"For example, dikes, tide gates, and ditches have disconnected rivers from their historic floodplains. This limits the amount of floodwaters that wetlands are able to soak up, putting nearby communities at risk of frequent flooding." (noaa.gov)
Is it correct to infer:
Using the word "are" or an equals sign implies some sort of universality that doesn't really seem valid.
It'd certainly be better to try:
Dikes were bad
As in when they were built. Because the equation now is much more complicated: generally large communities with many lives and great developed value versus much smaller surrounding areas. Are implies at this time, but looking at just the current, removing people from major existing developments is a really complex issue to approach.
But even this direction misses a lot.
Because: why were dikes built? Generally one of two reasons:
You could say it was bad for people to develop in a floodplain. Though in many cases this goes back to early history when there was less understanding (and even, one could argue, more necessity to build in the most beneficial areas, as life was much more difficult as a whole).
The second option for why a dike was/is built is kind of the underlying complexity to the whole topic of dikes. It's about weighing cost vs benefits. And for the dike to be built, it was deemed the benefits outweighed the costs (both monetary and secondary consequences). Yes, almost certainly the recognition of the consequences wasn't well understood/considered in the past (and may well not be today in some instances). But now you've replaced a definitive "are bad" with a much more nuanced "should be more carefully considered"
But, you could actually go a whole different avenue too, maybe one much more applicable to today's choices:
Yes, it is generally correct to infer that dikes and similar flood control mechanisms tend to divert floodwater to other areas (there's X water that falls in a given day/season, Y would've been removed by the previous floodplain, but isn't, so there's Y more water to continue to other areas that aren't protected).
(Though it's worth seeing there's all kinds of complex topics even in this one... is there same amount of water to start out with? Things like paving can mean less infiltration, so more water going into waterways... or land can sink/rise near the coast from development.
Do climate changes affect the amount of precipitation falling/ocean levels?
Does water get removed in other ways by man? [see Colorado River for example]
Does the related planning of man mean more room is actually created [flow rate in dams and locks are generally adjusted to prepare for likely predicted precipitation events, and evacuation orders are sent out to protect people in endangered areas]?)
But that may be the most straightforward solution to the problem dikes have created:
In the end that's what happens naturally. The floodplain removes less water, it has to go somewhere else.
Aside from the extreme challenge of attempting to restore the region to pre-man situations, the best option may be to avoid making more problems; designate/construct so that nearby areas are flood plains, such that the costs/consequences are greatly limited, and taken on by a select few that know what they're getting into. (Often floodplain land is still farmed... after all such areas tend to have great soil generally [another added factor to consider in flood control!]... but with the understanding that in a certain percentage of years, it will wind up useless)
It's the same thing we do when building in cities themselves. We drain swamps for new construction. But then we put in retention ponds/divert the water elsewhere. If it's done well, the danger that water poses can be much better controlled and often nearly removed. It's kind of the great victory of cities in the first place. There are bad floods. But in general most modern cities are much better at mitigating flood risks, both from seasonal barrages and from daily deluges, than in past centuries. They can still often be better. It's a challenging science where it's a complex mathematical balancing, and any mistakes tend to lead to suffering.
(And it's the same complex questions that come for related topics like fire control, coastal development, (heck all disaster planning really), biodiversity, pollution, etc, and each is accounted for to varying degrees of what they should be)
But to say comprehensively that dikes are bad seems an unsupported leap, one that sometimes is even clearly wrong.
Dikes etc... divert floodwater away from large, well funded, urban centres, usually by locking the water course into a single lower capacity but straighter channel than it would otherwise occupy and putting in flood defenses that create a high capacity overflow zone. This means that when there is flooding the water in the channel is flowing faster than the watershed's natural rate and at a higher volume. When this mass of high speed water leaves the heavily protected areas it slows down, piles up (much like a breaking wave), and spreads out into less well defended downstream communities.
