You are on the right track in that flood mitigation/control is best handled at a community/suburb level rather than as individuals who may work against each other's efforts.
Your best bet is to take this up with the local authorities (councils/local government) and if as you hint it is a commercial sector, then a united "chamber of commerce" approach rather than individual petitions might get more notice and effect.
This is one situation where the "TEAM" (Together Everybody Achieves More) approach has significant benefit above individuals working alone.
For instance, the effort and materials to protect one street frontage for 10 shops is much less than the materials to build 10 individual levees around each shop.
I would suggest that you need two different strategic approaches. One with a long term objective for earth levees, groundworks and even downstream drainage, and maybe even upstream detention ponds to reduce the peak flow and spread it over a longer time. The other is a plan for how to react when flooding is imminent and how to arrange materials for the best benefit of the community.
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Just an Engineer from the land down under.
Your description is too vague...also, if you close the gates, where will the water drain to? How big is this commercial sector? Obviously you must be in a low lying part of town, otherwise you wouldn't have the problem...
Have you seen flood waters washing away roads and houses ? How can you know how strong to build the gates so that they wouldn't give way to the water pressure ? In fact, once you are inside you enclosed area, with a metre of flood water at the gates, how would you get out ?
Honestly, the business owners should all chip in and hire a registered professional (Civil Engineer) to do a site survey and compile a recommendation. Probably find that a good drainage system will work better than a flood gate, and possibly easier to build.
Flood Relief Solutions
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