[Leonard_of_Q]

Put dikes around it, make channels to collect the seepage, pump water out of channels over the dikes into the sea. Problem solved in the same way the Netherlands has been solving this problem for many centuries. The pumps can run on solar power with some diesel backups for when the sun doesn't co-operate. As long as the system is kept in good shape and the channels are kept open Miami can lie several meters under sea level without the need for further action. The house I lived in in the Netherlands was at -4.5 m below sea level, it is still standing and will remain doing so if history can be a guide.

[mapotofu]

I imagine this type of system is not designed for large, sudden and prolonged inundation of water, something New Orleans faces from seasonal hurricanes and their storm surges. Or maybe it is and it’s just a question of magnitude?

[Leonard_of_Q]

Yes, it is a question of magnitude and also of planning for those specific threats. To catch storm surges you'd use catch areas, dry basins and some sacrificial areas - parks come to mind - where storm surge water can be temporarily held until the pumps catch up. There should be extra pump capacity held in spare for these occurrences, both regular pumps as well as mobile units which can be placed where the need is highest. You also don't just use one dike around the whole area but divide it into sections with 'sleeper dikes' - dikes which normally do not border flooded areas but which can catch water which somehow makes it past the main dikes - behind the main ones. There are reams of literature on the subject to be had from places like the Netherlands where all this has been daily life for centuries, it is not a new problem.

[selimthegrim]

The problem is saltwater intrusion into the drinking water table - a problem New Orleans only has one when it comes up the Mississippi river - Miami is a whole different level

[Leonard_of_Q]

That can be solved using desalination of seawater, an energy-intensive process which is tailor-made for the abundance of solar power in the area. If for some reason desalination is not deemed sufficient it may be possible to slow the seepage by creating deep barriers between coast and land [1]. If this results in groundwater emergence so much the better, just pump it out and send it to the water treatment plant. Excess water can be pumped elsewhere, either over the dikes or into the ground outside the dikes or wherever else it may be needed or beneficial. Since pumps are needed anyway the criticism in the article - reliance on pumps is costly and can lead to a point of failure in flood mitigation plans - is negated. Also, pumps have been used as part of flood mitigation plans for centuries in places like the Netherlands so there is a lot of data to be found for those who need it.

[1] https://coastalscience.noaa.gov/news/hardening-shorelines-ma...