Eureka! We have Water!!!

Now here's the thing.
I would like a clever person's explanation for this - failing that A'desk, perhaps you can add your mathematical understanding.

We put a pipe up the hill beside us a few months ago (see todays foto) to get water for our house. The water comes in through holes in the side of this 50mm diameter pipe as it sits in a barrel buried in the stream. The end of the pipe is blocked completely, the idea being the water is strained in through the small holes drilled in the side and so less debris ends up in my coffee in the morning!! The pipe sits about 30m higher than our house and thus creates around 3Bar pressure for us.

Since installing it however it has constantly sucked in debris to the small drilled holes and caused it to block. It is clear that a great amount of suction is created by this. For some reason eventually it seemed sensible to increase the number of holes drilled in to reduce the suction force. This has worked brilliantly and we now have a much better flow of unblocked water!!

What is the Physics or mathematical explanation for this though?