Story highlights Douglas Brinkley: Flooded areas in Houston can't wait for DC support. Texans with boats need to spring into civic-minded action. Right now.

Katrina left 72-hour window to get medical help to those with medical conditions, aid elderly, escape dangerous gas leaks and more. People must get out, he says

Douglas Brinkley is professor of history at Rice University in Houston and author of The Great Deluge: Hurricane Katrina, New Orleans, and the Mississippi Gulf Coast. The opinions expressed in this commentary are solely those of the author.

(CNN) As the floodwaters rush and rage around greater Houston, as thousands of people are trapped in their homes, as the Coast Guard fights the torrential rain and fierce winds to rescue the stranded, more Texans with boats need to spring into civic-minded action. Right now. No urban drainage system can handle this type of deluge.

Flooded communities can't wait for help to materialize from Washington. That is a terrible mistake. The magic cavalry doesn't always arrive after a hurricane makes landfall. Houstonians have to save Houstonians now (as they're already courageously doing).

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This is especially true because President Donald Trump seems preoccupied with tweeting about NAFTA, Sheriff Joe Arpaio and transgender bans, and shamelessly hawking a sheriff's memoir on Amazon instead of being fully engaged as Emergency-Manager-in-Chief.

As a survivor of Hurricane Katrina, I saw firsthand how recreational boats — used for fishing, hunting and waterskiing — can become a kind of People's Navy. All boats in South Texas and Lousiana that Hurricane Harvey didn't damage or destroy, those anchored in the marinas of Clear Lake City and Baytown, should be deployed into action.

This must be done, of course, after checking in with state, local and federal authorities about how your vessel can be best utilized -- extremely important for both safety reasons and to avoid duplication of effort.

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