Road Drains in the UK query

[N Cook]

No obvious group to place this query For a low lying road near me if you monitor the water level under the grill of drains in that road this last week of high tides it goes up and down at the high tides. In fact for similar weeks but low atmospheric pressure , so the sea water level can rise much further, then local flooding starts from water flowing up out of these drains. So defeating the 0.5 metre or so of elevated ground beteween this road and the tidal river. Where do I find out about whether this is normal or failure of flap valves at drain outflows to the river. ? Responsibility of local council,county council, highways authority, harbour board, environment agency or water/sewage authority ? As I cannot see any obvious such hinged flap valves anywhere nearby and as there seems to be no lag between rising river water and rising drain trap water I would have thought it was not due to ground water seepage.

[Steve A.]

Since I've never seen flap valves on this side of the pond either, my answer is that it's poor drainage engineering. A road next to water that has tidal variations should be built above the spring tide level (it can flood once a year during storms if it must, I'm assuming it's not a major road). Since drains tend to be open to the water, relying on the assumption that water levels won't rise to the point of flooding the road, you get what you observed. Question for you though: There must be some sort of seawall here, right? If high tide level is rising above the road without flooding it...

[N Cook]

There are various structues that in effect make a sea wall that will hold back a tide of height 5.5 metres which is quite rare , relatively calm so no waves to speak of. Unfortunately any tides of 5.1m or more start coming up the road drains and of course 5.1m tides are a lot more common.