Actually, before it was dug out, there was a channel running from left to right as you look into the dig. Obviously water-worn and going downhill into a hole under the right-hand wall. Theory was that water was coming from the left (or straight ahead), backing up against the mud fill and then flowing over the top of the mud and down into the aforementioned hole.
What is probably happening now is that you've dug down through the mud fill to reach the gravel underneath, this has created a more free-flowing route that has captured the previous run-off after the end has flooded.
This does sound like there could be an active stream during wet weather. But what actually happens is that the water table rises and floods the end resulting in a static sump. There are some small holes (now mostly blocked) that lead off to the left from which water can drain into the dig. There never was much evidence for anything coming from straight ahead.
Any drainage of water is just going down into the underlying gravel to either join the local water table which can't be far below or to seep out and emerge from the lower entrances at river level.
The passage obviously continues straight ahead although it seems to be dropping deeper again and I reckon will eventually hit the water table. There is also a possibility of something to the left and there is the passage to the right that looks like quite a sizable one if emptied of fill. So which way to go is anybodies guess and probably a matter of pot luck.
So, hah-bloody-hah!
