the tank at about 1 pint every minute. The water, of course, is now
murky, muddy and horrible!

What a bloody mess! When is the water going to drain away? Does climate
change mean that the water table will forever remain high
(Whittlesford, South Cambs), so the system is stuffed?

I suppose I could dig up the soakaway pipe and insert a one-way valve
to interrupt the flow.

Or I could block off the overflow entirely and use electronic means to
pump excess water out using the pump, and deliver the excess water down
the garden somewhere!

I'm not sure I can route the overflow outlet to the sewer instead of
soakaway because the sewer is probably not deep enough. It's about 70cm
deep itself where it passed by the house.

Check your house location against the flood risk map!

What a bloody pain in the neck.

Any other ideas?

Break into the soakaway pipe and use some temporary shallow bends to
raise the level? Presumably you still need the harvester tank working to
dispose of collected rainwater.

good luck!

--
Tim Lamb