It's clouding over now, and rain is forecast tomorrow... I'm still hopeful that there'll be enough rain to sustain tadpoles and froglets over the coming months. On Sunday, one of the pond's 3 deep points (the northerly one) had a few inches of water in. I dug the southerly a few inches deeper into the boulder clay and it too filled with a few inches. I left the middle one with sludge in it, as it seemed to be attracting a lot of insect activity.
The chart above shows average rainfall for Glasgow, in March we'd expect 69mm. But the actual rainfall in the last 2 weeks (see below), since 10th March is neglible, just over a millimeter. Which might indicate that the last couple of weeks are unusual, and that if at least part of the pond can retain a few inches of water, then, Bob's your uncle, this is exceptional and it won't normally be in danger of drying out. If it's exceptional, then topping it up from the water barrels is a reasonable course.
It'll be interesting to see how the pond fills when it does rain, (probably over Easter weekend, according to the forecast this morning). Hitherto after an exceptionally wet winter, rain was falling onto already waterlogged ground. Now, after a couple of dry weeks, it's drying out nicely, and will perhaps absorb a lot more rain before it drains down into the pond. Or something, because I'm just theorizing here. And I'm saying "nicely" despite wanting rain, because digging is a going to be a hell of a lot easier.
Best case, an allotment which drains well but precipitation sufficient to keep a frog-pond in business. Fingers crossed.