Multi-stage process question

[9xxNick]

Consider a drain system which has a single entry point (domestic drain grid with normally-spaced bars across it, area of about 1.5 sq ft) and an exit to the sewer in the street. In this particular drain the exit to the main drain is badly blocked, so that the water flowing into the sewer enters the sewer at a very low rate, causing the drain to back up and overflow when it rains any more than lightly.

I propose to place a fine wire mesh comprising sub-1mm diameter wire arranged to form a mesh with square holes of side 6mm under the drain cover to stop small stones and so on falling in and blocking the drain even more.

For the moment, assume nothing has been done to the blockage between drain and sewer.

I contend that the rate of drainage with the mesh will be the same as before.

Person B contends that the rate of drainage will be slower (how much slower is not specified). I suspect they are drawing on knowledge of airflow into vehicle cooling systems and engine induction systems.

My argument is that although placing the mesh over the drain cover will limit its air flow capability for any given air pressure, the rate determining step in this process is the blockage between drain and sewer and that therefore a relatively tiny decrease in airflow capability will have precisely zero effect on the absolute rate of drainage.

Who's right?

As an aside, I know we need to fix the main blockage, but the question is specifically on the overall system as set out above.

[C4ME]

You are right as long as the mesh will flow at a rate equal or greater than the flow of the blockage.

[9xxNick]

It will, maybe to the tune of several hundred times as much.

[Monty Python]

The mesh will reduce flow once it starts collecting stuff.