Yes, I see your point Mimi, but think of it this way. If you get an inch of rain on your pond in a few hours, and you rely on a pond overflow, that`s a lot of water to lose in a short time. However, if the pond overflows into the bog a lot of the water will be temporarily absorbed in the bog, and will be released much more slowly over a much longer period, so you would only need a smaller soakaway for the bog to cope with it.
After all, that is precisely what happens to the rainfall in the Scottish Western Highlands, which often have greater rainfall even than Wales. There are no flash floods there, but the bogs absorb the rainfall and then release it slowly into the streams so that they run even in dry weather (probably happens the same in the welsh mountains too).
