Thanks for all the input to my project to divert rainwater from the roof of the workshop into the "small" pond (it's ~11m in diameter. I have a "big" pond about 4 or 5 times the size, too) to try and prevent it drying up in the summer without cutting down the weeping willow growing next to it. The workshop is about 40ft by 20ft and has a gable roof which gives somewhat over (probably in the ratio 4:5, depending on the pitch of the roof, so 1000sg ft, perhaps?) 800 sq ft of collector but it doesn't really matter for this.
So ... I bought 30m of ribbed (ooh, err) 38mm pipe on eBay and ran it under the grass from the workshop to the pond. Just finished putting the turf back this morning. This was a compromise between size of pipe and amount of digging required since I was doing it by hand.
I also bought a 200l ex-food-use plastic drum to use as a buffer and a
38mm tank fitting and backnut, also from eBay.Just for a laugh, since there was rain forecast, I cut through one of the (two) downspouts the day before yesterday and gaffer taped the free end of the 38mm pipe into it. Lo and behold, I have rainwater running into the pond! (No reason it shouldn't, but it was nice to see!!) No sign of any increase in water level yet. :o(
I also just ordered the relevant bits of guttering from Screwfix to connect the downspouts to the barrel. Need something to stand the drum on, so I was going to drop into the BM tomorrow & get some blocks.
So ... Can anyone suggest a means of connecting a 68mm pipe to the drum to act as overflow back into the original drain in case the drum "backs up"? I found a 68mm tank fitting online, but it's £19 + VAT + P&P! Failing that, I shall bodge it with a 90 deg bend, silicone and cable ties...
If this works, I'm also going to raise the level of the drain from the pond (by putting a 90deg bend and a bit of pipe on the end of it - it looks like standard 4" drain pipe) to get the water level a bit closer to ground level.
Oh, and total expenditure so far? Just over £100, the vast majority of which was the 38mm pipe.