Quote:
Originally Posted by Neil
That makes sense, the water in the river is high so it keeps the one way valve closed. Water flowing down hill into the underground storage tank then has nowhere to go so comes out of manholes. The cause is the drains being below the river level
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Correct the significant factor is the hight of the land you are draining. In flat land with a river running through it the drains will normally be below the highest level the river can reach. Old drains were passive and produced the situation described. Modern drains should have pumps, but as with much of our infrastructure bringing things up to date tends to lag behind need.